[移动开发] 【Android 】零基础到飞升 | Handler消息传递机制浅析

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[移动开发]【Android 】零基础到飞升 | Handler消息传递机制浅析

3.3 Handler消息传递机制浅析

分类 Android 基础入门教程

本节引言

前两节中我们对Android中的两种事件处理机制进行了学习，关于响应的事件响应就这两种；本节给大家讲解的是Activity中UI组件中的信息传递Handler，相信很多朋友都知道，Android为了线程安全，并不允许我们在UI线程外操作UI；很多时候我们做界面刷新都需要通过Handler来通知UI组件更新！除了用Handler完成界面更新外，还可以使用runOnUiThread()来更新，甚至更高级的事务总线，当然，这里我们只讲解Handler，什么是Handler，执行流程，相关方法，子线程与主线程中中使用Handler的区别等！

1.学习路线图：

2.Handler类的引入:

3.Handler的执行流程图：

流程图解析: 相关名词

UI线程:就是我们的主线程,系统在创建UI线程的时候会初始化一个Looper对象,同时也会创建一个与其关联的MessageQueue;
Handler:作用就是发送与处理信息,如果希望Handler正常工作,在当前线程中要有一个Looper对象
Message:Handler接收与处理的消息对象
MessageQueue:消息队列,先进先出管理Message,在初始化Looper对象时会创建一个与之关联的MessageQueue;
Looper:每个线程只能够有一个Looper,管理MessageQueue,不断地从中取出Message分发给对应的Handler处理！

简单点说：

当我们的子线程想修改Activity中的UI组件时,我们可以新建一个Handler对象,通过这个对象向主线程发送信息;而我们发送的信息会先到主线程的MessageQueue进行等待,由Looper按先入先出顺序取出,再根据message对象的what属性分发给对应的Handler进行处理！

4.Handler的相关方法:

void handleMessage(Message msg):处理消息的方法,通常是用于被重写!
sendEmptyMessage(int what):发送空消息
sendEmptyMessageDelayed(int what,long delayMillis):指定延时多少毫秒后发送空信息
sendMessage(Message msg):立即发送信息
sendMessageDelayed(Message msg):指定延时多少毫秒后发送信息
final boolean hasMessage(int what):检查消息队列中是否包含what属性为指定值的消息如果是参数为(int what,Object object):除了判断what属性,还需要判断Object属性是否为指定对象的消息

5.Handler的使用示例：

1）Handler写在主线程中

在主线程中,因为系统已经初始化了一个Looper对象,所以我们直接创建Handler对象,就可以进行信息的发送与处理了！

代码示例： 简单的一个定时切换图片的程序,通过Timer定时器,定时修改ImageView显示的内容,从而形成帧动画

运行效果图：

实现代码：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    xmlns:tools="http://schemas.android.com/tools"  
    android:id="@+id/RelativeLayout1"  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    android:gravity="center"  
    tools:context="com.jay.example.handlerdemo1.MainActivity" >  
  
    <ImageView  
        android:id="@+id/imgchange"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignParentLeft="true"  
        android:layout_alignParentTop="true" />  
  
</RelativeLayout>

MainActivity.java：

public class MainActivity extends Activity {  
</span><span class="com">//定义切换的图片的数组id  </span><span class="pln">
</span><span class="kwd">int</span><span class="pln"> imgids</span><span class="pun">[]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="kwd">int</span><span class="pun">[]{</span><span class="pln">  
    R</span><span class="pun">.</span><span class="pln">drawable</span><span class="pun">.</span><span class="pln">s_1</span><span class="pun">,</span><span class="pln"> R</span><span class="pun">.</span><span class="pln">drawable</span><span class="pun">.</span><span class="pln">s_2</span><span class="pun">,</span><span class="pln">R</span><span class="pun">.</span><span class="pln">drawable</span><span class="pun">.</span><span class="pln">s_3</span><span class="pun">,</span><span class="pln">  
    R</span><span class="pun">.</span><span class="pln">drawable</span><span class="pun">.</span><span class="pln">s_4</span><span class="pun">,</span><span class="pln">R</span><span class="pun">.</span><span class="pln">drawable</span><span class="pun">.</span><span class="pln">s_5</span><span class="pun">,</span><span class="pln">R</span><span class="pun">.</span><span class="pln">drawable</span><span class="pun">.</span><span class="pln">s_6</span><span class="pun">,</span><span class="pln">  
    R</span><span class="pun">.</span><span class="pln">drawable</span><span class="pun">.</span><span class="pln">s_7</span><span class="pun">,</span><span class="pln">R</span><span class="pun">.</span><span class="pln">drawable</span><span class="pun">.</span><span class="pln">s_8  
</span><span class="pun">};</span><span class="pln">  
</span><span class="kwd">int</span><span class="pln"> imgstart </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln">

????final Handler myHandler = new Handler()
{
@Override
//重写handleMessage方法,根据msg中what的值判断是否执行后续操作
public void handleMessage(Message msg) {
if(msg.what == 0x123)
{
imgchange.setImageResource(imgids[imgstart++ % 8]);
}
}
};
????
????
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final ImageView imgchange = (ImageView) findViewById(R.id.imgchange);

