创建自定义画廊

Question

我想创建一个自定义画廊，其中画廊中的中心最多视图显示缩小动画。所以当我滚动我的画廊时，到达中心的物品会变得放大。所以我需要知道的是：

1. 如何找到画廊中的中心项目（如果显示5个项目，我需要第三个项目作为中心项目）。
2. 当滚动发生时，如何将它制作成动画以获得平滑的凸起效果？

Answer 1

借助于使用队列的管道类结构的帮助，我在与addViewToLayout方法相结合时得到了它。

代码：

自定义库类

public class NGallery extends Gallery { 

private Pipe<View> childViews; 
private int pipeSize; 
private View previousAnimatedView; 
private boolean isScrollLeft; 

public NGallery(Context context, AttributeSet attrs) { 
    super(context, attrs); 
    final Timer tmr = new Timer(); 
    TimerTask task = new TimerTask() { 

     @Override 
     public void run() { 
      initialize(); 
      if (pipeSize > 0) { 
       tmr.cancel(); 
      } 
     } 
    }; 
    tmr.scheduleAtFixedRate(task, 100, 100); 
} 

private void initialize() { 
    View childView = getChildAt(0); 
    if (childView != null && childView.getWidth() > 0) { 
     pipeSize = getWidth()/childView.getWidth(); 
     childViews = new Pipe<View>(pipeSize); 
    } 
} 

@Override 
protected boolean addViewInLayout(View child, int index, 
     android.view.ViewGroup.LayoutParams params, 
     boolean preventRequestLayout) { 
    View viewToAnimate = getViewToAnimate(child); 
    if (viewToAnimate != null) { 
     if (previousAnimatedView != null) { 
      previousAnimatedView.clearAnimation(); 
     } 
     viewToAnimate.requestFocus(); 
     AnimationSet animationSet = getAnimationSet(viewToAnimate); 
     viewToAnimate.startAnimation(animationSet); 
     previousAnimatedView = viewToAnimate; 
    } 
    return super 
      .addViewInLayout(child, index, params, preventRequestLayout); 
} 

@Override 
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, 
     float distanceY) { 
    isScrollLeft = distanceX > 0; 
    return super.onScroll(e1, e2, distanceX, distanceY); 
} 

private AnimationSet getAnimationSet(View viewToAnimate) { 
    AnimationSet animationSet = new AnimationSet(false); 

    Animation scaleAnimation = new ScaleAnimation(1, 1.5f, 1, 1.5f); 
    scaleAnimation.setDuration(100); 
    animationSet.addAnimation(scaleAnimation); 

    Animation transAnimation = new TranslateAnimation(0, 0, 0, 25); 
    transAnimation.setDuration(100); 
    animationSet.addAnimation(transAnimation); 

    animationSet.setFillAfter(true); 

    return animationSet; 
} 

private View getViewToAnimate(View child) { 
    if (childViews != null) { 
     if (isScrollLeft) { 
      childViews.addFirst(child); 
     } else { 
      childViews.addLast(child); 
     } 
     return childViews.getCenterItem(); 
    } else { 
     return null; 
    } 
} 

} 

管材类：

public class Pipe<E> { 

private LinkedList<E> list; 
private int pipeSize; 

public Pipe(int size) { 
    list = new LinkedList<E>(); 
    pipeSize = size; 
} 

public E getItemAt(int position) { 
    return list.get(position); 
} 

public E getCenterItem() { 
    int pos = pipeSize/2; 
    if (pos < list.size()) { 
     return list.get(pos); 
    } else { 
     return null; 
    } 
} 

public void addFirst(E item) { 
    if (list.size() >= pipeSize) { 
     list.removeLast(); 
    } 
    list.addFirst(item); 
} 

public void addLast(E item) { 
    if (list.size() >= pipeSize) { 
     list.removeFirst(); 
    } 
    list.addLast(item); 
} 

}