iOS中UISearchBar改变系统默认实现方法

       _searchBar = [[UISearchBar alloc] init];
        _searchBar.backgroundColor = [UIColor clearColor];
        _searchBar.showsCancelButton = NO;
        _searchBar.tintColor = [UIColor orangeColor];
        _searchBar.placeholder = @"搜索感兴趣的内容"；

   for (UIView *subView in _searchBar.subviews) {
            if ([subView isKindOfClass:[UIView  class]]) {
                [[subView.subviews objectAtIndex:0] removeFromSuperview];
                if ([[subView.subviews objectAtIndex:0] isKindOfClass:[UITextField class]]) {
                    UITextField *textField = [subView.subviews objectAtIndex:0];
                    textField.backgroundColor = [UIColor colorWithRed:240/255.0 green:240/255.0 blue:240/255.0 alpha:1];
                    
                    //设置输入框边框的颜色
//                    textField.layer.borderColor = [UIColor blackColor].CGColor;
//                    textField.layer.borderWidth = 1;
                    
                    //设置输入字体颜色
//                    textField.textColor = [UIColor lightGrayColor];
                    
                    //设置默认文字颜色
                    UIColor *color = [UIColor grayColor];
                    [textField setAttributedPlaceholder:[[NSAttributedString alloc] initWithString:@"搜索感兴趣的内容"
                                                                                        attributes:@{NSForegroundColorAttributeName:color}]];
                    //修改默认的放大镜图片
                    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 13, 13)];
                    imageView.backgroundColor = [UIColor clearColor];
                    imageView.image = [UIImage imageNamed:@"gww_search_ misplaces"];
                    textField.leftView = imageView;
                }
            }
        }