runtime實戰（二）動態新增方法
阿新 • • 發佈：2018-11-01
runtime的實戰二就是動態新增方法
一：建立一個Person類
我們在Person類的標頭檔案宣告一個eat方法，並不去實現它，當我們呼叫時，會出現如下的崩潰棧
2017-05-01 20:43:06.483 SH_Runtime[2133:104550] -[Person eat]: unrecognized selector sent to instance 0x618000018a20
2017-05-01 20:43:06.495 SH_Runtime[2133:104550] *** Terminating app due to uncaught exception 'NSInvalidArgumentException' 注意：第三、第四行我們看到Terminating app due to uncaught exception ‘NSInvalidArgumentException’,這個是什麼呢？
其實這是蘋果給開發者的一個捕獲異常的機會，NSObject類有方法：
// 捕獲未實現的類方法
+ (BOOL)resolveClassMethod:(SEL)sel OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);
// 捕獲未實現的例項方法
+ (BOOL)resolveInstanceMethod:(SEL)sel OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);在Person.m檔案實現這兩個方法,便實現動態新增的功能；
#import "Person.h"
#import <objc/runtime.h>
@implementation Person
// 捕獲未實現的類方法
+ (BOOL)resolveClassMethod:(SEL)sel
{
return NO;
}
// 捕獲未實現的例項方法
+(BOOL)resolveInstanceMethod:(SEL)sel
{
NSLog(@"the sel is :%@",NSStringFromSelector(sel));
if (sel == @selector(eat)) {
// runtime 新增方法;
// class: 所要新增的類;
// SEL: 方法編號；
// IMP(Implementation):方法實現，一個方法指標
// type: 型別
class_addMethod([Person class], sel, (IMP)eat, "");
return YES;
}
return NO;
}
void eat() {
NSLog(@"person eat");
}
@end另：class_addMethod方法的第四個引數一般情況為空字串即程式碼沒有引數和返回值，對於有返回值和引數方法，看蘋果開發者文件：
| Tables | Are |
|---|---|
| Code | Meaning |
| c | A char |
| i | An int |
| s | A short |
| l | A long l is treated as a 32-bit quantity on 64-bit programs. |
| q | A long long |
| C | An unsigned char |
| I | An unsigned int |
| S | An unsigned short |
| L | An unsigned long |
| Q | An unsigned long long |
| f | A float |
| d | A double |
| B | A C++ bool or a C99 _Bool |
| v | A void |
| * | A character string (char *) |
| @ | An object (whether statically typed or typed id) |
| # | A class object (Class) |
| : | A method selector (SEL) |
| [array type] | An array |
| {name=type…} | A structure |
| (name=type…) | A union |
| bnum | A bit field of num bits |
| ^type | A pointer to type |
| ? | An unknown type (among other things, this code is used for function pointers) |
參閱Type Encoding表我們可知：
class_addMethod([self class], @selector(resolveThisMethodDynamically), (IMP) myMethodIMP, "[email protected]:");An array of characters that describe the types of the arguments to the
method. For possible values, see Objective-C Runtime Programming Guide
Type Encodings. Since the function must take at least two arguments—self and _cmd, the second and third characters must be “@:”
(the first character is the return type).
方法的返回值為void，而@：是必須的引數。
我的GitHub程式碼地址：https://github.com/lvshaohua/SH_Runtime