绘图
android的绘图应该继承View组件，并重写onDraw(Canvas canvas)方法即可。
重写onDraw(Canvas canvas)方法时涉及一个绘图API:Canvas，Canvas代表了“依附”于指定View的画布，其提供了如下图所示的方法——用于绘制各种图像：
注意：在Canvas提供的绘制方法中还用到了一个API:Path,Path代表任意多条直线连接而成的任意图形，当Canvas根据Path绘制时，可以绘制出任意的形状。
实例如下：
布局文件==》
<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"
android:orientation="vertical"
tools:context=".MainActivity" > <com.example.mycanvas.MyView
android:id="@+id/myView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content" /> </LinearLayout> 代码实现==》
package com.example.mycanvas; import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.RectF;
import android.graphics.Shader;
import android.util.AttributeSet;
import android.view.View; public class MyView extends View
{
public MyView(Context context, AttributeSet set)
{
super(context, set);
} @Override
protected void onDraw(Canvas canvas)
{
super.onDraw(canvas);
// 把整张布绘制成白色
canvas.drawColor(Color.WHITE);
Paint p = new Paint();
// 去除锯齿
p.setAntiAlias(true);
p.setColor(Color.BLUE);
p.setStyle(Paint.Style.STROKE);
p.setStrokeWidth(3);
// 绘制圆形
canvas.drawCircle(40, 40, 30, p);
// 绘制正方形
canvas.drawRect(10, 80, 70, 140, p);
// 绘制矩形
canvas.drawRect(10, 150, 70, 190, p);
RectF rect = new RectF(10, 200, 70, 230);
// 绘制圆角矩形
canvas.drawRoundRect(rect, 15, 15, p);
RectF rect1 = new RectF(10, 240, 70, 270);
// 绘制椭圆
canvas.drawOval(rect1, p); paintTriangle(canvas, p);
paintFivePointStar(canvas, p);
paintGraph(canvas, p);
paintGraph2(canvas, p);
paintGraph3(canvas, p);
} /* 设置字符大小后绘制 */
private void paintGraph3(Canvas canvas, Paint paint)
{
paint.setTextSize(26);
paint.setShader(null);
// 绘制字符串
canvas.drawText("圆形", 260, 50, paint);
// canvas.drawText("方形", 260, 120, paint);
// canvas.drawText("长方形", 240, 170, paint);
// canvas.drawText("圆角矩形", 230, 220, paint);
// canvas.drawText("圆形", 240, 260, paint);
// canvas.drawText("三角形", 240, 325, paint);
// canvas.drawText("五角形", 240, 390, paint);
} private void paintGraph2(Canvas canvas, Paint paint)
{
// 设置渐变器后绘制
Shader shader = new LinearGradient(0, 0, 40, 60, new int[] { Color.RED, Color.GREEN,
Color.BLUE, Color.YELLOW }, null, Shader.TileMode.REPEAT);
paint.setShader(shader);
// 设置阴影
paint.setShadowLayer(45, 10, 10, Color.GRAY);
// 绘制圆形
canvas.drawCircle(200, 40, 30, paint);
// 绘制正方形
canvas.drawRect(170, 80, 230, 140, paint);
// 绘制矩形
canvas.drawRect(170, 150, 230, 190, paint);
// 绘制圆角矩形
RectF r = new RectF(170, 200, 230, 230);
canvas.drawRect(r, paint); // 绘制椭圆
RectF rel2 = new RectF(170, 240, 230, 270);
canvas.drawOval(rel2, paint); // 绘制三角形
Path path = new Path();
path.moveTo(170, 340);
path.lineTo(230, 340);
path.lineTo(200, 290);
path.close();
// 根据Path进行绘制，绘制三角形
canvas.drawPath(path, paint); // 定义一个Path对象，封闭成一个三角形
Path p1 = new Path();
p1.moveTo(186, 360);
p1.lineTo(214, 360);
p1.lineTo(230, 392);
p1.lineTo(200, 420);
p1.lineTo(170, 392);
p1.close();
// 根据Path进行绘制，绘制三角形
canvas.drawPath(p1, paint);
} private void paintGraph(Canvas canvas, Paint p)
{
// 设置填充风格后绘制
p.setStyle(Paint.Style.FILL);
p.setColor(Color.RED);
canvas.drawCircle(120, 40, 30, p);
// 绘制正方形
canvas.drawRect(90, 80, 150, 140, p);
// 绘制矩形
canvas.drawRect(90, 150, 150, 190, p);
RectF re2 = new RectF(90, 200, 150, 230);
// 绘制圆角矩形
canvas.drawRoundRect(re2, 15, 15, p); RectF rel2 = new RectF(90, 240, 150, 270);
// 绘制椭圆
canvas.drawOval(rel2, p); // 绘制三角形
Path path = new Path();
path.moveTo(90, 340);
path.lineTo(150, 340);
path.lineTo(120, 290);
path.close();
// 根据Path进行绘制，绘制三角形
canvas.drawPath(path, p); // 定义一个Path对象，封闭成一个三角形
Path p1 = new Path();
p1.moveTo(106, 360);
p1.lineTo(134, 360);
p1.lineTo(150, 390);
p1.lineTo(120, 420);
p1.lineTo(90, 392);
p1.close();
// 根据Path进行绘制，绘制三角形
canvas.drawPath(p1, p);
} private void paintFivePointStar(Canvas canvas, Paint p)
{
// 定义一个Path对象，封闭成一个五角星
Path p2 = new Path();
p2.moveTo(26, 360);
p2.lineTo(54, 360);
p2.lineTo(70, 392);
p2.lineTo(40, 420);
p2.lineTo(10, 392);
p2.close();
// 根据Path进行绘制，绘制五角形
canvas.drawPath(p2, p);
} private void paintTriangle(Canvas canvas, Paint p)
{
// 定义一个Path对象，封闭成一个三角形
Path p1 = new Path();
p1.moveTo(10, 340);
p1.lineTo(70, 340);
p1.lineTo(40, 290);
p1.close();
// 根据Path进行绘制，绘制三角形
canvas.drawPath(p1, p);
} }
注：将自定义组件拖放到布局文件，即可看到效果，如下图所示：
