实现所必需的OnFragmentInteractionListener --在何处以及如何报告

Question

I have found this post for this problem already，这个问题涵盖了我的情况，但是这个问题是不同的。

我将简要地描述它：*实现OnFragmentInteractionListener是必要的，以便活动使用扩展Fragment的类，例如，在使用activity为其他页面设置与activity附加的页面时，会出现以下异常：

java.lang.RuntimeException: com.example...TheActivity@efebfcf必须实现

The link to the post says hints检查是否在fragment的onAttach方法中完成。但是，检查Fragment类中onAttach的源代码：

@CallSuper
    public void onAttach(@NonNull Context context) {
        mCalled = true;
        final Activity hostActivity = mHost == null ? null : mHost.getActivity();
        if (hostActivity != null) {
            mCalled = false;
            onAttach(hostActivity);
        }
    }

这是从安卓工作室ctrl+right_click Fragment类获得的。如果activity实现了OnFragmentInteractionListener方法，我看不出检查是在哪里进行的。这个检查是在哪里完成的，编译器是如何抛出这个异常的，甚至知道我们已经实现了这个方法(可能会用另一个侦听器覆盖它)？

最新情况:以下是有关这一问题的更多信息：

** logcat错误：**

E/memtrack(16281): Couldn't load memtrack module (No such file or directory)
E/android.os.Debug(16281): failed to load memtrack module: -2
E/memtrack(16294): Couldn't load memtrack module (No such file or directory)
E/android.os.Debug(16294): failed to load memtrack module: -2
E/dalvikvm(16305): Could not find class 'androidx.core.view.ViewCompat$2', referenced from method androidx.core.view.ViewCompat.addOnUnhandledKeyEventListener
E/dalvikvm(16305): Could not find class 'android.view.WindowInsets', referenced from method androidx.core.view.ViewCompat.dispatchApplyWindowInsets
E/dalvikvm(16305): Could not find class 'android.view.WindowInsets', referenced from method androidx.core.view.ViewCompat.onApplyWindowInsets
E/dalvikvm(16305): Could not find class 'android.view.View$OnUnhandledKeyEventListener', referenced from method androidx.core.view.ViewCompat.removeOnUnhandledKeyEventListener
E/dalvikvm(16305): Could not find class 'androidx.core.view.ViewCompat$1', referenced from method androidx.core.view.ViewCompat.setOnApplyWindowInsetsListener
E/dalvikvm(16305): Could not find class 'android.graphics.drawable.RippleDrawable', referenced from method androidx.appcompat.widget.AppCompatImageHelper.hasOverlappingRendering
E/dalvikvm(16305): Could not find class 'android.view.textclassifier.TextClassificationManager', referenced from method androidx.appcompat.widget.AppCompatTextClassifierHelper.getTextClassifier
E/DEBUG:  (16305): ******************* RESUMING LOGOANIMATION ACTIVITY ********************
E/DEBUG:  (16305): ******************* RESUMING LOGOANIMATION ACTIVITY ********************
E/DEBUG:  (16305): ******************* RESUMING LOGOANIMATION ACTIVITY ********************
E/DEBUG:  (16305): ******************* DESTROYING STARTUPMANAGER ACTIVITY ********************
E/DEBUG:  (16305): ******************* DESTROYING STARTUPMANAGER ACTIVITY ********************
E/DEBUG:  (16305): ******************* DESTROYING STARTUPMANAGER ACTIVITY ********************
E/DEBUG:  (16305): ******************* PAUSING LOGOANIMATION ACTIVITY ********************
E/DEBUG:  (16305): ******************* PAUSING LOGOANIMATION ACTIVITY ********************
E/DEBUG:  (16305): ******************* PAUSING LOGOANIMATION ACTIVITY ********************
E/AndroidRuntime(16305): FATAL EXCEPTION: main
E/AndroidRuntime(16305): Process: com.nailit.www, PID: 16305
E/AndroidRuntime(16305): java.lang.RuntimeException: com.nailit.www.StartupSetup.StartupPreference@41f23c90 must implement OnFragmentInteractionListener
E/AndroidRuntime(16305):        at com.nailit.www.StartupSetup.Frag_StartPref_Theme.onAttach(Frag_StartPref_Theme.java:86)
E/AndroidRuntime(16305):        at androidx.fragment.app.Fragment.performAttach(Fragment.java:2574)
E/AndroidRuntime(16305):        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:828)
E/AndroidRuntime(16305):        at androidx.fragment.app.FragmentTransition.addToFirstInLastOut(FragmentTransition.java:1197)
E/AndroidRuntime(16305):        at androidx.fragment.app.FragmentTransition.calculateFragments(FragmentTransition.java:1080)
E/AndroidRuntime(16305):        at androidx.fragment.app.FragmentTransition.startTransitions(FragmentTransition.java:119)
E/AndroidRuntime(16305):        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1866)
E/AndroidRuntime(16305):        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)
