Android藍牙開發深入解析

2020-04-11 12:02:01

字體：大中小

來源：轉載

供稿：網友

1. 使用藍牙的響應權限

<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />

2. 配置本機藍牙模塊

在這里首先要了解對藍牙操作一個核心類BluetoothAdapter

復制代碼代碼如下:

BluetoothAdapter adapter = BluetoothAdapter.getDefaultAdapter();
//直接打開系統的藍牙設置面板
Intent intent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(intent, 0x1);
//直接打開藍牙
adapter.enable();
//關閉藍牙
adapter.disable();
//打開本機的藍牙發現功能（默認打開120秒，可以將時間最多延長至300秒）
Intent discoveryIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300);//設置持續時間（最多300秒）

3.搜索藍牙設備

使用BluetoothAdapter的startDiscovery()方法來搜索藍牙設備

startDiscovery()方法是一個異步方法，調用后會立即返回。該方法會進行對其他藍牙設備的搜索，該過程會持續12秒。該方法調用后，搜索過程實際上是在一個System Service中進行的，所以可以調用cancelDiscovery()方法來停止搜索（該方法可以在未執行discovery請求時調用）。

請求Discovery后，系統開始搜索藍牙設備，在這個過程中，系統會發送以下三個廣播：

ACTION_DISCOVERY_START：開始搜索

ACTION_DISCOVERY_FINISHED：搜索結束

ACTION_FOUND：找到設備，這個Intent中包含兩個extra fields：EXTRA_DEVICE和EXTRA_CLASS，分別包含BluetooDevice和BluetoothClass。

我們可以自己注冊相應的BroadcastReceiver來接收響應的廣播，以便實現某些功能

復制代碼代碼如下:

// 創建一個接收ACTION_FOUND廣播的BroadcastReceiver
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        // 發現設備
        if (BluetoothDevice.ACTION_FOUND.equals(action)) {
            // 從Intent中獲取設備對象
            BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
            // 將設備名稱和地址放入array adapter，以便在ListView中顯示
            mArrayAdapter.add(device.getName() + "/n" + device.getAddress());
        }
    }
};
// 注冊BroadcastReceiver
IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
registerReceiver(mReceiver, filter); // 不要忘了之后解除綁定

4. 藍牙Socket通信

如果打算建議兩個藍牙設備之間的連接，則必須實現服務器端與客戶端的機制。當兩個設備在同一個RFCOMM channel下分別擁有一個連接的BluetoothSocket，這兩個設備才可以說是建立了連接。

服務器設備與客戶端設備獲取BluetoothSocket的途徑是不同的。服務器設備是通過accepted一個incoming connection來獲取的，而客戶端設備則是通過打開一個到服務器的RFCOMM channel來獲取的。

服務器端的實現

通過調用BluetoothAdapter的listenUsingRfcommWithServiceRecord(String, UUID)方法來獲取BluetoothServerSocket（UUID用于客戶端與服務器端之間的配對）

調用BluetoothServerSocket的accept()方法監聽連接請求，如果收到請求，則返回一個BluetoothSocket實例（此方法為block方法，應置于新線程中）

如果不想在accept其他的連接，則調用BluetoothServerSocket的close()方法釋放資源（調用該方法后，之前獲得的BluetoothSocket實例并沒有close。但由于RFCOMM一個時刻只允許在一條channel中有一個連接，則一般在accept一個連接后，便close掉BluetoothServerSocket）

復制代碼代碼如下:

private class AcceptThread extends Thread {
private final BluetoothServerSocket mmServerSocket;

    public AcceptThread() {
        // Use a temporary object that is later assigned to mmServerSocket,
        // because mmServerSocket is final
        BluetoothServerSocket tmp = null;
        try {
            // MY_UUID is the app's UUID string, also used by the client code
            tmp = mBluetoothAdapter.listenUsingRfcommWithServiceRecord(NAME, MY_UUID);
        } catch (IOException e) { }
        mmServerSocket = tmp;
    }

    public void run() {
        BluetoothSocket socket = null;
        // Keep listening until exception occurs or a socket is returned
        while (true) {
            try {
                socket = mmServerSocket.accept();
            } catch (IOException e) {
                break;
            }
            // If a connection was accepted
            if (socket != null) {
                // Do work to manage the connection (in a separate thread)
                manageConnectedSocket(socket);
                mmServerSocket.close();
                break;
            }
        }
    }

