我有一项活动 - MainActivity
。在这个活动中,我有两个片段,这两个片段都是我在 xml 中以声明方式创建的。
我正在尝试将String
用户输入的文本传递Fragment A
到Fragment B
. 然而,事实证明这是非常困难的。有谁知道我如何做到这一点?
我知道片段可以使用getActivity()
. 所以我猜我会从那里开始?
我有一项活动 - MainActivity
。在这个活动中,我有两个片段,这两个片段都是我在 xml 中以声明方式创建的。
我正在尝试将String
用户输入的文本传递Fragment A
到Fragment B
. 然而,事实证明这是非常困难的。有谁知道我如何做到这一点?
我知道片段可以使用getActivity()
. 所以我猜我会从那里开始?
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 中定义一个接口,并让您的 Activity 实现该接口。现在你可以在你的 Fragment 中调用接口方法,你的 Activity 就会收到这个事件。现在在您的活动中,您可以调用您的第二个片段以使用接收到的值更新文本视图
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);
}
}
Fragment A定义了一个Interface,需要的时候调用该方法
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
}
}
其他一些示例(甚至在撰写本文时的文档)使用过时的onAttach
方法。这是一个完整更新的示例。
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);
}
}
activity_main.xml
<?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>
片段绿色.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>
片段蓝色.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>
最好和推荐的方法是使用共享 ViewModel。
https://developer.android.com/topic/libraries/architecture/viewmodel#sharing
来自谷歌文档:
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:两个片段从不直接通信
考虑我的 2 个片段 A 和 B,假设我需要将数据从 B 传递到 A。
然后在 B 中创建一个接口,并将数据传递给 Main Activity。在那里创建另一个接口并将数据传递给片段 A。
分享一个小例子:
片段 A 看起来像
public class FragmentA extends Fragment implements InterfaceDataCommunicatorFromActivity {
public InterfaceDataCommunicatorFromActivity interfaceDataCommunicatorFromActivity;
String data;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
return super.onCreateView(inflater, container, savedInstanceState);
}
@Override
public void updateData(String data) {
// TODO Auto-generated method stub
this.data = data;
//data is updated here which is from fragment B
}
@Override
public void onAttach(Activity activity) {
// TODO Auto-generated method stub
super.onAttach(activity);
try {
interfaceDataCommunicatorFromActivity = (InterfaceDataCommunicatorFromActivity) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement TextClicked");
}
}
}
片段B看起来像
class FragmentB extends Fragment {
public InterfaceDataCommunicator interfaceDataCommunicator;
@Override
public void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
// call this inorder to send Data to interface
interfaceDataCommunicator.updateData("data");
}
public interface InterfaceDataCommunicator {
public void updateData(String data);
}
@Override
public void onAttach(Activity activity) {
// TODO Auto-generated method stub
super.onAttach(activity);
try {
interfaceDataCommunicator = (InterfaceDataCommunicator) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement TextClicked");
}
}
}
主要活动是
public class MainActivity extends Activity implements InterfaceDataCommunicator {
public InterfaceDataCommunicatorFromActivity interfaceDataCommunicatorFromActivity;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public void updateData(String data) {
// TODO Auto-generated method stub
interfaceDataCommunicatorFromActivity.updateData(data);
}
public interface InterfaceDataCommunicatorFromActivity {
public void updateData(String data);
}
}
看看https://github.com/greenrobot/EventBus 或http://square.github.io/otto/
甚至...... http://nerds.weddingpartyapp.com/tech/2014/12/24/implementing-an-event-bus-with-rxjava-rxbus/
有一种简单的方法可以使用架构组件实现活动片段之间的通信。可以使用 ViewModel 和 LiveData 在活动的片段之间传递数据。
参与通信的片段需要使用与活动生命周期相关的相同视图模型对象。视图模型对象包含 livedata 对象,数据由一个片段传递到该对象,第二个片段侦听 LiveData 上的更改并接收从片段一发送的数据。
有关完整示例,请参见http://www.zoftino.com/passing-data-between-android-fragments-using-viewmodel
学习“setTargetFragment()”
其中“ startActivityForResult() ”建立了 2 个活动之间的关系,“ setTargetFragment() ”定义了 2 个片段之间的调用者/被调用者关系。
我为我的活动提供了一个所有片段都可以使用的界面。如果您在同一个活动上有许多片段,这可以节省大量代码重写,并且比为具有相似功能的每个片段制作单独的界面更清洁/更模块化。我也喜欢它的模块化方式。不利的一面是,一些片段可以访问他们不需要的功能。
public class MyActivity extends AppCompatActivity
implements MyActivityInterface {
private List<String> mData;
@Override
public List<String> getData(){return mData;}
@Override
public void setData(List<String> data){mData = data;}
}
public interface MyActivityInterface {
List<String> getData();
void setData(List<String> data);
}
public class MyFragment extends Fragment {
private MyActivityInterface mActivity;
private List<String> activityData;
public void onButtonPress(){
activityData = mActivity.getData()
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof MyActivityInterface) {
