Question

晚上好。我的应用程序从启动屏幕活动开始，为此活动我使用android:noHistory="true"（对于MainActivity我也使用noHistory）。我的MainActivity是android.support.design.widget.NavigationView. Inside onCreate()方法，我使用showMethod()来绘制Home片段（主页）。因此，当我单击“后退”按钮时，它绝对可以正常工作，应用程序会记住以正确顺序打开的所有片段。 但是！当我单击主页上的后退按钮（在应用程序启动后打开）时，显示空白的屏幕并显示先前的活动标题。

public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    DrawerLayout 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.addDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);
    showHome();
}
Fragment fragment = null;

private void showHome(){
    fragment = new Home();
    if (fragment != null){
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.content_main , fragment,fragment.getTag());
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();
    }

}


@Override
public void onBackPressed() {
    int count = getFragmentManager().getBackStackEntryCount();

    if (count == 0) {
        super.onBackPressed();

    } else {
        getFragmentManager().popBackStack();
    }
}


private void displaySelectedScreen(int id){


    switch (id){
        case R.id.nav_cafe_restaurants:
            fragment = new Cafe_restaurants();
            break;
        case R.id.nav_cinemas:
            fragment = new Cinemas();
            break;
        case R.id.nav_enjoys:
            fragment = new Enjoys();
            break;
        case R.id.nav_night_clubs:
            fragment = new Night_clubs();
            break;
        case R.id.nav_theaters:
            fragment = new Theaters();
            break;
        case R.id.nav_museums:
            fragment = new Museums();
            break;
        case R.id.nav_sports:
            fragment = new Sports();
            break;
        case R.id.nav_sights:
            fragment = new Sights();
            break;
        case R.id.nav_current_actions:
            fragment = new Current_events();
            break;
        case R.id.nav_future_actions:
            fragment = new Future_events();
            break;
        case R.id.nav_contacts:
            fragment = new Contacts();
            break;

    }


    if (fragment != null){
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.content_main , fragment,fragment.getTag());
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();
    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);

}

您可以查看2个屏幕截图以了解我的问题。尝试自己解决几个小时。

enter image description here

Answer 1

您的问题是，您要将初始Home Fragment添加到后堆栈中。这意味着从“无片段”到“本地”的事务可以撤消。当您按下后退按钮时，您将从堆栈中弹出该事务，这将使您不显示任何Fragment。

只需从您的fragmentTransaction.addToBackStack(null);方法中删除showHome()。

带有片段的onBackPressed（）android

1 个答案: