class_getInstanceMethod和class_getClassMethod的区别

https://blog.csdn.net/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.

1. *
2. * @param cls The class you want to inspect.
3. * @param name The selector of the method you want to retrieve.
4. *
5. * @return The method that corresponds to the implementation of the selector specified by
6. * \e name for the class specified by \e cls, or \c NULL if the specified class or its
7. * superclasses do not contain an instance method with the specified selector.
8. *
9. * @note This function searches superclasses for implementations, whereas \c class_copyMethodList does not.
10. */
11. OBJC_EXPORT Method class_getInstanceMethod(Class cls, SEL name)
12. __OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0);
13. /**
14. * Returns a pointer to the data structure describing a given class method for a given class.
15. *
16. * @param cls A pointer to a class definition. Pass the class that contains the method you want to retrieve.
17. * @param name A pointer of type \c SEL. Pass the selector of the method you want to retrieve.
18. *
19. * @return A pointer to the \c Method data structure that corresponds to the implementation of the
20. * selector specified by aSelector for the class specified by aClass, or NULL if the specified
21. * class or its superclasses do not contain an instance method with the specified selector.
22. *
23. * @note Note that this function searches superclasses for implementations,
24. * whereas \c class_copyMethodList does not.
25. */
26. OBJC_EXPORT Method class_getClassMethod(Class cls, SEL name)
27. __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>

1. @interface Person : NSObject
2. @property(nonatomic, assign) NSInteger age;
3. @property(nonatomic, copy) NSString * name;
4. +(Person *)sharedManager;
5. - (instancetype)init;
6. + (void) printDZ;
7. - (void) printDZL;
8. @end
9. #import "Person.h"
10. @interface Person ()
11. @property(nonatomic, strong) NSString * sex;
12. @end
13. @implementation Person
14. +(Person *)sharedManager
15. {
16. static Person *sharedManager;
17. static dispatch_once_t onceTest;
18. dispatch_once(&onceTest, ^{
19.         sharedManager = [[Person alloc] init];
20.     });
21. NSLog(@"+ method");
22. return sharedManager;
23. }
24. - (instancetype)init
25. {
26. self = [super init];
27. if (self) {
28. self = [super init];
29. self.sex = @"-----------";
30. self.age = 19;
31. self.name = @"sb";
32.     }
33. return self;
34. }
35. + (void)printDZ
36. {
37. NSLog(@"this is a class method");
38. }
39. - (void)printDZL
40. {
41. NSLog(@"this is a instance method");
42. }
43. @end

测试Demo: 

 

 

 

- (void)viewDidLoad {

[super viewDidLoad];

1. // Do any additional setup after loading the view, typically from a nib.
2. Person * p1 = [[Person alloc] init];
3. Method m1 = class_getInstanceMethod([p1 class], @selector(printDZL));
4. Method m2 = class_getClassMethod([Person class], @selector(printDZ));
5. NSLog(@"测试前：");
6.     [p1 printDZL];
7.     [Person printDZ];
8.     method_exchangeImplementations(m1, m2);
9. NSLog(@"测试后：");
10.     [p1 printDZL];
11.     [Person printDZ];
12. }

输出: 

 

 

1.  
   2016-06-30 22:37:08.539 02-runtime[2776:69899] 测试前：
2.  
   2016-06-30 22:37:08.539 02-runtime[2776:69899] this is a instance method
3.  
   2016-06-30 22:37:08.539 02-runtime[2776:69899] this is a class method
4.  
   2016-06-30 22:37:08.540 02-runtime[2776:69899] 测试后：
5.  
   2016-06-30 22:37:08.540 02-runtime[2776:69899] this is a class method
6.  
   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：

1.  
   - (void)viewDidLoad {
2.  
   [super viewDidLoad];
3.  
   // Do any additional setup after loading the view, typically from a nib.
4.  
    
5.  
   Person * p1 = [[Person alloc] init];
6.  
    
7.  
   // Method m1 = class_getInstanceMethod([p1 class], @selector(printDZL));
8.  
   // Method m2 = class_getClassMethod([Person class], @selector(printDZ));
9.  
   Method m1 = class_getInstanceMethod([Person class], @selector(printDZ));
10.  
    Method m2 = class_getClassMethod([p1 class], @selector(printDZL));
11.  
    NSLog(@"测试前：");
12.  
    [p1 printDZL];
13.  
    [Person printDZ];
14.  
    method_exchangeImplementations(m1, m2);
15.  
    NSLog(@"测试后：");
16.  
    [p1 printDZL];
17.  
    [Person printDZ];
18.  
    }

输出:

 

1.  
   2016-06-30 22:38:10.050 02-runtime[2793:70426] 测试前：
2.  
   2016-06-30 22:38:10.051 02-runtime[2793:70426] this is a instance method
3.  
   2016-06-30 22:38:10.051 02-runtime[2793:70426] this is a class method
4.  
   2016-06-30 22:38:10.051 02-runtime[2793:70426] 测试后：
5.  
   2016-06-30 22:38:10.051 02-runtime[2793:70426] this is a instance method
6.  
   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。 

 

 

参考: http://blog.csdn.net/lvdezhou/article/details/49636561