利用Canvas实现在屏幕随机位置绘制10个大小(边长为10-160)颜色随机的空心五角星移动开发weixin43624626的博客-

Android不但能够显示图片，而且还能够直至一些简单的二维绘图，其实对于我们常见的一些Android基本组件，如TextView、Button等都是系统绘制出来的，其绘制的操作在View类的onDraw(Canvas canvas) 方法中，每个组件都需要实现onDraw(Canvas canvas) 方法进行自定义绘制。

下面实现的是利用Canvas在屏幕随机位置绘制10个大小(边长为10-160)和颜色随机的空心五角星，先看下面的效果图：

利用中学三角函数相关知识，以最左边顶点为基准，五角星的各个拐点点坐标表示如下（草图）：

XML文件 :

<RelativeLayout xmlns:android="https://schemas.android.com/apk/res/android" xmlns:app="https://schemas.android.com/apk/res-auto" xmlns:tools="https://schemas.android.com/tools" android:id="@+id/wujiaoxing" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity">      <com.example.myapplication.CanvasView         android:layout_width="wrap_content" android:layout_height="wrap_content" /> </RelativeLayout> 

MainActavity.java :

package com.example.myapplication; import androidx.appcompat.app.AppCompatActivity; import android.os.Bundle; public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } } 

CanvasView.java :

import android.content.Context; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.util.AttributeSet; import android.view.View; import java.util.Random; public class CanvasView extends View { public CanvasView(Context context, AttributeSet attrs) { super(context, attrs); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); //自定义相关三角函数值 float sin18 = (float) Math.sin(18 * Math.PI / 180); float cos18 = (float) Math.cos(18 * Math.PI / 180); float sin36 = (float) Math.sin(36 * Math.PI / 180); float cos36 = (float) Math.cos(36 * Math.PI / 180); float sin27 = (float) Math.sin(27 * Math.PI / 180); float cos27 = (float) Math.cos(27 * Math.PI / 180); float sin54 = (float) Math.sin(54 * Math.PI / 180); float cos54 = (float) Math.cos(54 * Math.PI / 180);         Paint paint = new Paint();//定义一个画笔对象         paint.setAntiAlias(true);//设置抗锯齿         paint.setStyle(Paint.Style.STROKE);//设置画笔风格         paint.setStrokeWidth(8);//设置画笔粗细 for(int i=0;i<10;i++) { //随机颜色(rgb)生成 int red = new Random().nextInt(255)+1; int green = new Random().nextInt(255)+1; int blue = new Random().nextInt(255)+1;             paint.setColor(Color.rgb(red,green,blue)); //随机(x,y),a生成 float x = (float) (new Random().nextInt(800) + 40); float y = (float) (new Random().nextInt(130)*10+100); float a= (float) (new Random().nextInt(150)+11); //五角星边的绘制             canvas.drawLine(x, y, x + a, y, paint);             canvas.drawLine(x + a, y, x + a + a * sin18, y - a * cos18, paint);             canvas.drawLine(x + a + a * sin18, y - a * cos18, x + a + 2 * a * sin18, y, paint);             canvas.drawLine(x + a + 2 * a * sin18, y, x + 2 * a + 2 * a * sin18, y, paint);             canvas.drawLine(x + 2 * a + 2 * a * sin18, y, (x + 2 * a + 2 * a * sin18 - a * cos36), y + a * sin36, paint);             canvas.drawLine(x + 2 * a + 2 * a * sin18 - a * cos36, y + a * sin36, x + (2 * a + 2 * a * sin18) * sin54, y + (2 * a + 2 * a * sin18) * cos54, paint);             canvas.drawLine(x + (2 * a + 2 * a * sin18) * sin54, y + (2 * a + 2 * a * sin18) * cos54, x + a * sin54 - a * sin27 + a * cos27, y + a * (cos54 + cos27 - sin27), paint);             canvas.drawLine(x + a * sin54 - a * sin27 + a * cos27, y + a * (cos54 + cos27 - sin27), x + a * sin54 - a * sin27, y + a * (cos54 + cos27), paint);             canvas.drawLine(x + a * sin54 - a * sin27, y + a * (cos54 + cos27), x + a * sin54, y + a * (cos54), paint);             canvas.drawLine(x + a * sin54, y + a * (cos54), x, y, paint); } } }