有時在專案中需要對一些類進行擴充套件，Apple又只提供了對方法的擴充套件，對屬性的擴充套件只能使用runtime機制，對分類進行屬性擴充套件。廢話不多說，直接上程式碼：
UIViewController+Information.h檔案
#import <UIKit/UIKit.h>
@interface UIViewController (Information)
@property (nonatomic, copy) NSString *name; //檢視名字
@property (nonatomic, assign) BOOL hasChildViewController; //是否有子檢視
@property (nonatomic, strong) UIImage *backgroundImage; //背景圖片
@end
複製程式碼再來看看其實現：
UIViewController+Information.m檔案
#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 - 字串型別的動態繫結
- (NSString *)name {
return objc_getAssociatedObject(self, kName);
}
- (void)setName:(NSString *)name {
objc_setAssociatedObject(self, kName, name, OBJC_ASSOCIATION_COPY_NONATOMIC);
}
#pragma mark - BOOL型別的動態繫結
- (BOOL)hasChildViewController {
return [objc_getAssociatedObject(self, kHasChildViewController) boolValue];
}
- (void)setHasChildViewController:(BOOL)hasChildViewController {
objc_setAssociatedObject(self, kHasChildViewController, [NSNumber numberWithBool:hasChildViewController], OBJC_ASSOCIATION_ASSIGN);
}
#pragma mark - 類型別的動態繫結
- (UIImage *)backgroundImage {
return objc_getAssociatedObject(self, kBackgroundImage);
}
- (void)setBackgroundImage:(UIImage *)backgroundImage {
objc_setAssociatedObject(self, kBackgroundImage, backgroundImage, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
@end
複製程式碼然後我們就可以引入這個標頭檔案，對UIViewController進行了3個屬性（name, hasChildViewController, backgroundImage）的擴充套件。
下面來個實際的應用，給鍵盤新增一個縮回的按鈕，以UITextField為例，原理如下：
- 給鍵盤新增ToolBar， ToolBar上有一個具有縮回功能的button
- 將UITextField繫結到這個button上
- 新增縮回的方法，在方法中通過button獲取這個UITextField，呼叫這個UITextField的 resignFirstResponder方法即可
定義一個工具類來隱藏鍵盤
YQTool.h檔案
#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
複製程式碼YQTool.m檔案
#import "YQTool.h"
#import <objc/runtime.h>
//獲取螢幕寬度的巨集
#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繫結到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上對應的屬性
[objc_getAssociatedObject(button, kTextField) resignFirstResponder];
}
@end
複製程式碼在需要縮回的按鈕中，使用一行程式碼就在鍵盤上展示縮回的按鈕：
[YQTool hideKeyboard:_nameTextField];
複製程式碼效果圖如下：
