Canvas画布，通过它我们可以自定义一个View，设置View的相关效果之类的。感觉用法差不多，重要的是要理解方法中传入的参数的含义，比如float类型的参数，传递的是坐标,已开是没有注意传入的参数时坐标，导致我迷糊了一段时间，希望大家不要犯我的错误，记住是坐标啊！。

一、Canvas画布介绍

The Canvas class holds the “draw” calls. To draw something, you need 4 basic components: A Bitmap to hold the pixels, a Canvas to host the draw calls (writing into the bitmap), a drawing primitive (e.g. Rect, Path, text, Bitmap), and a paint (to describe the colors and styles for the drawing). 　

　　关于Canvas网上也没有什么好的介绍， 我就直接从API中复制过来的，这里翻译一下。

　　Canvas 支持“绘制”调用，想要进行绘制，你需要4个基本组成：一个由像素构成的位图，支持绘制调用的画布（绘制位图），一个图元（如矩形，路径，文本，位图），和油漆（用于绘制图的颜色和样式）。

（上面的四个基本组成会在后面代码部分进行解释）

　　API中说的究竟是什么意思呢？我们可以把这个Canvas理解成系统提供给我们的一块内存区域(但实际上它只是一套画图的API，真正的内存是下面的Bitmap)，而且它还提供了一整套对这个内存区域进行操作的方法，所有的这些操作都是画图API。这样我们就可以在画布上进行绘制了。

二、使用步骤

　　上面说了那么多是不是特别想知道它要怎样使用呢？现在我们就来说说他的使用步骤。

2.1使用步骤

1、写一个class类继承自View

2、在继承的class中写它的两个构造器，以前的版本中我们只需要写它的两个构造器（一个构造器参数为View（Context）另一个构造器参数为 View（Context AttributeSet） ），现在版本的升级又新出了两个构造器（View（Context attribute style）带有主题样式的），不管那么多，我们还是只写本来的两个构造器就OK了。

3、在该class中调用onDraw方法和onMeasure()方法。

4、在布局中使用该View

5、进行绘制

2.1使用示例

　　下面我们按照上面的步骤一步步进行

1、写一个class类继承自View

public class MyView extends View

2、在继承的class中写它的两个构造器

public MyView(Context context) {

super(context);

}

public MyView(Context context, AttributeSet attrs) {

super(context, attrs);

}

1. 在该class中重写onDraw方法和onMeasure()方法。

onDraw（我们将在该方法中进行绘制图形）

@Override

protected void onDraw(Canvas canvas) {

super.onDraw(canvas);

}

onMeasure（获得画布的高度与宽度）

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

super.onMeasure(widthMeasureSpec, heightMeasureSpec);

width = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);

height = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);

}

补充：由于onMeasure方法中本身就有获取高度与宽度的方法，我们直接点进去（ctrl+左键），复制出来就可以了。

2. 在布局中使用该View（布局时必须写全包名+类名）

<RelativeLayout 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=".MainActivity" >

<com.example.myview.MyView

android:layout_width="match_parent"

android:layout_height="match_parent"

5、进行绘制

我们要如何进行绘制呢？首先我们看些Canvas都能绘制写什么。

drawRect(float left, float top, float right, float bottom, Paint paint)

//绘制矩形（左上右下的坐标,我们可以理解为左上的坐标为我们确定了矩形的左上角点，右下坐标为我们确定了右下角的点，这样一个矩形区域就确定出来了，paint为画笔）

drawRoundRect(float left, float top, float right, float bottom, float rx, float ry, Paint paint)

//绘制圆角矩形（左上右下的坐标）

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

//绘制弧（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,包括椭圆中心的电弧,并关闭它，实际绘制的是扇形,如果它是假这将是一个弧线,参数五是Paint对象）

drawOval(float left, float top, float right, float bottom, Paint paint)

//绘制椭圆

drawLine(float startX, float startY, float stopX, float stopY, Paint paint)

//绘制直线（XY起止坐标）

drawCircle(float cx, float cy, float radius, Paint paint)

//绘制圆形

drawText(String text, float x, float y, Paint paint)

//绘制文本

其他的不再进行列举，有需要可以查看API文档。

在参数中可以看到我们画图是需要画笔的，下面我们再来看下画笔（画漆）。这里展示一段代码相信你就能够明白了。

Paint mpaintline = new Paint();

mpaintline.setColor(Color.RED);

//设置线宽

mpaintline.setStrokeWidth(10);

//设置抗锯齿

mpaintline.setAntiAlias(true);