E/AndroidRuntime(16305):        at androidx.fragment.app.FragmentManagerImpl.execSingleAction(FragmentManagerImpl.java:1696)
E/AndroidRuntime(16305):        at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:299)
E/AndroidRuntime(16305):        at androidx.fragment.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:235)
E/AndroidRuntime(16305):        at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1244)
E/AndroidRuntime(16305):        at androidx.viewpager.widget.ViewPager.populate(ViewPager.java:1092)
E/AndroidRuntime(16305):        at androidx.viewpager.widget.ViewPager.onMeasure(ViewPager.java:1622)
E/AndroidRuntime(16305):        at android.view.View.measure(View.java:16677)
E/AndroidRuntime(16305):        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5286)
E/AndroidRuntime(16305):        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
E/AndroidRuntime(16305):        at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1052)
E/AndroidRuntime(16305):        at android.widget.LinearLayout.onMeasure(LinearLayout.java:590)
E/AndroidRuntime(16305):        at android.view.View.measure(View.java:16677)
E/AndroidRuntime(16305):        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5286)
E/AndroidRuntime(16305):        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
E/AndroidRuntime(16305):        at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
E/AndroidRuntime(16305):        at android.view.View.measure(View.java:16677)
E/AndroidRuntime(16305):        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5286)
E/AndroidRuntime(16305):        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
E/AndroidRuntime(16305):        at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
E/AndroidRuntime(16305):        at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
E/AndroidRuntime(16305):        at android.view.View.measure(View.java:16677)
E/AndroidRuntime(16305):        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5286)
E/AndroidRuntime(16305):        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
E/AndroidRuntime(16305):        at android.view.View.measure(View.java:16677)
E/AndroidRuntime(16305):        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5286)
E/AndroidRuntime(16305):        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404)
E/AndroidRuntime(16305):        at android.widget.LinearLayout.measureVertical(LinearLayout.java:695)
E/AndroidRuntime(16305):        at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
E/AndroidRuntime(16305):        at android.view.View.measure(View.java:16677)
E/AndroidRuntime(16305):        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5286)
E/AndroidRuntime(16305):        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
E/AndroidRuntime(16305):        at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2421)
E/AndroidRuntime(16305):        at android.view.View.measure(View.java:16677)
E/AndroidRuntime(16305):        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1927)
E/AndroidRuntime(16305):        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1119)
E/AndroidRuntime(16305):        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1301)
E/AndroidRuntime(16305):        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1006)
E/AndroidRuntime(16305):        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5652)
E/AndroidRuntime(16305):        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
E/AndroidRuntime(16305):        at android.view.Choreographer.doCallbacks(Choreographer.java:574)
E/AndroidRuntime(16305):        at android.view.Choreographer.doFrame(Choreographer.java:544)
E/AndroidRuntime(16305):        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
E/AndroidRuntime(16305):        at android.os.Handler.handleCallback(Handler.java:733)
E/AndroidRuntime(16305):        at android.os.Handler.dispatchMessage(Handler.java:95)
E/AndroidRuntime(16305):        at android.os.Looper.loop(Looper.java:136)
E/AndroidRuntime(16305):        at android.app.ActivityThread.main(ActivityThread.java:5433)
E/android.os.Debug(  615): !@Dumpstate > sdumpstate -k -t -z -d -m 16305 -o /data/log/dumpstate_app_error  

