1、背景
? ?为了防止在多线程并发访问情况下，子线程更新UI线程，? ?会使UI控件处于不可预期的状态,Handler发送消息，统一有一个 消息队列接收.
2、现状
1、内存泄漏
Handler在使用过程中，用作UI组件的引用，如果为非静态内部类，则会默认持有this对象。当ui组件销毁时，Handler可能并未执行完，从而引起内存泄漏！
改进，看下面的代码MyHandle，申明为static静态同部内
以下演示的UI xml配置
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/sendMsgBtn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="发送消息" android:textSize="30sp"></Button>
<TextView
android:id="@+id/showMsg"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="20sp"
></TextView>
</LinearLayout>
/**
* 模似业务代码块
*/
public void businessCodeBlock(){
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
private static class MyHandle extends Handler {
WeakReference<MainActivity> weakReference;
public MyHandle(@NonNull Looper looper, MainActivity activity){
super(looper);
weakReference = new WeakReference<MainActivity>(activity);
}
@Override
public void handleMessage(@NonNull Message msg) {
super.handleMessage(msg);
MainActivity mainActivity = weakReference.get();
if(mainActivity!=null){
switch (msg.what){
case 0:
Log.i(TAG,"命令"+msg.what);
break;
case 1:
updateTxt(mainActivity,(String)msg.obj);
break;
case 3:
Log.i(TAG,"命令"+msg.what);
break;
default:
Log.i(TAG,"命令"+msg.what);
}
}
}
}
private static void updateTxt(MainActivity mainActivity, String s) {
mainActivity.showMsg.setText(s);
}
子线程更新UI 报错
new Thread(()->{
businessCodeBlock();
showMsg.setText("子线程更新UI");
}).start();
2021-07-26 10:42:19.546 6213-6241/com.mw.handlertest E/AndroidRuntime: FATAL EXCEPTION: Thread-2
? ? Process: com.mw.handlertest, PID: 6213
? ? android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
? ? ? ? at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:7784)
? ? ? ? at android.view.ViewRootImpl.requestLayout(ViewRootImpl.java:1233)
? ? ? ? at android.view.View.requestLayout(View.java:23097)
? ? ? ? at android.view.View.requestLayout(View.java:23097)
? ? ? ? at android.view.View.requestLayout(View.java:23097)
? ? ? ? at android.view.View.requestLayout(View.java:23097)
? ? ? ? at android.view.View.requestLayout(View.java:23097)
? ? ? ? at android.view.View.requestLayout(View.java:23097)
? ? ? ? at android.view.View.requestLayout(View.java:23097)
? ? ? ? at android.widget.TextView.checkForRelayout(TextView.java:8908)
? ? ? ? at android.widget.TextView.setText(TextView.java:5730)
? ? ? ? at android.widget.TextView.setText(TextView.java:5571)
? ? ? ? at android.widget.TextView.setText(TextView.java:5528)
? ? ? ? at com.mw.handlertest.MainActivity.lambda$onCreate$0$MainActivity(MainActivity.java:34)
? ? ? ? at com.mw.handlertest.-$$Lambda$MainActivity$D5xJq535IDoXU9AsiYKLL2iudzA.run(Unknown Source:2)
? ? ? ? at java.lang.Thread.run(Thread.java:764)
?
在更新UI上除直接使用Handler外还有多种方式，以下post 和 runOnUiThread?底层原理还是用的handler
(1)view.post??
showMsg = findViewById(R.id.showMsg);
new Thread(()->{
businessCodeBlock();
showMsg.post(()->{
showMsg.setText("子线程切换主线程-->更新UI");
});
}).start();
(2)runOnUiThread
showMsg = findViewById(R.id.showMsg);
new Thread(()->{
businessCodeBlock();
runOnUiThread(()->{
showMsg.setText("子线程切换主线程-->更新UI2");
});
}).start();
3、Handler使用
1、创建Message消息对象，不建议直接new Message();Message内部保存了一个缓存的消息池，用obtain从缓存池获得一个Message对象，Message使用完后系统会调用recycle回收
????????//1创建消息方法
????????Message message=handler.obtainMessage();
?