//设置空心,比如画实心圆还是空心圆

mpaintcircle.setStyle(Paint.Style.STROKE);

mpainttext.setTextSize(30);

//设置字的位置

mpainttext.setTextAlign(Align.CENTER);

mpainttext.setColor(Color.BLACK);

2.2表盘示例

上面说了那么多，我们来看一个具体而完整的实例，来整理一下思路。

public class MyView extends View

private int width;

private int height;

private Paint mpaintline;

private Paint mpaintcircle;

private Paint mpainttext;

private Calendar mcalendar;

private static final int NEED_INVALIDATE=0x23;

private Handler mhandler=new Handler(){

public void handleMessage(android.os.Message msg) {

switch (msg.what) {

case NEED_INVALIDATE:

//重新获取时间

mcalendar=Calendar.getInstance();

//重新绘制界面

invalidate();//告诉UI主线程重新绘制

//再次发送消息，递归调用，再次监测秒针

mhandler.sendEmptyMessageDelayed(NEED_INVALIDATE, 1000);

break;

default:

break;

}

};

};

public MyView(Context context) {

super(context);

}

public MyView(Context context, AttributeSet attrs) { //为了不是每次都创建Paint，我们在这里创建

super(context, attrs);

mcalendar=Calendar.getInstance();

mpaintline = new Paint();

mpaintline.setColor(Color.RED);

//设置线宽

mpaintline.setStrokeWidth(10);

//设置抗锯齿

mpaintline.setAntiAlias(true);

mpaintcircle = new Paint();

mpaintcircle.setColor(Color.GREEN);

mpaintcircle.setStrokeWidth(10);

//设置空心

mpaintcircle.setStyle(Paint.Style.STROKE);

mpainttext=new Paint();

mpainttext.setTextSize(30);

mpainttext.setTextAlign(Align.CENTER);

mpainttext.setColor(Color.BLACK);

//发送消息，监测秒针

mhandler.sendEmptyMessage(NEED_INVALIDATE);

}

//在此方法中进行绘制

@Override

protected void onDraw(Canvas canvas) {

super.onDraw(canvas);

//绘制圆形

canvas.drawCircle(width/2, height/2, width/2-20, mpaintcircle);

//绘制表芯

canvas.drawCircle(width/2, height/2, 5, mpaintcircle);

//绘制表盘时我们采用旋转画布的思想，让画布进行旋转一定角度，绘制

for(int i=1;i<=12;i++){

//保存画布当前状态

canvas.save();

//指定旋转角度与旋转点

canvas.rotate(360/12*i,width/2,height/2);

//绘制表盘

canvas.drawLine(width/2, height/2-(width/2-20), width/2,height/2-width/2+40, mpaintline);

//绘制文字

canvas.drawText(""+i, width/2, height/2-width/2+70, mpainttext);

//恢复开始位置

canvas.restore();

}

int minute=mcalendar.get(Calendar.MINUTE);

int hour=mcalendar.get(Calendar.HOUR);

int second=mcalendar.get(Calendar.SECOND);

float minudegrees=minute/60f*360;

float hourdregrees=hour*60/12f/60*360;

float senconddegree=second/60f*360;

//绘制分针

canvas.save();

canvas.rotate(minudegrees,width/2,height/2);

canvas.drawLine(width/2, height/2, width/2, height/2-width/2+90, mpaintline);

canvas.restore();

//绘制时针

canvas.save();

canvas.rotate(hourdregrees,width/2,height/2);

canvas.drawLine(width/2, height/2, width/2, height/2-width/2+100, mpaintline);

canvas.restore();

//绘制秒针

canvas.save();

canvas.rotate(senconddegree,width/2,height/2);

canvas.drawLine(width/2, height/2, width/2, height/2-width/2+60, mpaintline);

canvas.restore();

}

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

super.onMeasure(widthMeasureSpec, heightMeasureSpec);

//固定

2.3绘制圆形progressbar

这里模拟下载，自定义了一个ProgressBar。在MyProgressCircle 中定义出最大进度和当前进度，给出当前进度的SET\GET方法，通过Mainactivity中改变Progres的当前进度，根据当前进度，不停修改半径，重新绘制表层绿色圆形。

public class MyProgressCircle extends View{

private int width;

private int height;

private int Maxprogress=100;

private int Currentprogress;

private Paint PaintBackGround;

private Paint PaintCurrent;

private Paint PaintText;

public int getMaxprogress() {

return Maxprogress;

