android 4.0.x listview的一个空指针问题

这里我使用了PinnedSectionListView这个控件，该控件用于模仿IOS的UITableView的section悬停在顶部的效果。

在android 4.0.x机型上，该控件引发空指针错误。

首先贴出错误log：

E/AndroidRuntime(18435): java.lang.NullPointerExceptionE/AndroidRuntime(18435): at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:472)E/AndroidRuntime(18435): at android.view.View.measure(View.java:12816)E/AndroidRuntime(18435): at com.handmark.pulltorefresh.library.PinnedSectionListView.createPinnedShadow(PinnedSectionListView.java:216)E/AndroidRuntime(18435): at com.handmark.pulltorefresh.library.PinnedSectionListView.ensureShadowForPosition(PinnedSectionListView.java:251)E/AndroidRuntime(18435): at com.handmark.pulltorefresh.library.PinnedSectionListView$1.onScroll(PinnedSectionListView.java:117)E/AndroidRuntime(18435): at android.widget.AbsListView.invokeOnItemScrollListener(AbsListView.java:1321)E/AndroidRuntime(18435): at android.widget.AbsListView.trackMotionScroll(AbsListView.java:4934)E/AndroidRuntime(18435): at android.widget.AbsListView.scrollIfNeeded(AbsListView.java:2949)E/AndroidRuntime(18435): at android.widget.AbsListView.startScrollIfNeeded(AbsListView.java:2894)E/AndroidRuntime(18435): at android.widget.AbsListView.onInterceptTouchEvent(AbsListView.java:3770)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1639)E/AndroidRuntime(18435): at com.handmark.pulltorefresh.library.PinnedSectionListView.dispatchTouchEvent(PinnedSectionListView.java:467)E/AndroidRuntime(18435): at com.handmark.pulltorefresh.library.PullToRefreshListView$InternalListView.dispatchTouchEvent(PullToRefreshListView.java:306)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1940)E/AndroidRuntime(18435): at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1392)E/AndroidRuntime(18435): at android.app.Activity.dispatchTouchEvent(Activity.java:2387)E/AndroidRuntime(18435): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1888)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2019)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1754)E/AndroidRuntime(18435): at android.view.ViewGroup.dispatchTransforme

第一反应是适配出了问题，后来发现情况并非如此，因为在android 其他版本上运行正常，而手中的两部android 4.0.x的手机均出现该问题。

按照bug所指位置，定位了下空指针位置的代码：

if (isWrapContentHeight) {            // Height already has top padding in it since it was calculated by looking at            // the bottom of each child view            height += mPaddingBottom;                       if (mLayoutParams.height >= 0) {<span style="color:#ff0000;">//空指针所在line</span>                height = Math.max(height, mLayoutParams.height);            }。。。。

以上代码是android 4.0.4_r1的代码，可见是mLayoutParams空指针导致
那么为什么Android其他版本没有该问题呢？接下来我查看了下android 4.4.2该位置的代码：

        if (isWrapContentHeight) {            // Height already has top padding in it since it was calculated by looking at            // the bottom of each child view            height += mPaddingBottom;            if (<span style="color:#ff0000;">mLayoutParams != null</span> && mLayoutParams.height >= 0) {                height = Math.max(height, mLayoutParams.height);            }

好吧，原来是Android工程师在后续版本修复了该问题，so……我可以理解为这是个Android系统原生bug么？

接下来要规避该问题了：

@Overridepublic View getView(int position, View convertView, ViewGroup parent) {<span style="white-space:pre"></span><span style="white-space:pre"></span>MainListViewHolder viewHolder;<span style="white-space:pre"></span><span style="white-space:pre"></span>if(convertView==null){<span style="white-space:pre"></span>viewHolder = new MainListViewHolder();<span style="white-space:pre"></span>convertView = LayoutInflater.from(con).inflate(R.layout.analyse_new_row, null,false);<span style="white-space:pre"></span><span style="color:#ff0000;"><span style="white-space:pre"></span>convertView.setLayoutParams(new AbsListView.LayoutParams(AbsListView.LayoutParams.MATCH_PARENT<span style="white-space:pre"></span>, AbsListView.LayoutParams.WRAP_CONTENT));</span><span style="white-space:pre"></span>。。。。。。

既然Listview在measure其成员时出现layoutparam为null，那么我们就在adapter的getview方法中为生成的list成员添加一个layoutparam。

OK，问题解决。