????????/2.通过Message获取
????????Message message=Message.obtain();
2、发送带参消息 handler.sendMessage(message)
new Thread(()->{
//带参消息
Message message = Message.obtain();
message.obj = "发送带参消息";
message.what = 1;
handler.sendMessage(message);
}).start();
3、发送带参延迟消息 handler.sendMessageDelayed(message, 3000);
new Thread(()->{
Message message = Message.obtain();
message.obj = "发送延迟带参消息";
message.what = 1;
handler.sendMessageDelayed(message, 3000); //发送延迟带参消息
}).start();
3、发送无参消息 handler.sendEmptyMessage(0);
new Thread(()->{
handler.sendEmptyMessage(0);
}).start();
4、发送无参延迟消息 handler.sendEmptyMessageDelayed(0,3000);
new Thread(()->{
handler.sendEmptyMessageDelayed(0,3000);
}).start();
5、定时发送带参消息 handler.sendMessageAtTime(message, SystemClock.uptimeMillis() + 5000)，以上发送的原码最终都是调用sendMessageAtTime
new Thread(()->{
Message message = Message.obtain();
message.obj = "定时发送带参消息";
message.what = 1;
handler.sendMessageAtTime(message, SystemClock.uptimeMillis() + 5000);
}).start();
6、post直接指定处理逻辑
? ? new Thread(()->{
? ? ? ? ? ? ? ? handler.post(new Runnable() {
? ? ? ? ? ? ? ? ? ? @Override
? ? ? ? ? ? ? ? ? ? public void run() {
? ? ? ? ? ? ? ? ? ? ? ? showMsg.setText("post无参callback回调方式,直接自定义处理逻辑");
? ? ? ? ? ? ? ? ? ? }
? ? ? ? ? ? ? ? });
? ? ? ? ? ? }).start();
7、postDelayed直接指定延迟处理逻辑
? ? ?new Thread(()->{
? ? ? ? ? ? ? ? handler.postDelayed(new Runnable() {
? ? ? ? ? ? ? ? ? ? @Override
? ? ? ? ? ? ? ? ? ? public void run() {
? ? ? ? ? ? ? ? ? ? ? ? showMsg.setText("post无参callback回调方式,直接自定义处理逻辑");
? ? ? ? ? ? ? ? ? ? }
? ? ? ? ? ? ? ? },3000);
? ? ? ? ? ? }).start();
8、postAtTime直接指定延迟处理逻辑
? ? ? new Thread(()->{
? ? ? ? ? ? ? ? handler.postAtTime(new Runnable() {
? ? ? ? ? ? ? ? ? ? @Override
? ? ? ? ? ? ? ? ? ? public void run() {
? ? ? ? ? ? ? ? ? ? ? ? showMsg.setText("post无参callback回调方式,直接自定义处理逻辑");
? ? ? ? ? ? ? ? ? ? }
? ? ? ? ? ? ? ? },SystemClock.uptimeMillis()+3000);
? ? ? ? ? ? }).start();
?
9、移出what=0的所有消息??handler.removeMessages(0);
new Thread(()->{
handler.sendEmptyMessageDelayed(0,3000);
handler.removeMessages(0);
}).start();
Handler.post(Runnable)其实生成的是一个what为0的Message,
调用Handler.removeMessages(0);
会使runnable任务从消息队列中清除。
10、移出what=1 and obj="需要删除的消息任务" 的所有消息??handler.removeMessages(1,obj);
? ? ? ? ? ? ? ? Object obj = "需要删除的消息任务";
? ? ? ? ? ? ? ? Message message = Message.obtain();
? ? ? ? ? ? ? ? message.obj = obj;
? ? ? ? ? ? ? ? message.what = 1;
? ? ? ? ? ? ? ? handler.sendMessageDelayed(message, 1000); //发送延迟带参消息
? ? ? ? ? ? ? ? handler.removeMessages(1,obj);
11、删除消息队列中的任何待处理消息 handler.removeCallbacks;
????????????????Runnable runnable1 = new Runnable() {
? ? ? ? ? ? ? ? ? ? @Override
? ? ? ? ? ? ? ? ? ? public void run() {
? ? ? ? ? ? ? ? ? ? ? ? showMsg.setText("1111");
? ? ? ? ? ? ? ? ? ? }
? ? ? ? ? ? ? ? };
? ? ? ? ? ? ? ? Runnable runnable2 = new Runnable() {
? ? ? ? ? ? ? ? ? ? @Override
? ? ? ? ? ? ? ? ? ? public void run() {
? ? ? ? ? ? ? ? ? ? ? ?showMsg.setText("22222");
? ? ? ? ? ? ? ? ? ? }
? ? ? ? ? ? ? ? };
? ? ? ? ? ? ? ? handler.post(runnable1);
? ? ? ? ? ? ? ? handler.post(runnable2);
? ? ? ? ? ? ? ? handler.removeCallbacks(runnable2);//指定清楚对应的回调任务消息
4、销毁
1、UI主线程销毁 handler.removeCallbacksAndMessages(null); 将所有的Callbacks和Messages全部清除掉.在Acticity退出的时候,可以避免内存泄露
@Override
protected void onDestroy() {
super.onDestroy();
if(handler != null){
handler.removeCallbacksAndMessages(null);
handler = null;
}
}
5.子线程创建Handler
private Handler handler = new MyHandle(this.getMainLooper(),this);//获取主线程的Looper对象
private Handler handler = new MyHandle(Looper.myLooper(),this);//获取当前进程的looper对象???????
1.handleMessage()可以做耗时操作，但是不能更新ui
2.如果不调用HandlerThread.quit()或者HandlerThread.quitSafely()方法,HandlerThread将会持续的接收新的任务事件.
