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);
            }
        }
    }


}

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);
          }

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);
    }

• 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);
    }

• 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);
            }
        }
    }

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;
    }