项目需求

运用蓝牙进程通信，实现两个手机的蓝牙进行通信聊天。

项目主要代码及功能实现

AndroidManifest.xml

给予项目蓝牙通信的相关权限

    <!-- 下面2个是普通权限，只需要在清单文件里注册，不需要在程序里动态申请 -->
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
    <uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.BLUETOOTH_ADVERTISE" />
    <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
    <uses-permission android:name="android.permission.BLUETOOTH_SCAN" />

res/values/string.xml

添加程序运行过程中的状态描述文本及配色代码等

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="app_name">蓝牙Demo</string> 
    <string name="send">发送</string>
    <string name="not_connected">你没有链接一个设备</string>
    <string name="bt_not_enabled_leaving">蓝牙不可用，离开聊天室</string>
    <string name="title_connecting">链接中...</string>
    <string name="title_connected_to">连接到：</string>
    <string name="title_not_connected">无链接</string> 
    <string name="scanning">蓝牙设备搜索中...</string>
    <string name="select_device">选择一个好友链接</string>
    <string name="none_paired">没有配对好友</string>
    <string name="none_found">附近没有发现好友</string>
    <string name="title_paired_devices">已配对好友</string>
    <string name="title_other_devices">其它可连接好友</string>
    <string name="button_scan">搜索好友</string>
    <string name="connect">我的好友</string>
    <string name="discoverable">设置在线</string>
    <string name="back">退出</string>
    <string name="startVideo">开始聊天</string>
    <string name="stopVideo">结束聊天</string>  
</resources>

activity_main.xml

添加1个Toolbar控件，其内包含2个水平的TextView控件；在Toolbar控件的下方添加1个ListView控件，用于显示聊天内容；最后在ListView控件的下方添加水平放置的1个EditText控件和一个Button控件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#E6CAFF">
    tools:context=".MainActivity">
    <!--新版Android支持的Toolbar，对标题栏布局-->
    <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="horizontal">
            <TextView
                android:id="@+id/title_left_text"
                style="?android:attr/windowTitleStyle"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_alignParentLeft="true"
                android:layout_weight="1"
                android:gravity="left"
                android:ellipsize="end"
                android:singleLine="true" />
            <TextView
                android:id="@+id/title_right_text"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_alignParentRight="true"
                android:layout_weight="1"
                android:ellipsize="end"
                android:gravity="right"
                android:singleLine="true"
                android:textColor="#fff" />
        </LinearLayout>
    </androidx.appcompat.widget.Toolbar>

    <ListView android:id="@+id/in"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:stackFromBottom="true"
        android:transcriptMode="alwaysScroll"
        android:layout_weight="1" />
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <EditText
            android:id="@+id/edit_text_out"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom"
            android:layout_weight="1"
            tools:ignore="SpeakableTextPresentCheck" />
        <Button android:id="@+id/button_send"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/send"/>
    </LinearLayout>

</LinearLayout>

ChatService

创建一个ChatService的java文件，作为工具类
部分代码如下：
构建蓝牙对象

//构造方法，接收UI主线程传递的对象
    public ChatService(Context context, Handler handler) {
        //构造方法完成蓝牙对象的创建
        mAdapter = BluetoothAdapter.getDefaultAdapter();
        mState = STATE_NONE;
        mHandler = handler;
    }

取消 CONNECTING 和 CONNECTED 状态下的相关线程，然后运行新的 mConnectThread 线程

    public synchronized void connect(BluetoothDevice device) {
        if (mState == STATE_CONNECTING) {
            if (mConnectThread != null) {
                mConnectThread.cancel();
                mConnectThread = null;
            }
        }
        if (mConnectedThread != null) {
            mConnectedThread.cancel();
            mConnectedThread = null;
        }
        mConnectThread = new ConnectThread(device);
        mConnectThread.start();
        setState(STATE_CONNECTING);
    }

