Android studio Java Recycler 启动时出现视图错误

Question

对不起我的英语我是法国人:)

我正在尝试学习如何在 Android studio 中编写代码，我从 Recycler 视图开始，不幸的是我遇到了一个错误，我不知道如何修复它。

提前感谢您的帮助

错误：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.mtoapp, PID: 4393
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mtoapp/com.example.mtoapp.Recycler.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View androidx.recyclerview.widget.RecyclerView.findViewById(int)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3450)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3602)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2067)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7660)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:975)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View androidx.recyclerview.widget.RecyclerView.findViewById(int)' on a null object reference
        at com.example.mtoapp.Recycler.MainActivity.onCreate(MainActivity.java:29)
        at android.app.Activity.performCreate(Activity.java:8000)
        at android.app.Activity.performCreate(Activity.java:7984)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1312)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3423)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3602) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2067) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:223) 
        at android.app.ActivityThread.main(ActivityThread.java:7660) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:975)

MainActivity.java（所有代码）


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


    String data1[], data2[];
    int images[];
    Context context;


    public MyAdapter(Context ct, String s1[], String s2[], int img[]){
    context = context;
    data1 = s1;
    data2 = s2;
    images = img;
    }


    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(context);
        View view = inflater.inflate(R.layout.my_row,parent, false);
        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
        holder.myText1.setText(data1[position]);
        holder.myText2.setText(data2[position]);
        holder.myImage.setImageResource(images[position]);
    }

    @Override
    public int getItemCount() {
        return images.length;
    }

    public class MyViewHolder extends RecyclerView.ViewHolder {

        TextView myText1, myText2;
        ImageView myImage;

        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            myText1 = itemView.findViewById(R.id.myText1);
            myText2 = itemView.findViewById(R.id.myText2);
            myImage = itemView.findViewById(R.id.myImageView);

        }
    }
}

MainActivity 中的错误部分

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

        //Find ID
---->   recyclerView.findViewById(R.id.recyclerView);

        //String S1 et S2
        s1 = getResources().getStringArray(R.array.days);
        s2 = getResources().getStringArray(R.array.description);

link 的外部代码：


import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.example.mtoapp.R;

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


    String data1[], data2[];
    int images[];
    Context context;


    public MyAdapter(Context ct, String s1[], String s2[], int img[]){
    context = context;
    data1 = s1;
    data2 = s2;
    images = img;
    }


    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(context);
        View view = inflater.inflate(R.layout.my_row,parent, false);
        return new MyViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
        holder.myText1.setText(data1[position]);
        holder.myText2.setText(data2[position]);
        holder.myImage.setImageResource(images[position]);
    }

    @Override
    public int getItemCount() {
        return images.length;
    }

    public class MyViewHolder extends RecyclerView.ViewHolder {

        TextView myText1, myText2;
        ImageView myImage;

        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            myText1 = itemView.findViewById(R.id.myText1);
            myText2 = itemView.findViewById(R.id.myText2);
            myImage = itemView.findViewById(R.id.myImageView);

        }
    }
}

再次感谢您，祝您有愉快的一天:)

Answer 1

首先你应该启动 recyclerview 像：

RecyclerView recyclerview = findViewById(R.id.recycler_view_id);

那么你可以使用recyclerview.findViewById()

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