按下返回按钮时的导航抽屉活动为空活动

问题描述：

我在导航抽屉菜单中使用带抽象的导航抽屉活动。我想要的是当用户按两次退出按钮退出应用程序。但相反，这是空白的活动。按下返回按钮时的导航抽屉活动为空活动

onCreate方法：

@Override 
protected void onCreate(Bundle savedInstanceState) { 

    if (broj == 1) { 
     startActivity(new Intent(this, Cover.class)); 
    } 

    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

    drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
      this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close); 
    drawer.setDrawerListener(toggle); 

    toggle.syncState(); 
    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view); 
    navigationView.setNavigationItemSelectedListener(this); 

    FragmentMainPage pocetnaFragment = new FragmentMainPage(); 
    FragmentManager fragmentManager = getSupportFragmentManager(); 
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction(); 
    fragmentTransaction.addToBackStack(null).replace(R.id.relativeLayoutZaFragment, pocetnaFragment, "1"); 

    fragmentTransaction.addToBackStack(null); 
    fragmentTransaction.commit(); 
    fragmentTransaction.addToBackStack(null); 
    // Pozivanje metode 

    getSupportActionBar().setTitle("Auto magazin"); 

    ActionBar.LayoutParams p = new ActionBar.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT); 
    p.gravity = Gravity.LEFT; 

    view = getLayoutInflater().inflate(R.layout.action_bar, null); 

    ActionBar.LayoutParams params = new ActionBar.LayoutParams(
      ActionBar.LayoutParams.WRAP_CONTENT, 
      ActionBar.LayoutParams.MATCH_PARENT, 
      Gravity.LEFT); 

    TextView Title = (TextView) view.findViewById(R.id.actionbar_title); 
    Title.setText("Auto magazin"); 

    getSupportActionBar().setCustomView(view,params); 
    getSupportActionBar().setDisplayShowCustomEnabled(true); //show custom title 
    getSupportActionBar().setDisplayShowTitleEnabled(false); //hide the default title 
// getSupportActionBar().setIcon(R.drawable.logo); 
}

onBackPressed（）方法是：

boolean doubleBackToExitPressedOnce = false; 

@Override 
public void onBackPressed() { 
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
    assert drawer != null; 

    if (drawer.isDrawerOpen(GravityCompat.START)) { 
     drawer.closeDrawer(GravityCompat.START); 
     return; 
    } 
    else if (doubleBackToExitPressedOnce) { 
     super.onBackPressed(); 
     return; 
    } 

    this.doubleBackToExitPressedOnce = true; 
    Toast.makeText(this, "Press again to exit", Toast.LENGTH_SHORT).show(); 

    new Handler().postDelayed(new Runnable() { 
     @Override 
     public void run() { 
      doubleBackToExitPressedOnce = false; 
     } 
    }, 2000); 
}

这是因为您已将FragmentTransaction添加到后端堆栈。 'super.onBackPressed（）'调用将首先弹出该事务。如果您不想通过按下后退按钮删除'Fragment'，请不要将'FragmentTransaction'添加到后退堆栈中。 –

是的，这是正确的答案。谢谢很多。 – smiljka

答

您可以处理回片段点击按钮。详情请参考this页面

按下返回按钮时的导航抽屉活动为空活动

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