    /** Will cancel the listening socket, and cause the thread to finish */
    public void cancel() {
        try {
            mmServerSocket.close();
        } catch (IOException e) { }
    }
}

客戶端的實現
通過搜索得到服務器端的BluetoothService

調用BluetoothService的listenUsingRfcommWithServiceRecord(String, UUID)方法獲取BluetoothSocket（該UUID應該同于服務器端的UUID）

調用BluetoothSocket的connect()方法（該方法為block方法），如果UUID同服務器端的UUID匹配，并且連接被服務器端accept，則connect()方法返回

注意：在調用connect()方法之前，應當確定當前沒有搜索設備，否則連接會變得非常慢并且容易失敗

復制代碼代碼如下:

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

    public ConnectThread(BluetoothDevice device) {
        // Use a temporary object that is later assigned to mmSocket,
        // because mmSocket is final
        BluetoothSocket tmp = null;
        mmDevice = device;

        // Get a BluetoothSocket to connect with the given BluetoothDevice
        try {
            // MY_UUID is the app's UUID string, also used by the server code
            tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
        } catch (IOException e) { }
        mmSocket = tmp;
    }

    public void run() {
        // Cancel discovery because it will slow down the connection
        mBluetoothAdapter.cancelDiscovery();

        try {
            // Connect the device through the socket. This will block
            // until it succeeds or throws an exception
            mmSocket.connect();
        } catch (IOException connectException) {
            // Unable to connect; close the socket and get out
            try {
                mmSocket.close();
            } catch (IOException closeException) { }
            return;
        }

        // Do work to manage the connection (in a separate thread)
        manageConnectedSocket(mmSocket);
    }

    /** Will cancel an in-progress connection, and close the socket */
    public void cancel() {
        try {
            mmSocket.close();
        } catch (IOException e) { }
    }
}

連接管理（數據通信）
分別通過BluetoothSocket的getInputStream()和getOutputStream()方法獲取InputStream和OutputStream

使用read(bytes[])和write(bytes[])方法分別進行讀寫操作

注意：read(bytes[])方法會一直block，知道從流中讀取到信息，而write(bytes[])方法并不是經常的block（比如在另一設備沒有及時read或者中間緩沖區已滿的情況下，write方法會block）

復制代碼代碼如下:

private class ConnectedThread extends Thread {
    private final BluetoothSocket mmSocket;
    private final InputStream mmInStream;
    private final OutputStream mmOutStream;

    public ConnectedThread(BluetoothSocket socket) {
        mmSocket = socket;
        InputStream tmpIn = null;
        OutputStream tmpOut = null;

        // Get the input and output streams, using temp objects because
        // member streams are final
        try {
            tmpIn = socket.getInputStream();
            tmpOut = socket.getOutputStream();
        } catch (IOException e) { }

        mmInStream = tmpIn;
        mmOutStream = tmpOut;
    }

    public void run() {
        byte[] buffer = new byte[1024]; // buffer store for the stream
        int bytes; // bytes returned from read()

        // Keep listening to the InputStream until an exception occurs
        while (true) {
            try {
                // Read from the InputStream
                bytes = mmInStream.read(buffer);
                // Send the obtained bytes to the UI Activity
                mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer)
                        .sendToTarget();
            } catch (IOException e) {
                break;
            }
        }
    }

    /* Call this from the main Activity to send data to the remote device */
    public void write(byte[] bytes) {
        try {
            mmOutStream.write(bytes);
        } catch (IOException e) { }
    }

    /* Call this from the main Activity to shutdown the connection */
    public void cancel() {
        try {
            mmSocket.close();
        } catch (IOException e) { }
    }
}

引用資料：Android官方SDK、《Android/OPhone完全開發講義》

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