有时在项目中需要对一些类进行扩展，Apple又只提供了对方法的扩展，对属性的扩展只能使用runtime机制，对分类进行属性扩展。废话不多说，直接上代码：
UIViewController+Information.h文件
#import <UIKit/UIKit.h>
@interface UIViewController (Information)
@property (nonatomic, copy) NSString *name; //视图名字
@property (nonatomic, assign) BOOL hasChildViewController; //是否有子视图
@property (nonatomic, strong) UIImage *backgroundImage; //背景图片
@end
再来看看其实现：
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 - 字符串类型的动态绑定
- (NSString *)name {
return objc_getAssociatedObject(self, kName);
}
- (void)setName:(NSString *)name {
objc_setAssociatedObject(self, kName, name, OBJC_ASSOCIATION_COPY_NONATOMIC);
}
#pragma mark - BOOL类型的动态绑定
- (BOOL)hasChildViewController {
return [objc_getAssociatedObject(self, kHasChildViewController) boolValue];
}
- (void)setHasChildViewController:(BOOL)hasChildViewController {
objc_setAssociatedObject(self, kHasChildViewController, [NSNumber numberWithBool:hasChildViewController], OBJC_ASSOCIATION_ASSIGN);
}
#pragma mark - 类类型的动态绑定
- (UIImage *)backgroundImage {
return objc_getAssociatedObject(self, kBackgroundImage);
}
- (void)setBackgroundImage:(UIImage *)backgroundImage {
objc_setAssociatedObject(self, kBackgroundImage, backgroundImage, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
@end
然后我们就可以引入这个头文件，对UIViewController进行了3个属性（name, hasChildViewController, backgroundImage）的扩展。
下面来个实际的应用，给键盘添加一个缩回的按钮，以UITextField为例，原理如下：
- 给键盘添加ToolBar， ToolBar上有一个具有缩回功能的button
- 将UITextField绑定到这个button上
- 添加缩回的方法，在方法中通过button获取这个UITextField，调用这个UITextField的
resignFirstResponder方法即可
定义一个工具类来隐藏键盘
YQTool.h文件
#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
@interface YQTool : NSObject
#pragma mark - 增加隐藏键盘按钮
+ (void)hideKeyboard:(UITextField *)textfield;
@end
YQTool.m文件
#import "YQTool.h"
#import <objc/runtime.h>
//获取屏幕宽度的宏
#define ScreenWidth ([[UIScreen mainScreen] bounds].size.width)
static const void *kTextField = "textField";
@implementation YQTool
#pragma mark - 增加隐藏键盘按钮
+ (void)hideKeyboard:(UITextField *)textfield {
//为键盘增加工具栏
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);
//将TextField绑定到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{
//获取button上对应的属性
[objc_getAssociatedObject(button, kTextField) resignFirstResponder];
}
@end
在需要缩回的按钮中，使用一行代码就在键盘上展示缩回的按钮：
[YQTool hideKeyboard:_nameTextField];
效果图如下：
效果图