3.只有handleMessage()方法执行完,这轮的任务才算完成,HandlerThread才会去执行下一个任务. 而且在此次执行时,即使手动的去调用quit()方法,HandlerThread的此次任务也不会停止,但是会停止下轮任务的接收. 第一个就是quit(),实际上执行了MessageQueue中的removeAllMessagesLocked方法，该方法的作用是把MessageQueue消息池中所有的消息全部清空，无论是延迟消息（带Delayed的）还是非延迟消息。
HandlerThread的2种停止接收事件的方法。
第一个就是quit(),实际上执行了MessageQueue中的removeAllMessagesLocked方法，该方法的作用是把MessageQueue消息池中所有的消息全部清空，无论是延迟消息（带Delayed的）还是非延迟消息。
第二个就是quitSafely(),执行了MessageQueue中的removeAllFutureMessagesLocked方法，该方法只会清空MessageQueue消息池中所有的延迟消息，并将消息池中所有的非延迟消息派发出去让Handler去处理，quitSafely相比于quit方法安全之处在于清空消息之前会派发所有的非延迟消息。
private HandlerThread sunThread = null;
private static Handler handler = null; //要用静态sunThread = new HandlerThread("MyHandlerThread");
sunThread.start();
sendMsgBtn.setOnClickListener((v)->{
if(handler==null){
Log.i(TAG,"创建");
handler = new Handler(sunThread.getLooper(),new Handler.Callback() {
// 这个运行在 handler-thread 线程中的,可以执行耗时操作,因此不能更新ui
@Override
public boolean handleMessage(@NonNull Message msg) {
Log.i(TAG,"子线程接收命令:"+msg.what);
if (msg.what == 1) {
businessCodeBlock();
}
return false;
}
});
}else{
handler.sendEmptyMessageDelayed(1,3000);
}
});
@Override
protected void onDestroy() {
super.onDestroy();
if(handler != null){
sunThread.quitSafely();
sunThread = null;
handler = null;
}
}
6、源码
/*
* Copyright (C) 2006 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.os;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.compat.annotation.UnsupportedAppUsage;
import android.util.Log;
import android.util.Printer;
import java.lang.reflect.Modifier;
/**
* A Handler allows you to send and process {@link Message} and Runnable
* objects associated with a thread's {@link MessageQueue}. Each Handler
* instance is associated with a single thread and that thread's message
* queue. When you create a new Handler it is bound to a {@link Looper}.
* It will deliver messages and runnables to that Looper's message
* queue and execute them on that Looper's thread.
*
* <p>There are two main uses for a Handler: (1) to schedule messages and
* runnables to be executed at some point in the future; and (2) to enqueue
* an action to be performed on a different thread than your own.
*
* <p>Scheduling messages is accomplished with the
* {@link #post}, {@link #postAtTime(Runnable, long)},
* {@link #postDelayed}, {@link #sendEmptyMessage},
* {@link #sendMessage}, {@link #sendMessageAtTime}, and
* {@link #sendMessageDelayed} methods. The <em>post</em> versions allow
* you to enqueue Runnable objects to be called by the message queue when
* they are received; the <em>sendMessage</em> versions allow you to enqueue
* a {@link Message} object containing a bundle of data that will be
* processed by the Handler's {@link #handleMessage} method (requiring that
* you implement a subclass of Handler).
*
* <p>When posting or sending to a Handler, you can either
* allow the item to be processed as soon as the message queue is ready
* to do so, or specify a delay before it gets processed or absolute time for
* it to be processed. The latter two allow you to implement timeouts,
* ticks, and other timing-based behavior.
*
* <p>When a
* process is created for your application, its main thread is dedicated to
* running a message queue that takes care of managing the top-level
* application objects (activities, broadcast receivers, etc) and any windows
* they create. You can create your own threads, and communicate back with
* the main application thread through a Handler. This is done by calling
* the same <em>post</em> or <em>sendMessage</em> methods as before, but from
* your new thread. The given Runnable or Message will then be scheduled
* in the Handler's message queue and processed when appropriate.
*/
public class Handler {
/*
* Set this flag to true to detect anonymous, local or member classes
* that extend this Handler class and that are not static. These kind
* of classes can potentially create leaks.
*/
private static final boolean FIND_POTENTIAL_LEAKS = false;
private static final String TAG = "Handler";
private static Handler MAIN_THREAD_HANDLER = null;
/**
* Callback interface you can use when instantiating a Handler to avoid
* having to implement your own subclass of Handler.
*/
public interface Callback {
/**
* @param msg A {@link android.os.Message Message} object
* @return True if no further handling is desired
*/
boolean handleMessage(@NonNull Message msg);
}
/**
* Subclasses must implement this to receive messages.
*/
public void handleMessage(@NonNull Message msg) {
}
/**
* Handle system messages here.
*/
public void dispatchMessage(@NonNull Message msg) {
if (msg.callback != null) {
handleCallback(msg);
} else {
if (mCallback != null) {
if (mCallback.handleMessage(msg)) {
return;
}
}
handleMessage(msg);
}
}
/**
* Default constructor associates this handler with the {@link Looper} for the
* current thread.
*
* If this thread does not have a looper, this handler won't be able to receive messages
* so an exception is thrown.
*
* @deprecated Implicitly choosing a Looper during Handler construction can lead to bugs
* where operations are silently lost (if the Handler is not expecting new tasks and quits),
* crashes (if a handler is sometimes created on a thread without a Looper active), or race
* conditions, where the thread a handler is associated with is not what the author
* anticipated. Instead, use an {@link java.util.concurrent.Executor} or specify the Looper
* explicitly, using {@link Looper#getMainLooper}, {link android.view.View#getHandler}, or
* similar. If the implicit thread local behavior is required for compatibility, use
* {@code new Handler(Looper.myLooper())} to make it clear to readers.
