如何检测片段 android 中按下后退按钮的时间？

Question

我的项目带有带片段的导航抽屉，有 5 个菜单，问题是当我转到菜单 4 并按下后退按钮时应用程序关闭，但我需要应用程序返回第一个菜单，这就是全部片段中的菜单。

这是 Main Activity（导航抽屉）

的代码

public class MainActivity extends AppCompatActivity{
DrawerLayout mDrawerLayout;
NavigationView mNavigationView;
FragmentManager mFragmentManager;
FragmentTransaction mFragmentTransaction;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    /**
     *Setup the DrawerLayout and NavigationView
     */

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawerLayout);
    mNavigationView = (NavigationView) findViewById(R.id.shitstuff) ;

    /**
     * Lets inflate the very first fragment
     * Here , we are inflating the TabFragment as the first Fragment
     */

    mFragmentManager = getSupportFragmentManager();
    mFragmentTransaction = mFragmentManager.beginTransaction();
    mFragmentTransaction.replace(R.id.containerView,new Recommendation()).commit();
    /**
     * Setup click events on the Navigation View Items.
     */

    mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(MenuItem menuItem) {
            mDrawerLayout.closeDrawers();



            if (menuItem.getItemId() == R.id.nav_item_lux_level_recomen) {
                FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();
                fragmentTransaction.replace(R.id.containerView,new Recommendation()).commit();

            }

            if (menuItem.getItemId() == R.id.nav_item_room_index_calc) {
                FragmentTransaction xfragmentTransaction = mFragmentManager.beginTransaction();
                xfragmentTransaction.replace(R.id.containerView,new RoomIndex()).commit();
            }

            if (menuItem.getItemId() == R.id.nav_item_utilization_factor_calc) {
                FragmentTransaction xfragmentTransaction = mFragmentManager.beginTransaction();
                xfragmentTransaction.replace(R.id.containerView,new UtilizationFactorCalculator()).commit();
            }

            if (menuItem.getItemId() == R.id.nav_item_conversions) {
                FragmentTransaction xfragmentTransaction = mFragmentManager.beginTransaction();
                xfragmentTransaction.replace(R.id.containerView,new Conversion()).commit();
            }
            if (menuItem.getItemId() == R.id.nav_item_lux) {
                FragmentTransaction xfragmentTransaction = mFragmentManager.beginTransaction();
                xfragmentTransaction.replace(R.id.containerView,new LuxSensor()).commit();
            }


            return false;
        }

    });

    /**
     * Setup Drawer Toggle of the Toolbar
     */

    android.support.v7.widget.Toolbar toolbar = (android.support.v7.widget.Toolbar) findViewById(R.id.toolbar);
    ActionBarDrawerToggle mDrawerToggle = new ActionBarDrawerToggle(this,mDrawerLayout, toolbar,R.string.app_name,
            R.string.app_name);

    mDrawerLayout.setDrawerListener(mDrawerToggle);

    mDrawerToggle.syncState();




}

这一个菜单（片段）

public class LuxSensor extends Fragment {
TextView textLIGHT_available, textLIGHT_reading;
FragmentManager mFragmentManager;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View x =  inflater.inflate(R.layout.lux_sensor,null);
    textLIGHT_reading
            = (TextView)x.findViewById(R.id.LIGHT_reading);

    SensorManager mySensorManager = (SensorManager)getActivity().getSystemService(Context.SENSOR_SERVICE);

    Sensor LightSensor = mySensorManager.getDefaultSensor(Sensor.TYPE_LIGHT);
    if(LightSensor != null){
        mySensorManager.registerListener(
                LightSensorListener,
                LightSensor,
                SensorManager.SENSOR_DELAY_NORMAL);

    }else{
        textLIGHT_available.setText("Sensor.TYPE_LIGHT NOT Available");
    }
    FragmentManager fm = getFragmentManager();

    return x;
}





private final SensorEventListener LightSensorListener
        = new SensorEventListener(){

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        if(event.sensor.getType() == Sensor.TYPE_LIGHT){
            textLIGHT_reading.setText(event.values[0]+" LUX");
        }
    }

};

}

我已经在网上试过解决方案，但它仍然关闭

Answer 1

在 main activity 中你需要覆盖下面的函数

@Override
public void onBackPressed()
{
     // code here to check what fragment you are on and handle that accordingly
     super.onBackPressed();  // this exits the app.
}

文档可在此处获得：https://developer.android.com/reference/android/app/Activity.html#onBackPressed()

Answer 2

您可以使用 setOnKeyListener() 在 android 中按键监听器。然后，如果你想处理后按，覆盖 onKey 方法：

@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
    if (event.getAction() == KeyEvent.ACTION_UP && keyCode == KeyEvent.KEYCODE_BACK) {
         // do your thing
    }

}

Answer 3

在您的 MainActivity 中

@Override
public void onBackPressed()
{
    FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.containerView,new Recommendation()).commit();
}

Answer 4

在片段中你应该使用这样的东西：

  @Override
    //Pressed return button - returns to the results menu
    public void onResume() {
        super.onResume();
        getView().setFocusableInTouchMode(true);
        getView().requestFocus();
        getView().setOnKeyListener(new View.OnKeyListener() {
            @Override
            public boolean onKey(View v, int keyCode, KeyEvent event) {

                if (event.getAction() == KeyEvent.ACTION_UP && keyCode == KeyEvent.KEYCODE_BACK){

                 //your code

                   return true;
                }
                return false;
            }
        });
    }

Answer 5

onCreateView 片段添加这个

Java

requireActivity().getOnBackPressedDispatcher().addCallback(activity, new OnBackPressedCallback(true) {
    @Override
    public void handleOnBackPressed() {
        // in here you can do logic when backPress is clicked
    }
});

科特林

requireActivity().onBackPressedDispatcher.addCallback(object : OnBackPressedCallback(true) {
    override fun handleOnBackPressed() {
        // in here you can do logic when backPress is clicked
    }
})

Answer 6

使用这个（在 kotlin 中）

activity?.onBackPressedDispatcher?.addCallback(this, object : OnBackPressedCallback(true) {
override fun handleOnBackPressed() {
    // in here you can do logic when backPress is clicked
}

})

我认为这是最优雅的方式

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