搜索栏子视图UITextField iphone

Question

我正在以编程方式使用带有uitextField子视图的搜索栏。我得到如下图像：

这里上面有一个深色。我怎样才能避免得到一条简洁的细线？

我使用此代码：

searchbar = [[UISearchBar alloc] initWithFrame:CGRectMake(0, (self.view.frame.size.height*10)/100, self.view.frame.size.width, (self.view.frame.size.height*13)/100)];
searchbar.delegate=self;

for (searchBarSubview in [searchbar subviews]) {
    if ([searchBarSubview conformsToProtocol:@protocol(UITextInputTraits)] ) {
        @try {

            [[searchbar.subviews objectAtIndex:0] removeFromSuperview];
            searchbar.backgroundColor=[UIColor clearColor];

        }
        @catch (NSException * e) {
            // ignore exception
        }
    }
}