如何在 Android 的片段中使用 onBackPress 按钮

Question

在我的应用程序中，我有NavigationView并在此NavigationView中设置了用于打开一些fragments的菜单！

<android.support.design.widget.NavigationView
    android:id="@+id/nav_view"
    android:layout_width="320dip"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    android:background="#000"
    android:fitsSystemWindows="true"
    app:headerLayout="@layout/tester_drawer_header"
    app:itemIconTint="#fff"
    app:itemTextColor="#fff"
    app:menu="@menu/tester_drawer_main"/>

我想在单击此菜单时打开一个fragment ，并且我想在 go 嵌套fragments并按onBack按钮打开第一个片段而不打开 backStack fragments时！

我写了下面的代码，但是在单击backStack中的后退button后返回fragments ，但我只想打开第一个fragment ！

我的活动代码：

public class TesterDashboardActivity extends AppCompatActivity {

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

        loadFragment(new TesterTestListFragment(), userName);
}

    @Override
    public void onBackPressed() {
        fragmentBackCount = getSupportFragmentManager().getBackStackEntryCount();

        if (fragmentBackCount <= 1) {
            if (drawer.isDrawerOpen(GravityCompat.START)) {
                drawer.closeDrawer(GravityCompat.START);
            } else {
                //finishAffinity();
                super.onBackPressed();
            }
        } else {
            getSupportFragmentManager().popBackStack();
        }
    }

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        int id = item.getItemId();
        switch (id) {
            case R.id.nav_home:
                loadFragment(new TesterTestListFragment(), userName);
                break;
            case R.id.nav_billing:
                loadFragment(new TesterFinanceFragment(), context.getString(R.string.menu_billing));
                break;
            case R.id.nav_edit_profile:
                loadFragment(new TesterProfileFilterEditFragment(), context.getString(R.string.menu_edit_profile));
                break;
            case R.id.nav_bank:
                loadFragment(new TesterShebaFragment(), context.getString(R.string.menu_bank));
                break;
            case R.id.nav_report:
                loadFragment(new TesterReportsFragment(), context.getString(R.string.menu_report));
                break;
            case R.id.nav_setting:
                loadFragment(new TesterSettingFragment(), context.getString(R.string.menu_setting));
                break;
        }
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    public void loadFragment(Fragment fragment, String toolbarTitle) {
        FragmentManager fm = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fm.beginTransaction();
        fragmentTransaction.replace(R.id.testerFragment, fragment,TAG_FRAGMENT);
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();

        toolbar.setTitle(toolbarTitle);
    }

我该如何解决？

Answer 1

在您的代码中，我发现当fragmentBackCount>1您只需调用getSupportFragmentManager().popBackStack(); 一次，因此您将在 backstack 上看到顶部片段。 我认为你应该调用getSupportFragmentManager().popBackStack(); ，fragmentBackCount-1次到达第一个fragmnet

 else {
       for(int i=0;i<fragmentBackCount-1;i++)
           getSupportFragmentManager().popBackStack();
      }

Answer 2

当你在 Fragments 之间转换时，调用 addToBackStack() 作为你的一部分

  FragmentTransaction:

FragmentTransaction tx = fragmentManager.beginTransation();
tx.replace( R.id.fragment, new MyFragment() ).addToBackStack( "tag" ).commit();