Android Backstack的片段功能

Question

我写了一段代码，试图在片段1、2、3、4之间导航。 导航类似于：1-> 2-> 3-> 4-> 2。

每个片段都有一个按钮，其onClickListener调用由mainactivity实现的接口中的方法，其中位置作为参数传递。

例如ononClick在第四个片段中的按钮上调用方法，其中我将位置参数传递为“ 2”以调用第二个片段。

现在，我使用后堆栈名称“ second”将事务1-> 2添加到了后堆栈。 当我尝试从4> 2开始时，我使用函数popBackStackImmediate（“ second”，0）。 但是，布尔响应为假，并且堆栈中未弹出任何内容。

我的问题是：

1. 为什么popBackStackImmediate返回false？
2. 在同一函数（即flag）中第二个参数有什么用？
3. 当我们将事务添加到后堆栈中时，将保存事务，而不是片段。 那么，片段对象实际上在哪里保存，而后堆栈将保存事务？

我的代码中的MainActivity是：

`

    public class MainActivity extends AppCompatActivity implements Frag1.OnFragmentInteractionListener, Frag2.OnFragmentInteractionListener, Frag3.OnFragmentInteractionListener, Frag4.OnFragmentInteractionListener {

LinearLayout layout;
Frag1 frag1;
Frag2 frag2;
Frag3 frag3;
Frag4 frag4;
android.support.v4.app.FragmentTransaction transaction;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.i("I", "Main Act");
    layout = (LinearLayout) findViewById(R.id.frag);
    frag1 = Frag1.newInstance();

    transaction = getSupportFragmentManager().beginTransaction();

    // Replace whatever is in the fragment_container view with this fragment,
    // and add the transaction to the back stack so the user can navigate back
    transaction.add(R.id.frag, frag1, "first");
  //  frag1 = Frag1.newInstance();
   // transaction.add(R.id.frag, frag1, "first1");
  //  transaction.add(R.id.frag, frag2, "second");
   // transaction.add(R.id.frag, frag2, "second");
 //  transaction.add(R.id.frag, frag3, "third");
    // Commit the transaction
  //  transaction.add(R.id.frag, frag3, "third");

  //  transaction.replace(R.id.frag, frag2, "second");

    transaction.commit();



}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

//片段到活动接口的实现

@Override
public void onFragmentInteraction(int pos) {

    if (pos == 2) {
       // Fragment f = getSupportFragmentManager().findFragmentByTag("second");
        FragmentManager manager = getSupportFragmentManager();

        boolean isAvail =  manager.popBackStackImmediate("second", 0);

        if (isAvail) {
           // frag2 = (Frag2) f;
            Log.i("MainAct", "Instance of 2 yes");
        }else{
            transaction = getSupportFragmentManager().beginTransaction();
           frag2 = Frag2.newInstance();
            Log.i("MainAct", "Instance of 2 No");
            transaction.replace(R.id.frag, frag2, "second");
            transaction.addToBackStack("second");
            transaction.commit();
        }



    } else if (pos == 3) {
        Fragment f = getSupportFragmentManager().findFragmentByTag("third");
        transaction = getSupportFragmentManager().beginTransaction();
        if (f instanceof Frag3) {
            frag3 = (Frag3) f;
            Log.i("MainAct", "Instance of 3 yes");
        }else{
            frag3 = Frag3.newInstance();
            Log.i("MainAct", "Instance of 3 No");
        }
        transaction.replace(R.id.frag, frag3, "third");

        transaction.commit();
        }

    else if (pos == 4) {
        Fragment f = getSupportFragmentManager().findFragmentByTag("four");
        transaction = getSupportFragmentManager().beginTransaction();
        if (f instanceof Frag3) {
            frag4 = (Frag4) f;
            Log.i("MainAct", "Instance of 4 yes");
        }else{
            frag4 = Frag4.newInstance();
            Log.i("MainAct", "Instance of 4 No");
        }
        transaction.replace(R.id.frag, frag4, "four");
        transaction.commit();
    }

    }

}`

Answer 1

您正在尝试调用popBackStackImmediate("second", 0); 而是替换片段。

尝试这个，

1. 创建Interface PageTraveller并在MainActivity中实现

    public interface PageTraveller { public void openPage(int pageNo); } 

2. 覆盖方法openPage（）

     @Override public void openPage(int pageNo) { android.support.v4.app.Fragment fragment; switch (pageNo){ case 1: fragment = getSupportFragmentManager().findFragmentByTag("fragmentOne"); fragmentManager.beginTransaction().replace(R.id.pageContainer,fragment).addToBackStack("fragmentOne").commit(); break; case 2: fragment = getSupportFragmentManager().findFragmentByTag("fragmentTwo"); if (fragment instanceof FragmentTwo) fragmentTwo = (FragmentTwo)fragment; else fragmentTwo = new FragmentTwo(); fragmentManager.beginTransaction().replace(R.id.pageContainer,fragmentTwo).addToBackStack("fragmentTwo").commit(); break; case 3: fragment = getSupportFragmentManager().findFragmentByTag("fragmentThree"); if (fragment instanceof FragmentTwo) fragmentThree = (FragmentThree)fragment; else fragmentThree = new FragmentThree(); fragmentManager.beginTransaction().replace(R.id.pageContainer,fragmentThree).addToBackStack("fragmentThree").commit(); break; case 4: fragment = getSupportFragmentManager().findFragmentByTag("fragmentFour"); if (fragment instanceof FragmentTwo) fragmentFour = (FragmentFour)fragment; else fragmentFour = new FragmentFour(); fragmentManager.beginTransaction().replace(R.id.pageContainer,fragmentFour).addToBackStack("fragmentFour").commit(); break; } } 

   3. 创建第一个片段FragmentOne

      public class FragmentOne extends Fragment{ PageTraveller pageTraveller; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View viewOne = inflater.inflate(R.layout.fragment_one,null); Button btnOne = (Button)viewOne.findViewById(R.id.text1); btnOne.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { pageTraveller.openPage(2); } }); return viewOne; } @Override public void onAttach(Context context) { super.onAttach(context); pageTraveller = (PageTraveller) context; } }

   在XMLfragment_one中添加

    <Button android:id="@+id/btnOne" android:layout_width="wrap_content" android:layout_height="wrap_content" android:textSize="40dp" android:layout_gravity="center|center_horizontal|center_vertical" android:text="Fragment 1"/> 

   4. 与上面相同的方式创建FragmentTwo，FragmentThree，FragmentFour。 但在您的FragmentFour调用pageTraveller.openPage(2);

有关更多参考，请尝试1. 返回Backstack中的上一个片段

2. Fragments官方Android开发人员网站

它对我有用，请尝试它可能对您有帮助。