android – 如果从Fragment调用,则DialogFragment会抛出ClassCastException

Android 2019-05-13
如果从Fragment调用,我的DialogFragment会抛出ClassCastException,而如果从Activity调用它则正常工作.我已经看过几个有类似问题的其他问题,基本上那些与导入有关,但我在实现中无法解决它.这是我对DialogFragment的实现. 
import android.app.AlertDialog;
import android.app.Dialog;
import android.app.DialogFragment;

public class HotspotScanDialog extends DialogFragment {

    SetupHotspotDialogListener mListener;

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        ...

        .setAdapter(hotspotAdapter,new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog,int which) {
                mListener.onHotspotSelectedListener(hotspotAdapter.getItem(
                        which).toString());
            }
        })...
    }

    public interface SetupHotspotDialogListener {
        public void onHotspotSelectedListener(String selection);

    }

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

        try {
            mListener = (SetupHotspotDialogListener) activity;
        } catch (ClassCastException ignore) {
            // Just to make sure if anyone will be pointing at my throwing
            // ClassCastException myself I have tried without this code as well.
            throw new ClassCastException(activity.toString()
                    + " must implement NoticeDialogListener");
        }
    }
}

这是我的Fragment使用上面的DialogFragment：

import android.app.AlertDialog;
import android.app.DialogFragment;
import android.support.v4.app.Fragment;
import com.xxx.yyy.ui.compontent.dialog.HotspotScanDialog;
import com.xxx.yyy.ui.compontent.dialog.HotspotScanDialog.SetupHotspotDialogListener;

public class SmartMode extends Fragment implements SetupHotspotDialogListener {

    private void showWifiSelectionDialog() {
        DialogFragment setupWifiSelectionDialog = new HotspotScanDialog();

        /*
         * using getFragmentManager() only says "The method
         * show(FragmentManager,String) in the type DialogFragment is not
         * applicable for the arguments (FragmentManager,String)"
         */

        setupWifiSelectionDialog.show(getActivity().getFragmentManager(),Keys.TAG.toString());
    }

    @Override
    public void onHotspotSelectedListener(String selection) {
        // Log.d(TAG,selection);
    }
}

这是错误日志：

02-01 13:11:32.750: E/AndroidRuntime(15061): FATAL EXCEPTION: main
02-01 13:11:32.750: E/AndroidRuntime(15061): java.lang.classCastException: com.milanix.tuki.UiMainActivity@41d75350 must implement NoticeDialogListener
02-01 13:11:32.750: E/AndroidRuntime(15061): at com.xxx.yyy.ui.compontent.dialog.HotspotScanDialog.onAttach(HotspotScanDialog.java:122)
02-01 13:11:32.750: E/AndroidRuntime(15061): at android.app.FragmentManagerImpl.movetoState(FragmentManager.java:787)
02-01 13:11:32.750: E/AndroidRuntime(15061): at android.app.FragmentManagerImpl.movetoState(FragmentManager.java:1035)
02-01 13:11:32.750: E/AndroidRuntime(15061): at android.app.BackStackRecord.run(BackStackRecord.java:635)
02-01 13:11:32.750: E/AndroidRuntime(15061): at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1397)
02-01 13:11:32.750: E/AndroidRuntime(15061): at android.app.FragmentManagerImpl$1.run(FragmentManager.java:426)
02-01 13:11:32.750: E/AndroidRuntime(15061): at android.os.Handler.handleCallback(Handler.java:615)
02-01 13:11:32.750: E/AndroidRuntime(15061): at android.os.Handler.dispatchMessage(Handler.java:92)
02-01 13:11:32.750: E/AndroidRuntime(15061): at android.os.Looper.loop(Looper.java:137)
02-01 13:11:32.750: E/AndroidRuntime(15061): at android.app.ActivityThread.main(ActivityThread.java:4898)
02-01 13:11:32.750: E/AndroidRuntime(15061): at java.lang.reflect.Method.invokeNative(Native Method)
02-01 13:11:32.750: E/AndroidRuntime(15061): at java.lang.reflect.Method.invoke(Method.java:511)
02-01 13:11:32.750: E/AndroidRuntime(15061): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006)
02-01 13:11:32.750: E/AndroidRuntime(15061): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)
02-01 13:11:32.750: E/AndroidRuntime(15061): at dalvik.system.NativeStart.main(Native Method)

我想知道是否有人可以暗示这个问题.

