通过多个活动保持android蓝牙连接

Question

我正在构建一个通过蓝牙与 Arduino 板通信的 Android 应用程序，我在它自己的一个名为 BlueComms 的类中拥有蓝牙代码。要连接到设备，我使用以下方法：

public boolean connectDevice() {
    CheckBt();
    BluetoothDevice device = mBluetoothAdapter.getRemoteDevice(address);
    Log.d(TAG, "Connecting to ... " + device);
    mBluetoothAdapter.cancelDiscovery();
    try {
        btSocket = device.createRfcommSocketToServiceRecord(MY_UUID);
        btSocket.connect();
        outStream = btSocket.getOutputStream();
        Log.d(TAG, "Connection made.");
        return true;

    } catch (IOException e) {
        try {
            btSocket.close();
        } catch (IOException e2) {
            Log.d(TAG, "Unable to end the connection");
            return false;
        }
        Log.d(TAG, "Socket creation failed");
    }
    return false;

}
    private void CheckBt() {
    mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();

    if (!mBluetoothAdapter.isEnabled()) {
        System.out.println("Bt dsbld");
    }

    if (mBluetoothAdapter == null) {
        System.out.println("Bt null");
    }
}

这个连接很好，但是一旦我离开我通过它连接的活动，就会断开连接，通过 LogCat 显示，

 D/dalvikvm(21623): GC_CONCURRENT freed 103K, 10% free 2776K/3056K, paused 5ms+2ms, total 35ms

我无法再连接到设备，但如果我调用 killBt()，它会引发致命错误，如果我尝试发送数据，我会收到“套接字创建失败”错误。我的发送消息代码如下：

public void sendData(String data, int recvAct) {
    try {
        outStream = btSocket.getOutputStream();
    } catch (IOException e) {
        Log.d(TAG, "Bug BEFORE Sending stuff", e);
    }

    String message = data;
    byte[] msgBuffer = message.getBytes();

    try {
        outStream.write(msgBuffer);
    } catch (IOException e) {
        Log.d(TAG, "Bug while sending stuff", e);
    }
}

当我切换不同的活动时，我应该如何防止连接被我连接的活动暂停，我正在使用以下代码切换活动：

Intent myIntent = new Intent(v.getContext(), Timelapse.class);
    startActivityForResult(myIntent, 0);

非常感谢， 罗兹

Answer 1

您将 BlueComms 类的实例存储在哪里？如果你把它放在第一个活动中，那么当你离开它并移动到下一个活动时，当那个活动被破坏时，类实例就会被杀死（NB活动也会在屏幕旋转时被破坏）

因此，您需要找到一种方法，让 BlueComms 类的实例在您需要时一直保持活动状态。您可以通过公共属性在活动之间传递它，并在轮换期间将其存储在 onRetainNonConfigurationInstance() 中。

一个更简单的技巧是创建一个扩展 Application 的类，将其用作应用程序的应用程序委托，并向其添加公共属性以在其中存储 BlueComms 类的实例。这样，BlueComms 类的实例将在您的应用程序的整个生命周期内一直存在。

扩展应用程序

import android.app.Application;

public class cBaseApplication extends Application {

    public BlueComms myBlueComms;

    @Override
    public void onCreate() 
    {
        super.onCreate();
        myBlueComms = new BlueComms();
    }

}

让你的类成为应用清单中的应用委托

<application
    android:name="your.app.namespace.cBaseApplication"
    android:icon="@drawable/icon"
    android:label="@string/app_name" >

像这样从您的任何活动中访问基础应用程序

((cBaseApplication)this.getApplicationContext()).myBlueComms.SomeMethod();

Answer 2

我所做的是，为 BluetoothConnection 创建了一个单例类。 所以套接字的创建只发生一次。

当任何活动的 onCreate 方法被创建时，它首先获取 BluetoothConnection 类的实例。

Handler用于通过设置Handler将消息从BluetoothConnection类中的线程发送到对应的Activity。

喜欢：

Class MyBTConnection{
  private static MyBTConnection connectionObj;

  private Handler mHandler;

  public MyBTConnection() { //constructor }

  public static MyBTConnection getInstance() {
    if(connectionObj == null) {
        connectionObj = new MyBTConnection();
    }
     return connectionObj;
    }
  }

  public void setHandler(Handler handler) {
     mHandler = handler;
  }


  ..... Code for Bluetooth Connection ....
  to send message : 
  mHandler.obtainMessage(what).sendToTarget();

}

// in first activity
class MainActivity extends Activity {
     private MyBTConnection connectionObj;

     public onCreate(....) {

         /*
          * Since this is first call for getInstance. A new object
          * of MyBTConnection will be created and a connection to
          * remote bluetooth device will be established.
          */
         connectionObj = MyBTConnection.getInstance();
         connectionObj.setHandler(mHandler);
     }

     private Handler mHandler = new Handler(){
          public void onReceive(...) {
               /// handle received messages here 
          }
     };