    </span><span class="com">//使用定时器,每隔200毫秒让handler发送一个空信息  </span><span class="pln">
    </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Timer</span><span class="pun">().</span><span class="pln">schedule</span><span class="pun">(</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">TimerTask</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">            
        </span><span class="lit">@Override</span><span class="pln">  
        </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> run</span><span class="pun">()</span><span class="pln"> </span><span class="pun">{</span><span class="pln">  
            myHandler</span><span class="pun">.</span><span class="pln">sendEmptyMessage</span><span class="pun">(</span><span class="lit">0x123</span><span class="pun">);</span><span class="pln">  
              
        </span><span class="pun">}</span><span class="pln">  
    </span><span class="pun">},</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="lit">200</span><span class="pun">);</span><span class="pln">  
</span><span class="pun">}</span><span class="pln">

}

2）Handler写在子线程中

如果是Handler写在了子线程中的话,我们就需要自己创建一个Looper对象了!创建的流程如下:

1 )直接调用Looper.prepare()方法即可为当前线程创建Looper对象,而它的构造器会创建配套的MessageQueue; 2 )创建Handler对象,重写handleMessage( )方法就可以处理来自于其他线程的信息了! 3 )调用Looper.loop()方法启动Looper

使用示例：输入一个数，计算后通过Toast输出在这个范围内的所有质数

实现代码： main.xml：

<LinearLayout  
    xmlns:android="http://schemas.android.com/apk/res/android"  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    android:orientation="vertical">  
    <EditText  
        android:id="@+id/etNum"  
        android:inputType="number"  
        android:layout_width="match_parent"  
        android:layout_height="wrap_content"  
        android:hint="请输入上限"/>  
    <Button  
        android:layout_width="match_parent"  
        android:layout_height="wrap_content"  
        android:onClick="cal"  
        android:text="计算"/>    
</LinearLayout>

MainActivity.java:

