新浪微博 AbsListView.obtainView调用关系

日前遇到Bug，出现

09-01 16:26:42.916 15952 15952 E AndroidRuntime: FATAL EXCEPTION: main
09-01 16:26:42.916 15952 15952 E AndroidRuntime: Process: com.sina.weibo, PID: 15952
09-01 16:26:42.916 15952 15952 E AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setDrawingCacheBackgroundColor(int)' on a null object reference
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at android.widget.AbsListView.obtainView(AbsListView.java:2360)
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at android.widget.ListView.makeAndAddView(ListView.java:1882)
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at android.widget.ListView.fillDown(ListView.java:704)
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at android.widget.ListView.fillSpecific(ListView.java:1362)
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at android.widget.ListView.layoutChildren(ListView.java:1669)
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at android.widget.AbsListView.onLayout(AbsListView.java:2151)
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at android.view.View.layout(View.java:15686)
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at android.view.ViewGroup.layout(ViewGroup.java:5107)
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at com.sina.weibo.view.PullDownView.onLayout(PullDownView.java:676)
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at android.view.View.layout(View.java:15686)
09-01 16:26:42.916 15952 15952 E AndroidRuntime: 	at android.view.ViewGroup.layout(ViewGroup.java:5107)

即空对象使用问题。

这里很明确，是

AbsListView中的obtainView函数报错；

这个函数里面有一句代码

final View child = mAdapter.getView(position, scrapView, this);

拿到child也就是view，但没有进行判断null，而是直接使用。非常的sb。

因为mAdapter的继承者过多，最后找到新浪微波是调用HeaderViewListAdapter.java中的

public View getView(int position, View convertView, ViewGroup parent) {
    Log.d("stl","HVLA getView");
        // Header (negative positions will throw an IndexOutOfBoundsException)
        int numHeaders = getHeadersCount();
        if (position < numHeaders) {
            return mHeaderViewInfos.get(position).view;
        }

        // Adapter
        final int adjPosition = position - numHeaders;
        int adapterCount = 0;
        if (mAdapter != null) {
            adapterCount = mAdapter.getCount();
            if (adjPosition < adapterCount) {
                return mAdapter.getView(adjPosition, convertView, parent);
            }
        }

        // Footer (off-limits positions will throw an IndexOutOfBoundsException)
        return mFooterViewInfos.get(adjPosition - adapterCount).view;
    }

目前刚分析到这里，由于其他紧急问题需要分析。后续跟进后，更新文章