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[英]How can i go back to A from fragment B when I click on the toolbar back press?
[英]go back to first fragment when press back
例如,當我在 Fragment 5 中按下返回按鈕時,應用程序就會出現。 我想要的是當我按下后退按鈕時,我打開第 1 號片段。我該怎么做?
我嘗試了很多代碼,但它不起作用,比如
FragmentManager fm = getActivity().getSupportFragmentManager();
for(int i = 0; i < fm.getBackStackEntryCount(); ++i) {
fm.popBackStack();
}
和
getSupportFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
這是我在 MainActivity 中的片段代碼
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;
}
});
}
添加 onBackPressed 方法:
@Override
public void onBackPressed() {
//super.onBackPressed(); delete this line
// and start your fragment:
NextFragment nextFrag= new NextFragment();
getActivity().getSupportFragmentManager().beginTransaction()
.replace(R.id.Layout_container, nextFrag, "findThisFragment")
.addToBackStack(null)
.commit();
}
首先,您必須在 Fragment 中實現 onBackPressed 方法。
創建一個名為 IOnBackPressed 的界面:單擊 package -> new Java Class -> 並選擇界面類型 -> 確定您的界面應如下所示:
public interface IOnBackPressed { boolean onBackPressed(); }
之后,您打開 MainActivity 並添加以下內容:
@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(); } }
你實現這個到你的片段:
public class Profil_Fragment extends Fragment implements IOnBackPressed
並將其添加到片段中:
@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; }
添加 backstack 和標簽(您可以使用像“HomeFragment”這樣的片段名稱)來替換片段。
replace(fragmentId, fragment, fragmentName).addToBackStack(fragmentName)
和這樣的流行片段
popBackStack(fragmentName,0)
嘗試添加 transaction.addToBackStack(tag);
例如:
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.fragment_layout, selectedFragment);
ft.addToBackStack( "tag" ).commit();
這會將您的片段添加到后台堆棧,以便后退按鈕可以正常工作。
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