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);
            }
        }



    }


}