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

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
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

巴特西

Android实现抽奖转盘

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