开启一个 ConnectedThread 来管理对应的当前连接。之前先取消任意现存的 mConnectThread 、mConnectedThread 、 mAcceptThread 线程，然后开启新 mConnectedThread ，传入当前刚刚接受的socket 连接。最后通过 Handler来通知UI连接

    public synchronized void connected(BluetoothSocket socket, BluetoothDevice device) {
        if (mConnectThread != null) {
            mConnectThread.cancel();
            mConnectThread = null;
        }
        if (mConnectedThread != null) {
            mConnectedThread.cancel();
            mConnectedThread = null;
        }
        if (mAcceptThread != null) {
            mAcceptThread.cancel();
            mAcceptThread = null;
        }
        mConnectedThread = new ConnectedThread(socket);
        mConnectedThread.start();
        Message msg = mHandler.obtainMessage(BluetoothChat.MESSAGE_DEVICE_NAME);
        Bundle bundle = new Bundle();
        bundle.putString(BluetoothChat.DEVICE_NAME, device.getName());
        msg.setData(bundle);
        mHandler.sendMessage(msg);
        setState(STATE_CONNECTED);
    }

连接线程，专门用来对外发出连接对方蓝牙的请求和处理流程。构造函数里通过 BluetoothDevice.createRfcommSocketToServiceRecord() ，从待连接的 device 产生 BluetoothSocket. 然后在 run 方法中 connect ，成功后调用 BluetoothChatSevice 的 connected() 方法。定义 cancel() 在关闭线程时能够关闭相关socket 。

private class ConnectThread extends Thread {
        private final BluetoothSocket mmSocket;
        private final BluetoothDevice mmDevice;

        public ConnectThread(BluetoothDevice device) {
            mmDevice = device;
            BluetoothSocket tmp = null;
            try {
                tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
            } catch (IOException e) {
                e.printStackTrace();
            }
            mmSocket = tmp;
        }

        @Override
        public void run() {
            setName("ConnectThread");
            mAdapter.cancelDiscovery();
            try {
                mmSocket.connect();
            } catch (IOException e) {
                connectionFailed();
                try {
                    mmSocket.close();
                } catch (IOException e2) {
                    e.printStackTrace();
                }
                ChatService.this.start();
                return;
            }
            synchronized (ChatService.this) {
                mConnectThread = null;
            }
            connected(mmSocket, mmDevice);
        }

        public void cancel() {
            try {
                mmSocket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

res/menu/option_menu.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@+id/scan"
          android:icon="@android:drawable/ic_menu_myplaces"
          android:title="@string/connect" />
    <item android:id="@+id/discoverable"
          android:icon="@android:drawable/ic_menu_view"
          android:title="@string/discoverable" />
    <item android:id="@+id/back"
          android:icon="@android:drawable/ic_menu_close_clear_cancel"
          android:title="@string/back" />
</menu>

device_list.xml

<?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">
    <TextView android:id="@+id/title_paired_devices"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/title_paired_devices"
        android:visibility="gone"
        android:background="#666"
        android:textColor="#fff"
        android:paddingLeft="5dp" />
    <ListView android:id="@+id/paired_devices"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1" />
    <TextView android:id="@+id/title_new_devices"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/title_other_devices"
        android:visibility="gone"
        android:background="#666"
        android:textColor="#fff"
        android:paddingLeft="5dp" />
    <!--android:visibility="gone"表示不占空间的隐藏，invisible是占空间-->
    <ListView android:id="@+id/new_devices"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="2" />
    <Button android:id="@+id/button_scan"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/button_scan" />
</LinearLayout>

DeviceList

新建一个名为DeviceList的activity文件
本程序供菜单项主界面的选项菜单“我的友好”调用，用于：

显示已配对的好友列表；
搜索可配对的好友进行配对
新选择并配对的蓝牙设备将刷新好友列表
注意：发现新的蓝牙设备并请求配对时，需要对应接受
关键技术：动态注册一个广播接收者，处理蓝牙设备扫描的结果
部分代码如下：
定义广播接收者，用于处理扫描蓝牙设备后的结果

    private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                if (device.getBondState() != BluetoothDevice.BOND_BONDED) {
                    mNewDevicesArrayAdapter.add(device.getName() + "\n" + device.getAddress());
                }
            } else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
                if (mNewDevicesArrayAdapter.getCount() == 0) {
                    String noDevices = getResources().getText(R.string.none_found).toString();
                    mNewDevicesArrayAdapter.add(noDevices);
                }
            }
        }
    };

