Android绘图基础：Canvas、Paint等的使用

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：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical" >    <com.lovo.view.MyView        android:layout_width="wrap_content"        android:layout_height="wrap_content" /></LinearLayout>

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@Overrideprotected 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：