**片段代码：**

package com.nailit.www.StartupSetup;


import android.content.Context;
import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.nailit.www.R;

/**
 * A simple {@link Fragment} subclass.
 */
public class Frag_StartPref_Layout extends Fragment {


    public Frag_StartPref_Layout() {
        // Required empty public constructor
    }




    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_startpref_layout, container, false);
    }



}

**和使用片段的活动：**

package com.nailit.www.StartupSetup;
import com.nailit.www.R;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentPagerAdapter;
import androidx.viewpager.widget.ViewPager;

import android.os.Bundle;
import android.util.Log;


public class StartupPreference extends AppCompatActivity{
    private final static int no_of_prefs = 2;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_startup_preference);
        //we're not using the layout natively, but using Fragment's layout
        //but setContentView is required since it is accessed by : R.id.startPref_pager


        StartPrefPagerAdapter prefPagerAdapter =
                new StartPrefPagerAdapter(getSupportFragmentManager());
        ViewPager StartPref_Viewpager = findViewById(R.id.startPref_pager);

        StartPref_Viewpager.setAdapter(prefPagerAdapter);
    }


    private class StartPrefPagerAdapter extends FragmentPagerAdapter {
        public StartPrefPagerAdapter(FragmentManager fm){
            super(fm, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
        }

        @Override
        public int getCount(){
            return StartupPreference.no_of_prefs;//no. of preference pages
        }

        @Override
        public Fragment getItem(int position) {
            switch (position){
                case 0:
                    return new Frag_StartPref_Layout();
                case 1:
                    return new Frag_StartPref_Theme();
            }
            return null;
        }

    }

}  

活动的布局：

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
>

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/startPref_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />

</LinearLayout>  

片段的布局

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    >

    <ImageView
        android:id="@+id/startPref_Layout"
        android:layout_width="0dp"
        android:layout_height="0dp"

        android:scaleType="centerCrop"
        app:layout_constraintBottom_toTopOf="@+id/startPref_layout_info"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@mipmap/ic_launcher" />


    <TextView
        android:id="@+id/startPref_layout_info"
        android:layout_width="0dp"
        android:layout_height="0dp"

        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        android:gravity="center"
        android:text="@string/Frag_startPref_layout_info"

        android:textSize="25sp"
        app:layout_constraintBottom_toTopOf="@+id/startPref_layout_select"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHeight_percent=".125"
        app:layout_constraintStart_toStartOf="parent" />

    <RadioGroup
        android:id="@+id/startPref_layout_select"
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:layout_marginStart="8dp"

        android:layout_marginEnd="8dp"
        android:orientation="vertical"
        app:layout_constraintBottom_toTopOf="@+id/dot_animation_holder"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHeight_percent=".125"
        app:layout_constraintStart_toStartOf="parent">

        <RadioButton
            android:id="@+id/radioButton1"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:checked="true"
            android:text="@string/Frag_startPref_Radio1"
            android:textSize="15sp" />

        <RadioButton
            android:id="@+id/radioButton2"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="@string/Frag_startPref_Radio2"
            android:textSize="15sp" />
    </RadioGroup>


    <LinearLayout
        android:id="@+id/dot_animation_holder"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginStart="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHeight_percent=".08"
        app:layout_constraintStart_toStartOf="parent">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center"
            android:text="dots animation here" />

    </LinearLayout>




</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

正如@MikeM在上面的注释中所指出的，异常是由于加载了Factory methods，默认情况下，在创建片段时会对其进行检查。代码包括对接口的检查。