Java 创建一个包含单词的矩形
因此,我试图在我的java项目中绘制一个矩形,由于某种原因,我得到一个错误,应用程序关闭。错误为03-28 09:05:50.332:E/AndroidRuntime(4611):致命异常:主 03-28 09:05:50.332:E/AndroidRuntime(4611):进程:com.Tripp.thebasics,PID:4611 03-28 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)”Java 创建一个包含单词的矩形,java,android,draw,android-drawable,drawrect,Java,Android,Draw,Android Drawable,Drawrect,因此,我试图在我的java项目中绘制一个矩形,由于某种原因,我得到一个错误,应用程序关闭。错误为03-28 09:05:50.332:E/AndroidRuntime(4611):致命异常:主 03-28 09:05:50.332:E/AndroidRuntime(4611):进程:com.Tripp.thebasics,PID:4611 03-28 09:05:50.332:E/AndroidRuntime(4611):java.lang.NullPointerException:尝试在空对象
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);
}
}
这是下面那个类的按钮
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);
}
}
在尝试使用构造函数之前,先初始化它<代码>绘制=新绘制()代码>这里有两个很好的资源,展示了如何创建自定义视图和绘制