*
*/
@Deprecated
public Handler() {
this(null, false);
}
/**
* Constructor associates this handler with the {@link Looper} for the
* current thread and takes a callback interface in which you can handle
* messages.
*
* If this thread does not have a looper, this handler won't be able to receive messages
* so an exception is thrown.
*
* @param callback The callback interface in which to handle messages, or null.
*
* @deprecated Implicitly choosing a Looper during Handler construction can lead to bugs
* where operations are silently lost (if the Handler is not expecting new tasks and quits),
* crashes (if a handler is sometimes created on a thread without a Looper active), or race
* conditions, where the thread a handler is associated with is not what the author
* anticipated. Instead, use an {@link java.util.concurrent.Executor} or specify the Looper
* explicitly, using {@link Looper#getMainLooper}, {link android.view.View#getHandler}, or
* similar. If the implicit thread local behavior is required for compatibility, use
* {@code new Handler(Looper.myLooper(), callback)} to make it clear to readers.
*/
@Deprecated
public Handler(@Nullable Callback callback) {
this(callback, false);
}
/**
* Use the provided {@link Looper} instead of the default one.
*
* @param looper The looper, must not be null.
*/
public Handler(@NonNull Looper looper) {
this(looper, null, false);
}
/**
* Use the provided {@link Looper} instead of the default one and take a callback
* interface in which to handle messages.
*
* @param looper The looper, must not be null.
* @param callback The callback interface in which to handle messages, or null.
*/
public Handler(@NonNull Looper looper, @Nullable Callback callback) {
this(looper, callback, false);
}
/**
* Use the {@link Looper} for the current thread
* and set whether the handler should be asynchronous.
*
* Handlers are synchronous by default unless this constructor is used to make
* one that is strictly asynchronous.
*
* Asynchronous messages represent interrupts or events that do not require global ordering
* with respect to synchronous messages. Asynchronous messages are not subject to
* the synchronization barriers introduced by {@link MessageQueue#enqueueSyncBarrier(long)}.
*
* @param async If true, the handler calls {@link Message#setAsynchronous(boolean)} for
* each {@link Message} that is sent to it or {@link Runnable} that is posted to it.
*
* @hide
*/
@UnsupportedAppUsage
public Handler(boolean async) {
this(null, async);
}
/**
* Use the {@link Looper} for the current thread with the specified callback interface
* and set whether the handler should be asynchronous.
*
* Handlers are synchronous by default unless this constructor is used to make
* one that is strictly asynchronous.
*
* Asynchronous messages represent interrupts or events that do not require global ordering
* with respect to synchronous messages. Asynchronous messages are not subject to
* the synchronization barriers introduced by {@link MessageQueue#enqueueSyncBarrier(long)}.
*
* @param callback The callback interface in which to handle messages, or null.
* @param async If true, the handler calls {@link Message#setAsynchronous(boolean)} for
* each {@link Message} that is sent to it or {@link Runnable} that is posted to it.
*
* @hide
*/
public Handler(@Nullable Callback callback, boolean async) {
if (FIND_POTENTIAL_LEAKS) {
final Class<? extends Handler> klass = getClass();
if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) &&
(klass.getModifiers() & Modifier.STATIC) == 0) {
Log.w(TAG, "The following Handler class should be static or leaks might occur: " +
klass.getCanonicalName());
}
}
mLooper = Looper.myLooper();
if (mLooper == null) {
throw new RuntimeException(
"Can't create handler inside thread " + Thread.currentThread()
+ " that has not called Looper.prepare()");
}
mQueue = mLooper.mQueue;
mCallback = callback;
mAsynchronous = async;
}
/**
* Use the provided {@link Looper} instead of the default one and take a callback
* interface in which to handle messages. Also set whether the handler
* should be asynchronous.
*
* Handlers are synchronous by default unless this constructor is used to make
* one that is strictly asynchronous.
*
* Asynchronous messages represent interrupts or events that do not require global ordering
* with respect to synchronous messages. Asynchronous messages are not subject to
* the synchronization barriers introduced by conditions such as display vsync.
*
* @param looper The looper, must not be null.
* @param callback The callback interface in which to handle messages, or null.
* @param async If true, the handler calls {@link Message#setAsynchronous(boolean)} for
* each {@link Message} that is sent to it or {@link Runnable} that is posted to it.
*
* @hide
*/
@UnsupportedAppUsage
public Handler(@NonNull Looper looper, @Nullable Callback callback, boolean async) {
mLooper = looper;
mQueue = looper.mQueue;
mCallback = callback;
mAsynchronous = async;
}
/**
* Create a new Handler whose posted messages and runnables are not subject to
* synchronization barriers such as display vsync.
*
* <p>Messages sent to an async handler are guaranteed to be ordered with respect to one another,
* but not necessarily with respect to messages from other Handlers.</p>
*
* @see #createAsync(Looper, Callback) to create an async Handler with custom message handling.
