两个片段之间的基本通信

Question

我有一个MainActivity.在这里String我有两个Fragment A,我在xml中以声明方式创建.

我试图Fragment B将用户输入的文本传递getActivity()到文本视图中MainActivity.然而,事实证明这非常困难.有谁知道我怎么做到这一点？

我知道片段可以使用它来获取对它的活动的引用String.所以我猜我会从那里开始？

Answer 1

看看Android开发者页面:http: //developer.android.com/training/basics/fragments/communicating.html#DefineInterface

基本上,您在Fragment A中定义了一个接口,并让您的Activity实现该接口.现在,您可以调用Fragment中的接口方法,并且您的Activity将接收该事件.现在,在您的活动中,您可以调用第二个片段以使用收到的值更新textview

您的Activity实现了您的界面(参见下面的FragmentA)

public class YourActivity implements FragmentA.TextClicked{
    @Override
    public void sendText(String text){
        // Get Fragment B
        FraB frag = (FragB)
            getSupportFragmentManager().findFragmentById(R.id.fragment_b);
        frag.updateText(text);
    }
}

片段A定义了一个接口,并在需要时调用该方法

public class FragA extends Fragment{

    TextClicked mCallback;

    public interface TextClicked{
        public void sendText(String text);
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        // This makes sure that the container activity has implemented
        // the callback interface. If not, it throws an exception
        try {
            mCallback = (TextClicked) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                + " must implement TextClicked");
        }
    }

    public void someMethod(){
        mCallback.sendText("YOUR TEXT");
    }

    @Override
    public void onDetach() {
        mCallback = null; // => avoid leaking, thanks @Deepscorn
        super.onDetach();
    }
}

片段B有一个公共方法来处理文本

public class FragB extends Fragment{

    public void updateText(String text){
        // Here you have it
    }
}

Answer 2

其他一些示例(甚至是撰写本文时的文档)使用过时的onAttach方法.这是一个完整的更新示例.

笔记

• 您不希望片段直接相互通信或与活动进行通信.这将它们与特定活动联系起来并使重用变得困难.
• 解决方案是创建一个Activity将实现的回调侦听器接口.当Fragment想要将消息发送到另一个Fragment或其父活动时,它可以通过该接口完成.
• Activity可以直接与其子片段公共方法进行通信.
• 因此,Activity充当控制器,将消息从一个片段传递到另一个片段.

码

MainActivity.java

public class MainActivity extends AppCompatActivity implements GreenFragment.OnGreenFragmentListener {

    private static final String BLUE_TAG = "blue";
    private static final String GREEN_TAG = "green";
    BlueFragment mBlueFragment;
    GreenFragment mGreenFragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // add fragments
        FragmentManager fragmentManager = getSupportFragmentManager();

        mBlueFragment = (BlueFragment) fragmentManager.findFragmentByTag(BLUE_TAG);
        if (mBlueFragment == null) {
            mBlueFragment = new BlueFragment();
            fragmentManager.beginTransaction().add(R.id.blue_fragment_container, mBlueFragment, BLUE_TAG).commit();
        }

        mGreenFragment = (GreenFragment) fragmentManager.findFragmentByTag(GREEN_TAG);
        if (mGreenFragment == null) {
            mGreenFragment = new GreenFragment();
            fragmentManager.beginTransaction().add(R.id.green_fragment_container, mGreenFragment, GREEN_TAG).commit();
        }
    }

    // The Activity handles receiving a message from one Fragment
    // and passing it on to the other Fragment
    @Override
    public void messageFromGreenFragment(String message) {
        mBlueFragment.youveGotMail(message);
    }
}

GreenFragment.java

public class GreenFragment extends Fragment {

    private OnGreenFragmentListener mCallback;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_green, container, false);

        Button button = v.findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String message = "Hello, Blue! I'm Green.";
                mCallback.messageFromGreenFragment(message);
            }
        });

        return v;
    }

    // This is the interface that the Activity will implement
    // so that this Fragment can communicate with the Activity.
    public interface OnGreenFragmentListener {
        void messageFromGreenFragment(String text);
    }

    // This method insures that the Activity has actually implemented our
    // listener and that it isn't null.
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnGreenFragmentListener) {
            mCallback = (OnGreenFragmentListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnGreenFragmentListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mCallback = null;
    }
}

BlueFragment.java

public class BlueFragment extends Fragment {

    private TextView mTextView;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_blue, container, false);
        mTextView = v.findViewById(R.id.textview);
        return v;
    }

    // This is a public method that the Activity can use to communicate
    // directly with this Fragment
    public void youveGotMail(String message) {
        mTextView.setText(message);
    }
}

XML

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp">

    <!-- Green Fragment container -->
    <FrameLayout
        android:id="@+id/green_fragment_container"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:layout_marginBottom="16dp" />

    <!-- Blue Fragment container -->
    <FrameLayout
        android:id="@+id/blue_fragment_container"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />

</LinearLayout>

fragment_green.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:background="#98e8ba"
              android:padding="8dp"
              android:layout_width="match_parent"
              android:layout_height="match_parent">

    <Button
        android:id="@+id/button"
        android:text="send message to blue"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

</LinearLayout>

fragment_blue.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:background="#30c9fb"
              android:padding="16dp"
              android:layout_width="match_parent"
              android:layout_height="match_parent">

    <TextView
        android:id="@+id/textview"
        android:text="TextView"
        android:textSize="24sp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

</LinearLayout>

Answer 3

最好的和推荐的方法是使用共享的ViewModel.

https://developer.android.com/topic/libraries/architecture/viewmodel#sharing

来自Google doc:

public class SharedViewModel extends ViewModel {
private final MutableLiveData<Item> selected = new MutableLiveData<Item>();

public void select(Item item) {
    selected.setValue(item);
}

public LiveData<Item> getSelected() {
    return selected;
}
}


public class MasterFragment extends Fragment {
private SharedViewModel model;
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    model = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);
    itemSelector.setOnClickListener(item -> {
        model.select(item);
    });
}
}


public class DetailFragment extends Fragment {
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    SharedViewModel model = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);
    model.getSelected().observe(this, { item ->
       // Update the UI.
    });
}
}

ps:两个片段永远不会直接通信