恢复行为后的Android处理程序

Question

I have an Android app which receives messages via Bluetooth (but that part is not relevant here). The messges are received by a handler. When starting the app after it has been killed by the Android task manager it works as it should. If I don't kill it and just bring it back to front it doesn't behave like it should. The code is quite simple:

public class MainActivity extends Activity 
{

private BtBase mBtBase;
private TextView mTvBluetooth;
private View mView;

@Override
protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    mBtBase = BtBase.getInstance(this, mHandler);
    setContentView(R.layout.bluetooth);
}

@Override
protected void onResume()
{
    super.onResume();
    mTvBluetooth = (TextView) findViewById(R.id.tvBluetooth);
    if(mBtBase.getErrorCode() == BtLibraryConstants.BT_CONNECTED)
    {
        mTvBluetooth.setText("Text 1");
    }
    else
    {
        mTvBluetooth.setText("Text 2");
    }

}


private final Handler mHandler = new Handler() 
{
    @Override
    public void handleMessage(Message msg) 
    {
        switch(msg.what)
        {
        case 0:
            if(msg.arg2 == 0)
            {
                Toast.makeText(getApplicationContext(), "Text 1", Toast.LENGTH_LONG).show();
                mTvBluetooth.setText("Text 1.");
            }
            else if(msg.arg2 == 1)
            {
                Toast.makeText(getApplicationContext(), "Text 2", Toast.LENGTH_LONG).show();
                mTvBluetooth.setText("Text 2");
            }
            break;
        case 1:
            Toast.makeText(getApplicationContext(), (String) msg.obj, Toast.LENGTH_LONG).show();
            mTvBluetooth.setText("Text 3: " + (String) msg.obj);

            break;
        default:

        }
    }
};  
}

What DOES work after starting app from a resume situation:

• the toast messages in the handler are displayed correctly
• the textview in onResume has the right value depending on the state

What does NOT work after starting app from a resume situation:

• The text view update in the handler is not working.

Keep in mind the toast works correctly, so the code is executed. Keep in mind it works fine after killing the app from the task manager, so it is not completely wrong. I assume it has something with the lifecycle management to do.

I tried several things

• passed the main looper into the handler, though since I create the handler from the main thread it shouldn't be necessary
• got the main view and invalidated it in the handler to force a redraw

Neither worked, but of course I might have done something wrong in these tries.

The debugger shows that my textView mTvBluetooth is not null and it looks like it is the one I am looking for. But maybe a new mTvBluetooth is created somehow and I am using the old mTvBluetooth.

Last but not least logCat doesn't show any errors.

Answer 1

Try to move this code

mTvBluetooth = (TextView) findViewById(R.id.tvBluetooth);

from onResume() to onCreate() method. Maybe it helps.

Also, TextView is not recreated when activity is resumed in common way. But sometimes it can be destroyed buy the system to obtain more memory. In such may, when you restore activity, method onCreate must be called before onResume .

If you don't want to move code, try to make mTvBluetooth volatile . Try to see mTvBlutooth value in mHandler and onResume() while debugging. Use "Inspect" tool in eclipse (Ctrl+Shift+I), you will see an variable id, eg 830032407656. Check ids at these two moments.

Please leave a comment is an answer helpful.