}

// in second activity
class SecondActivity extends Activity {

     private MyBTConnection connectionObj;

     public onCreate(....) {

         /*
          * Since this is second call for getInstance.
          * Object for MyBTConnection was already created in previous 
          * activity. So getInstance will return that previously
          * created object and in that object, connection to remote
          * bluetooth device is already established so you can                
          * continue your work here.
          */
         connectionObj = MyBTConnection.getInstance();
         connectionObj.setHandler(mHandler);
     }

     private Handler mHandler = new Handler(){
          public void onReceive(...) {
               /// handle received messages here 
          }
     };
}

Answer 3

我目前遇到了完全相同的问题，我正在考虑每次活动请求时打开/关闭蓝牙套接字。每个 Activity 都有自己的 BlueComms 实例。

因为我的应用程序会变得有点复杂，并且会有来自不同活动的蓝牙线程请求，我认为这种方式将变得非常难以使用和排除故障。

我在这里阅读时遇到的另一种方式...... https://developer.android.com/guide/components/services.html

可以在始终开启蓝牙套接字的后台创建服务。所有蓝牙请求都可以使用 Intent 向该服务发出。这也造成了相当多的复杂性，但感觉更加整洁和有条理。

我目前处于两难境地，要么为每个活动使用线程，要么使用服务。我不知道哪种方式实际上更好。

Answer 4

当您选择要连接的设备以​​及单击设备列表项以请求连接到设备时，请使用 AsyncTask 并将连接方法放在 AsyncTask 中，如下所示：-

 AsyncTask.execute(new Runnable() {
                    @Override
                    public void run() {

                        try {

                            bluetoothSocket = Globals.bluetoothDevice.createRfcommSocketToServiceRecord(Globals.DEFAULT_SPP_UUID);
                            bluetoothSocket.connect();

                            // After successful connect you can open InputStream
                       } catch (IOException e) {
                         e.printStackTrace();
                       }


**Here is the full code for the same problem that i have cracked :-**

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
          @Override
          public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

              lablelexconnected.setText("Connecting ...");
              bdDevice = arrayListBluetoothDevices.get(position);
              //bdClass = arrayListBluetoothDevices.get(position)
              //    Toast.makeText(getApplicationContext()," " + bdDevice.getAddress(),Toast.LENGTH_SHORT).show();
              Log.i("Log", "The dvice : " + bdDevice.toString());

              bdDevice = bluetoothAdapter.getRemoteDevice(bdDevice.getAddress());


              Globals.bluetoothDevice = bluetoothAdapter.getRemoteDevice(bdDevice.getAddress());
              System.out.println("Device in GPS Settings : " + bdDevice);
              //       startService(new Intent(getApplicationContext(),MyService.class));

             /* Intent i = new Intent(GpsSettings.this, MyService.class);
              startService(i);*/
              //  finish();


            //  connectDevice();


             AsyncTask.execute(new Runnable() {
                 @Override
                 public void run() {

                     try {

                         bluetoothSocket = Globals.bluetoothDevice.createRfcommSocketToServiceRecord(Globals.DEFAULT_SPP_UUID);
                         bluetoothSocket.connect();

                         // After successful connect you can open InputStream

                         InputStream in = null;
                         in = bluetoothSocket.getInputStream();
                         InputStreamReader isr = new InputStreamReader(in);
                         br = new BufferedReader(isr);

                         while (found == 0) {
                             String nmeaMessage = br.readLine();
                             Log.d("NMEA", nmeaMessage);
                             // parse NMEA messages
                             sentence = nmeaMessage;

                             System.out.println("Sentence : " + sentence);


                             if (sentence.startsWith("$GPRMC")) {
                                 String[] strValues = sentence.split(",");
                                 System.out.println("StrValues : " + strValues[3] + " " + strValues[5] + " " + strValues[8]);
                                 if (strValues[3].equals("") && strValues[5].equals("") && strValues[8].equals("")) {
                                     Toast.makeText(getApplicationContext(), "Location Not Found !!! ", Toast.LENGTH_SHORT).show();

                                 } else {

                                     latitude = Double.parseDouble(strValues[3]);
                                     if (strValues[4].charAt(0) == 'S') {
                                         latitude = -latitude;
                                     }
                                     longitude = Double.parseDouble(strValues[5]);
                                     if (strValues[6].charAt(0) == 'W') {
                                         longitude = -longitude;
                                     }
                                     course = Double.parseDouble(strValues[8]);

                                     //    Toast.makeText(getApplicationContext(), "latitude=" + latitude + " ; longitude=" + longitude + " ; course = " + course, Toast.LENGTH_SHORT).show();
                                     System.out.println("latitude=" + latitude + " ; longitude=" + longitude + " ; course = " + course);
                                 //    found = 1;

                                     NMEAToDecimalConverter(latitude, longitude);


                                 }
                             }


                         }


                     } catch (IOException e) {
                         e.printStackTrace();
                     }


                 }
             });


          }

      });