java - 创建一个上面有文字的矩形

Question

所以我试图在我的java项目中绘制一个矩形，由于某种原因我收到错误并且应用程序关闭。错误是 03-28 09:05:50.332: E/AndroidRuntime(4611): 致命异常: main03-28 09:05:50.332:E/AndroidRuntime(4611):进程:com.Tripp.thebasics，PID:461103-28 09:05:50.332: E/AndroidRuntime(4611): java.lang.NullPointerException: 尝试在空对象引用上调用虚拟方法“void android.graphics.Paint.setColor(int)”

package com.Tripp.thebasics;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.View;

public class DrawingView extends View {
    Paint paint;

    public DrawingView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
    }

    public DrawingView(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
    }

    public DrawingView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        // TODO Auto-generated constructor stub
    }

    @Override
    protected void onDraw(Canvas canvas){
        super.onDraw(canvas);

        Rect ourRect = new Rect();

        ourRect.set(0,0,canvas.getWidth(),canvas.getHeight()/2 );
        paint.setColor(Color.RED);

        canvas.drawRect(ourRect, paint);
    }

}

这是转到下面该类的按钮

public class JokeOfTheDay extends Activity {

    DrawingView v;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        v = new DrawingView(this);
        setContentView(v);  

    }



}

Answer 1

在尝试使用绘制变量之前，请在构造函数中初始化它。 paint = new Paint();