Android 将接口传递给 Fragment

Passing interface to Fragment

提问by Niko

Let's consider a case where I have Fragment Aand Fragment B.

让我们考虑一个我有Fragment A和 的情况Fragment B。

Bdeclares:

B声明：

public interface MyInterface {
    public void onTrigger(int position);
}

Aimplements this interface.

A实现这个接口。

When pushing Fragment Binto stack, how should I pass reference of Fragment Afor it in Bundleso Acan get the onTriggercallback when needed.

当推Fragment B入堆栈时，我应该如何传递Fragment A对它的引用，Bundle以便在需要时A获得onTrigger回调。

My use case scenario is that Ahas ListViewwith items and Bhas ViewPagerwith items. Both contain same items and when user goes from B -> Abefore popping Bit should trigger the callback for Ato update it's ListViewposition to match with Bpager position.

我的用例场景是A有ListView项目和B有ViewPager项目。两者都包含相同的项目，当用户从B -> A弹出之前开始时，B它应该触发回调A以更新它的ListView位置以匹配B寻呼机位置。

Thanks.

谢谢。

回答by Amit Gupta

Passing interface to Fragment

I think you are communicating between two Fragment

我想你是在两个人之间交流 Fragment

In order to do so, you can have a look into Communicating with Other Fragments

为此，您可以查看Communicating with Other Fragments

public class FragmentB extends Fragment{
    MyInterface mCallback;

    // Container Activity must implement this interface
    public interface MyInterface {
        public void onTrigger();
    }

    @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 = (MyInterface ) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement MyInterface ");
        }
    }

    ...
}

回答by Krtko

For Kotlin 1.0.0-beta-3595

对于 Kotlin 1.0.0-beta-3595

interface SomeCallback {}

class SomeFragment() : Fragment(){

    var callback : SomeCallback? = null //some might want late init, but I think this way is safer

    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        callback = activity as? SomeCallback //returns null if not type 'SomeCallback'

        return inflater!!.inflate(R.layout.frag_some_view, container, false);
    }
}

回答by Yaya

It is optimal for two fragments to only communicate through an activity. So you can define an interface in Fragment B that is implemented in the activity. Then in the activity, define in the interface method what you want to happen in fragment A.

两个片段仅通过一个活动进行通信是最佳的。因此，您可以在 Fragment B 中定义一个在活动中实现的接口。然后在活动中，在接口方法中定义您希望在片段 A 中发生的事情。

In Fragment B,

在片段 B 中，

MyInterface mCallback;
 public interface MyInterface {
        void onTrigger(int position);
    }

@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 = (MyInterface) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement MyInterface");
        }
}

Method for determining if user goes from B to A

判断用户是否从B到A的方法

public void onChangeFragment(int position){
//other logic here
 mCallback.onTrigger(position);
}

In Activity,

在活动中，

public void onTrigger(int position) {
    //Find listview in fragment A
    listView.smoothScrollToPosition(position);
    }

Goodluck!

祝你好运！

回答by Yaroslav Ovdiienko

I think you should use communication, as I've written below. This code comes from this Android Dev page of communication between Fragments:

我认为你应该使用交流，正如我在下面写的。此代码来自Fragments 之间通信的 Android Dev 页面：

HeadlinesFragment

头条新闻片段

public class HeadlinesFragment extends ListFragment {
OnHeadlineSelectedListener mCallback;

public void setOnHeadlineSelectedListener(Activity activity) {
    mCallback = activity;
}

// Container Activity must implement this interface
public interface OnHeadlineSelectedListener {
    public void onArticleSelected(int position);
}

// ...
}

MainActivity

主要活动

public static class MainActivity extends Activity
    implements HeadlinesFragment.OnHeadlineSelectedListener{
// ...

@Override
public void onAttachFragment(Fragment fragment) {
    if (fragment instanceof HeadlinesFragment) {
        HeadlinesFragment headlinesFragment = (HeadlinesFragment) fragment;
        headlinesFragment.setOnHeadlineSelectedListener(this);
    }
}

public static class MainActivity extends Activity
    implements HeadlinesFragment.OnHeadlineSelectedListener {
...

public void onArticleSelected(int position) {
    // The user selected the headline of an article from the HeadlinesFragment
    // Do something here to display that article
}

回答by EdmundYeung99

Using @Amit's answer, and adapting to the OPs question, here is all the relevant code:

使用@Amit 的回答，并适应 OPs 问题，这里是所有相关代码：

public class FragmentA extends BaseFragment implements MyInterface {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        // THIS IS JUST AN EXAMPLE OF WHERE YOU MIGHT CREATE FragmentB
        FragmentB myFragmentB = new FragmentB();        
    }


    void onTrigger(int position){
        // My Callback Happens Here!
    }
}

...

...

public class FragmentB extends BaseFragment {

    private MyInterface callback;

    public interface MyInterface {
        void onTrigger(int position);
    }   

    @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 {
            callback = (MyInterface ) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString() + " must implement MyInterface");
        }
    }
}