有時(shí)在項(xiàng)目中需要對(duì)一些類進(jìn)行擴(kuò)展，Apple又只提供了對(duì)方法的擴(kuò)展，對(duì)屬性的擴(kuò)展只能使用runtime機(jī)制，對(duì)分類進(jìn)行屬性擴(kuò)展。廢話不多說(shuō)，直接上代碼：

UIViewController+Information.h文件

#import <UIKit/UIKit.h>
@interface UIViewController (Information)
@property (nonatomic, copy) NSString *name; //視圖名字
@property (nonatomic, assign) BOOL hasChildViewController; //是否有子視圖
@property (nonatomic, strong) UIImage *backgroundImage; //背景圖片@end

再來(lái)看看其實(shí)現(xiàn)：

UIViewController+Information.m文件

#import "UIViewController+Information.h"
#import <objc/runtime.h>
static const void *kName = "name";
static const void *kHasChildViewController = @"hasChildViewController";
static const void *kBackgroundImage = @"backgroundImage";
@implementation UIViewController (Information)

#pragma mark - 字符串類型的動(dòng)態(tài)綁定
- (NSString *)name { return objc_getAssociatedObject(self, kName);}
- (void)setName:(NSString *)name { 
objc_setAssociatedObject(self, kName, name, OBJC_ASSOCIATION_COPY_NONATOMIC);
}
#pragma mark - BOOL類型的動(dòng)態(tài)綁定
- (BOOL)hasChildViewController {
 return [objc_getAssociatedObject(self, kHasChildViewController) boolValue];
}
- (void)setHasChildViewController:(BOOL)hasChildViewController {
 objc_setAssociatedObject(self, kHasChildViewController, [NSNumber numberWithBool:hasChildViewController], OBJC_ASSOCIATION_ASSIGN);
}
#pragma mark - 類類型的動(dòng)態(tài)綁定
- (UIImage *)backgroundImage { 
return objc_getAssociatedObject(self, kBackgroundImage);
}

- (void)setBackgroundImage:(UIImage *)backgroundImage { 
objc_setAssociatedObject(self, kBackgroundImage, backgroundImage, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end

然后我們就可以引入這個(gè)頭文件，對(duì)UIViewController進(jìn)行了3個(gè)屬性（name, hasChildViewController, backgroundImage）的擴(kuò)展。
下面來(lái)個(gè)實(shí)際的應(yīng)用，給鍵盤添加一個(gè)縮回的按鈕，以UITextField為例，原理如下：
給鍵盤添加ToolBar， ToolBar上有一個(gè)具有縮回功能的button
將UITextField綁定到這個(gè)button上
添加縮回的方法，在方法中通過(guò)button獲取這個(gè)UITextField，調(diào)用這個(gè)UITextField的resignFirstResponder方法即可

定義一個(gè)工具類來(lái)隱藏鍵盤

YQTool.h文件

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
@interface YQTool : NSObject
#pragma mark - 增加隱藏鍵盤按鈕
+ (void)hideKeyboard:(UITextField *)textfield;
@end

YQTool.m文件

#import "YQTool.h"
#import <objc/runtime.h>

//獲取屏幕寬度的宏
#define ScreenWidth ([[UIScreen mainScreen] bounds].size.width)

static const void *kTextField = "textField";

@implementation YQTool

#pragma mark - 增加隱藏鍵盤按鈕
+ (void)hideKeyboard:(UITextField *)textfield {
    //為鍵盤增加工具欄
    UIToolbar * topView = [[UIToolbar alloc] initWithFrame:CGRectMake(0, 0, ScreenWidth, 30)];
    [topView setBarStyle:UIBarStyleDefault];

    UIBarButtonItem * btnSpace = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil];

    UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];
    btn.frame = CGRectMake(2, 5, 50, 25);
    //將TextField綁定到button上
    objc_setAssociatedObject(btn, kTextField, textfield, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

    [btn addTarget:self action:@selector(dismissKeyBoard:) forControlEvents:UIControlEventTouchUpInside];
    [btn setBackgroundImage:[UIImage imageNamed:@"closed"] forState:UIControlStateNormal];
    UIBarButtonItem *doneBtn = [[UIBarButtonItem alloc] initWithCustomView:btn];
    NSArray * buttonsArray = [NSArray arrayWithObjects:btnSpace,doneBtn,nil];
    [topView setItems:buttonsArray];
    [textfield setInputAccessoryView:topView];
}

+ (void)dismissKeyBoard:(UIButton *)button{
    //獲取button上對(duì)應(yīng)的屬性
    [objc_getAssociatedObject(button, kTextField) resignFirstResponder];
}

@end

在需要縮回的按鈕中，使用一行代碼就在鍵盤上展示縮回的按鈕：

[YQTool hideKeyboard:_nameTextField];

效果圖如下：

效果圖

12-16
最近看到一個(gè)比較好的寫法記錄下:

- (BOOL)wl_useDefaultBackButton{
    NSNumber *number = objc_getAssociatedObject(self, _cmd);
    if (number) {
        return number.boolValue;
    }
    self.wl_useDefaultBackButton = NO;
    return YES;
}

- (void)setWl_useDefaultBackButton:(BOOL)wl_useDefaultBackButton{
    SEL key = @selector(wl_useDefaultBackButton);
    objc_setAssociatedObject(self, key, @(wl_useDefaultBackButton), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}