例如,当我在 Fragment 5 中时,按下后退按钮,应用程序就会出现。我想要的是,当我按“后退”按钮时,我打开第 1 号 fragment 。我该怎么做?
我尝试了很多代码,但都不起作用,例如
FragmentManager fm = getActivity().getSupportFragmentManager();
for(int i = 0; i < fm.getBackStackEntryCount(); ++i) {
fm.popBackStack();
}
和
getSupportFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
这是我在 MainActivity 中的 fragment 代码
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// make new object and find the view "BottomNavigationView"
BottomNavigationView navigationView = findViewById(R.id.bottom_navigation);
// To make the first fragment shows when the app start.
// We will ignore the "activity_main" and we will make new activity(fragment) called "fragment_home"
// and we will add all views we want to display them on it.
// (fragment_layout) it is a fragment have id was defined in "activity_main"
getSupportFragmentManager().beginTransaction().replace(R.id.fragment_layout,
new HomeFragment()).commit();
// make Listener to call the fragments on buttons
// to start new fragment
navigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
Fragment selectedFragment = null;
switch (item.getItemId()) {
// first fragment "home"
case R.id.home_item:
selectedFragment = new HomeFragment();
break;
// second fragment "videos"
case R.id.videos_item:
selectedFragment = new VideosFragment();
break;
// third fragment "ebadat"
case R.id.ebadat_item:
selectedFragment = new EbadatFragment();
break;
// fourth fragment "images"
case R.id.images_item:
selectedFragment = new ImagesFragment();
break;
// fifth fragment "more"
case R.id.settings_item:
selectedFragment = new MoreFragment();
break;
}
assert selectedFragment != null;
getSupportFragmentManager().beginTransaction().replace(R.id.fragment_layout, selectedFragment).commit();
return true;
}
});
}
最佳答案
首先,您必须在 fragment 中实现 onBackPressed 方法。
创建一个名为 IOnBackPressed 的接口(interface): 单击 package -> new Java Class -> 并在 Kind 中选择接口(interface) -> OK 您的界面应如下所示:
public interface IOnBackPressed { boolean onBackPressed(); }
之后打开 MainActivity 并添加以下内容:
@Override public void onBackPressed() { //super.onBackPressed(); delete this line // and start your fragment: Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.fragment_container); if (!(fragment instanceof IOnBackPressed) || !((IOnBackPressed) fragment).onBackPressed()) { super.onBackPressed(); } }
您将其实现到您的 fragment 中:
public class Profil_Fragment extends Fragment implements IOnBackPressed
并将其添加到 fragment 中:
@Override public boolean onBackPressed() { //do what you want NextFragment nextFrag= new NextFragment(); getActivity().getSupportFragmentManager().beginTransaction() .replace(R.id.fragment_container, nextFrag, "findThisFragment") .addToBackStack(null) .commit(); return true; }
关于java - 按返回键返回第一个 fragment ,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/62472105/