原文链接：

一：复习原作者提到的基础知识：

1、Handler

子线程处理完耗时操作后，通过Message传递数据给Handler，Handler把消息放在主线程队列中，配合主线程更新UI。

Handler有两个作用：  

(1):定时执行Message和Runnalbe 对象 

(2):让一个动作，在不同的线程中执行。 

Tip:

message是放置信息，可以传递一些参数，

Handler获取这些信息并将判度如何处理，

Runnable则是直接给出处理的方法。

2、绘制扇形

在Canvas上绘制扇形的函数：

(RectF oval, float startAngle, float sweepAngle, boolean useCenter, Paint paint)//画弧，

参数一是RectF对象，一个矩形区域椭圆形的界限用于定义在形状、大小、电弧，参数二是起始角(度)在电弧的开始，

参数三扫描角(度)开始顺时针测量的，参数四是如果这是真的话,包括椭圆中心的扇形,并关闭它,如果它是假这将是一个弧线,参数五是Paint对象

建议看这下篇

3、Shader类

用于渲染图像以及几何形状，包括：

BitmapShader主要用来渲染图像

LinearGradient 用来进行梯度渲染

RadialGradient 用来进行环形渲染

SweepGradient 用来进行梯度渲染

ComposeShader则是一个 混合渲染，可以和其它几个子类组合起来使用。 

使用方法：

先构建Shader对象，然后通过Paint的setShader方法设置渲染对象，然后设置渲染对象，然后再绘制时使用这个Paint对象即可。

建议：

4、旋转Canvas类

流程：保存现场——>操作——>恢复现场

  canvas.save(); 
  旋转
 canvas.restore();

二：Canvas基础例子、

自定义一个View，在onDraw中绘制简单的形状

public class BasicUsageView extends View { Paint paint1 = new Paint(); Paint paint2 = new Paint(); Paint paint3 = new Paint(); Paint paint4 = new Paint(); public BasicUsageView(Context context){ super(context); } public BasicUsageView(Context context,Attributes attributes){ super(context,null); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); initPaint(); drawLine(canvas); drawRect(canvas); drawCircle(canvas); drawText(canvas); drawImg(canvas); drawOval(canvas); drawPathLine(canvas); drawArc(canvas); } private void drawArc(Canvas canvas){ //350, 900 20 250 RectF oval = new RectF(400,500,600,800); canvas.drawArc(oval,0,20,true,paint1); canvas.drawArc(oval,60,100,false,paint3); Shader mShader = new LinearGradient(0,0,100,100, new int[]{Color.BLUE,Color.GREEN,Color.YELLOW,Color.RED}, null,Shader.TileMode.REPEAT); paint1.setShader(mShader); canvas.drawArc(oval,110,160,true,paint1); } private void drawPathLine(Canvas canvas){ Path path = new Path(); path.moveTo(30, 900); path.lineTo(50, 700); path.lineTo(80, 900); // path.lineTo(30,900); path.moveTo(30,900); path.lineTo(100, 900); path.lineTo(75, 700); path.lineTo(80, 900); path.moveTo(100, 900); path.lineTo(150, 400); path.lineTo(180, 700); path.lineTo(220, 370); path.lineTo(300, 810); path.lineTo(350, 900); path.lineTo(100,900); path.close(); canvas.drawPath(path,paint4); } private void drawOval(Canvas canvas){ RectF f = new RectF(300,300,600,500); canvas.drawOval(f,paint2); } private void drawImg(Canvas canvas){ canvas.drawBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.img),20,350,paint1); } private void drawText(Canvas canvas){ canvas.drawText("这是字符串",10,260,paint4); } private void drawCircle(Canvas canvas){ //150,100 canvas.drawCircle(150,100,50,paint3); canvas.drawCircle(150,100,30,paint4); } private void drawRect(Canvas canvas){ canvas.drawRect(30, 30, 290, 190, paint1); RectF rectF = new RectF(50,50,260,150); canvas.drawRoundRect(rectF,20,20,paint2); } private void drawLine(Canvas canvas){ canvas.drawLine(10,10,310,10,paint1); canvas.drawLine(10,215,310,215,paint2); canvas.drawLine(10,10,10,215,paint3); canvas.drawLine(310,10,310,215,paint4); } private void initPaint(){ paint1.setAntiAlias(true);//抗锯齿效果 paint1.setColor(Color.parseColor("#C0FF3E"));//画笔颜色 paint1.setAlpha(79); paint1.setStyle(Paint.Style.FILL);//实心的 paint1.setStrokeWidth(12); paint2.setColor(Color.CYAN); paint2.setTextSize(50); paint2.setStyle(Paint.Style.STROKE);//空心的 paint2.setStrokeWidth(5); paint3.setColor(Color.RED); paint3.setTextSize(100); paint3.setStyle(Paint.Style.STROKE);//空心的 paint3.setStrokeWidth(2); paint3.setAntiAlias(false); paint4.setColor(Color.DKGRAY); paint4.setTextSize(40); paint4.setStyle(Paint.Style.STROKE);//空心的 paint4.setStrokeWidth(3); paint4.setAntiAlias(true); paint4.setDither(true);//设定是否使用图像抖动处理，会使绘制出来的图片颜色更加平滑和饱满，图像更加清晰 } }
效果图：