無法決議“NetworkChangeListener”中的方法“getSupportFragmentManager”

當wifi關閉時，我為偵聽器開發了一個類，并撰寫了一個警報對話框來顯示一條訊息。現在我專門用一個類來顯示每個類中的訊息，但我無法解決錯誤。

    public class Messages extends AppCompatDialogFragment {
    
        private String message;
    
        public Messages(String message){
            this.message = message;
        }
    
        @NonNull
        @Override
        public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
            AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
            builder.setTitle("Warning!!!")
                   .setMessage(this.message)
                   .setPositiveButton("ok", new DialogInterface.OnClickListener() {
                       @Override
                       public void onClick(DialogInterface dialog, int which) {
    
                       }
                   });
            return builder.create();
        }
    }

    public class NetworkChangeListener extends BroadcastReceiver {

    private static final String CONNECTION_WIFI_OFF ="WIFI OFF.";

    @Override
    public void onReceive(Context context, Intent intent) {
      
        if(ConnectivityManager.CONNECTIVITY_ACTION.equals(intent.getAction())){
           
                Messages messages = new Messages(CONNECTION_WIFI_OFF);
                messages.show(getSupportFragmentManager(),"messages");
            }
        }

    }
}

我換messages.show(getSupportFragmentManager(),"messages");了messages.show(messages.getChildFragmentManager(),"messages");，但它不起作用。我收到此錯誤：

java.lang.RuntimeException: Error receiving broadcast Intent { act=android.net.conn.CONNECTIVITY_CHANGE flg=0x4000010 (has extras) } in com.example.connectivity.NetworkChangeListener@44fa736
        at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:891)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:5417)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
     Caused by: java.lang.IllegalStateException: Fragment Messages{f08eacf} (69334c8a-e786-46b5-bf7a-61a6b901b9d5) has not been attached yet.
        at androidx.fragment.app.Fragment.getChildFragmentManager(Fragment.java:1075)
        at com.example.connectivity.NetworkChangeListener.onReceive(NetworkChangeListener.java:49)
        at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:881)
        at android.os.Handler.handleCallback(Handler.java:739) 
        at android.os.Handler.dispatchMessage(Handler.java:95) 
        at android.os.Looper.loop(Looper.java:148) 
        at android.app.ActivityThread.main(ActivityThread.java:5417) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

uj5u.com熱心網友回復：

試試這個，你應該只更換getSupportFragmentManager()同messages.getChildFragmentManager()

public class Messages extends AppCompatDialogFragment {

    private String message;
    private Context mContext;

    public Messages(String message,Context context){
        this.message = message;
        mContext = context;
    }

    @NonNull
    @Override
    public Dialog onCreateDialog(@Nullable Bundle savedInstanceState) {
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        builder.setTitle("Warning!!!")
                .setMessage(this.message)
                .setPositiveButton("ok", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {

                    }
                });
        return builder.create();
    }
}

public class NetworkChangeListener extends BroadcastReceiver {

    private static final String CONNECTION_WIFI_OFF ="WIFI OFF.";

    @Override
    public void onReceive(Context context, Intent intent) {

        if(ConnectivityManager.CONNECTIVITY_ACTION.equals(intent.getAction())){

            Messages messages = new Messages(CONNECTION_WIFI_OFF);
            messages.show(messages.getChildFragmentManager(), "messages");
        }
    }

}

uj5u.com熱心網友回復：

為了訪問FragmentManager片段本身必須附加到活動。您只是在創建片段，但它并未在任何地方使用和顯示。它只是無用的物件。

您需要首先MessagesFragment在活動中顯示 Messages 片段（請命名），然后您可以在其中運行廣播接收器并將其系結到它的生命周期

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