class_getInstanceMethod和class_getClassMethod的区别

最新推荐文章于 2024-05-03 12:06:54 发布

转载最新推荐文章于 2024-05-03 12:06:54 发布 · 959 阅读

CC 4.0 BY-SA版权

原文链接：https://blog.youkuaiyun.com/baidu_25743639/article/details/51793764

本文介绍了在Objective-C中使用`class_getInstanceMethod`和`class_getClassMethod`获取实例方法与类方法，并通过`method_exchangeImplementations`进行方法交换的实践。通过示例代码展示了正确和错误的使用方式，以及方法交换的效果，强调了两者之间的区别和正确使用的重要性。

转载自：https://blog.youkuaiyun.com/baidu_25743639/article/details/51793764

今天在学习runtime的method_exchangeImplementations进行方法交换的时候,将class_getInstanceMethod方法误写成class_getClassMethod,结果发现方法交换失败,

找了好久发现在获取方法的时候写错了;

先简单介绍下这两个方法是干什么用的:

class_getInstanceMethod 得到类的实例方法

class_getClassMethod 得到类的类方法

从官方文档中我们可以看到:

/**
* Returns a specified instance method for a given class.
*
* @param cls The class you want to inspect.
* @param name The selector of the method you want to retrieve.
*
* @return The method that corresponds to the implementation of the selector specified by
* \e name for the class specified by \e cls, or \c NULL if the specified class or its
* superclasses do not contain an instance method with the specified selector.
*
* @note This function searches superclasses for implementations, whereas \c class_copyMethodList does not.
*/
OBJC_EXPORT Method class_getInstanceMethod(Class cls, SEL name)
__OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0);
/**
* Returns a pointer to the data structure describing a given class method for a given class.
*
* @param cls A pointer to a class definition. Pass the class that contains the method you want to retrieve.
* @param name A pointer of type \c SEL. Pass the selector of the method you want to retrieve.
*
* @return A pointer to the \c Method data structure that corresponds to the implementation of the
* selector specified by aSelector for the class specified by aClass, or NULL if the specified
* class or its superclasses do not contain an instance method with the specified selector.
*
* @note Note that this function searches superclasses for implementations,
* whereas \c class_copyMethodList does not.
*/
OBJC_EXPORT Method class_getClassMethod(Class cls, SEL name)
__OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0);

好了废话不多说,上代码来说明一下:

DEMO:

测试所用的Person类:

#import <Foundation/Foundation.h>
@interface Person : NSObject
@property(nonatomic, assign) NSInteger age;
@property(nonatomic, copy) NSString * name;
+(Person *)sharedManager;
- (instancetype)init;
+ (void) printDZ;
- (void) printDZL;
@end
#import "Person.h"
@interface Person ()
@property(nonatomic, strong) NSString * sex;
@end
@implementation Person
+(Person *)sharedManager
{
static Person *sharedManager;
static dispatch_once_t onceTest;
dispatch_once(&onceTest, ^{
sharedManager = [[Person alloc] init];
});
NSLog(@"+ method");
return sharedManager;
}
- (instancetype)init
{
self = [super init];
if (self) {
self = [super init];
self.sex = @"-----------";
self.age = 19;
self.name = @"sb";
}
return self;
}
+ (void)printDZ
{
NSLog(@"this is a class method");
}
- (void)printDZL
{
NSLog(@"this is a instance method");
}
@end

测试Demo:

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
Person * p1 = [[Person alloc] init];
Method m1 = class_getInstanceMethod([p1 class], @selector(printDZL));
Method m2 = class_getClassMethod([Person class], @selector(printDZ));
NSLog(@"测试前：");
[p1 printDZL];
[Person printDZ];
method_exchangeImplementations(m1, m2);
NSLog(@"测试后：");
[p1 printDZL];
[Person printDZ];
}

输出:

2016-06-30 22:37:08.539 02-runtime[2776:69899] 测试前：
2016-06-30 22:37:08.539 02-runtime[2776:69899] this is a instance method
2016-06-30 22:37:08.539 02-runtime[2776:69899] this is a class method
2016-06-30 22:37:08.540 02-runtime[2776:69899] 测试后：
2016-06-30 22:37:08.540 02-runtime[2776:69899] this is a class method
2016-06-30 22:37:08.540 02-runtime[2776:69899] this is a instance method

由输出可见，方法体交换了，说明class_getInstanceMethod成功得到了实例方法，class_getClassMethod成功得到了类方法

但是当用class_getInstanceMethod来取类方法，用class_getClassMethod来取实例方法时：

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
Person * p1 = [[Person alloc] init];
// Method m1 = class_getInstanceMethod([p1 class], @selector(printDZL));
// Method m2 = class_getClassMethod([Person class], @selector(printDZ));
Method m1 = class_getInstanceMethod([Person class], @selector(printDZ));
Method m2 = class_getClassMethod([p1 class], @selector(printDZL));
NSLog(@"测试前：");
[p1 printDZL];
[Person printDZ];
method_exchangeImplementations(m1, m2);
NSLog(@"测试后：");
[p1 printDZL];
[Person printDZ];
}

输出:

2016-06-30 22:38:10.050 02-runtime[2793:70426] 测试前：
2016-06-30 22:38:10.051 02-runtime[2793:70426] this is a instance method
2016-06-30 22:38:10.051 02-runtime[2793:70426] this is a class method
2016-06-30 22:38:10.051 02-runtime[2793:70426] 测试后：
2016-06-30 22:38:10.051 02-runtime[2793:70426] this is a instance method
2016-06-30 22:38:10.051 02-runtime[2793:70426] this is a class method

由输出可见，没有发生交换，可知这样是取不到的