一 方法調用的本質
1.runtime 的使用方法 ，首先導入objc/message.h ,在build setting 里面輸入msg 設置為NO 因為從xcode5開始蘋果不推薦使用底層的東西了擦！！ runtime是運行時的機制，也就是說所有方法的調用在編譯command+b的時候不會真正檢測到底調用誰，只會在運行時候（動態）調用方法 ，方法調用的本質順序; e.g.
[p eat] ---> [p performselector:@selector:eat] -> objc_msgsend(p,@selector:eat);
[Person eat] --> 先轉化成類對象 Class personClass = [Person Class]; --> [personClass eat] --> [personClass performselector:@selector:eat]; ---> objc_msgsend([Person Class],@selector:eat);
無論是類調用放還是類對象調用方法本質都是 轉化成objc_msgsend
- (void)text1 {
person *p = [[person alloc] init];
// xcode5 之后使用運行時方法
// 蘋果不推薦調用底層的方法
// 在 buildsettings 搜索msg 設置為NO
// 讓p 發送消息
objc_msgSend(p, @selector(eat));
//
objc_msgSend([person class], @selector(eat)); // 類對象
// 類名調用類方法 其實就是用類對象調用方法
[person eat];
// 獲取類對象
Class personClass = [person class];
[personClass performSelector:@selector(eat)];
[personClass eat];
}
二 交換方法的實現
本質先得到兩個方法 然后交換兩個方法的實現請見官方文檔
開發時候的作用很大比如更改文字的大小顏色等等替換官方的方法實現換成自己的但是記得回調官方的方法哦！！ 這樣可以替換所有的方法如果用分類的方法只能替換將來的已經使用的方法就沒辦法了一勞永逸！！！ 裝逼利器！
/**
* Sets the implementation of a method.
*
* @param m The method for which to set an implementation.
* @param imp The implemention to set to this method.
*
* @return The previous implementation of the method.
*/
OBJC_EXPORT IMP method_setImplementation(Method m, IMP imp)
__OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);
/**
* Exchanges the implementations of two methods.
*
* @param m1 Method to exchange with second method.
* @param m2 Method to exchange with first method.
*
* @note This is an atomic version of the following:
* \code
* IMP imp1 = method_getImplementation(m1);
* IMP imp2 = method_getImplementation(m2);
* method_setImplementation(m1, imp2);
* method_setImplementation(m2, imp1);
* \endcode
*/
OBJC_EXPORT void method_exchangeImplementations(Method m1, Method m2)
__OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);
#import "UIImage+myImage.h"
#import <objc/message.h>
@implementation UIImage (myImage)
+ (void)load {
// 方法和屬性等都是在類中所以用class_
Method m1 = class_getClassMethod([UIImage class], @selector(imageNamed:));
Method m2 = class_getClassMethod([UIImage class], @selector(stimageNamed:));
method_exchangeImplementations(m1 , m2 );
}
+ (UIImage *)stimageNamed:(NSString *)imageName {
UIImage *image = [UIImage stimageNamed:imageName];
if (image ==nil) {
NSLog(@"圖片為nil");
}
return image;
}
三 動態的為某個類添加方法的實現
class_addMethod(self , @selector(eat:), (IMP)eatsssss, "v@:@");
#import "person.h"
#import <objc/message.h>
@implementation person
// 調用了一個沒有實現的方法就會調用這個方法 可以知道哪些方法沒有實現 self _cmd //隱私參數
+ (BOOL)resolveInstanceMethod:(SEL)sel {
// 動態添加方法
if ([NSStringFromSelector(sel) isEqualToString:@"eat:"]) {
/**
cls: 給哪個類添加方法
SEL:添加方法的方法編號
IMP:函數名 方法實現 函數入口
types : 方法類型
*/
class_addMethod(self , @selector(eat:), (IMP)eatsssss, "v@:@");
}
return [super resolveInstanceMethod:sel];
}
// 定義函數
void eatsssss (id self ,SEL _cmd,id parames)
{
NSLog(@"hahha%@",parames);
}
官方文檔
Dynamic Method Resolution
There are situations where you might want to provide an implementation of a method dynamically. For example, the Objective-C declared properties feature (see Declared Properties in The Objective-C Programming Language) includes the @dynamic directive:
@dynamic propertyName;
which tells the compiler that the methods associated with the property will be provided dynamically.
You can implement the methods resolveInstanceMethod: and resolveClassMethod: to dynamically provide an implementation for a given selector for an instance and class method respectively.
An Objective-C method is simply a C function that take at least two arguments—self and _cmd. You can add a function to a class as a method using the function class_addMethod. Therefore, given the following function:
void dynamicMethodIMP(id self, SEL _cmd) {
// implementation ....
}
you can dynamically add it to a class as a method (called resolveThisMethodDynamically) using resolveInstanceMethod: like this:
@implementation MyClass
+ (BOOL)resolveInstanceMethod:(SEL)aSEL
{
if (aSEL == @selector(resolveThisMethodDynamically)) {
class_addMethod([self class], aSEL, (IMP) dynamicMethodIMP, "v@:");
return YES;
}
return [super resolveInstanceMethod:aSEL];
}
@end
Forwarding methods (as described in Message Forwarding) and dynamic method resolution are, largely, orthogonal. A class has the opportunity to dynamically resolve a method before the forwarding mechanism kicks in. If respondsToSelector: or instancesRespondToSelector: is invoked, the dynamic method resolver is given the opportunity to provide an IMP for the selector first. If you implement resolveInstanceMethod: but want particular selectors to actually be forwarded via the forwarding mechanism, you return NO for those selectors.
Dynamic Loading
An Objective-C program can load and link new classes and categories while it’s running. The new code is incorporated into the program and treated identically to classes and categories loaded at the start.
Dynamic loading can be used to do a lot of different things. For example, the various modules in the System Preferences application are dynamically loaded.
In the Cocoa environment, dynamic loading is commonly used to allow applications to be customized. Others can write modules that your program loads at runtime—much as Interface Builder loads custom palettes and the OS X System Preferences application loads custom preference modules. The loadable modules extend what your application can do. They contribute to it in ways that you permit but could not have anticipated or defined yourself. You provide the framework, but others provide the code.
Although there is a runtime function that performs dynamic loading of Objective-C modules in Mach-O files (objc_loadModules, defined in objc/objc-load.h), Cocoa’s NSBundle class provides a significantly more convenient interface for dynamic loading—one that’s object-oriented and integrated with related services. See the NSBundle class specification in the Foundation framework reference for information on the NSBundle class and its use. See OS X ABI Mach-O File Format Reference for information on Mach-O files.
四 動態的為某個類添加屬性
#import "NSObject+name.h"
#import <objc/message.h>
// @property在分類里面只會生成方法的set get方法的生明不會生成實現和_成員變量
@implementation NSObject (name)
- (void)setName:(NSString *)name {
// 添加屬性一般也給對象添加的 objc
/***
objc 給哪個對象添加屬性
key 屬性名 根據key 去獲取關聯的對象 void * == id
value 關聯的值賦給的值name
policy weak retain copy
*/
objc_setAssociatedObject(self, @"name", name, OBJC_ASSOCIATION_COPY);
}
- (NSString *)name {
return objc_getAssociatedObject(self, @"name");
}
