如何去除UISearchBar默认的灰色背景颜色

在iOS7.0之前，UISearchBar视图里直接包含UISearchBarBackground和UISearchBarTextField两个视图，在iOS7.0及之后，UISearchBar视图里包含的是一个UIView视图，UIView视图里才是 UISearchBarBackground和UISearchBarTextField两个视图。经多次试验，发现去除UISearchbar视图里的 UISearchBarBackground后UISearchBar的背景就透明了，代码如下：

for (UIView *view in self.searchBar.subviews) {    // for before iOS7.0    if ([view isKindOfClass:NSClassFromString(@"UISearchBarBackground")]) {        [view removeFromSuperview];        break;    }    // for later iOS7.0(include)    if ([view isKindOfClass:NSClassFromString(@"UIView")] && view.subviews.count > 0) {        [[view.subviews objectAtIndex:0] removeFromSuperview];        break;    }