使用线程和USB连接后的空白应用程序屏幕

Question

我是Android的初学者。我试图开发一个基本的应用程序来通过USB连接进行通信。我必须等待传入的数据，因为我不知道它到了哪一刻，所以我用解决了它，而（真）。对于这个while循环，我尝试使用Thread。我没有太多的线程经验。

但问题是，现在每次按下手机上的后退按钮，然后我尝试再次打开我的应用程序，它只显示一个空白的应用程序屏幕。

请问您能帮我吗？谢谢。

MainActivity类别：

public class MainActivity extends AppCompatActivity { 

UsbDevice device; 
Button bShow; 
private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION"; 
UsbManager mUsbManager; 
PendingIntent mPermissionIntent; 
TextView tvTest, tvAppend; 
String sendText = "@V\r\n"; 
private byte[] bytes; 
private static int TIMEOUT = 0; 
private boolean forceClaim = true; 
int controlTransferResult; 
byte[] readBytes = new byte[128]; 
//byte[] data = new byte[4096]; 
UsbEndpoint epOut = null, epIn = null; 
UsbDeviceConnection connection; 
int recvBytes; 
String readString = ""; 
Thread thread; 
Runnable r; 
UsbInterface intf; 

Handler handler= new Handler(){ 
    @Override 
    public void handleMessage(Message msg) { 
     tvAppend.append(readString); 
    } 
}; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    tvTest = (TextView) findViewById(R.id.textView); 
    tvAppend = (TextView) findViewById(R.id.textView2); 
    bShow= (Button)findViewById(R.id.button); 
    showData(); 

} 

@Override 
public void onPause() { 
    super.onPause(); // Always call the superclass method first 
    thread.interrupt(); 
} 

@Override 
protected void onStop() { 
    super.onStop(); 
    thread.interrupt(); 

} 

@Override 
protected void onResume() { 
    super.onResume(); 
    thread = new Thread(r); 
    thread.start(); 
} 

@Override 
protected void onDestroy() { 
    super.onDestroy(); 
    thread.interrupt(); 

} 

@Override 
protected void onRestart() { 
    super.onRestart(); 
    thread = new Thread(r); 
    thread.start(); 
} 

public void showData(){ 
    UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE); 
    HashMap<String, UsbDevice> deviceList = manager.getDeviceList(); 

    if(deviceList.toString().equals("{}")){ 
     Toast.makeText(MainActivity.this,"No USB device found!", Toast.LENGTH_SHORT).show(); 
     return; 
    }else{ 
     tvTest.setText(deviceList.toString()); 
    } 
    Iterator<UsbDevice> deviceIterator = deviceList.values().iterator(); 
    device = deviceIterator.next(); 
    mUsbManager = (UsbManager) getSystemService(Context.USB_SERVICE); 
    mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0); 
    IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION); 
    registerReceiver(mUsbReceiver, filter); 
    mUsbManager.requestPermission(device, mPermissionIntent); 

    bShow.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 

      r = new Runnable() { 
       @Override 
       public void run() { 
        synchronized (this) { 
         while (true) { 
          Arrays.fill(readBytes, (byte) 0); 

          recvBytes = connection.bulkTransfer(epIn, readBytes, readBytes.length, 0); 
          if (recvBytes != 2) { 
           readString = new String(readBytes); 
           readString = readString.replace("\u0001`",""); 
           handler.sendEmptyMessage(0); 
          } 

         } 
        } 
       } 

      }; 
      thread = new Thread(r); 
      thread.start(); 
     } 
    }); 
} 
private final BroadcastReceiver mUsbReceiver = new BroadcastReceiver() { 

    public void onReceive(Context context, Intent intent) { 
     String action = intent.getAction(); 
     if (ACTION_USB_PERMISSION.equals(action)) { 
      synchronized (this) { 
       UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE); 

       if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) { 
        if(device != null){ 
         //call method to set up device communication 
         intf = device.getInterface(0); 

         // look for our bulk endpoints 
         for (int i = 0; i < intf.getEndpointCount(); i++) { 
          UsbEndpoint ep = intf.getEndpoint(i); 

          if (ep.getType() == UsbConstants.USB_ENDPOINT_XFER_BULK) { 
           if (ep.getDirection() == UsbConstants.USB_DIR_OUT) { 
            epOut = ep; 
           } else if (ep.getDirection() == UsbConstants.USB_DIR_IN) { 
            epIn = ep; 
           } 
          } 
         } 
         if (epOut == null || epIn == null) { 
          throw new IllegalArgumentException("Not all endpoints found."); 
         } 
         connection = mUsbManager.openDevice(device); 
         connection.claimInterface(intf, forceClaim); 
         bytes = sendText.getBytes(); 
         tvAppend.setText("a" + bytes.length); 
         connection.controlTransfer(0x40, 0, 0, 0, null, 0, 0);// reset 
         connection.controlTransfer(0x40, 0, 1, 0, null, 0, 0);// clear Rx 
         connection.controlTransfer(0x40, 0, 2, 0, null, 0, 0);// clear Tx 
         controlTransferResult = connection.controlTransfer(0x40, 0x03, 0x4138, 0, null, 0, 0); 
         ByteBuffer buffer = ByteBuffer.allocate(bytes.length+1); 
         UsbRequest request = new UsbRequest(); 
         buffer.put(bytes); 
         request.initialize(connection, epOut); 
         request.queue(buffer, bytes.length); 



        } 
       } 
       else { 
        Log.d("MyActivity", "permission denied for device " + device); 
       } 
      } 
     } 
    } 
}; 


} 

编辑：

现在我意识到，一两分钟后，按钮和TextViews出现在屏幕上。 我不知道是否有帮助，但Android Studio中显示我以下消息：

这个处理程序类应该是静态的或可能发生泄漏（空）

Answer 1

我会觉得很难辨别确切的问题没有运行代码，但这里有一些可能有用的指针。

首先onRestart（）在您的活动停止后再次启动之前调用，onResume（）在活动开始与用户交互时调用。在这两种情况下，r可能没有值，因为A按钮没有被按下，或者B被卸载以释放内存。