在自定义的view中使用了[self layoutIfNeeded]方法，在iOS8\9上都没有错误，但是在iOS7上出现了页面错乱，解决方案就是在自定义的view里面添加如下代码：
+ (void)load
{
Method existing = class_getInstanceMethod(self, @selector(layoutSubviews));
Method new = class_getInstanceMethod(self, @selector(_autolayout_replacementLayoutSubviews));
method_exchangeImplementations(existing, new);
}
- (void)_autolayout_replacementLayoutSubviews
{
[super layoutSubviews];
[self _autolayout_replacementLayoutSubviews]; // not recursive due to method swizzling
[super layoutSubviews];
}