Android 自定义View 之 RectF用法详解

在之前通过Circle画了一个奥运五环，这次通过RectF来画矩形，常规的就是长方形正方形之类的。

还是新建一个自定义View,CustomViewRectF，然后继承View,实现里面的两个基本的构造方法，这样就可以在布局中显示了，自定义View代码如下：

package com.llw.paintdemo;

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

import androidx.annotation.Nullable;

public class CustomViewRectF extends View {

    public CustomViewRectF(Context context) {
        super(context);
    }

    public CustomViewRectF(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    private Paint customPaint(int color) {
        Paint paint = new Paint();
        paint.setColor(color);//画笔颜色
        paint.setStyle(Paint.Style.FILL);//实心
        paint.setStrokeWidth(6);//画笔宽度
        paint.setAntiAlias(true);//光滑
        return paint;
    }

    /**
     * 在纸上画矩形
     * @param canvas 纸
     */
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        /**
         * 画矩形  以两个点来画，起点和终点，通常是左上为起点，右下为终点  以下面这个图来看
         * 参数一：起点的Y轴坐标
         * 参数二：起点的X轴坐标
         * 参数三：终点的Y轴坐标
         * 参数四：终点的Y轴坐标
         * 
         *      *  
         *      *  
         *      *  top
         *  ****************
         *      *          *
         * left *          *  right
         *      *          * 
         *      *          *
         *      ******************
         *         bottom  *
         *                 *
         *                 *
         *  可以看到，左和上无限延长就会在一个点，右和下也是如此，这样应该理解了吧           
         *      
         */
        RectF rectF = new RectF(10,10,200,200);
        canvas.drawRect(rectF, customPaint(Color.BLUE));
        
    }

}

运行一下：

这个看到就是这样的。
然后改一下

paint.setStyle(Paint.Style.STROKE);//空心

可以看到左边有一部分被遮挡住了

再画长方形

RectF rectF = new RectF(10,10,100,200);//长方形

然后运行

再多画几个长方形

		RectF rectF2 = new RectF(120,10,210,200);//长方形2
        canvas.drawRect(rectF2, customPaint(Color.BLUE));

        RectF rectF3 = new RectF(240,10,330,200);//长方形3
        canvas.drawRect(rectF3, customPaint(Color.BLUE));

        RectF rectF4 = new RectF(360,10,450,200);//长方形4
        canvas.drawRect(rectF4, customPaint(Color.BLUE));

再改一下

		RectF rectF = new RectF(10,10,100,200);//长方形
        canvas.drawRect(rectF, customPaint(Color.GREEN));

        RectF rectF2 = new RectF(100,10,190,200);//长方形2
        canvas.drawRect(rectF2, customPaint(Color.YELLOW));

        RectF rectF3 = new RectF(190,10,280,200);//长方形3
        canvas.drawRect(rectF3, customPaint(Color.BLUE));

        RectF rectF4 = new RectF(280,10,370,200);//长方形4
        canvas.drawRect(rectF4, customPaint(Color.RED));

再通过改边top的位置，形成从低到高

		RectF rectF = new RectF(10,160,100,200);//长方形
        canvas.drawRect(rectF, customPaint(Color.GREEN));

        RectF rectF2 = new RectF(100,120,190,200);//长方形2
        canvas.drawRect(rectF2, customPaint(Color.YELLOW));

        RectF rectF3 = new RectF(190,80,280,200);//长方形3
        canvas.drawRect(rectF3, customPaint(Color.BLUE));

        RectF rectF4 = new RectF(280,40,370,200);//长方形4
        canvas.drawRect(rectF4, customPaint(Color.RED));

运行一下

再整体改一下形成旋转的效果。

	RectF rectF = new RectF(10,10,300,100);//长方形
        canvas.drawRect(rectF, customPaint(Color.GREEN));

        RectF rectF2 = new RectF(300,10,390,300);//长方形2
        canvas.drawRect(rectF2, customPaint(Color.YELLOW));

        RectF rectF3 = new RectF(100,300,390,390);//长方形3
        canvas.drawRect(rectF3, customPaint(Color.BLUE));

        RectF rectF4 = new RectF(10,100,100,390);//长方形4
        canvas.drawRect(rectF4, customPaint(Color.RED));

运行一下

再改一下：

		RectF rectF = new RectF(10,100,300,190);//长方形
        canvas.drawRect(rectF, customPaint(Color.GREEN));

        RectF rectF2 = new RectF(300,10,390,300);//长方形2
        canvas.drawRect(rectF2, customPaint(Color.YELLOW));

        RectF rectF3 = new RectF(190,300,480,390);//长方形3
        canvas.drawRect(rectF3, customPaint(Color.BLUE));

        RectF rectF4 = new RectF(100,190,190,480);//长方形4
        canvas.drawRect(rectF4, customPaint(Color.RED));

画矩形记住一点，bottom - top等于矩形的高度，right - left 等于矩形的宽度就可以了。相信你的理解已经很深了吧。