可能重复：尝试在空对象引用上调用虚拟方法“void android.widget.TextView.setText(java.lang.CharSequence)”

Question

It works fine on the emulator, however on the box I'm getting this error:

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.m3uplayer, PID: 10042
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at com.example.m3uplayer.Adapter.onBindViewHolder(Adapter.java:44)
    at com.example.m3uplayer.Adapter.onBindViewHolder(Adapter.java:22)
    at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7254)
    at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7337)
    at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6194)
    at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6460)
    at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6300)
    at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6296)
    at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2330)
    at androidx.recyclerview.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1631)
    at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1591)
    at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:668)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4309)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:4012)
    at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4578)
    at android.view.View.layout(View.java:20672)
    at android.view.ViewGroup.layout(ViewGroup.java:6194)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at android.view.View.layout(View.java:20672)
    at android.view.ViewGroup.layout(ViewGroup.java:6194)
    at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1083)
    at android.view.View.layout(View.java:20672)
    at android.view.ViewGroup.layout(ViewGroup.java:6194)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at android.view.View.layout(View.java:20672)
    at android.view.ViewGroup.layout(ViewGroup.java:6194)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
    at android.view.View.layout(View.java:20672)
    at android.view.ViewGroup.layout(ViewGroup.java:6194)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at com.android.internal.policy.DecorView.onLayout(DecorView.java:753)
    at android.view.View.layout(View.java:20672)
    at android.view.ViewGroup.layout(ViewGroup.java:6194)
    at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2796)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2323)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1462)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7187)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
    at android.view.Choreographer.doCallbacks(Choreographer.java:761)
    at android.view.Choreographer.doFrame(Choreographer.java:696)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:951)

I/Process: Sending signal. PID: 10042 SIG: 9

here's my layout : custom_channels.xml :

<?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:background="@drawable/item_selector"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:focusable="true">

<androidx.cardview.widget.CardView
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginBottom="8dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">

    <TextView
        android:id="@+id/streamURL"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="invisible"
        tools:visibility="invisible" />

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">


        <ImageView
            android:id="@+id/coverImage"
            android:layout_width="75dp"
            android:layout_height="75dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:srcCompat="@drawable/ic_launcher_background"
            tools:ignore="ContentDescription,VectorDrawableCompat" />

        <TextView
            android:id="@+id/channelName"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="16dp"
            android:layout_marginTop="8dp"
            android:text="@string/channel_name"
            android:textSize="18sp"
            android:textStyle="bold"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toEndOf="@+id/coverImage"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.0"
            android:layout_marginLeft="16dp" />
        <TextView
            android:id="@+id/channelCountry"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="16dp"
            android:layout_marginLeft="16dp"
            android:paddingTop="50dp"
            android:text="@string/country"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toEndOf="@+id/coverImage"
            app:layout_constraintTop_toBottomOf="@+id/songTitle"
            tools:ignore="UnknownId" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</androidx.cardview.widget.CardView>

</androidx.constraintlayout.widget.ConstraintLayout>

and the Adapter class:

public class Adapter extends RecyclerView.Adapter<Adapter.ViewHolder>  {
LayoutInflater inflater;
List<Channels> channels;
public Adapter(Context ctx, List<Channels> channels){
    this.inflater = LayoutInflater.from(ctx);
    this.channels = channels;    }

@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType)  {
    View view = inflater.inflate(R.layout.custom_channels, parent, false);
    return new ViewHolder(view);
}

@Override
public void onBindViewHolder(@NonNull ViewHolder holder, 
@SuppressLint("RecyclerView") int position) {
    holder.channelName.setText(channels.get(position).getName());
    holder.channelCountry.setText(channels.get(position).getCountry());       
Picasso.get().load(channels.get(position).getCoverImg()).into(holder.channelImage);
    holder.itemView.setId(position);
}


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


public class ViewHolder extends RecyclerView.ViewHolder {
    TextView channelName, channelCountry, streamUrl;
    ImageView channelImage;
    public ViewHolder(@NonNull View itemView) {
        super(itemView);
        channelName = itemView.findViewById(R.id.channelName);
        channelCountry = itemView.findViewById(R.id.channelCountry);
        channelImage = itemView.findViewById(R.id.coverImage);
        streamUrl = itemView.findViewById(R.id.streamURL);

    }
  }

 }

I came to you, because after days of struggling, I didn't find the solution here or on Google. the weird part, this app works fine on the emulator Thank you in advance

Answer 1

使用相同的代码创建一个新项目后，它可以工作，很奇怪，但仅此而已