mActivity = (MyActivityInterface) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement MyActivityInterface");
}
}
@Override
public void onDetach() {
super.onDetach();
mActivity = null;
}
}
您可以使用 2 方法在 2 之间进行通信fragments
:
可以LiveData
用来观察一个fragment
在另一个的数据变化
创建共享 ViewModel
public class SharedViewModel extends ViewModel {
private MutableLiveData<String> name;
public void setNameData(String nameData) {
name.setValue(nameData);
}
public MutableLiveData<String> getNameData() {
if (name == null) {
name = new MutableLiveData<>();
}
return name;
}
}
片段一
private SharedViewModel sharedViewModel;
public FragmentOne() {
}
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
sharedViewModel = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
submitButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
sharedViewModel.setNameData(submitText.getText().toString());
}
});
}
片段二
private SharedViewModel sharedViewModel;
public FragmentTwo() {
}
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
sharedViewModel = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
sharedViewModel.getNameData().observe(this, nameObserver);
}
Observer<String> nameObserver = new Observer<String>() {
@Override
public void onChanged(String name) {
receivedText.setText(name);
}
};
有关 viewmodel 的更多详细信息,您可以参考:mvvm-viewmodel-livedata,通信片段
您可以使用eventbus来实现相同的目的
implementation 'org.greenrobot:eventbus:3.2'
定义事件
public static class MessageEvent { /* Additional fields if needed */ }
注册/注销订阅者
@Override
public void onStart() {
super.onStart();
EventBus.getDefault().register(this);
}
@Override
public void onStop() {
super.onStop();
EventBus.getDefault().unregister(this);
}
收听事件
@Subscribe(threadMode = ThreadMode.MAIN)
public void onMessageEvent(MessageEvent event) {/* Do something */};
发布活动
EventBus.getDefault().post(new MessageEvent());
从 Fragment 1.3.0 开始,我们提供了一种在 Fragment 之间进行通信的新方式。
从 Fragment 1.3.0 开始,每个 FragmentManager 都实现了 FragmentResultOwner。这意味着 FragmentManager 可以充当片段结果的中央存储。此更改允许组件通过设置块结果并侦听这些结果来相互通信,而无需这些组件相互直接引用。
片段监听器:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
// Use the Kotlin extension in the fragment-ktx artifact
setFragmentResultListener("requestKey") { requestKey, bundle ->
// We use a String here, but any type that can be put in a Bundle is supported
val result = bundle.getString("bundleKey")
// Do something with the result
}
}
片段发射器:
button.setOnClickListener {
val result = "result"
// Use the Kotlin extension in the fragment-ktx artifact
setFragmentResult("requestKey", bundleOf("bundleKey" to result))
}
基本上,以下是两个片段之间的通信方式:
i) ViewModel
ii) Fragment Result API
iii) Interface
忽略这个答案。并不是说它不起作用。但是有更好的方法可用。此外,Android 强烈反对 Fragment 之间的直接通信。见官方文档。感谢用户@Wahib Ul Haq 的提示。
好吧,您可以在 Fragment B 中创建一个私有变量和 setter,并从 Fragment A 本身设置值,
片段B.java
private String inputString;
....
....
public void setInputString(String string){
inputString = string;
}
片段A.java
//go to fragment B
FragmentB frag = new FragmentB();
frag.setInputString(YOUR_STRING);
//create your fragment transaction object, set animation etc
fragTrans.replace(ITS_ARGUMENTS)
或者您可以按照您的建议使用 Activity ..
我最近创建了一个库,它使用注释为您生成那些类型转换样板代码。 https://github.com/zeroarst/callbackfragment
这是一个例子。单击一个TextView
onDialogFragment
触发回调MainActivity
,onTextClicked
然后获取MyFagment
要与之交互的实例。
public class MainActivity extends AppCompatActivity implements MyFragment.FragmentCallback, MyDialogFragment.DialogListener {
private static final String MY_FRAGM = "MY_FRAGMENT";
private static final String MY_DIALOG_FRAGM = "MY_DIALOG_FRAGMENT";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getSupportFragmentManager().beginTransaction()
.add(R.id.lo_fragm_container, MyFragmentCallbackable.create(), MY_FRAGM)
.commit();
findViewById(R.id.bt).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
MyDialogFragmentCallbackable.create().show(getSupportFragmentManager(), MY_DIALOG_FRAGM);
}
});
}
Toast mToast;
@Override
public void onClickButton(MyFragment fragment) {
if (mToast != null)
mToast.cancel();
mToast = Toast.makeText(this, "Callback from " + fragment.getTag() + " to " + this.getClass().getSimpleName(), Toast.LENGTH_SHORT);
mToast.show();
}
@Override
public void onTextClicked(MyDialogFragment fragment) {
MyFragment myFragm = (MyFragment) getSupportFragmentManager().findFragmentByTag(MY_FRAGM);
if (myFragm != null) {
myFragm.updateText("Callback from " + fragment.getTag() + " to " + myFragm.getTag());
}
}
}