嘗試在 Android Studio 中的 null object 參考上調用虛擬方法

Question

我開始學習 Android Studio 所以請繞過我的無知。

我收到此錯誤代碼：

2020-05-12 19:32:35.398 13918-13918/com.fdev.Exploding_Tomatoes E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.fdev.Exploding_Tomatoes, PID: 13918
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
        at android.view.LayoutInflater.from(LayoutInflater.java:282)
        at com.fdev.Exploding_Tomatoes.Adapter.onCreateViewHolder(Adapter.java:25)
        at com.fdev.Exploding_Tomatoes.Adapter.onCreateViewHolder(Adapter.java:12)
        at androidx.recyclerview.widget.RecyclerView$Adapter.createViewHolder(RecyclerView.java:7078)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6235)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6118)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6114)
        at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2303)
        at androidx.recyclerview.widget.LinearLayoutManager.layout
2020-05-12 19:32:35.398 13918-13918/com.fdev.Exploding_Tomatoes E/AndroidRuntime:     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:957)
        at android.os.Handler.handleCallback(Handler.java:907)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:216)
        at android.app.ActivityThread.main(ActivityThread.java:7506)
        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:956)

這是我的適配器腳本，用於獲得（希望）工作的 Recyclerview。 錯誤是，或者至少我認為是這樣，在“View view = LayoutInflater.from(context).inflate(R.layout.row, null);” 我嘗試搜索但找不到任何工作。 我用“this”替換了“null”，刪除了它。 但什么都沒有。

package com.fdev.Exploding_Tomatoes;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

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

import java.util.ArrayList;

public class Adapter extends RecyclerView.Adapter<MyHolder> {
    private Context context;
    Context c;
    ArrayList<Model> models;

    public Adapter(Context c, ArrayList<Model> models) {
        this.c = c;
        this.models = models;
    }

    @NonNull
    @Override
    public MyHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(context).inflate(R.layout.row, null);
        return new MyHolder(view);

    }

    @Override
    public void onBindViewHolder(@NonNull MyHolder myholder, int position) {
        myholder.mTitle.setText(models.get(1).getTitle());
        myholder.mNumber.setText(models.get(1).getNumber());
    }

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

任何幫助表示贊賞！ 謝謝

Answer 1

代替：

View view = LayoutInflater.from(context).inflate(R.layout.row, null);

將其替換為：

View view = LayoutInflater.from(context).inflate(R.layout.row, parent, false);

onCreateViewHolder 方法將是：

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

        }

Answer 2

這個：

@Override
public MyHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(context).inflate(R.layout.row, null);
    return new MyHolder(view);

}

必須是這樣的：

@Override
public MyHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.row, parent, false);
    return new MyHolder(view);

}