需求: 移除所有子视图
[view.subviews makeObjectsPerformSelector:@selector(removeFromSuperview)];
for(UIView *view in [self.view subviews]){
[view removefromsuperview]
}
[[self.view subviews] enumerateObjectsUsingBlock:^(id _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
[(UIView*)obj removeFromSuperview];
}];