Android 2D绘图解析之 Canvas，Paint

转载http://blog.csdn.net/leejizhou/article/details/51524948
【Android 2D绘图解析】系列文章将全面介绍Android绘图相关，这篇简单介绍下如何利用Android API进行一些简单图形的绘制，绘图的前提是需要继承自View，然后重写它的onDraw(Canvas canvas) 方法即可。

首先我们新建一个类继承自View，并重写onDraw方法。

package com.leejz.androiddrawing;//blog:www.lijizhou.compublic class CustomView extends View {    public CustomView(Context context, AttributeSet attrs) {        super(context, attrs);    }    @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);    }}

然后在Layout中进行添加此View

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context="com.leejz.androiddrawing.MainActivity">    <com.leejz.androiddrawing.CustomView        android:layout_width="match_parent"        android:layout_height="match_parent" /></LinearLayout

这样一个大体的自定义View的流程就搭建起来了，当然现在运行会显示一片空白，因为我们还没在onDraw方法进行任何的绘制，进行绘制前需要了解两个API，Canvas和Paint。

Canvas翻译成中文就是画布的意思，Canvas负责进行绘制各种各样的图形，它有如下的一些绘制图形方法
drawArc 绘制弧
drawBitmap 绘制位图
drawCircle 绘制圆形
drawLine 绘制线
drawOval 绘制椭圆
drawPath 绘制路径
drawPoint 绘制一个点
drawPoints 绘制多个点
drawRect 绘制矩形
drawRoundRect 绘制圆角矩形
drawText 绘制字符串
drawTextOnPath 沿着路径绘制字符串
更多的绘制方法参考
https://developer.android.com/reference/android/graphics/Canvas.html （需要科学上网）
Paint翻译成中文有油漆涂料的意思，Paint主要负责设置绘图的风格，包括画笔的颜色，粗细，填充风格等，它有如下的一些设置方法。

setARGB/setColor 设置颜色
setAlpha 设置透明度
setAntiAlias 设置是否抗锯齿
setShader 设置画笔的填充效果
setShadowLayer 设置阴影
setStyle 设置画笔风格
setStrokeWidth 设置空心边框的宽度
setTextSize 设置绘制文本时文字的大小

绘制圆形：drawCircle(float cx, float cy, float radius, Paint paint)

cx>圆心的x坐标
cy>圆心的y坐标
radius>圆的半径
paint>绘制风格

@Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        Paint paint=new Paint();        //去锯齿        paint.setAntiAlias(true);        //设置颜色        paint.setColor(getResources().getColor(android.R.color.holo_blue_light));        //绘制普通圆        canvas.drawCircle(200,200,100,paint);        //设置空心Style        paint.setStyle(Paint.Style.STROKE);        //设置空心边框的宽度        paint.setStrokeWidth(20);        //绘制空心圆        canvas.drawCircle(200,500,90,paint);    }

绘制矩形：drawRect(float left, float top, float right, float bottom, Paint paint) / drawRect(RectF rect, Paint paint)

left>矩形left的x坐标
top>矩形top的y坐标
right>矩形right的x坐标
bottom>矩形bottom的y坐标
paint>绘制风格

 @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        Paint paint = new Paint();        //去锯齿        paint.setAntiAlias(true);        //设置颜色        paint.setColor(getResources().getColor(android.R.color.holo_blue_light));        //绘制正方形        canvas.drawRect(100, 100, 300, 300, paint);        //上面代码等同于        //RectF rel=new RectF(100,100,300,300);        //canvas.drawRect(rel, paint);        //设置空心Style        paint.setStyle(Paint.Style.STROKE);        //设置空心边框的宽度        paint.setStrokeWidth(20);        //绘制空心矩形        canvas.drawRect(100, 400, 600, 800, paint);    }

绘制圆角矩形：drawRoundRect(float left, float top, float right, float bottom, float rx, float ry, Paint paint) / drawRoundRect(RectF rect, float rx, float ry, Paint paint)

left>图形left的x坐标
top>图形top的y坐标
right>图形right的x坐标
bottom>图形bottom的y坐标
rx>x方向的圆角半径
ry>y方向的圆角半径
paint>绘制风格

@Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        Paint paint = new Paint();        //去锯齿        paint.setAntiAlias(true);        //设置颜色        paint.setColor(getResources().getColor(android.R.color.holo_blue_light));        //绘制圆角矩形        canvas.drawRoundRect(100, 100, 300, 300, 30, 30, paint);        //上面代码等同于        //RectF rel=new RectF(100,100,300,300);        //canvas.drawRoundRect(rel,30,30,paint);        //设置空心Style        paint.setStyle(Paint.Style.STROKE);        //设置空心边框的宽度        paint.setStrokeWidth(20);        //绘制空心圆角矩形        canvas.drawRoundRect(100, 400, 600, 800, 30, 30, paint);    }

绘制椭圆：drawOval(float left, float top, float right, float bottom, Paint paint)

left>图形left的x坐标
top>图形top的y坐标
right>图形right的x坐标
bottom>图形bottom的y坐标
paint>绘制风格

@Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        Paint paint = new Paint();        //去锯齿        paint.setAntiAlias(true);        //设置颜色        paint.setColor(getResources().getColor(android.R.color.holo_orange_dark));        //绘制椭圆        canvas.drawOval(100, 100, 500, 300, paint);        //设置空心Style        paint.setStyle(Paint.Style.STROKE);        //设置空心边框的宽度        paint.setStrokeWidth(20);        //绘制空心椭圆        canvas.drawOval(100, 400, 600, 800, paint);    }

绘制弧：drawArc(RectF oval, float startAngle, float sweepAngle, boolean useCenter, Paint paint)

oval>指定圆弧的外轮廓矩形区域
startAngle>圆弧起始角度，单位为度
sweepAngle>圆弧扫过的角度，顺时针方向，单位为度
useCenter>如果为True时，在绘制圆弧时将圆心包括在内，通常用来绘制扇形
paint>绘制风格

@Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        Paint paint = new Paint();        //去锯齿        paint.setAntiAlias(true);        //设置颜色        paint.setColor(getResources().getColor(android.R.color.holo_orange_dark));        RectF rel = new RectF(100, 100, 300, 300);        //实心圆弧        canvas.drawArc(rel, 0, 270, false, paint);        //实心圆弧 将圆心包含在内        RectF rel2 = new RectF(100, 400, 300, 600);        canvas.drawArc(rel2, 0, 270, true, paint);        //设置空心Style        paint.setStyle(Paint.Style.STROKE);        paint.setStrokeWidth(20);        RectF rel3 = new RectF(100, 700, 300, 900);        canvas.drawArc(rel3, 0, 270, false, paint);        RectF rel4 = new RectF(100, 1000, 300, 1200);        canvas.drawArc(rel4, 0, 270, true, paint);    }

绘制文字：drawText(String text, float x, float y, Paint paint)

text>文本
x>文本origin的x坐标
y>文本baseline的y坐标
paint>绘制风格

*origin和baseline示意图

@Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        Paint paint = new Paint();        //去锯齿        paint.setAntiAlias(true);        //设置颜色        paint.setColor(getResources().getColor(android.R.color.holo_orange_dark));        paint.setTextSize(100);        //绘制文本        canvas.drawText("jEh", 80, 150, paint);    }