}

public void setMaxprogress(int maxprogress) {

Maxprogress = maxprogress;

}

//当前进度的set、get方法

public int getCurrentprogress() {

return Currentprogress;

}

public void setCurrentprogress(int currentprogress) {

Currentprogress = currentprogress;

invalidate();

}

public MyProgressCircle(Context context) {

super(context);

// TODO Auto-generated constructor stub

}

public MyProgressCircle(Context context, AttributeSet attrs) {

super(context, attrs);

PaintBackGround=new Paint();

PaintBackGround.setColor(Color.GRAY);

PaintBackGround.setAntiAlias(true);

PaintBackGround.setStrokeWidth(10);

PaintCurrent=new Paint();

PaintCurrent.setColor(Color.GREEN);

PaintCurrent.setAntiAlias(true);

PaintCurrent.setStrokeWidth(10);

PaintText=new Paint();

PaintText.setColor(Color.BLACK);

PaintText.setAntiAlias(true);

PaintText.setTextAlign(Align.CENTER);

}

@Override

protected void onDraw(Canvas canvas) {

super.onDraw(canvas);

canvas.drawCircle(width/2, height/2,width/2-30 , PaintBackGround);

//根据当前进度改变半径，绘制圆形

canvas.drawCircle(width/2, height/2,(float) (width/2-30)*Currentprogress/Maxprogress, PaintCurrent);

canvas.drawText(Currentprogress*100f/Maxprogress+"%", width/2,height/2, PaintText);

}

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

super.onMeasure(widthMeasureSpec, heightMeasureSpec);

width = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);

height = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);

}

}

MainActivity中改变progress进度

public class MainActivity extends Activity implements OnClickListener{

private Button btn_circle_progress;

private MyProgressCircle myprogresscircle;

private int progress;

private Handler mhanHandler=new Handler(){

public void handleMessage(android.os.Message msg) {

switch (msg.what) {

case 0x23:

progress++;

if(progress<=100){

myprogresscircle.setCurrentprogress(progress);

mhanHandler.sendEmptyMessageDelayed(0x23, 200);

}

break;

default:

break;

}

};

};

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.circle_progress);

btn_circle_progress=(Button) findViewById(R.id.mbtn_circleprogress);

myprogresscircle=(MyProgressCircle) findViewById(R.id.mycircleprogress);

btn_circle_progress.setOnClickListener(this);

}

@Override

public void onClick(View v) {

mhanHandler.sendEmptyMessageDelayed(0x23, 1000);

}

}

2.4绘制弧形progressbar

@Override

protected void onDraw(Canvas canvas) {

super.onDraw(canvas);

//设置画弧的区域

RectF oval1=new RectF(width/2-100,height/2-100,width/2+100,height/2+100);

canvas.drawArc(oval1, 270, Currentprogress, false, PaintCurrent);//第二个参数：顺时针起始位置；第三个参数：顺时针转的弧

canvas.drawText(Currentprogress*100f/Maxprogress+"%", width/2,height/2, PaintText);

}

MainActivity

public class MainActivity_ARC extends Activity implements OnClickListener{

private Button btn_arc_progress;

private MyArcProgress myprogressarc;

private int progress;

private Handler mhanHandler=new Handler(){

public void handleMessage(android.os.Message msg) {

switch (msg.what) {

case 0x23:

progress++;

if(progress<=360){

myprogressarc.setCurrentprogress(progress);

mhanHandler.sendEmptyMessageDelayed(0x23, 200);

}

break;

default:

break;

}

};

};

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.arc_progress);

btn_arc_progress=(Button) findViewById(R.id.mbtn_arcprogress);

myprogressarc= (MyArcProgress) findViewById(R.id.myarcprogress);

btn_arc_progress.setOnClickListener(this);

}

@Override

public void onClick(View v) {

mhanHandler.sendEmptyMessageDelayed(0x23, 1000);

}

}

2.5绘制多条线与矩形

public class MyRectProgress extends View{

private int width;

private int height;

private int Maxprogress=100;

private int Currentprogress;

private Paint PaintBackGround;

private Paint PaintCurrent;

private Paint PaintText;

private int i;

private float[] lines=new float[400];

public int getMaxprogress() {

return Maxprogress;

}

public void setMaxprogress(int maxprogress) {

Maxprogress = maxprogress;

}

public int getCurrentprogress() {

return Currentprogress;

