Android绘图基础：Canvas、Paint等的使用

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在Android中的绘图应该继承View组件，并重写它的onDraw(Canvas canvas)方法，Canvas代表了“依附”于指定View的画布，它提供了如下方法绘制各种图形：

Canvas还提供了如下方法进行变换：

在Canvas提供的绘制方法中用到了一个API：Paint，Paint 代表了Canvas上的画笔，主要用于绘制风格，包括画笔颜色、画笔笔触粗细、填充风格等。它提供了如下方法：

在Canvas提供的绘制方法中还用到了一个API：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。

下面这个实例中绘制了几种不同风格的图形，代码如下：

Activity:

package com.lovo.testcanvasactivity;

import android.os.Bundle;
import android.app.Activity;

public class TestCanvasActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_test_canvas);
    }
    
}

布局XML：

自定义组件类MyView（关键）：

package com.lovo.view;

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 attrs) {
		super(context, attrs);
	}

	// 重写该方法，进行绘图
	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		// 把整张画布绘制成白色
		canvas.drawColor(Color.WHITE);
		Paint paint = new Paint();
		// 去锯齿
		paint.setAntiAlias(true);
		paint.setColor(Color.BLUE);
		paint.setStyle(Paint.Style.STROKE);
		paint.setStrokeWidth(3);
		// 绘制圆形
		canvas.drawCircle(40, 40, 30, paint);
		// 绘制正方形
		canvas.drawRect(10, 80, 70, 140, paint);
		// 绘制矩形
		canvas.drawRect(10, 150, 70, 190, paint);
		// 绘制圆角矩形
		RectF rel = new RectF(10, 200, 70, 230);
		canvas.drawRoundRect(rel, 15, 15, paint);
		// 绘制椭圆
		RectF rell = new RectF(10, 240, 70, 270);
		canvas.drawOval(rell, paint);
		// 定义一个Path对象，封闭成一个三角形
		Path path1 = new Path();
		path1.moveTo(10, 340);
		path1.lineTo(70, 340);
		path1.lineTo(40, 290);
		path1.close();
		// 根据Path进行绘制，绘制三角形
		canvas.drawPath(path1, paint);
		// 定义一个Path对象，封闭成一个五角形
		Path path2 = new Path();
		path2.moveTo(26, 360);
		path2.lineTo(54, 360);
		path2.lineTo(70, 392);
		path2.lineTo(40, 420);
		path2.lineTo(10, 392);
		path2.close();
		// 根据Path进行绘制，绘制五角形
		canvas.drawPath(path2, paint);

		// -----设置填充风格后绘制------
		paint.setStyle(Paint.Style.FILL);
		paint.setColor(Color.RED);
		// 绘制圆形
		canvas.drawCircle(120, 40, 30, paint);
		// 绘制正方形
		canvas.drawRect(90, 80, 150, 140, paint);
		// 绘制矩形
		canvas.drawRect(90, 150, 150, 190, paint);
		// 绘制圆角矩形
		RectF re2 = new RectF(90, 200, 150, 230);
		canvas.drawRoundRect(re2, 15, 15, paint);
		// 绘制椭圆
		RectF re21 = new RectF(90, 240, 150, 270);
		canvas.drawOval(re21, paint);
		// 定义一个Path对象，封闭成一个三角形
		Path path3 = new Path();
		path3.moveTo(90, 340);
		path3.lineTo(150, 340);
		path3.lineTo(120, 290);
		path3.close();
		// 绘制三角形
		canvas.drawPath(path3, paint);
		// 定义一个Path对象，封闭成一个五角形
		Path path4 = new Path();
		path4.moveTo(106, 360);
		path4.lineTo(134, 360);
		path4.lineTo(150, 392);
		path4.lineTo(120, 420);
		path4.lineTo(90, 392);
		path4.close();
		// 绘制五角形
		canvas.drawPath(path4, paint);

		// -----设置渐变器后绘制--------
		// 为Paint设置渐变器
		Shader mShader = new LinearGradient(0, 0, 40, 60, new int[] {
				Color.RED, Color.GREEN, Color.BLUE, Color.YELLOW }, null,
				Shader.TileMode.REPEAT);
		paint.setShader(mShader);
		// 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 re3 = new RectF(170, 200, 230, 230);
		canvas.drawRoundRect(re3, 15, 15, paint);
		// 绘制椭圆
		RectF re31 = new RectF(170, 240, 230, 270);
		canvas.drawOval(re31, paint);
		// 定义一个Path对象，封闭成一个三角形
		Path path5 = new Path();
		path5.moveTo(170, 340);
		path5.lineTo(230, 340);
		path5.lineTo(200, 290);
		path5.close();
		// 绘制三角形
		canvas.drawPath(path5, paint);

		// 定义一个Path对象，封闭成一个五角形
		Path path6 = new Path();
		path6.moveTo(186, 360);
		path6.lineTo(214, 360);
		path6.lineTo(230, 392);
		path6.lineTo(200, 420);
		path6.lineTo(170, 392);
		path6.close();
		// 绘制五角形
		canvas.drawPath(path6, paint);
		
		
		// ------设置字符大小后绘制-------
		paint.setTextSize(22);
		paint.setShader(null);
		// 绘制7个字符串
		canvas.drawText("圆形", 240, 50, paint);
		canvas.drawText("正方形", 240, 120, paint);
		canvas.drawText("矩形", 240, 175, paint);
		canvas.drawText("圆角矩形", 230, 220, paint);
		canvas.drawText("椭圆", 240, 260, paint);
		canvas.drawText("三角形", 240, 325, paint);
		canvas.drawText("五角形", 240, 390, paint);
	}
}

附上图片效果：