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标题: 自定义ListView下拉弹起效果 [打印本页]

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作者: SKY精英    时间: 2013-6-11 21:53
标题: 自定义ListView下拉弹起效果


    在实现ListView下拉弹起效果，最重要的是如何监听到ListView的底部及顶部，AbstractListView的trackMotionScroll(int,int)方法中，分析出ListView是如何判断滑动到底部及顶部的方法。
private boolean isHeader(int deltay) {
  int firstTop = getChildAt(0).getTop();
  int effectivePaddingTop = getListPaddingTop();
  int spaceAbove = effectivePaddingTop - firstTop;
  return getFirstVisiblePosition() == 0&&spaceAbove<=0&&deltay<0;
}
private boolean isButtom(int deltay) {
   int lastBottom = getChildAt(getChildCount() - 1).getBottom();
   int effectivePaddingBottom = getListPaddingBottom();
   return getLastVisiblePosition() == (getCount() - 1)&&lastBottom<=(getHeight()-effectivePaddingBottom)&&deltay>0;
}
通过以上两个方法可以判断ListView是否滑动到底部及顶部。
但是为了实现弹起效果，必须用到scrollBy（）和scrollTo()两个方法。具体实现代码如下：
import android.os.Handler;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.ListView;
import android.widget.Scroller;
public class MyListView extends ListView {
private Context mContext;
private Scroller mScroller;
private int mLastMotionY = 0;
public MyListView(Context context, AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);
  // TODO Auto-generated constructor stub
}
public MyListView(Context context, AttributeSet attrs) {
  super(context, attrs);
  this.mContext = context;
  mScroller = new Scroller(mContext);
}
public MyListView(Context context) {
  super(context);
  // TODO Auto-generated constructor stub
}
@Override
public void computeScroll() {
   scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
   postInvalidate();
  }
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
  // TODO Auto-generated method stub
  int y = (int) event.getY();
  switch (event.getAction()) {
  case MotionEvent.ACTION_DOWN:
   if (mScroller != null) {
    if (!mScroller.isFinished()) {
     mScroller.abortAnimation();
    }
   }
   mLastMotionY = y;
   break;
  case MotionEvent.ACTION_MOVE:
   int deltay = (int) (mLastMotionY - y);
   mLastMotionY = y;
   if (isButtom(deltay)) {
    setVerticalScrollBarEnabled(false);
    scrollBy(0, deltay);
    return true;
   }
   if (isHeader(deltay)) {
    setVerticalScrollBarEnabled(false);
    scrollBy(0, deltay);
    return true;
   }
   break;
  case MotionEvent.ACTION_UP:
   mLastMotionY = 0;
   if (getScrollY()!=0) {
    mScroller.startScroll(0, getScrollY(), 0, -getScrollY(), 1000);
    invalidate();
    return true;
   }
   break;
  default:
   break;
  }
  return super.dispatchTouchEvent(event);
}
private boolean isHeader(int deltay) {
  int firstTop = getChildAt(0).getTop();
  int effectivePaddingTop = getListPaddingTop();
  int spaceAbove = effectivePaddingTop - firstTop;
  return getFirstVisiblePosition() == 0&&spaceAbove<=0&&deltay<0;
}
private boolean isButtom(int deltay) {
   int lastBottom = getChildAt(getChildCount() - 1).getBottom();
   int effectivePaddingBottom = getListPaddingBottom();
   return getLastVisiblePosition() == (getCount() - 1)&&lastBottom<=(getHeight()-effectivePaddingBottom)&&deltay>0;
}
Handler handler = new Handler(){
  public void handleMessage(android.os.Message msg) {
   int what = msg.what;
   switch (what) {
   case 0:
    setVerticalScrollBarEnabled(true);
    invalidate();
    break;
   default:
    break;
   }
  };
};
}

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