}

public void setCurrentprogress(int currentprogress) {

Currentprogress = currentprogress;

lines[i]=50;

i++;

lines[i]=50+250f*Currentprogress/Maxprogress;

i++;

lines[i]=300;

i++;

lines[i]=50+250f*Currentprogress/Maxprogress;

invalidate();

}

public MyRectProgress(Context context) {

super(context);

// TODO Auto-generated constructor stub

}

public MyRectProgress(Context context, AttributeSet attrs) {

super(context, attrs);

PaintBackGround=new Paint();

PaintBackGround.setColor(Color.GRAY);

PaintBackGround.setAntiAlias(true);

PaintBackGround.setStrokeWidth(10);

PaintCurrent=new Paint();

PaintCurrent.setColor(Color.GREEN);

PaintCurrent.setAntiAlias(true);

PaintCurrent.setStrokeWidth(5);

PaintText=new Paint();

PaintText.setColor(Color.BLACK);

PaintText.setAntiAlias(true);

PaintText.setTextAlign(Align.CENTER);

PaintText.setTextSize(30);

}

@Override

protected void onDraw(Canvas canvas) {

super.onDraw(canvas);

//canvas.drawCircle(width/2, height/2,width/2-30 , PaintBackGround);

canvas.drawRect(50,50 ,300, 300, PaintBackGround);

canvas.drawLines(lines, PaintCurrent);

//canvas.drawLine(50,50+250f*Currentprogress/Maxprogress, 300, 50+250f*Currentprogress/Maxprogress, PaintCurrent);

canvas.drawText(Currentprogress*100f/Maxprogress+"%", width/2,height/2, PaintText);

}

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

super.onMeasure(widthMeasureSpec, heightMeasureSpec);

width = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);

height = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);

}

}

2.5绘制渐变

样式就是我们开始时图片展示的样式

package com.example.myview;

import android.content.Context;

import android.graphics.Canvas;

import android.graphics.Color;

import android.graphics.LinearGradient;

import android.graphics.Paint;

import android.graphics.Paint.Align;

import android.graphics.RectF;

import android.graphics.Shader;

import android.util.AttributeSet;

import android.view.View;

public class MyotherProgress extends View{

private int width;

private int height;

private int Maxprogress=100;

private int Currentprogress;

private Paint PaintBackGround;

private Paint PaintCurrent;

private Paint PaintText;

public int getMaxprogress() {

return Maxprogress;

}

public void setMaxprogress(int maxprogress) {

Maxprogress = maxprogress;

}

public int getCurrentprogress() {

return Currentprogress;

}

public void setCurrentprogress(int currentprogress) {

Currentprogress = currentprogress;

invalidate();

}

public MyotherProgress(Context context) {

super(context);

// TODO Auto-generated constructor stub

}

public MyotherProgress(Context context, AttributeSet attrs) {

super(context, attrs);

PaintBackGround=new Paint();

PaintBackGround.setColor(Color.GRAY);

PaintBackGround.setAntiAlias(true);

PaintBackGround.setStrokeWidth(10);

PaintCurrent=new Paint();

PaintCurrent.setColor(Color.GREEN);

PaintCurrent.setAntiAlias(true);

PaintCurrent.setStrokeWidth(10);

/* 设置渐变色 颜色是改变的 */

Shader mShader = new LinearGradient(0, 0, 100, 100,

new int[] { Color.RED, Color.GREEN, Color.BLUE, Color.YELLOW,

Color.LTGRAY }, null, Shader.TileMode.REPEAT);

PaintCurrent.setShader(mShader);

PaintText=new Paint();

PaintText.setColor(Color.BLACK);

PaintText.setAntiAlias(true);

PaintText.setTextAlign(Align.CENTER);

PaintText.setTextSize(30);

}

@Override

protected void onDraw(Canvas canvas) {

super.onDraw(canvas);

//底层圆形

canvas.drawCircle(width/2, height/2,width/2-30 , PaintBackGround);

// 设置个新的长方形，扫描测量

RectF oval = new RectF(30,height/2-(width/2-30 ) , width-30 , height/2+width/2-30 );

//绘制扇形

// 画弧，第一个参数是RectF（确定绘制区域）：

//该类是第二个参数是角度的开始，

//第三个参数是多少度，

//第四个参数是真的时候画扇形，是假的时候画弧线

canvas.drawArc(oval, 0, Currentprogress*360f/100, true, PaintCurrent);

canvas.drawText(Currentprogress*100f/Maxprogress+"%", width/2,height/2, PaintText);

}

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

super.onMeasure(widthMeasureSpec, heightMeasureSpec);

width = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);

height = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);

}

}