活动界面：

private void init() {
        Button scanButton = findViewById(R.id.button_scan);
        scanButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Toast.makeText(DeviceList.this, R.string.scanning, Toast.LENGTH_LONG).show();
                doDiscovery();  //搜索蓝牙设备
            }
        });
        mPairedDevicesArrayAdapter = new ArrayAdapter<String>(this, R.layout.device_name);
        mNewDevicesArrayAdapter = new ArrayAdapter<String>(this, R.layout.device_name);
        //已配对蓝牙设备列表
        ListView pairedListView =findViewById(R.id.paired_devices);
        pairedListView.setAdapter(mPairedDevicesArrayAdapter);
        pairedListView.setOnItemClickListener(mPaireDeviceClickListener);
        //未配对蓝牙设备列表
        ListView newDevicesListView = findViewById(R.id.new_devices);
        newDevicesListView.setAdapter(mNewDevicesArrayAdapter);
        newDevicesListView.setOnItemClickListener(mNewDeviceClickListener);
        //动态注册广播接收者
        IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
        registerReceiver(mReceiver, filter);
        filter = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
        registerReceiver(mReceiver, filter);
        mBtAdapter = BluetoothAdapter.getDefaultAdapter();
        Set<BluetoothDevice> pairedDevices = mBtAdapter.getBondedDevices();
        if (pairedDevices.size() > 0) {
            findViewById(R.id.title_paired_devices).setVisibility(View.VISIBLE);
            for (BluetoothDevice device : pairedDevices) {
                mPairedDevicesArrayAdapter.add(device.getName() + "\n" + device.getAddress());
            }
        } else {
            String noDevices = getResources().getText(R.string.none_paired).toString();
            mPairedDevicesArrayAdapter.add(noDevices);
        }
    }

BlueToothChat

将MainActivity重命名为BlueToothChat
检查蓝牙权限

    public void checkBlePermission() {
        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.ACCESS_COARSE_LOCATION)
                != PackageManager.PERMISSION_GRANTED) {

            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.ACCESS_COARSE_LOCATION},
                    1);
        } else {
            Log.i("tag","已申请权限");
        }
    }

判断是否支持蓝牙，并打开蓝牙，获取到BluetoothAdapter之后，还需要判断是否支持蓝牙，以及蓝牙是否打开。如果没打开，需要让用户打开蓝牙：

private void checkBleDevice() {
        //首先获取BluetoothManager
        BluetoothManager bluetoothManager =
                (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
        //获取BluetoothAdapter
        if (bluetoothManager != null) {
            BluetoothAdapter mBluetoothAdapter = bluetoothManager.getAdapter();
            if (mBluetoothAdapter != null) {
                if (!mBluetoothAdapter.isEnabled()) {
                    //调用enable()方法直接打开蓝牙
                    if (!mBluetoothAdapter.enable()){
                        Log.i("tag","蓝牙打开失败");
                    }
                    else{
                        Log.i("tag","蓝牙已打开");
                    }
                    //该方法也可以打开蓝牙，但是会有一个很丑的弹窗，可以自行尝试一下
//                    Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
//                    enableBtIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
//                    startActivity(enableBtIntent);
                }
            } else {
                Log.i("tag","同意申请");
            }
        }
    }

返回进入好友列表操作后的数回调方法

public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        switch (requestCode) {
            case REQUEST_CONNECT_DEVICE:
                if (resultCode == Activity.RESULT_OK) {
                    String address = data.getExtras().getString(DeviceList.EXTRA_DEVICE_ADDRESS);
                    BluetoothDevice device = mBluetoothAdapter.getRemoteDevice(address);
                    mChatService.connect(device);
                } else if (resultCode == Activity.RESULT_CANCELED) {
                    Toast.makeText(this, "未选择任何好友！", Toast.LENGTH_SHORT).show();
                }
                break;
            case REQUEST_ENABLE_BT:
                if (resultCode == Activity.RESULT_OK) {
                    setupChat();
                } else {
                    Toast.makeText(this, R.string.bt_not_enabled_leaving, Toast.LENGTH_SHORT).show();
                    finish();
                }
        }
    }