public class CalPrime extends Activity  
{  
    static final String UPPER_NUM = "upper";  
    EditText etNum;  
    CalThread calThread;  
    // 定义一个线程类  
    class CalThread extends Thread  
    {  
        public Handler mHandler;  
    </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> run</span><span class="pun">()</span><span class="pln">  
    </span><span class="pun">{</span><span class="pln">  
        </span><span class="typ">Looper</span><span class="pun">.</span><span class="pln">prepare</span><span class="pun">();</span><span class="pln">  
        mHandler </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Handler</span><span class="pun">()</span><span class="pln">  
        </span><span class="pun">{</span><span class="pln">  
            </span><span class="com">// 定义处理消息的方法  </span><span class="pln">
            </span><span class="lit">@Override</span><span class="pln">  
            </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> handleMessage</span><span class="pun">(</span><span class="typ">Message</span><span class="pln"> msg</span><span class="pun">)</span><span class="pln">  
            </span><span class="pun">{</span><span class="pln">  
                </span><span class="kwd">if</span><span class="pun">(</span><span class="pln">msg</span><span class="pun">.</span><span class="pln">what </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0x123</span><span class="pun">)</span><span class="pln">  
                </span><span class="pun">{</span><span class="pln">  
                    </span><span class="kwd">int</span><span class="pln"> upper </span><span class="pun">=</span><span class="pln"> msg</span><span class="pun">.</span><span class="pln">getData</span><span class="pun">().</span><span class="pln">getInt</span><span class="pun">(</span><span class="pln">UPPER_NUM</span><span class="pun">);</span><span class="pln">  
                    </span><span class="typ">List</span><span class="pun">&lt;</span><span class="typ">Integer</span><span class="pun">&gt;</span><span class="pln"> nums </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">ArrayList</span><span class="pun">&lt;</span><span class="typ">Integer</span><span class="pun">&gt;();</span><span class="pln">  
                    </span><span class="com">// 计算从2开始、到upper的所有质数  </span><span class="pln">
                    outer</span><span class="pun">:</span><span class="pln">  
                    </span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> i </span><span class="pun">=</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span><span class="pun">;</span><span class="pln"> i </span><span class="pun">&lt;=</span><span class="pln"> upper </span><span class="pun">;</span><span class="pln"> i</span><span class="pun">++)</span><span class="pln">  
                    </span><span class="pun">{</span><span class="pln">  
                        </span><span class="com">// 用i处于从2开始、到i的平方根的所有数  </span><span class="pln">
                        </span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> j </span><span class="pun">=</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span><span class="pun">;</span><span class="pln"> j </span><span class="pun">&lt;=</span><span class="pln"> </span><span class="typ">Math</span><span class="pun">.</span><span class="pln">sqrt</span><span class="pun">(</span><span class="pln">i</span><span class="pun">)</span><span class="pln"> </span><span class="pun">;</span><span class="pln"> j</span><span class="pun">++)</span><span class="pln">  
                        </span><span class="pun">{</span><span class="pln">  
                            </span><span class="com">// 如果可以整除，表明这个数不是质数  </span><span class="pln">
                            </span><span class="kwd">if</span><span class="pun">(</span><span class="pln">i </span><span class="pun">!=</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span><span class="pun">&amp;&amp;</span><span class="pln"> i </span><span class="pun">%</span><span class="pln"> j </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">)</span><span class="pln">  
                            </span><span class="pun">{</span><span class="pln">  
                                </span><span class="kwd">continue</span><span class="pln"> outer</span><span class="pun">;</span><span class="pln">  
                            </span><span class="pun">}</span><span class="pln">  
                        </span><span class="pun">}</span><span class="pln">  
                        nums</span><span class="pun">.</span><span class="pln">add</span><span class="pun">(</span><span class="pln">i</span><span class="pun">);</span><span class="pln">  
                    </span><span class="pun">}</span><span class="pln">  
                    </span><span class="com">// 使用Toast显示统计出来的所有质数  </span><span class="pln">
                    </span><span class="typ">Toast</span><span class="pun">.</span><span class="pln">makeText</span><span class="pun">(</span><span class="typ">CalPrime</span><span class="pun">.</span><span class="kwd">this</span><span class="pln"> </span><span class="pun">,</span><span class="pln"> nums</span><span class="pun">.</span><span class="pln">toString</span><span class="pun">()</span><span class="pln">  
                        </span><span class="pun">,</span><span class="pln"> </span><span class="typ">Toast</span><span class="pun">.</span><span class="pln">LENGTH_LONG</span><span class="pun">).</span><span class="pln">show</span><span class="pun">();</span><span class="pln">  
                </span><span class="pun">}</span><span class="pln">  
            </span><span class="pun">}</span><span class="pln">  
        </span><span class="pun">};</span><span class="pln">  
        </span><span class="typ">Looper</span><span class="pun">.</span><span class="pln">loop</span><span class="pun">();</span><span class="pln">  
    </span><span class="pun">}</span><span class="pln">  
</span><span class="pun">}</span><span class="pln">  
</span><span class="lit">@Override</span><span class="pln">  
</span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> onCreate</span><span class="pun">(</span><span class="typ">Bundle</span><span class="pln"> savedInstanceState</span><span class="pun">)</span><span class="pln">  
</span><span class="pun">{</span><span class="pln">  
    </span><span class="kwd">super</span><span class="pun">.</span><span class="pln">onCreate</span><span class="pun">(</span><span class="pln">savedInstanceState</span><span class="pun">);</span><span class="pln">  
    setContentView</span><span class="pun">(</span><span class="pln">R</span><span class="pun">.</span><span class="pln">layout</span><span class="pun">.</span><span class="pln">main</span><span class="pun">);</span><span class="pln">  
    etNum </span><span class="pun">=</span><span class="pln"> </span><span class="pun">(</span><span class="typ">EditText</span><span class="pun">)</span><span class="pln">findViewById</span><span class="pun">(</span><span class="pln">R</span><span class="pun">.</span><span class="pln">id</span><span class="pun">.</span><span class="pln">etNum</span><span class="pun">);</span><span class="pln">  
    calThread </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">CalThread</span><span class="pun">();</span><span class="pln">  
    </span><span class="com">// 启动新线程  </span><span class="pln">
    calThread</span><span class="pun">.</span><span class="pln">start</span><span class="pun">();</span><span class="pln">  
</span><span class="pun">}</span><span class="pln">  
</span><span class="com">// 为按钮的点击事件提供事件处理函数  </span><span class="pln">
</span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> cal</span><span class="pun">(</span><span class="typ">View</span><span class="pln"> source</span><span class="pun">)</span><span class="pln">  
</span><span class="pun">{</span><span class="pln">  
    </span><span class="com">// 创建消息  </span><span class="pln">
    </span><span class="typ">Message</span><span class="pln"> msg </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Message</span><span class="pun">();</span><span class="pln">  
    msg</span><span class="pun">.</span><span class="pln">what </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0x123</span><span class="pun">;</span><span class="pln">  
    </span><span class="typ">Bundle</span><span class="pln"> bundle </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Bundle</span><span class="pun">();</span><span class="pln">  
    bundle</span><span class="pun">.</span><span class="pln">putInt</span><span class="pun">(</span><span class="pln">UPPER_NUM </span><span class="pun">,</span><span class="pln">  
        </span><span class="typ">Integer</span><span class="pun">.</span><span class="pln">parseInt</span><span class="pun">(</span><span class="pln">etNum</span><span class="pun">.</span><span class="pln">getText</span><span class="pun">().</span><span class="pln">toString</span><span class="pun">()));</span><span class="pln">  
    msg</span><span class="pun">.</span><span class="pln">setData</span><span class="pun">(</span><span class="pln">bundle</span><span class="pun">);</span><span class="pln">  
    </span><span class="com">// 向新线程中的Handler发送消息  </span><span class="pln">
    calThread</span><span class="pun">.</span><span class="pln">mHandler</span><span class="pun">.</span><span class="pln">sendMessage</span><span class="pun">(</span><span class="pln">msg</span><span class="pun">);</span><span class="pln">  
</span><span class="pun">}</span><span class="pln">