Android/Java-Fehler: "java.lang.IllegalStateException: Das angegebene Kind hat bereits einen Elternteil"

Question

Ich bin dabei, einen einfachen Recycler zu bauen und zu testen, was ich bisher habe. (neu zu Android) Ich habe es untersucht und ich denke, der Fehler liegt in meiner "MainActivity.java" oder dem Adapter "MyAdapter.java", aber ich kann es nicht lösen. Jede Eingabe wäre fantastisch. Ich erhalte diesen Fehler in meinem logcat:

07-16 15:15:55.743 2997-2997/com.example.duncan.recyclerviewproject E/AndroidRuntime: FATAL EXCEPTION: main 
                        Process: com.example.duncan.recyclerviewproject, PID: 2997 
                        java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first. 
                         at android.view.ViewGroup.addViewInner(ViewGroup.java:3949) 
                         at android.view.ViewGroup.addView(ViewGroup.java:3799) 
                         at android.view.ViewGroup.addView(ViewGroup.java:3740) 
                         at android.support.v7.widget.RecyclerView$5.addView(RecyclerView.java:727) 
                         at android.support.v7.widget.ChildHelper.addView(ChildHelper.java:107) 
                         at android.support.v7.widget.RecyclerView$LayoutManager.addViewInt(RecyclerView.java:7921) 
                         at android.support.v7.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:7879) 
                         at android.support.v7.widget.RecyclerView$LayoutManager.addView(RecyclerView.java:7867) 
                         at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1556) 
                         at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1502) 
                         at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:595) 
                         at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3625) 
                         at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3354) 
                         at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3886) 
                         at android.view.View.layout(View.java:16067) 
                         at android.view.ViewGroup.layout(ViewGroup.java:5051) 
                         at android.support.constraint.ConstraintLayout.onLayout(ConstraintLayout.java:1197) 
                         at android.view.View.layout(View.java:16067) 
                         at android.view.ViewGroup.layout(ViewGroup.java:5051) 
                         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579) 
                         at android.widget.FrameLayout.onLayout(FrameLayout.java:514) 
                         at android.view.View.layout(View.java:16067) 
                         at android.view.ViewGroup.layout(ViewGroup.java:5051) 
                         at android.support.v7.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:434) 
                         at android.view.View.layout(View.java:16067) 
                         at android.view.ViewGroup.layout(ViewGroup.java:5051) 
                         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579) 
                         at android.widget.FrameLayout.onLayout(FrameLayout.java:514) 
                         at android.view.View.layout(View.java:16067) 
                         at android.view.ViewGroup.layout(ViewGroup.java:5051) 
                         at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703) 
                         at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557) 
                         at android.widget.LinearLayout.onLayout(LinearLayout.java:1466) 
                         at android.view.View.layout(View.java:16067) 
                         at android.view.ViewGroup.layout(ViewGroup.java:5051) 
                         at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579) 
                         at android.widget.FrameLayout.onLayout(FrameLayout.java:514) 
                         at android.view.View.layout(View.java:16067) 
                         at android.view.ViewGroup.layout(ViewGroup.java:5051) 
                         at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2122) 
                         at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1879) 
                         at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1090) 
                         at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5982) 
                         at android.view.Choreographer$CallbackRecord.run(Choreographer.java:781) 
                         at android.view.Choreographer.doCallbacks(Choreographer.java:592) 
                         at android.view.Choreographer.doFrame(Choreographer.java:560) 
                         at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:767) 
                         at android.os.Handler.handleCallback(Handler.java:739) 
                         at android.os.Handler.dispatchMessage(Handler.java:95) 
                         at android.os.Looper.loop(Looper.java:135) 
                         at android.app.ActivityThread.main(ActivityThread.java:5484) 
                         at java.lang.reflect.Method.invoke(Native Method) 
                         at java.lang.reflect.Method.invoke(Method.java:372) 
                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:984) 
                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779) 

