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一： 问题描述，为什么要去完全自定义searchBar
相 信许多同学在开发中，会遇到UISearchBar的自订制问题。比如一个简单的placeholder永远居左，且关键字会不断变化，就会逼疯很多人， 使用空格符达到效果。自从iOS7之后，如果不想使用自带的searchBar的默认效果就更容易遇到各种问题。因此，使用textField去完全解决 自定义的方法无疑是最有效率的。

二：思路，如何去自定义searchBar
作为苹果的封装类，searchBar无非是给大家便利的提供了一种使用textField的类。其核心还是textField。因此，我们的封装，也必须是围绕textField来完成的。
1：主体是一个view
2：放大镜图片，可以在主view上添加imageView，也可以使用textField的leftView；
3：取消按钮，完全可以不放到主view中，在外界使用的时候再去自行创建使用。
4：textField
5：重点：代理的实现，无非是将textField的代理无缝结合移植到封装类，可以参考系统的searchbar的代理，也写代理。
6：既然是自封装，属性完全可以多设置一些，方便大家调用。

三：代码示例
下面就是我花了半天时间简单封装的searchBar，虽然还会有些不太完善的地方，但是绝大部分功能都可以正常使用了。可以根据自己的需求，继续完善属性，添加方法，甚至代理方法。先是.h中。

//
//  OCSearchBar.h
//  OpenCourse
//
//  Created by 徐坤 on 15/11/27.
//
// 不让外界直接调用textField，用起来会更像系统的searchBar的API，完善属性后，会将textField拿到.m中

#import <UIKit/UIKit.h>

@class OCSearchBar;

@protocol OCSearchBarDelegate <NSObject>

@optional

- (BOOL)OCSearchBarShouldBeginEditing:(OCSearchBar *)searchBar;
- (void)OCSearchBarTextDidBeginEditing:(OCSearchBar *)searchBar;
- (BOOL)OCSearchBarShouldEndEditing:(OCSearchBar *)searchBar;
- (void)OCSearchBarTextDidEndEditing:(OCSearchBar *)searchBar;

- (void)OCSearchBar:(OCSearchBar *)searchBar textDidChange:(NSString *)searchText;
- (BOOL)OCSearchBar:(OCSearchBar *)searchBar shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text;
- (void)OCSearchBarSearchButtonClicked:(OCSearchBar *)searchBar;

@end

@interface OCSearchBar : UIView <UITextFieldDelegate>

@property (nonatomic, strong) UIImage *backViewImage;
@property (nonatomic, strong) UITextField *textField;
@property (nonatomic, strong) UIImageView *leftImageView;//左侧放大镜
@property (nonatomic, copy  ) NSString *placeholder;
@property (nonatomic, strong) UIFont *font;
@property (nonatomic, copy)   NSString *text;
@property (nonatomic, strong) UIColor *placeholderColor;
@property (nonatomic, strong) UIColor *textColor;

@property (nonatomic, assign) BOOL isFirstResponder;

@property (nonatomic, weak) id <OCSearchBarDelegate>delegate;

- (instancetype)initWithFrame:(CGRect)frame;

- (void)resignFirstResponder;
- (void)becomeFirstResponder;

@end

============然后是实现文件.m=========自行粘贴到自己项目中即可。
//
//  OCSearchBar.m
//  OpenCourse
//
//  Created by 徐坤 on 15/11/27.
//
//

#import "OCSearchBar.h"

@interface OCSearchBar ()
@property (nonatomic, strong) UIImageView *backGroundView;

@end

@implementation OCSearchBar

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

- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextFieldTextDidChangeNotification object:nil];
}

- (void)setupSubviews {
   
    self.backGroundView = [[UIImageView alloc] initWithFrame:self.bounds];
    [self addSubview:self.backGroundView];
   
    self.textField = [[UITextField alloc] initWithFrame:self.bounds];
    self.textField.backgroundColor = [UIColor clearColor];
    self.textField.delegate = self;
    self.textField.clearButtonMode = YES;
    self.textField.autocapitalizationType = UITextAutocapitalizationTypeNone;
    self.textField.returnKeyType = UIReturnKeySearch;
    //self.textField.leftViewMode = UITextFieldViewModeAlways;
    [self addSubview:self.textField];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(OCSearchBarDidChange:) name:UITextFieldTextDidChangeNotification object:nil];
    [self setupDefaultLeftImageView];
    [self setupDefaultBackGroundView];
}

