RelativeLayout执行measure（w,h）方法时，出现NullPointerException的异常情况

在编写下啦刷新的项目代码的时候，在Listview的HeaderView中的head.xml文件中，根布局为RelativeLayout的时候，在计算headerView.measure的时候，出现空指针异常，当将更布局改为Linearlayout就运行正常了。

在思考为何在RelativeLayout出现异常的问题的时候，在查阅官方网站的时候，我注意到这个段话：

Note: In platform version 17 and lower, RelativeLayout was affected by a measurement bug that could cause child views to be measured with incorrect

MeasureSpec

values.
(See

MeasureSpec.makeMeasureSpec

for
more details.) This was triggered when a RelativeLayout container was placed in a scrolling container, such as a ScrollView or HorizontalScrollView. If a custom view not equipped to properly measure with the MeasureSpec mode

UNSPECIFIED

was
placed in a RelativeLayout, this would silently work anyway as RelativeLayout would pass a very large

AT_MOST

MeasureSpec
instead.

This behavior has been preserved for apps that set

android:targetSdkVersion="17"

or older in their manifest's

uses-sdk

tag
for compatibility. Apps targeting SDK version 18 or newer will receive the correct behavior
翻下来就是说：
在android系统版本在17级以下（包含17的时候）。使用measure会出现NULL异常情况，这个是一个BUG。原因是在RelativeLayout的控件使用在含有scrolling的时候，该含有scrolling的控件中计算空间大小的时候，没有使用MeasureSpec
mode

UNSPECIFIED的布局方式在RelativeLayout。自定义的控件则会尽可能的使用AT_MOST

来替换对齐方式。

如果你想解决这个问题有2个方法：

1.讲SDK的目标版本升级

2.将需要使用RelativeLayout的上层包一个LinearLayout即可、

关于具体的核心解释，我也不太理解，希望大牛阅读到的时候能够回复一下，谢谢