解决方法

从 docs开始： 
onAttach(Activity) called once the fragment is associated with its activity.

在你的代码中

mListener = (SetupHotspotDialogListener) activity;

line抛出ClassCastException,因为您的活动未实现SetupHotspotDialogListener接口. (片段直接与包含它的活动相关联,以及DialogFragment,因为DialogFragment扩展了Fragment).

从docs开始

在某些情况下,您可能需要一个片段来与活动共享事件.一种好方法是在片段内定义一个回调接口,并要求主机活动实现它.当活动通过接口收到回调时,它可以根据需要与布局中的其他片段共享信息.

所以如果你想从Fragment创建FragmentDialog我建议通过回调来组织它到活动：

>使用createDialogRequest()等方法在SmartMode Fragment类中创建回调接口(就像在dialogFragment中一样).
>让您的活动实现该界面
>然后,当您需要创建对话框时,将回调从Fragment发送到Activity
>将“show dialog logics”放入Activity

它看起来像片段询问活动来创建对话框,活动显示对话框.

编辑：
我想我已经找到了更好的实现你需要的东西.我写了一个简单的例子,从片段创建片段对话框,接收片段对话框回调事件到片段.

活动：

public class MyFragmentActivity extends FragmentActivity {

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

    // first start of activity
    if (savedInstanceState == null) {
        // put fragment to activity layout 
        MyFragment fragment = new MyFragment();
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.replace(R.id.fragmentContainer,fragment,"fragment");
        ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        ft.commit();
    }
}}

分段：

public class MyFragment extends Fragment implements MyDialogInterface {

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

    View fragmentView = inflater.inflate(R.layout.fragment,null);

    // button which shows dialog
    Button showDialogButton = (Button) fragmentView.findViewById(R.id.showDialog);
    showDialogButton.setonClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // create fragment dialog.
            FragmentDialog dialog = FragmentDialog.getInstance(MyFragment.this);
            dialog.show(getActivity().getSupportFragmentManager(),"dialog");
        }
    });
    return fragmentView;
}

@Override
public void onClickEvent() {
    // receive click events from dialog fragment
    Log.e(getClass().getSimpleName(),"onClickEvent");
}

}

FragmentDialog：

public class FragmentDialog extends DialogFragment {

public interface MyDialogInterface extends Serializable {
    public void onClickEvent();
}

private MyDialogInterface callbackListener;

/**
 * dialogInterface - instance of MyDialogInterface which will handle
 * callback events
 */
public static FragmentDialog getInstance(MyDialogInterface dialogInterface) {
    FragmentDialog fragmentDialog = new FragmentDialog();

    // set fragment arguments
    Bundle args = new Bundle();
    args.putSerializable("dialogInterface",dialogInterface);
    fragmentDialog.setArguments(args);

    return fragmentDialog;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setStyle(STYLE_NO_TITLE,0);
}

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

    View pushDialogView = getActivity().getLayoutInflater().inflate(R.layout.fragment_dialog,null);

    // get reference to MyDialogInterface instance from arguments
    callbackListener = (MyDialogInterface) getArguments().getSerializable("dialogInterface");

    Button cancelButton = (Button) pushDialogView.findViewById(R.id.button);
    cancelButton.setonClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
            // send click event
            callbackListener.onClickEvent();
        }
    });

    return pushDialogView;
}}

我使用了支持4个库片段(android.support.v4.app.Fragment,android.support.v4.app.DialogFragment,android.support.v4.app.FragmentActivity).

和布局：

activity_my_fragment.xml：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/fragmentContainer"
android:layout_width="match_parent"
android:layout_height="match_parent" />

fragment.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:background="#a00"
android:orientation="vertical" >
<Button
    android:id="@+id/showDialog"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="show doalog" />
</LinearLayout>

fragment_dialog.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:background="#fe3"
android:orientation="vertical" >

<Button
    android:id="@+id/button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="click me" />
 </LinearLayout>

我的想法是发送引用接口,它将捕获回调事件.

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