- (void)setupDefaultBackGroundView {
   
    // 使用颜色创建UIImage
    CGSize imageSize = self.bounds.size;
    UIGraphicsBeginImageContextWithOptions(imageSize, 0, [UIScreen mainScreen].scale);
    [RGB(26, 66, 38) set];
    UIRectFill(CGRectMake(0, 0, imageSize.width, imageSize.height));
    UIImage *colorImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
   
    self.backGroundView.layer.cornerRadius = 6;
    self.backGroundView.layer.masksToBounds = YES;
   
    [self.backGroundView setImage:colorImage];
   
}

- (void)setupDefaultLeftImageView {
    UIImageView *leftImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"search_fdj"]];
    [leftImageView setFrame:CGRectMake(13, 6, 18, 18)];
    self.leftImageView = leftImageView;
}

- (void)setFont:(UIFont *)font {
    self.textField.font = font;
   
}

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

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

- (void)setText:(NSString *)text {
    self.textField.text = text;
}

- (NSString *)text {
    return self.textField.text;
}

- (void)setBackViewImage:(UIImage *)backViewImage {
    [self.backGroundView setImage:backViewImage];
   
}

- (void)setLeftImageView:(UIImageView *)leftImageView {
    if (self.leftImageView.superview) {
        [self.leftImageView removeFromSuperview];
    }
    [self addSubview:leftImageView];
    CGRect rect = self.textField.bounds;
    rect.origin.x = rect.origin.x+leftImageView.frame.origin.x+leftImageView.frame.size.width+5;
    rect.size.width = rect.size.width - leftImageView.frame.origin.x - leftImageView.frame.size.width-5;
    [self.textField setFrame:rect];
   
}

- (void)setPlaceholder:(NSString *)placeholder {
    self.textField.placeholder = placeholder;
}

- (void)resignFirstResponder {
    [self.textField resignFirstResponder];
}

- (void)becomeFirstResponder {
    [self.textField becomeFirstResponder];
}

#pragma mark -
#pragma mark - OCTextFieldDelegate

- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField {
    if (self.delegate && [self.delegate respondsToSelector:@selector(OCSearchBarShouldBeginEditing:)] ) {
        return [self.delegate OCSearchBarShouldBeginEditing:self];
    }
    return YES;
}

- (void)textFieldDidBeginEditing:(UITextField *)textField {
    self.isFirstResponder = YES;
    if (self.delegate && [self.delegate respondsToSelector:@selector(OCSearchBarTextDidBeginEditing:)]) {
        [self.delegate OCSearchBarTextDidBeginEditing:self];
    }
   
}

- (BOOL)textFieldShouldEndEditing:(UITextField *)textField {
    if (self.delegate && [self.delegate respondsToSelector:@selector(OCSearchBarShouldEndEditing:)]) {
         return [self.delegate OCSearchBarShouldEndEditing:self];
    }
    return YES;
}

- (void)textFieldDidEndEditing:(UITextField *)textField {
    if (self.delegate && [self.delegate respondsToSelector:@selector(OCSearchBarTextDidEndEditing:)]) {
         [self.delegate OCSearchBarTextDidEndEditing:self];
    }
}

- (BOOL)textField:(UITextField *)textField
            shouldChangeCharactersInRange:(NSRange)range
            replacementString:(NSString *)string {
    if (self.delegate && [self.delegate respondsToSelector:@selector(OCSearchBar:shouldChangeTextInRange:replacementText:)]) {
         return [self.delegate OCSearchBar:self shouldChangeTextInRange:range replacementText:string];
    }
    return YES;
}

- (BOOL)textFieldShouldClear:(UITextField *)textField {
    return YES;
}

- (BOOL)textFieldShouldReturn:(UITextField *)textField {
    if (self.delegate && [self.delegate respondsToSelector:@selector(OCSearchBarSearchButtonClicked:)]) {
         [self.delegate OCSearchBarSearchButtonClicked:self];
    }
    return YES;
}

- (void)OCSearchBarDidChange:(NSNotification *)notification {
    UITextField *textField = [notification object];
    if (self.delegate && [self.delegate respondsToSelector:@selector(OCSearchBar:textDidChange:)]) {
         [self.delegate OCSearchBar:self textDidChange:textField.text];  
    }
}

@end