android学习笔记42——图形图像处理2——绘图

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：