*
* @param looper the Looper that the new Handler should be bound to
* @return a new async Handler instance
*/
@NonNull
public static Handler createAsync(@NonNull Looper looper) {
if (looper == null) throw new NullPointerException("looper must not be null");
return new Handler(looper, null, true);
}
/**
* Create a new Handler whose posted messages and runnables are not subject to
* synchronization barriers such as display vsync.
*
* <p>Messages sent to an async handler are guaranteed to be ordered with respect to one another,
* but not necessarily with respect to messages from other Handlers.</p>
*
* @see #createAsync(Looper) to create an async Handler without custom message handling.
*
* @param looper the Looper that the new Handler should be bound to
* @return a new async Handler instance
*/
@NonNull
public static Handler createAsync(@NonNull Looper looper, @NonNull Callback callback) {
if (looper == null) throw new NullPointerException("looper must not be null");
if (callback == null) throw new NullPointerException("callback must not be null");
return new Handler(looper, callback, true);
}
/** @hide */
@UnsupportedAppUsage
@NonNull
public static Handler getMain() {
if (MAIN_THREAD_HANDLER == null) {
MAIN_THREAD_HANDLER = new Handler(Looper.getMainLooper());
}
return MAIN_THREAD_HANDLER;
}
/** @hide */
@NonNull
public static Handler mainIfNull(@Nullable Handler handler) {
return handler == null ? getMain() : handler;
}
/** {@hide} */
@NonNull
public String getTraceName(@NonNull Message message) {
if (message.callback instanceof TraceNameSupplier) {
return ((TraceNameSupplier) message.callback).getTraceName();
}
final StringBuilder sb = new StringBuilder();
sb.append(getClass().getName()).append(": ");
if (message.callback != null) {
sb.append(message.callback.getClass().getName());
} else {
sb.append("#").append(message.what);
}
return sb.toString();
}
/**
* Returns a string representing the name of the specified message.
* The default implementation will either return the class name of the
* message callback if any, or the hexadecimal representation of the
* message "what" field.
*
* @param message The message whose name is being queried
*/
@NonNull
public String getMessageName(@NonNull Message message) {
if (message.callback != null) {
return message.callback.getClass().getName();
}
return "0x" + Integer.toHexString(message.what);
}
/**
* Returns a new {@link android.os.Message Message} from the global message pool. More efficient than
* creating and allocating new instances. The retrieved message has its handler set to this instance (Message.target == this).
* If you don't want that facility, just call Message.obtain() instead.
*/
@NonNull
public final Message obtainMessage()
{
return Message.obtain(this);
}
/**
* Same as {@link #obtainMessage()}, except that it also sets the what member of the returned Message.
*
* @param what Value to assign to the returned Message.what field.
* @return A Message from the global message pool.
*/
@NonNull
public final Message obtainMessage(int what)
{
return Message.obtain(this, what);
}
/**
*
* Same as {@link #obtainMessage()}, except that it also sets the what and obj members
* of the returned Message.
*
* @param what Value to assign to the returned Message.what field.
* @param obj Value to assign to the returned Message.obj field.
* @return A Message from the global message pool.
*/
@NonNull
public final Message obtainMessage(int what, @Nullable Object obj) {
return Message.obtain(this, what, obj);
}
/**
*
* Same as {@link #obtainMessage()}, except that it also sets the what, arg1 and arg2 members of the returned
* Message.
* @param what Value to assign to the returned Message.what field.
* @param arg1 Value to assign to the returned Message.arg1 field.
* @param arg2 Value to assign to the returned Message.arg2 field.
* @return A Message from the global message pool.
*/
@NonNull
public final Message obtainMessage(int what, int arg1, int arg2)
{
return Message.obtain(this, what, arg1, arg2);
}
/**
*
* Same as {@link #obtainMessage()}, except that it also sets the what, obj, arg1,and arg2 values on the
* returned Message.
* @param what Value to assign to the returned Message.what field.
* @param arg1 Value to assign to the returned Message.arg1 field.
* @param arg2 Value to assign to the returned Message.arg2 field.
* @param obj Value to assign to the returned Message.obj field.
* @return A Message from the global message pool.
*/
@NonNull
public final Message obtainMessage(int what, int arg1, int arg2, @Nullable Object obj) {
return Message.obtain(this, what, arg1, arg2, obj);
}
/**
* Causes the Runnable r to be added to the message queue.
* The runnable will be run on the thread to which this handler is
* attached.
*
* @param r The Runnable that will be executed.
*
* @return Returns true if the Runnable was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean post(@NonNull Runnable r) {
return sendMessageDelayed(getPostMessage(r), 0);
}
/**
* Causes the Runnable r to be added to the message queue, to be run
* at a specific time given by <var>uptimeMillis</var>.
* <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
* Time spent in deep sleep will add an additional delay to execution.
* The runnable will be run on the thread to which this handler is attached.
*
* @param r The Runnable that will be executed.
* @param uptimeMillis The absolute time at which the callback should run,
* using the {@link android.os.SystemClock#uptimeMillis} time-base.
*
* @return Returns true if the Runnable was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting. Note that a
* result of true does not mean the Runnable will be processed -- if
* the looper is quit before the delivery time of the message
* occurs then the message will be dropped.
