https://github.com/nirhart/ParallaxScroll这个gethub上的地址

本文转自http://www.2cto.com/kf/201502/376970.html

最近在项目中，有用到一个仿照Path的Parallax效果，苦苦搜寻，在github上面，有一个类似的效果，不过是listview的，加一个顶部的headerView，实现了该效果，不过我需要的是ScrollerView的，于是对该代码进行的修改，实现了ScrollerView下面的Parallax效果，效果图参照如下：

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在阅读下面代码前，可以先查看下Github上面的源码

 

我对于原先的代码进行了大量的删减，只实现了我需要的效果，看起来简单易懂，最怕那种绕来绕去的代码了，看核心的实现代码：

 

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public class ParallaxScollView extends ScrollView implements OnScrollListener {
 
    public final static double NO_ZOOM = 1;
    public final static double ZOOM_X2 = 2;
 
    private ImageView mImageView;
    private int mImageViewHeight = -1;
    private int mDefaultImageViewHeight = 0;
    private int originImageViewHeight;
    private int mMaxHeight;
 
    private interface OnOverScrollByListener {
        public boolean overScrollBy(int deltaX, int deltaY, int scrollX,
                                    int scrollY, int scrollRangeX, int scrollRangeY,
                                    int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent);
    }
 
    private interface OnTouchEventListener {
        public void onTouchEvent(MotionEvent ev);
    }
 
    public ParallaxScollView(Context context, AttributeSet attrs,
                                 int defStyle) {
        super(context, attrs, defStyle);
        init(context);
    }
 
    public ParallaxScollView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }
 
    public ParallaxScollView(Context context) {
        super(context);
        init(context);
    }
 
    public void init(Context context) {
        mDefaultImageViewHeight = context.getResources().getDimensionPixelSize(R.dimen.size_default_height);
        originImageViewHeight = context.getResources().getDimensionPixelSize(R.dimen.size_default_height);
    }
 
    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
    }
 
    @Override
    protected boolean overScrollBy(int deltaX, int deltaY, int scrollX,
                                   int scrollY, int scrollRangeX, int scrollRangeY,
                                   int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {
        boolean isCollapseAnimation = false;
         
        isCollapseAnimation = scrollByListener.overScrollBy(deltaX, deltaY,
                scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX,
                maxOverScrollY, isTouchEvent)
                || isCollapseAnimation;
 
        /*return isCollapseAnimation ? true : super.overScrollBy(deltaX, deltaY,
                scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX,
                0, isTouchEvent);*/
        return false;
    }
 
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
                         int visibleItemCount, int totalItemCount) {
    }
     
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }
 
    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
        View firstView = (View) mImageView.getParent();
        // firstView.getTop < getPaddingTop means mImageView will be covered by top padding,
        // so we can layout it to make it shorter
        if (firstView.getTop() < getPaddingTop() && mImageView.getHeight() > mImageViewHeight) {
            mImageView.getLayoutParams().height = Math.max(mImageView.getHeight() - (getPaddingTop() - firstView.getTop()), mImageViewHeight);
            // to set the firstView.mTop to 0,
            // maybe use View.setTop() is more easy, but it just support from Android 3.0 (API 11)
            firstView.layout(firstView.getLeft(), 0, firstView.getRight(), firstView.getHeight());
            mImageView.requestLayout();
        }
    }
 
    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        touchListener.onTouchEvent(ev);
        return super.onTouchEvent(ev);
    }
 
    public void setParallaxImageView(ImageView iv) {
        mImageView = iv;
        mImageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
    }
 
    public void setViewsBounds(double zoomRatio) {
        if (mImageViewHeight == -1) {
            mImageViewHeight = mImageView.getHeight();
            if (mImageViewHeight <= 0) {
                mImageViewHeight = mDefaultImageViewHeight;
            }
            double ratio = ((double) mImageView.getDrawable().getIntrinsicWidth()) / ((double) mImageView.getWidth());
 
        }
    }
 
    private OnOverScrollByListener scrollByListener = new OnOverScrollByListener() {
        @Override
        public boolean overScrollBy(int deltaX, int deltaY, int scrollX,
                                    int scrollY, int scrollRangeX, int scrollRangeY,
                                    int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {
            if (isTouchEvent) {
                if (true) {
                        mImageView.getLayoutParams().height = mImageView.getHeight() - deltaY / 2;
                        mImageView.requestLayout();
                }
            }
            return false;
        }
    };
 
    private OnTouchEventListener touchListener = new OnTouchEventListener() {
        @Override
        public void onTouchEvent(MotionEvent ev) {
            if (ev.getAction() == MotionEvent.ACTION_UP) {
                if (mImageViewHeight - 1 < mImageView.getHeight()) {
                    ResetAnimimation animation = new ResetAnimimation(
                            mImageView, mImageViewHeight);
                    animation.setDuration(300);
                    mImageView.startAnimation(animation);
                }
            }
        }
    };
 
    public class ResetAnimimation extends Animation {
        int targetHeight;
        int originalHeight;
        int extraHeight;
        View mView;
 
        protected ResetAnimimation(View view, int targetHeight) {
            this.mView = view;
            this.targetHeight = targetHeight;
            originalHeight = view.getHeight();
            extraHeight = this.originalHeight - originImageViewHeight;
            Log.i(debug, target heitht  + targetHeight +  original height  + originalHeight  +  extraheight  + extraHeight);
        }
 
        @Override
        protected void applyTransformation(float interpolatedTime, Transformation t) {
 
            int newHeight;
            newHeight = (int) (originImageViewHeight + extraHeight * (1 - interpolatedTime));
            mView.getLayoutParams().height = newHeight;
            mView.requestLayout();
        }
    }
}



 

第二布：在xml中，引用该ParallaxScollView：


最后一步，在activity中，引用ParallaxScrollerView，并且设置imageview：

 

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mImageView = (ImageView) findViewById(R.id.headview);
        scrollView = (ParallaxScollView) findViewById(R.id.parallax_scroll_view);
        scrollView.setParallaxImageView(mImageView);



 

大功告成，也可以在ScrollerView上实现炫酷的Parallax效果了