在主/細節流中切換碎片

Question

我正在嘗試創建一個使用Fragments具有Master / Detail流程的應用程序。 選擇一個項目將打開一個細節片段，然后可以“打開”另一個片段並將其添加到后台堆棧。

我已經重命名了類來幫助說明他們的工作。

public class ListOfDetails extends FragmentActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...
    }

    //Callback method indicating that an item with the given ID was selected.
    public void onItemSelected(String id) {
        // Performing logic to determine what fragment to start omitted

        if (ifTwoPanes()) {
            Fragment fragment = new DetailFragmentType1();
            getSupportFragmentManager().beginTransaction().replace(R.id.aContainer, fragment).commit();
        } else {
            Intent newIntent = new Intent(this, SinglePaneFragmentWrapper.class);
            newIntent.putExtra("id", id);
            startActivity(newIntent);
        }
    }

    // My attempt at making it possible to change displayed fragment from within fragments
    public void changeDetailFragment(Fragment fragment) {
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        transaction.addToBackStack(null);
        transaction.replace(R.id.aContainer, fragment);
        transaction.commit();
    }
}

其中一個細節片段的示例。 可以在不同情況下創建許多不同的片段。

public class DetailFragmentType1 extends Fragment {
    private ListOfDetails parent;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Activity a = getActivity();
        if (a instanceof ListOfDetails) {
            parent = (ListOfDetails) a;
        }
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        Button aButton = (Button) getActivity().findViewById(R.id.aButton);
        aButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                parent.changeDetailFragment(new SubDetailFragment());
            }
        });
    }
}

在電話上時，使用包裝器活動來保存片段

public class SinglePaneFragmentWrapper extends FragmentActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Duplicate logic must be performed to start fragment
        // Performing logic to determine what fragment to start omitted
        String id = getIntent().getStringExtra("id");
        if(id == "DetailFragmentType1") {
            Fragment fragment = new DetailFragmentType1();
            getSupportFragmentManager().beginTransaction().replace(R.id.aContainer, fragment).commit();
        } else {
            ...
        }
    }
}

在這種情況下，更改詳細信息窗格中打開的片段的正確方法是什么？ 我的方法在使用兩個窗格時感覺像是一個黑客，並且在僅使用一個窗格時甚至不起作用，因為SinglePaneFragmentWrapper中的getParent()返回null，使我無法調用parent.changeDetailFragment() 。

這是一個復雜的問題，希望我能很好地解釋。 如果我錯過了什么，請告訴我。 謝謝

Answer 1

圍繞這個有很多意見，有很多方法可以做到這一點。 我認為在這種情況下，問題是“誰負責更改片段？” 從表面上看，按鈕上的監聽器似乎是顯而易見的地方，但是片段不應該知道它所托管的內容（這種情況的一個症狀是從getParent（）獲得一個不合理的結果，如null）。

在您的情況下，我建議您在父級中實現“偵聽器”接口，並從片段中“通知”..當通知父級時，它會更改片段。 這樣片段本身不會改變（所以不需要知道如何）..所以...對於你的情況..

添加新界面：

public interface FragmentChangeListener {
  void onFragmentChangeRequested(Fragment newFragment);
}

在ListOfDetails活動中實現接口

public class ListOfDetails extends FragmentActivity implements FragmentChangeListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ...
}

//Callback method indicating that an item with the given ID was selected.
public void onItemSelected(String id) {
    // Performing logic to determine what fragment to start omitted

    if (ifTwoPanes()) {
        Fragment fragment = new DetailFragmentType1();
        getSupportFragmentManager().beginTransaction().replace(R.id.aContainer, fragment).commit();
    } else {
        Intent newIntent = new Intent(this, SinglePaneFragmentWrapper.class);
        newIntent.putExtra("id", id);
        startActivity(newIntent);
    }
}

// My attempt at making it possible to change displayed fragment from within fragments
public void changeDetailFragment(Fragment fragment) {
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
    transaction.addToBackStack(null);
    transaction.replace(R.id.aContainer, fragment);
    transaction.commit();
}

// This is the interface implementation that will be called by your fragments
void onFragmentChangeRequested(Fragment newFragment) {
    changeDetailFragment(newFragment);
}

}

添加了詳細信息片段的監聽器

public class DetailFragmentType1 extends Fragment {

    private FragmentChangeListener fragmentChangeListener;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Actually you might not have an activity here.. you should probably be 
        // doing this in onAttach
        //Activity a = getActivity();
        //if (a instanceof ListOfDetails) {
        //    parent = (ListOfDetails) a;
        //}
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        Button aButton = (Button) getActivity().findViewById(R.id.aButton);
        aButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
               // parent.changeDetailFragment(new SubDetailFragment());
               notifyFragmentChange(new SubDetailFragment());
            }
        });
    }

    @Override
    public void onAttach(Activity activity) {
      // This is called when the fragment is attached to an activity..
      if (activity instanceof FragmentChangeListener) {
          fragmentChangeListener = (FragmentChangeListener) activity;
      } else {
         // Find your bugs early by making them clear when you can...
         if (BuildConfig.DEBUG) {
           throw new IllegalArgumentException("Fragment hosts must implement FragmentChangeListener");
         }
      }
    }

    private void notifyFragmentChange(Fragment newFragment) {
      FragmentChangeListener listener = fragmentChangeListener;
      if (listener != null) {
         listener.onFragmentChangeRequested(newFragment);
      }
    }
}

並為您的單一窗格活動實現相同的界面......

public class SinglePaneFragmentWrapper extends FragmentActivity implements FragmentChangeListener {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Duplicate logic must be performed to start fragment
        // Performing logic to determine what fragment to start omitted
        String id = getIntent().getStringExtra("id");
        if(id == "DetailFragmentType1") {
            Fragment fragment = new DetailFragmentType1();
            getSupportFragmentManager().beginTransaction().replace(R.id.aContainer, fragment).commit();
        } else {
            ...
        }
    }
// My attempt at making it possible to change displayed fragment from within fragments
public void changeDetailFragment(Fragment fragment) {
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
    transaction.addToBackStack(null);
    transaction.replace(R.id.aContainer, fragment);
    transaction.commit();
}

// This is the interface implementation that will be called by your fragments
void onFragmentChangeRequested(Fragment newFragment) {
    changeDetailFragment(newFragment);
}

}

請注意單個窗格和多窗格活動之間的相似性。這表明您可以將所有重復的代碼（changefragment等）放入一個它們都擴展的活動中，或者可能是相同的活動布局...

祝希望有所幫助，祝你好運。

此致，CJ