*/
public final boolean postAtTime(@NonNull Runnable r, long uptimeMillis) {
return sendMessageAtTime(getPostMessage(r), uptimeMillis);
}
/**
* Causes the Runnable r to be added to the message queue, to be run
* at a specific time given by <var>uptimeMillis</var>.
* <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
* Time spent in deep sleep will add an additional delay to execution.
* The runnable will be run on the thread to which this handler is attached.
*
* @param r The Runnable that will be executed.
* @param token An instance which can be used to cancel {@code r} via
* {@link #removeCallbacksAndMessages}.
* @param uptimeMillis The absolute time at which the callback should run,
* using the {@link android.os.SystemClock#uptimeMillis} time-base.
*
* @return Returns true if the Runnable was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting. Note that a
* result of true does not mean the Runnable will be processed -- if
* the looper is quit before the delivery time of the message
* occurs then the message will be dropped.
*
* @see android.os.SystemClock#uptimeMillis
*/
public final boolean postAtTime(
@NonNull Runnable r, @Nullable Object token, long uptimeMillis) {
return sendMessageAtTime(getPostMessage(r, token), uptimeMillis);
}
/**
* Causes the Runnable r to be added to the message queue, to be run
* after the specified amount of time elapses.
* The runnable will be run on the thread to which this handler
* is attached.
* <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
* Time spent in deep sleep will add an additional delay to execution.
*
* @param r The Runnable that will be executed.
* @param delayMillis The delay (in milliseconds) until the Runnable
* will be executed.
*
* @return Returns true if the Runnable was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting. Note that a
* result of true does not mean the Runnable will be processed --
* if the looper is quit before the delivery time of the message
* occurs then the message will be dropped.
*/
public final boolean postDelayed(@NonNull Runnable r, long delayMillis) {
return sendMessageDelayed(getPostMessage(r), delayMillis);
}
/** @hide */
public final boolean postDelayed(Runnable r, int what, long delayMillis) {
return sendMessageDelayed(getPostMessage(r).setWhat(what), delayMillis);
}
/**
* Causes the Runnable r to be added to the message queue, to be run
* after the specified amount of time elapses.
* The runnable will be run on the thread to which this handler
* is attached.
* <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
* Time spent in deep sleep will add an additional delay to execution.
*
* @param r The Runnable that will be executed.
* @param token An instance which can be used to cancel {@code r} via
* {@link #removeCallbacksAndMessages}.
* @param delayMillis The delay (in milliseconds) until the Runnable
* will be executed.
*
* @return Returns true if the Runnable was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting. Note that a
* result of true does not mean the Runnable will be processed --
* if the looper is quit before the delivery time of the message
* occurs then the message will be dropped.
*/
public final boolean postDelayed(
@NonNull Runnable r, @Nullable Object token, long delayMillis) {
return sendMessageDelayed(getPostMessage(r, token), delayMillis);
}
/**
* Posts a message to an object that implements Runnable.
* Causes the Runnable r to executed on the next iteration through the
* message queue. The runnable will be run on the thread to which this
* handler is attached.
* <b>This method is only for use in very special circumstances -- it
* can easily starve the message queue, cause ordering problems, or have
* other unexpected side-effects.</b>
*
* @param r The Runnable that will be executed.
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean postAtFrontOfQueue(@NonNull Runnable r) {
return sendMessageAtFrontOfQueue(getPostMessage(r));
}
/**
* Runs the specified task synchronously.
* <p>
* If the current thread is the same as the handler thread, then the runnable
* runs immediately without being enqueued. Otherwise, posts the runnable
* to the handler and waits for it to complete before returning.
* </p><p>
* This method is dangerous! Improper use can result in deadlocks.
* Never call this method while any locks are held or use it in a
* possibly re-entrant manner.
* </p><p>
* This method is occasionally useful in situations where a background thread
* must synchronously await completion of a task that must run on the
* handler's thread. However, this problem is often a symptom of bad design.
* Consider improving the design (if possible) before resorting to this method.
* </p><p>
* One example of where you might want to use this method is when you just
* set up a Handler thread and need to perform some initialization steps on
* it before continuing execution.
* </p><p>
* If timeout occurs then this method returns <code>false</code> but the runnable
* will remain posted on the handler and may already be in progress or
* complete at a later time.
* </p><p>
* When using this method, be sure to use {@link Looper#quitSafely} when
* quitting the looper. Otherwise {@link #runWithScissors} may hang indefinitely.
* (TODO: We should fix this by making MessageQueue aware of blocking runnables.)
* </p>
*
* @param r The Runnable that will be executed synchronously.
* @param timeout The timeout in milliseconds, or 0 to wait indefinitely.
*
* @return Returns true if the Runnable was successfully executed.
* Returns false on failure, usually because the
* looper processing the message queue is exiting.
*
* @hide This method is prone to abuse and should probably not be in the API.
* If we ever do make it part of the API, we might want to rename it to something
* less funny like runUnsafe().
