仿网易云音乐 专辑图片折叠轮播

先不多说现上一张效果图

首先简述一下实现原理

1.首先让我们的imageview**动起来**

其实是不断的.invalidate();函数 让他不断的调用ondarw函数
（显然我们不必要不断的调用ondarw函数 只有在我们让他动的时候调用即可 所以我们要声明一个变量记录change记录是否产生动画）

2.实现我们的可折叠效果

Matrix的setPolyToPoly方法的使用
可参考（http://blog.csdn.net/lmj623565791/article/details/44278417）

3.实现图片一上一下的来回切换

paint.setXfermode(xfermode); xfermode就是如何处理两张图片的重叠效果 共有16种处理方式

实现自定义imageview

属性

存放bitmap的list
动画间隔的变量
动画桢间隔的变量
两个handler用于发送消息
前景与背景的索引

代码

package com.cust.myview;import java.util.ArrayList;import java.util.List;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Canvas;import android.graphics.Matrix;import android.graphics.Paint;import android.graphics.PorterDuff.Mode;import android.graphics.PorterDuffXfermode;import android.graphics.Xfermode;import android.os.Handler;import android.util.AttributeSet;import android.widget.ImageView;import com.cust.uischool.R;public class musicImageView extends ImageView{    private List<Bitmap> mbitmaps;    private Paint paint;    private Xfermode xfermode;    private boolean change; //当前是否变换    private int  bhjg=5000; //变换间隔时间    private int  bhsj=50; //变换时间    private int frontindex;//前景索引    private int backindex;//背景索引    private boolean setbitmap=false; //是否设置bitmap;    private Matrix matrix;    private int count=0;    private int henght;    public musicImageView(Context context) {        this(context,null);    }    public musicImageView(Context context, AttributeSet attrs) {        this(context, attrs, 0);    }    public musicImageView(Context context, AttributeSet attrs, int defStyle) {        super(context, attrs, defStyle);        paint=new Paint();        paint.setAntiAlias(true);        xfermode=new PorterDuffXfermode(Mode.SRC_OVER);        change=false;        matrix=new Matrix();        Bitmap map1=BitmapFactory.decodeResource(getResources(),R.drawable.im2);        Bitmap map2=BitmapFactory.decodeResource(getResources(),R.drawable.st);        List<Bitmap> mbitmaps=new ArrayList<Bitmap>();        mbitmaps.add(map1);        mbitmaps.add(map2);        setBitmaps(mbitmaps);        henght=map1.getHeight();        bhjg=(int)Math.random()*(5000-2000)+2000;    }    public void setBitmaps(List<Bitmap> mbitmaps)    {        this.mbitmaps=mbitmaps;        setbitmap=true;        if(mbitmaps.size()>=2)        {            frontindex=0;            backindex=1;        }        else{            frontindex=0;            backindex=0;        }      new Thread(){          public void run() {              handler.postDelayed(run, bhjg);                handler1.postDelayed(run1, bhsj);          };      } .start();    }    Runnable run1 = new Runnable() {        @Override        public void run() {           if(change)           {              musicImageView.this.invalidate();           }           handler1.postDelayed(run1, bhsj);        }    };    Runnable run = new Runnable() {        @Override        public void run() {            change=true;            handler.postDelayed(run, bhjg);        }    };    Handler handler1= new Handler();    Handler handler= new Handler();    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        Bitmap bmp=mbitmaps.get(backindex);        setMeasuredDimension(bmp.getWidth(), bmp.getHeight());    }       @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        if(change)        {            Bitmap bmp=mbitmaps.get(frontindex);            Bitmap bmp1=mbitmaps.get(backindex);            count++;             if(bmp1.getHeight() - 5*count>=bmp1.getHeight()/2)             {                 //绘制上半部分图像                 canvas.save();                 canvas.clipRect( 0, 0, bmp1.getWidth(), bmp1.getHeight()/2);                 canvas.drawBitmap(bmp1, 0, 0, paint);                 canvas.restore();                 //绘制下班部分图像                 canvas.save();                 canvas.clipRect( 0, bmp1.getHeight()/2, bmp1.getWidth(), bmp1.getHeight());                 canvas.drawBitmap(bmp, 0, 0, paint);                 canvas.restore();                 //动态改变下半部分图像                 float[] src = { 0, bmp1.getHeight()/2,//                               bmp1.getWidth(), bmp1.getHeight()/2,//                               bmp1.getWidth(), bmp1.getHeight(),//                               0, bmp1.getHeight() };                   henght=bmp1.getHeight() - 5*count;                  float[] dst = { 0, bmp1.getHeight()/2,//                           bmp1.getWidth(), bmp1.getHeight()/2,//                           bmp1.getWidth(), henght,//                            0, henght };                    System.out.println(count+"");                  canvas.save();                  matrix.setPolyToPoly(src, 0, dst, 0, src.length >> 1);                   canvas.clipRect( 0, bmp1.getHeight()/2, bmp1.getWidth(), henght);                  paint.setXfermode(null);                  paint.setXfermode(xfermode);                  canvas.drawBitmap(bmp1,matrix, paint);                  canvas.restore();                  paint.setXfermode(null);             }             else{                 //绘制上半部分图像                 canvas.save();                 canvas.clipRect( 0, 0, bmp1.getWidth(), bmp1.getHeight()/2);                 canvas.drawBitmap(bmp1, 0, 0, paint);                 canvas.restore();                 //绘制下班部分图像                 canvas.save();                 canvas.clipRect( 0, bmp1.getHeight()/2, bmp1.getWidth(), bmp1.getHeight());                 canvas.drawBitmap(bmp, 0, 0, paint);                 canvas.restore();                 //动态改变上半部分图像                 float[] src = { 0,0,//                               bmp1.getWidth(), 0,//                               bmp1.getWidth(), bmp1.getHeight()/2,//                               0, bmp1.getHeight()/2 };                   henght=bmp1.getHeight() - 5*count;                  float[] dst = { 0, henght,//                           bmp1.getWidth(), henght,//                           bmp1.getWidth(), bmp1.getHeight()/2,//                           0, bmp1.getHeight()/2 };                   System.out.println(count+"");                  canvas.save();                  matrix.setPolyToPoly(src, 0, dst, 0, src.length >> 1);                   canvas.clipRect( 0, bmp1.getHeight()/2, bmp1.getWidth(), henght);                  paint.setXfermode(null);                  paint.setXfermode(xfermode);                  canvas.drawBitmap(bmp,matrix, paint);                  canvas.restore();                  paint.setXfermode(null);                  if(henght<=0)                  { //说明动画结束 重置动画参数                      count=0;                      change=false;                      int temp=frontindex;                      frontindex=backindex;                      backindex=temp;                      System.out.println("change false");                      bhjg=(int)(Math.random()*(8000-5000))+5000;                      System.out.println("bhjg: "+bhjg+"");                  }             }        }        else{            if(!setbitmap)            {                canvas.drawBitmap(BitmapFactory.decodeResource(getResources(),R.drawable.im2),  matrix, paint);            }        }    }}