android - 按下按钮后应用程式当机，但 Action 正常

Question

也许有人看到一个错误，问题是当我按btn2 (button 2)和btn3 (button 3)应用程序crashes时，但操作仍然有效，即video正在运行并且PDF打开，而button 1正常工作...

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    configureImageButton();

    mCamera = getCameraInstance();

    mPreview = new CameraPreview(this, mCamera);
    FrameLayout layout = (FrameLayout) findViewById(R.id.camera_View);
    layout.addView(mPreview);


    controlInflater = LayoutInflater.from(getBaseContext());
    View view = getLayoutInflater().inflate(R.layout.activity_main, layout, false);
    layout.addView(view);

}

public Camera getCameraInstance(){
    Camera c = null;
    try {
        c = Camera.open();
        c.setDisplayOrientation(90);
    }
    catch (Exception e){
    }
    return c;
}

@Override
protected void onPause() {
    super.onPause();
    mpAudio.release();
}

private void configureImageButton() {

    ImageButton btn1 = (ImageButton) findViewById(R.id.imageButton);// audio button
    ImageButton btn2 = (ImageButton) findViewById(R.id.imageButton2); // video button
    ImageButton btn3= (ImageButton) findViewById(R.id.imageButton3);//reading button

    btn1.setOnClickListener(new View.OnClickListener() {
                                @Override
                                public void onClick(View v) {
                                    mpAudio = MediaPlayer.create(MainActivity.this,R.raw.tirepressuremonitoringsystem);
                                    mpAudio.start();
                                }
                            }
    );

    btn2.setOnClickListener(new View.OnClickListener() {
                                @Override
                                public void onClick(View v) {
                                    startActivity(new Intent(MainActivity.this, Activity2.class));
                                }
                            }
    );

    btn3.setOnClickListener(new View.OnClickListener() {
                                @Override
                                public void onClick(View v) {
                                    readPDF();
                                }
                            }
    );
}

private void readPDF()
{
    AssetManager assetManager = getAssets();

    InputStream in = null;
    OutputStream out = null;
    File file = new File(getFilesDir(), "tirepressuremonitoringsystem3.pdf");
    try
    {
        in = assetManager.open("tirepressuremonitoringsystem3.pdf");
        out = openFileOutput(file.getName(), Context.MODE_WORLD_READABLE);

        copyFile(in, out);
        in.close();
        in = null;
        out.flush();
        out.close();
        out = null;
    } catch (Exception e)
    {
        Log.e("tag", e.getMessage());
    }

    Intent intent = new Intent(Intent.ACTION_VIEW);
    intent.setDataAndType(
            Uri.parse("file://" + getFilesDir() + "/tirepressuremonitoringsystem3.pdf"),
            "application/pdf");

    startActivity(intent);
}

private void copyFile(InputStream in, OutputStream out) throws IOException
{
    byte[] buffer = new byte[1024];
    int read;
    while ((read = in.read(buffer)) != -1)
    {
        out.write(buffer, 0, read);
    }
}

public void playSound () throws IOException {
    AssetFileDescriptor afd = getAssets().openFd("tirepressuremonitoringsystem.mp3");
    mpAudio = new MediaPlayer();
    mpAudio.setDataSource(afd.getFileDescriptor(),afd.getStartOffset(),afd.getLength());
    mpAudio.prepare();
    mpAudio.start();

}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}



}

Answer 1

如果不按btn1，则崩溃，因为如果不按btn1，mpAudio将为null。
然后当onPause调用时，mpAudio.release();将导致NullPointerException。

请注意:只要 Activity 未显示在屏幕上但仍在运行，就会调用onPause(在您的情况下，您将使用btn2,3启动其他 Activity ，然后它将被调用)。

请更正为

@Override
protected void onPause() {
    super.onPause();
    if(mpAudio!=null)
        mpAudio.release();
}

玩得开心!