*/
public final boolean runWithScissors(@NonNull Runnable r, long timeout) {
if (r == null) {
throw new IllegalArgumentException("runnable must not be null");
}
if (timeout < 0) {
throw new IllegalArgumentException("timeout must be non-negative");
}
if (Looper.myLooper() == mLooper) {
r.run();
return true;
}
BlockingRunnable br = new BlockingRunnable(r);
return br.postAndWait(this, timeout);
}
/**
* Remove any pending posts of Runnable r that are in the message queue.
*/
public final void removeCallbacks(@NonNull Runnable r) {
mQueue.removeMessages(this, r, null);
}
/**
* Remove any pending posts of Runnable <var>r</var> with Object
* <var>token</var> that are in the message queue. If <var>token</var> is null,
* all callbacks will be removed.
*/
public final void removeCallbacks(@NonNull Runnable r, @Nullable Object token) {
mQueue.removeMessages(this, r, token);
}
/**
* Pushes a message onto the end of the message queue after all pending messages
* before the current time. It will be received in {@link #handleMessage},
* in the thread attached to this handler.
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendMessage(@NonNull Message msg) {
return sendMessageDelayed(msg, 0);
}
/**
* Sends a Message containing only the what value.
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendEmptyMessage(int what)
{
return sendEmptyMessageDelayed(what, 0);
}
/**
* Sends a Message containing only the what value, to be delivered
* after the specified amount of time elapses.
* @see #sendMessageDelayed(android.os.Message, long)
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendEmptyMessageDelayed(int what, long delayMillis) {
Message msg = Message.obtain();
msg.what = what;
return sendMessageDelayed(msg, delayMillis);
}
/**
* Sends a Message containing only the what value, to be delivered
* at a specific time.
* @see #sendMessageAtTime(android.os.Message, long)
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendEmptyMessageAtTime(int what, long uptimeMillis) {
Message msg = Message.obtain();
msg.what = what;
return sendMessageAtTime(msg, uptimeMillis);
}
/**
* Enqueue a message into the message queue after all pending messages
* before (current time + delayMillis). You will receive it in
* {@link #handleMessage}, in the thread attached to this handler.
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting. Note that a
* result of true does not mean the message will be processed -- if
* the looper is quit before the delivery time of the message
* occurs then the message will be dropped.
*/
public final boolean sendMessageDelayed(@NonNull Message msg, long delayMillis) {
if (delayMillis < 0) {
delayMillis = 0;
}
return sendMessageAtTime(msg, SystemClock.uptimeMillis() + delayMillis);
}
/**
* Enqueue a message into the message queue after all pending messages
* before the absolute time (in milliseconds) <var>uptimeMillis</var>.
* <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
* Time spent in deep sleep will add an additional delay to execution.
* You will receive it in {@link #handleMessage}, in the thread attached
* to this handler.
*
* @param uptimeMillis The absolute time at which the message should be
* delivered, using the
* {@link android.os.SystemClock#uptimeMillis} time-base.
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting. Note that a
* result of true does not mean the message will be processed -- if
* the looper is quit before the delivery time of the message
* occurs then the message will be dropped.
*/
public boolean sendMessageAtTime(@NonNull Message msg, long uptimeMillis) {
MessageQueue queue = mQueue;
if (queue == null) {
RuntimeException e = new RuntimeException(
this + " sendMessageAtTime() called with no mQueue");
Log.w("Looper", e.getMessage(), e);
return false;
}
return enqueueMessage(queue, msg, uptimeMillis);
}
/**
* Enqueue a message at the front of the message queue, to be processed on
* the next iteration of the message loop. You will receive it in
* {@link #handleMessage}, in the thread attached to this handler.
* <b>This method is only for use in very special circumstances -- it
* can easily starve the message queue, cause ordering problems, or have
* other unexpected side-effects.</b>
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendMessageAtFrontOfQueue(@NonNull Message msg) {
MessageQueue queue = mQueue;
if (queue == null) {
RuntimeException e = new RuntimeException(
this + " sendMessageAtTime() called with no mQueue");
Log.w("Looper", e.getMessage(), e);
return false;
}
return enqueueMessage(queue, msg, 0);
}
/**
* Executes the message synchronously if called on the same thread this handler corresponds to,
* or {@link #sendMessage pushes it to the queue} otherwise
*
* @return Returns true if the message was successfully ran or placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
* @hide
*/
public final boolean executeOrSendMessage(@NonNull Message msg) {
if (mLooper == Looper.myLooper()) {
dispatchMessage(msg);
return true;
}
return sendMessage(msg);
}
private boolean enqueueMessage(@NonNull MessageQueue queue, @NonNull Message msg,
long uptimeMillis) {
msg.target = this;
msg.workSourceUid = ThreadLocalWorkSource.getUid();
if (mAsynchronous) {
msg.setAsynchronous(true);
}
return queue.enqueueMessage(msg, uptimeMillis);
}
/**
* Remove any pending posts of messages with code 'what' that are in the
* message queue.
*/
public final void removeMessages(int what) {
mQueue.removeMessages(this, what, null);
}
/**
* Remove any pending posts of messages with code 'what' and whose obj is
* 'object' that are in the message queue. If <var>object</var> is null,
* all messages will be removed.
