Android-Implementation Code for Switching Fragment Page Function

Scenario: Use Fragment to implement page switching.

Class structure:

First: Activity

In the Activity, use getSupportFragmentManager().beginTransaction() to fill a Fragment (the managing FragmentA)

Activity part code:

FragmentA fragment = FragmentA.newInstant(null);
getSupportFragmentManager().beginTransaction().add(R.id.f_tab_fragment,fragment).commit(); 

XML:

     <FrameLayout
        android:id="@"+id/fl_container"
        android:layout_width="match_parent"
        android:layout_above="@"+id/f_tab_fragment"
        android:layout_height="match_parent"/>
      <FrameLayout
        android:id="@"+id/f_tab_fragment"
        android:layout_width="match_parent"
        android:layout_height="52dp"
        android:layout_alignParentBottom="true"/> 

Second: FragmentA

Load a main FragmentA as the manager of other sub-leaves FragmentX.

Now, for example, there are two sub-leaves FragmentB and FragmentC.

FragmentA uses FragmentManager and FragmentTransaction to manage the switching of FragmentB and FragmentC　

FragmentA code:

 public class FragmentA extends BaseFragment {
  private static final String TAB_HOME = com.timediffproject.module.home.MyMainFragment.class.getName();
  private static final String TAB_TEST = com.timediffproject.module.home.TestFragment.class.getName();
  private BaseFragment mLastShowFragment;
  private static TabFragment fragment;
  public static TabFragment newInstant(Bundle bundle){
    if (fragment == null){
      fragment = new TabFragment();
      fragment.setArguments(bundle);
    }
    return fragment;
  }
  @Override
  public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    initTabInfo();
  }
  private void initTabInfo(){
    FragmentManager fm = getFragmentManager();
    if (fm == null){
      return;
    }
    FragmentTransaction ft = fm.beginTransaction();
    BaseFragment home = (BaseFragment) fm.findFragmentByTag(TAB_HOME);
    if (home != null){
      ft.hide(home);
    }
    BaseFragment test = (BaseFragment) fm.findFragmentByTag(TAB_TEST);
    if (test != null){
      ft.hide(test);
    }
    ft.commit();
  }
  @Nullable
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    return inflater.inflate(R.layout.fragment_tab, container, false);
  }
  @Override
  public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    view.findViewById(R.id.btn_change_home).setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View view) {
        switchTo(TAB_HOME, null);
      }
    });
    view.findViewById(R.id.btn_change_test).setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View view) {
        switchTo(TAB_TEST, null);
      }
    });
    switchTo(TAB_HOME, null);
  }
  //The method of switching Fragments (FragmentB, FragmentC)
  //tab is the class name of the Fragment (e.g., FragmentB.class.getName())
  //R.id.fl_container is in the layout of the Activity, not in the layout of FragmentA
  private void switchTo(String tab, Bundle bundle){
    //Initialize the class that manages Fragments
    FragmentManager fm = getFragmentManager();
    if (fm == null){
      return;
    }
    FragmentTransaction ft = fm.beginTransaction();
    //Find the Fragment with class name tab from the FragmentManager
    BaseFragment fragment = (BaseFragment) fm.findFragmentByTag(tab);
    if (fragment == null){
      fragment = (BaseFragment) Fragment.instantiate(getActivity(), tab);
      fragment.setArguments(bundle);
      ft.add(R.id.fl_container, fragment, tab);
    }else{
      ft.show(fragment);
    }
    //Hide the currently displayed Fragment
    if (mLastShowFragment != null) {
      ft.hide(mLastShowFragment);
    }
    //Record the last clicked Fragment
    mLastShowFragment = fragment;
    ft.commitAllowingStateLoss();
  }
} 

XML:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="horizontal" android:layout_width="match_parent"
  android:layout_height="52dp">
  <Button
    android:id="@"+id/btn_change_home"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Switch home"
    />
  <Button
    android:id="@"+id/btn_change_test"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Switch test"
    />
</LinearLayout> 

3: FragmentX (FragmentB, FragmentC)

The logic of the sub-page should be defined according to the specific business, and implemented in the same way as a general Fragment

　For example:

public class TestFragment extends BaseFragment {
  @Nullable
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {return inflater.inflate(R.layout.fragment_test, container, false);}
  }
  @Override
  public void onViewCreated(View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
  }
} 

Now, it can be simply implemented-Implement page switching function by using bottom Tab to switch Fragment

Attachment:

　

PS: Errors encountered during implementation　

java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.

Correct way: The initialization layout of the related fragment should be added with false to establish a relationship with the parent layout.

Reason: Without it, the system will bind an unknown parent class to the view generated by this inflater. When you bind this fragment as a child page to an Activity or another fragment, the above error will occur.

@Nullable
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    //The correct way is:
    //return inflater.inflate(R.layout.fragment_test, container, false);
    return inflater.inflate(R.layout.fragment_test, container);
   }   

　That's all for this article. I hope it will be helpful to everyone's learning and that everyone will support the Yelling Tutorial more.

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