Android实现抽奖转盘

一、SurfaceView认识及的应用的思路

• SurfaceView继承自（extends）View，View是在UI线程中进行绘制；
• 而SurfaceView是在一个子线程中对自己进行绘制，优势：避免造成UI线程阻塞；
• SurfaceView中包含一个专门用于绘制的Surface，Surface中包含一个Canvas;
• 获得Canvas:可以从SurfaceView中方法的getHolder()获得SurfaceHolder,从holder获得Canvas;
• holder还管理着SurfaceView的生命周期：

①surfaceCreated()创建子线程，子线程的run()方法中开启SurfaceView的绘制。

②surfaceChanged()。

           ③surfaceDestoryed()中关闭子线程。

二、SurfaceView的一般写法

 package com.example.luckypan;

 import android.content.Context;
 import android.graphics.Canvas;
 import android.util.AttributeSet;
 import android.view.SurfaceHolder;
 import android.view.SurfaceHolder.Callback;
 import android.view.SurfaceView;

 public class SurfaceViewTemplate extends SurfaceView implements Callback, Runnable {

     private SurfaceHolder mHolder;
     private Canvas mCanvas;
     /**
      * 用于绘制线程
      */
     private Thread thread;
     /**
      * 线程的控制开关
      */
     private boolean isRunning;
     public SurfaceViewTemplate(Context context) {
         this(context, null);
     }
     public SurfaceViewTemplate(Context context, AttributeSet attrs) {
         super(context, attrs);
         mHolder=getHolder();
         mHolder.addCallback(this);
         //可获得焦点
         setFocusable(true);
         setFocusableInTouchMode(true);
         //设置常量
         setKeepScreenOn(true);
     }
     public void surfaceCreated(SurfaceHolder holder) {
         isRunning=true;
         thread=new Thread(this);
         thread.start();

     }
     public void surfaceChanged(SurfaceHolder holder, int format, int width,
             int height) {
         // TODO Auto-generated method stub

     }
     public void surfaceDestroyed(SurfaceHolder holder) {
         isRunning=false;

     }
     public void run() {
         //不断进行绘制
         while (isRunning)
         {
             draw();
         }
     }
     private void draw() {
         try {
             mCanvas=mHolder.lockCanvas();
             if (mCanvas!=null) {
                 //
             }
         }
         catch (Exception e) {

         }
         finally
         {
             if (mCanvas!=null) {
                 mHolder.unlockCanvasAndPost(mCanvas);
             }
         }
     }

 }

SurfaceViewTemplate

三、代码编写

• 绘制抽奖转盘的盘快

1.         绘制背景：drawBg(), Canvas的两个方法：drawColor(color the color to draw onto the canvas)，这里我设置背景色为白色0xFFFFFFFF、drawBitmap(Bitmap bitmap, Rect src, Rect dst, Paint paint),这个bitmap是背景图片，背景是一个矩形new Rect(),其他参数设置为null。

   1.  private void drawBg() {
               mCanvas.drawColor(0xFFFFFFFF);
               mCanvas.drawBitmap(mBgBitmap, null, new Rect(mPadding/2, mPadding/2, getMeasuredWidth()-mPadding/2, getMeasuredHeight()-mPadding/2), null);
           }

      drawBg

2. 绘制盘快：

 //绘制盘快
                 float tmpAngle=mStartAngle;
                 float sweepAngle=360/mItemCount;
                 for (int i = 0; i < mItemCount; i++) {
                     mArcPaint.setColor(mColor[i]);
                     //绘制盘快
                     mCanvas.drawArc(mRange, tmpAngle, sweepAngle,true, mArcPaint);

• 绘制抽奖转盘的奖项文字

 /**
      * 绘制每个盘快的文本
      * @param tmpAngle
      * @param sweepAngle
      * @param string
      */
     private void drawText(float tmpAngle, float sweepAngle, String string) {
         Path path=new Path();
         path.addArc(mRange, tmpAngle, sweepAngle);
         //利用水平偏移量让文字居中
         float textWidth=mTextPaint.measureText(string);
         int hOffset=(int) (mRadius*Math.PI/mItemCount/2-textWidth/2);
         int vOffset=mRadius/2/6;//垂直偏移量
         mCanvas.drawTextOnPath(string, path, hOffset, vOffset, mTextPaint);
     }

drawText

• 绘制抽奖转盘的图片

 /**
      * 绘制图片
      * @param tmpAngle
      * @param bitmap
      */
     private void drawIcon(float tmpAngle, Bitmap bitmap) {
         //设置图片的宽度为直径的1/8
         int imgWidth=mRadius/8;
         float angle=(float) ((tmpAngle+360/mItemCount/2)*Math.PI/180);
         int x=(int) (mCenter+mRadius/2/2*Math.cos(angle));
         int y=(int) (mCenter+mRadius/2/2*Math.sin(angle));
         //确定图片位置
         Rect rect=new Rect(x-imgWidth/2, y-imgWidth/2, x+imgWidth/2, y+imgWidth/2);
         mCanvas.drawBitmap(bitmap, null, rect,null);
     }

drawIcon

• 转盘滚动及设置停止的指向

 private void draw() {
         try {
             mCanvas=mHolder.lockCanvas();
             if (mCanvas!=null) {
                 //绘制背景
                 drawBg();
                 //绘制盘快
                 float tmpAngle=mStartAngle;
                 float sweepAngle=360/mItemCount;
                 for (int i = 0; i < mItemCount; i++) {
                     mArcPaint.setColor(mColor[i]);
                     //绘制盘快
                     mCanvas.drawArc(mRange, tmpAngle, sweepAngle,true, mArcPaint);
                     //绘制文本
                     drawText(tmpAngle,sweepAngle,mStrings[i]);
                     //绘制图片
                     drawIcon(tmpAngle,mImagBitmaps[i]);
                     tmpAngle+=sweepAngle;
                 }
                 mStartAngle+=mSpeed;
                 //判断是否点击停止按钮
                 if (isShouldEnd) {
                     mSpeed-=1;
                 }
                 if (mSpeed<=0)
                 {
                     mSpeed=0;
                     isShouldEnd=false;
                 }
             }
         }
         catch (Exception e) {

         }
         finally
         {
             if (mCanvas!=null) {
                 mHolder.unlockCanvasAndPost(mCanvas);
             }
         }
     }

draw

四、抽奖转盘的秘密

 /**
      * 电机启动旋转
      * 控制指定盘快停止范围
      * @param index
      */
     public void luckyStart(int index)
     {
         //计算每一项的角度
         float angle=360/mItemCount;
         //计算每一项的中奖范围
         //1->150~210
         //0->210~270
         float from=270-(index+1)*angle;
         float end=from+angle;
     //        设置停下来需要旋转的距离
         float targetFrom=4*360+from;
         float targetEnd=4*360+end;
         /**
          * <pre>
          * v1->0 且每次-1
          * (v1+0)*(v1+1)/2=targetFrom 等差数列求和公式;
          * v1*v1+v1-2*targetFrom=0;
          * v1=(-1+Math.sqrt(1+8*targetFrom))/2 一元二次方程求根公式
          * </pre>
          */
         float v1=(float) ((-1+Math.sqrt(1+8*targetFrom))/2);
         float v2=(float) ((-1+Math.sqrt(1+8*targetEnd))/2);
         mSpeed=v1+Math.random()*(v2-v1);
 //        mSpeed=v2;
         isShouldEnd=false;
     }

luckyStart