Android 获取listview中Item的可视百分比

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需求：做新闻埋点上报的时候有种上报叫展现上报。服务端要求当新闻展现超过50%后才算展现，手指做了抛的动作（手指离开屏幕前，用力滑了一下）这种在listview中显示的不算展现。

猛的一看，实现太难了，后来发现函数

public final boolean getLocalVisibleRect(Rect r)

获取View的可视区域，比如listView 最顶层的ItemView显示一半，通过函数的到Rect(0, 60 - 1080, 120)

0 和 1080 是itemView的left right

60 和 120 是itemView的top bottom

如果显示全 itemView的top就是0。

如果是最低层的itemView显示一点，通过函数得到的Rect(0, 0 - 1080, 21)

top为0，说明上面没有覆盖，

bottom为21，说明下面覆盖了（120-21）个点

所以计算显示百分比的函数

    public int getVisibilityPercents(View view){        View tv =  view;        tv.getLocalVisibleRect(rect);        int height = tv.getHeight();        int  percents = 100;        if(rect.top==0 && rect.bottom == height){            percents = 100;        }else if(rect.top > 0){            percents =  (height - rect.top) * 100 / height;        }else if(rect.bottom > 0 && rect.bottom <height) {            percents =rect.bottom * 100 / height;        }        return percents;    }

listview的滑动事件有三个

SCROLL_STATE_IDLE = 0; 停止滚动

SCROLL_STATE_TOUCH_SCROLL = 1; 正在滚动

SCROLL_STATE_FLING = 2; 惯性滑动

惯性滑动的时候展现的新闻不算展现，也就是说，在SCROLL_STATE_IDLE的时候计算整个屏幕的itemView的展现百分比，在SCROLL_STATE_TOUCH_SCROLL的时候，只计算最下面itemView的百分比就好。

关键代码：

public class DataListItem extends Object{    public String mTitle;    public Rect rect = new Rect();    public DataListItem(String title){        mTitle = title;    }    public int getVisibilityPercents(View view){        View tv =  view;        tv.getLocalVisibleRect(rect);        int height = tv.getHeight();        int  percents = 100;        if(rect.top==0 && rect.bottom == height){            percents = 100;        }else if(rect.top > 0){            percents =  (height - rect.top) * 100 / height;        }else if(rect.bottom > 0 && rect.bottom <height) {            percents =rect.bottom * 100 / height;        }        return percents;    }}

  for (int i = 0; i < 50; i++) {            mArrayList.add(new DataListItem("" + i));        }        mMyAdapter = new MyAdapter(getBaseContext().getApplicationContext(), mArrayList);        mListView.setAdapter(mMyAdapter);        mListView.setOnScrollListener(new AbsListView.OnScrollListener() {            @Override            public void onScrollStateChanged(AbsListView view, int scrollState) {                //正在滚动时回调，回调2-3次，手指没抛则回调2次。scrollState = 2的这次不回调                //回调顺序如下                //第1次：scrollState = SCROLL_STATE_TOUCH_SCROLL(1) 正在滚动                //第2次：scrollState = SCROLL_STATE_FLING(2) 手指做了抛的动作（手指离开屏幕前，用力滑了一下）                //第3次：scrollState = SCROLL_STATE_IDLE(0) 停止滚动                //当屏幕停止滚动时为0；当屏幕滚动且用户使用的触碰或手指还在屏幕上时为1；                //由于用户的操作，屏幕产生惯性滑动时为2                mScrollState = scrollState;                Log.d("onScrollStateChanged","scrollState = " +scrollState );                Log.d("onScrollStateChanged", "view.getFirstVisiblePosition() = " +view.getFirstVisiblePosition() +"view.getLastVisiblePosition() = "+view.getLastVisiblePosition() );                if(mScrollState == 0){                    for (int i = view.getFirstVisiblePosition(),j=0;i<=view.getLastVisiblePosition();i++,j++){                        View v = view.getChildAt(j);                        if(v==null)return;                        DataListItem d =  mArrayList.get(i);                       int percents = d.getVisibilityPercents(v);                        Log.d(TAG ,d.mTitle +"  "+percents+"%");                    }                }            }            @Override            public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {                //滚动时一直回调，直到停止滚动时才停止回调。单击时回调一次。                //firstVisibleItem：当前能看见的第一个列表项ID（从0开始）                //visibleItemCount：当前能看见的列表项个数（小半个也算）                //totalItemCount：列表项共数                Log.d("onScroll", "firstVisibleItem = " + firstVisibleItem + " visibleItemCount = " + visibleItemCount + " totalItemCount = " + totalItemCount);                if(mScrollState == 0){                    for (int i = firstVisibleItem ,j=0;i<visibleItemCount;i++,j++){                        View v = view.getChildAt(j);                        DataListItem d =  mArrayList.get(i);                        int percents = d.getVisibilityPercents(v);                        Log.d(TAG ,d.mTitle +"  "+percents+"%");                    }                }else if(mScrollState == 1){                    DataListItem d =  mArrayList.get(firstVisibleItem);                    View v = view.getChildAt(0);                    int percents = d.getVisibilityPercents(v);                    Log.d(TAG ,d.mTitle +"  "+percents+"%");                    d =  mArrayList.get(firstVisibleItem +visibleItemCount-1);                     v = view.getChildAt(visibleItemCount-1);                     percents = d.getVisibilityPercents(v);                    Log.d(TAG ,d.mTitle +"  "+percents+"%");                }            }        });

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