android图片视差滚动效果

实际上只需要一个图片的矩阵变换就能做到了

在listview滚动监听setOnScrollListener中设置图片所在的位置，用来改变图片显示的区域。

@Override
            public void onScroll(AbsListView view, int firstVisibleItem,
                    int visibleItemCount, int totalItemCount) {
                for (int i = 0; i < totalItemCount; i++) {
                    if (view.getChildAt(i)!=null) {
                        int[] position = new int[2];  
                        //获取控件在屏幕中位置
                        view.getChildAt(i).getLocationOnScreen(position);  
                        ViewGroup fl = (ViewGroup) view.getChildAt(i);
                        //获取自定义控件NewsClassifyImageView
                        if (fl.getChildCount()!=0) {
                            ViewGroup vg = (ViewGroup) fl.getChildAt(0);
                            if (vg.getChildCount()!=0) {
                            //设置位置信息
                            ((NewsClassifyImageView)  (vg.getChildAt(0))).setPicPostion(position[1]);
                            }
                        }
                    }
                }
            }

接下来是自定义控件NewsClassifyImageView extends ImageView
重写构造方法后，只需加入下面的代码即可

private int maxTop;
    private float scale = 1.0f;
    private  Matrix mMatrix=new Matrix();
    private  Matrix mCurrentMatrix=new Matrix();

    public void setPicPostion(int position){
        mCurrentMatrix.set(mMatrix);//初始化Matrix
        int left = 0,top = 0;
        if (getDrawable()!=null) {
            int boundsWidth= 0,boundsHeight=0;
            boundsWidth = getDrawable().getBounds().width();
            boundsHeight = getDrawable().getBounds().height();
            //小图放大
            if (boundsWidth1.0f/boundsWidth;

                mCurrentMatrix.postScale(scale , scale ,0,0); 
            }

            maxTop = (int) (getHeight()-boundsHeight*scale);
            left = (DensityUtil.getWindowWidth(mContext)-boundsWidth)/2;// 横向显示中心位置
            top = -position/5;
            left = left<0?left:0;
            top = top>maxTop?top:maxTop;
        }
        mCurrentMatrix.postTranslate(left,top);
        setImageMatrix(mCurrentMatrix);
        invalidate();
    }

由于android屏幕尺寸太多，所以需要对图片先放大或缩小，然后进行上下滚动处理，
项目需要我这里只对小图放大，大图显示的横向中间位置，大图缩小去掉判断条件即可。
图片上下滚动距离由top控制，我这里随便取得值显示效果，top = -position/5应根据需求计算

最后显示的图片放大上移效果，在adapter中写上属性动画

if (position>currentPosition) {
            AnimationSet as = new AnimationSet(true);
            Animation ta = new TranslateAnimation(Animation.RELATIVE_TO_SELF, 0,
                    Animation.RELATIVE_TO_SELF, 0, 
                    Animation.RELATIVE_TO_SELF, 0.2f,
                    Animation.RELATIVE_TO_SELF, 0);
            ta.setDuration(500);
            as.addAnimation(ta);

            final ValueAnimator animator = ValueAnimator.ofFloat(200,0);  
            animator.setTarget(news_classify_rl);
            animator.setDuration(500);
            if (position<4) {
                news_classify_rl.setVisibility(View.INVISIBLE);
                handler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        news_classify_rl.setVisibility(View.VISIBLE);
                        animator.start();
                    }
                }, 500);
            }else{
                animator.start();
            }
            animator.addUpdateListener(new AnimatorUpdateListener()  
            {  
                @Override  
                public void onAnimationUpdate(ValueAnimator animation)  
                {  
                    ((View) news_classify_rl.getParent()).setTranslationY((Float) animation.getAnimatedValue()); 
                    ((View) news_classify_rl.getParent()).setScaleX(1-(Float) animation.getAnimatedValue()/2000);  
                    ((View) news_classify_rl.getParent()).setScaleY(1-(Float) animation.getAnimatedValue()/2000); 
                }  
            });  

            currentPosition = position;
        }