UISearchbar的取消按钮设置图片

我想给搜索栏设置图片，通过搜索栏的子视图UISearchBarBackground可以实现，但是不能给搜索栏的取消按钮设置图片，我获取到搜索栏的子视图设置按钮的UINavigationButton，但是不知道怎么添加自定义图片在里面？谢谢。

 for (UIView *searchbuttons in searchBar.subviews)
    {
        if ([searchbuttons isKindOfClass:[UIButton class]])
        {
            UIButton *cancelButton = (UIButton*)searchbuttons;
            cancelButton.enabled = YES;
            [cancelButton setBackgroundImage:[UIImage imageNamed:@"yourImageName"] forState:UIControlStateNormal];
            break;
        }
    }

你这是把代码添加哪里了呀，为什么我添加就不起作用呢

对呀 每个人都这么说 写在那里都不知道 viewdidload里面没效果

self.bondMarketSearchBar.showsCancelButton = YES;
UIButton cancelButton;
UIView *topView = self.bondMarketSearchBar.subviews[0];
for (UIView *subView in topView.subviews) {
if ([subView isKindOfClass:NSClassFromString(@"UINavigationButton")]) {
cancelButton = (UIButton)subView;
}
}
if (cancelButton) {
[cancelButton setTitle:@"取消" forState:UIControlStateNormal];
cancelButton.backgroundColor =[UIColor redColor];
[cancelButton setTitleColor:[UIColor grayColor] forState:UIControlStateNormal];
}