*/
public final void removeMessages(int what, @Nullable Object object) {
mQueue.removeMessages(this, what, object);
}
/**
* Remove any pending posts of messages with code 'what' and whose obj is
* 'object' that are in the message queue. If <var>object</var> is null,
* all messages will be removed.
*
*@hide
*/
public final void removeEqualMessages(int what, @Nullable Object object) {
mQueue.removeEqualMessages(this, what, object);
}
/**
* Remove any pending posts of callbacks and sent messages whose
* <var>obj</var> is <var>token</var>. If <var>token</var> is null,
* all callbacks and messages will be removed.
*/
public final void removeCallbacksAndMessages(@Nullable Object token) {
mQueue.removeCallbacksAndMessages(this, token);
}
/**
* Remove any pending posts of callbacks and sent messages whose
* <var>obj</var> is <var>token</var>. If <var>token</var> is null,
* all callbacks and messages will be removed.
*
*@hide
*/
public final void removeCallbacksAndEqualMessages(@Nullable Object token) {
mQueue.removeCallbacksAndEqualMessages(this, token);
}
/**
* Check if there are any pending posts of messages with code 'what' in
* the message queue.
*/
public final boolean hasMessages(int what) {
return mQueue.hasMessages(this, what, null);
}
/**
* Return whether there are any messages or callbacks currently scheduled on this handler.
* @hide
*/
public final boolean hasMessagesOrCallbacks() {
return mQueue.hasMessages(this);
}
/**
* Check if there are any pending posts of messages with code 'what' and
* whose obj is 'object' in the message queue.
*/
public final boolean hasMessages(int what, @Nullable Object object) {
return mQueue.hasMessages(this, what, object);
}
/**
* Check if there are any pending posts of messages with code 'what' and
* whose obj is 'object' in the message queue.
*
*@hide
*/
public final boolean hasEqualMessages(int what, @Nullable Object object) {
return mQueue.hasEqualMessages(this, what, object);
}
/**
* Check if there are any pending posts of messages with callback r in
* the message queue.
*/
public final boolean hasCallbacks(@NonNull Runnable r) {
return mQueue.hasMessages(this, r, null);
}
// if we can get rid of this method, the handler need not remember its loop
// we could instead export a getMessageQueue() method...
@NonNull
public final Looper getLooper() {
return mLooper;
}
public final void dump(@NonNull Printer pw, @NonNull String prefix) {
pw.println(prefix + this + " @ " + SystemClock.uptimeMillis());
if (mLooper == null) {
pw.println(prefix + "looper uninitialized");
} else {
mLooper.dump(pw, prefix + " ");
}
}
/**
* @hide
*/
public final void dumpMine(@NonNull Printer pw, @NonNull String prefix) {
pw.println(prefix + this + " @ " + SystemClock.uptimeMillis());
if (mLooper == null) {
pw.println(prefix + "looper uninitialized");
} else {
mLooper.dump(pw, prefix + " ", this);
}
}
@Override
public String toString() {
return "Handler (" + getClass().getName() + ") {"
+ Integer.toHexString(System.identityHashCode(this))
+ "}";
}
@UnsupportedAppUsage
final IMessenger getIMessenger() {
synchronized (mQueue) {
if (mMessenger != null) {
return mMessenger;
}
mMessenger = new MessengerImpl();
return mMessenger;
}
}
private final class MessengerImpl extends IMessenger.Stub {
public void send(Message msg) {
msg.sendingUid = Binder.getCallingUid();
Handler.this.sendMessage(msg);
}
}
private static Message getPostMessage(Runnable r) {
Message m = Message.obtain();
m.callback = r;
return m;
}
@UnsupportedAppUsage
private static Message getPostMessage(Runnable r, Object token) {
Message m = Message.obtain();
m.obj = token;
m.callback = r;
return m;
}
private static void handleCallback(Message message) {
message.callback.run();
}
@UnsupportedAppUsage
final Looper mLooper;
final MessageQueue mQueue;
@UnsupportedAppUsage
final Callback mCallback;
final boolean mAsynchronous;
@UnsupportedAppUsage
IMessenger mMessenger;
private static final class BlockingRunnable implements Runnable {
private final Runnable mTask;
private boolean mDone;
public BlockingRunnable(Runnable task) {
mTask = task;
}
@Override
public void run() {
try {
mTask.run();
} finally {
synchronized (this) {
mDone = true;
notifyAll();
}
}
}
public boolean postAndWait(Handler handler, long timeout) {
if (!handler.post(this)) {
return false;
}
synchronized (this) {
if (timeout > 0) {
final long expirationTime = SystemClock.uptimeMillis() + timeout;
while (!mDone) {
long delay = expirationTime - SystemClock.uptimeMillis();
if (delay <= 0) {
return false; // timeout
}
try {
wait(delay);
} catch (InterruptedException ex) {
}
}
} else {
while (!mDone) {
try {
wait();
} catch (InterruptedException ex) {
}
}
}
}
return true;
}
}
}
参考
https://blog.csdn.net/qq_37321098/article/details/81535449
https://blog.csdn.net/qq_34304620/article/details/107082677
https://segmentfault.com/a/1190000018995735
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