Mein MainActivity.java:

package com.example.duncan.recyclerviewproject; 

import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.support.v7.widget.LinearLayoutManager; 
import android.support.v7.widget.RecyclerView; 

import java.util.ArrayList; 
import java.util.List; 

public class MainActivity extends AppCompatActivity { 


    private RecyclerView recyclerView; 
    private RecyclerView.Adapter adapter; 

    private List<ListItem> listItems; 

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

     recyclerView = (RecyclerView) findViewById(R.id.recyclerView); 
     recyclerView.setHasFixedSize(true); 
     recyclerView.setLayoutManager(new LinearLayoutManager(this)); 

     listItems = new ArrayList<>(); 

     for(int i = 0; i<=10; i++){ 
      ListItem listItem = new ListItem(
        "heading " + (i+1), 
        "Lorem ipsum dummy text" 
      ); 

      listItems.add(listItem); 
     } 

     adapter = new MyAdapter(listItems, this); 

     recyclerView.setAdapter(adapter); 
    } 
} 

MyAdapter.java:

package com.example.duncan.recyclerviewproject; 

import android.content.Context; 
import android.support.v7.widget.RecyclerView; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.TextView; 

import java.util.List; 

/** 
* Created by Duncan on 7/16/17. 
*/ 

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> { 

    private List<ListItem> listItems; 
    private Context context; 

    public MyAdapter(List<ListItem> listItems, Context context) { 
     this.listItems = listItems; 
     this.context = context; 
    } 

    @Override 
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
     View v = LayoutInflater.from(parent.getContext()) 
       .inflate(R.layout.list_item, parent); 
     return new ViewHolder(v); 

    } 

    @Override 
    public void onBindViewHolder(ViewHolder holder, int position) { 
     ListItem listItem = listItems.get(position); 

     holder.textViewHead.setText(listItem.getHead()); 
     holder.textViewDesc.setText(listItem.getDesc()); 
    } 

    @Override 
    public int getItemCount() { 
     return listItems.size(); 
    } 

    public class ViewHolder extends RecyclerView.ViewHolder { 

     public TextView textViewHead; 
     public TextView textViewDesc; 

     public ViewHolder(View itemView) { 
      super(itemView); 

      textViewHead = (TextView) itemView.findViewById(R.id.textViewHead); 
      textViewDesc = (TextView) itemView.findViewById(R.id.textViewDesc); 


} 
} 

}

Ich habe erstellt 2 XML-Dateien

list_items.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="wrap_content" 
    android:orientation="vertical"> 

    <android.support.v7.widget.CardView 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content"> 

     <LinearLayout 
      android:padding="16dp" 
      android:orientation="vertical" 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content"> 

      <TextView 
       android:id="@+id/textViewHead" 
       android:text="Heading" 
       android:textAppearance="@style/Base.TextAppearance.AppCompat.Large" 
       android:layout_width="match_parent" 
       android:layout_height="wrap_content" /> 

      <TextView 
       android:id="@+id/textViewDesc" 
       android:text="Body" 
       android:layout_width="match_parent" 
       android:layout_height="wrap_content" /> 

     </LinearLayout> 
    </android.support.v7.widget.CardView> 

</LinearLayout> 

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?> 
<android.support.constraint.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_width="match_parent" 
    android:layout_height="match_parent" 
    tools:context="com.example.duncan.recyclerviewproject.MainActivity"> 

    <android.support.v7.widget.RecyclerView 
     android:id="@+id/recyclerView" 
     android:layout_width="784dp" 
     android:layout_height="1127dp" 
     tools:layout_editor_absoluteY="8dp" 
     tools:layout_editor_absoluteX="8dp"></android.support.v7.widget.RecyclerView> 

</android.support.constraint.ConstraintLayout> 

Answer 1

try

View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, parent); 

zu

View v = LayoutInflater.from(context).inflate(R.layout.list_item, parent, false);