开发应用实现搜索页面就需要创建搜索框，为了满足设计师的需求可能需要自定义搜索框，既然 Objective-C 为我们提供了 UISearchBar，原生控件提供了完整的接口供开发者调用，我们是否可以通过对原生控件的继承或者添加类目的方式修改 UISearchBar 的样式来满足我们的需求呢？

实现效果

为了方便理解小主用最通俗的代码进行分析:

#import <UIKit/UIKit.h>

@interface WJKSearchBar : UISearchBar

@end

#import "WJKSearchBar.h"

@implementation WJKSearchBar

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.tintColor = [UIColor whiteColor];
        self.backgroundColor = [UIColor clearColor];
    }
    return self;
}

-(void) layoutSubviews
{
    [super layoutSubviews];
    
    UITextField *searchField = nil;
    for (UIView *subview in self.subviews) {
        for(UIView *moduleView in subview.subviews){
            if ([moduleView isKindOfClass:NSClassFromString(@"UISearchBarBackground")]) {
                moduleView.alpha = 0.3f;
            }else if([moduleView isKindOfClass:NSClassFromString(@"UISearchBarTextField")] ){
                searchField = (UITextField *)moduleView;
            }else{
                moduleView.alpha = 0.0f;
            }
        }
    }
    if(searchField) {
        searchField.textAlignment = NSTextAlignmentLeft;
        searchField.tintColor = [UIColor whiteColor];
        searchField.layer.cornerRadius = 15;
        searchField.frame = CGRectMake(0, 0, self.frame.size.width, self.frame.size.height);
        [searchField setBorderStyle:UITextBorderStyleRoundedRect];
        [searchField setBackgroundColor:[UIColor colorWithWhite:1 alpha:0.3]];
        [searchField setValue:[UIColor whiteColor] forKeyPath:@"_placeholderLabel.textColor"];
        [searchField setTextColor:[UIColor whiteColor]];
    }
}

@end

- (void)_setUpSearchBar {
    
    UIView *titleView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, SCREENWIDTH, 27)];
    if (@available(iOS 11.0, *)) {
        self.searchBar = [[WJKSearchBar alloc] initWithFrame:CGRectMake(8, 0, SCREENWIDTH - 70, 28)];
    } else {
        self.searchBar = [[WJKSearchBar alloc] initWithFrame:CGRectMake(-30, 0, SCREENWIDTH - 70, 28)];
    }
    self.searchBar.placeholder = @"搜索感兴趣的内容";
    [[self searchBar] setImage:[UIImage imageNamed:@"home_search"] forSearchBarIcon:UISearchBarIconSearch state:UIControlStateNormal];
    self.searchBar.font = [UIFont systemFontOfSize:14];
    self.searchBar.delegate = self;
    self.searchBar.layer.cornerRadius = 15;
    self.searchBar.layer.masksToBounds = YES;
    [titleView addSubview:[self searchBar]];
    
    self.navigationItem.titleView = titleView;
}

通过类目进行扩充:

#import <UIKit/UIKit.h>

@interface UISearchBar (Categories)

@property (strong, nonatomic, readonly) UITextField* textField;

@property (strong, nonatomic) UIColor* textColor;
@property (strong, nonatomic) UIFont* font;
@property (strong, nonatomic) UIColor* backgroundColor;
@property (strong, nonatomic) UIColor* placeholderColor;

@end

#import "UISearchBar+Categories.h"
#import "CategoryMacros.h"

CategoryKit_LoadCategory(UISearchBar_Categories)

@implementation UISearchBar (Categories)

- (UITextField*)textFieldInView:(UIView *)view;{
    for (UIView *subview in [view subviews]){
        if ([subview isKindOfClass:[UITextField class]]){
            return (UITextField*)subview;
        } else if ([subview subviews] && [[subview subviews] count]){
            UITextField *textField = [self textFieldInView:subview];
            if (textField) {
                return textField;
            }
        }
    }
    return nil;
}

- (UITextField*)textField;{
    return [self textFieldInView:self];
}

- (void)setFont:(UIFont *)font{
    [[self textField] setFont:font];
}

- (UIFont*)font{
    return [[self textField] font];
}

- (void)setTextColor:(UIColor *)textColor{
    [[self textField] setTextColor:textColor];
}

- (UIColor*)textColor{
    return [[self textField] textColor];
}

- (void)setBackgroundColor:(UIColor *)backgroundColor{
    [[self textField] setBackgroundColor:backgroundColor];
}

- (UIColor *)backgroundColor{
    return [[self textField] backgroundColor];
}

- (void)setPlaceholderColor:(UIColor *)placeholderColor{
    [[self textField] setValue:placeholderColor forKeyPath:@"_placeholderLabel.textColor"];
}

- (UIColor *)placeholderColor{
    return [[self textField] valueForKeyPath:@"_placeholderLabel.textColor"];
}
@end

仅提供部分思路，满足自己的开发需求即可。