首先通过 KVC 获取到内部的 textField, 然后自定制处理

UITextField *searchField = [searchBar valueForKey:@"searchField"];

if (searchField) {

[searchField setBorderStyle:UITextBorderStyleNone];

//placeHolder颜色

[searchField setValue:_placeholderColor forKeyPath:@"_placeholderLabel.textColor"];

searchField.frame = CGRectMake(0, 0, self.bounds.size.width, self.bounds.size.height);

searchField.textColor = _textColor;

//字体大小

[searchField setValue:_placeHolderFont forKeyPath:@"_placeholderLabel.font"];

searchField.font = _textFont;

UIImage *image = _leftImage;

UIImageView *leftImg = [[UIImageView alloc] initWithImage:image];

leftImg.frame = CGRectMake(0,0,image.size.width, image.size.height);

searchField.leftView = leftImg;

}

其他: 添加圆角(放在一个有圆角的 bgView上面)

UIView *bg = [[UIView alloc]initWithFrame:CGRectMake(20, 220, 300, 30)];

bg.backgroundColor = [UIColor whiteColor];

[self.view addSubview:bg];

bg.layer.cornerRadius = 15;

bg.layer.masksToBounds = YES;

UISearchBar *bar = [[UISearchBar alloc]initWithFrame: bg.bounds];

[bg addSubview:bar];

bar.placeholder = @"搜索...";

[bar setBackgroundImage:[UIImage imageNamed:@"clearImage@2x"]];

修改圆角大小

首先在 UIView 的 category 里加一个方法：
- (UIView*)subViewOfClassName:(NSString*)className {

    for (UIView* subView in self.subviews) {

        if ([NSStringFromClass(subView.class) isEqualToString:className]) {

            return subView;

        }

        UIView* resultFound = [subView subViewOfClassName:className];

        if (resultFound) {

            return resultFound;

        }

    }

    return nil;

}

用的时候：

UIView* backgroundView = [searchBar subViewOfClassName:@"_UISearchBarSearchFieldBackgroundView"];

backgroundView.layer.cornerRadius = 14.0f;

backgroundView.clipsToBounds = YES;

用这个方法还可以改取消按钮的颜色、字体什么的。