一、關於runtime
之前在專案中有遇到過用runtime解決改變全域性字型的問題，所以再一次感受到了runtime黑魔法的強大，趁現在有機會分享一下對runtime的一些理解。
在物件呼叫方法是Objective-C中經常使用的功能，也就是訊息的傳遞，而Objective-C是C的超集，所以和C不同的是，Objective-C使用的是動態繫結，也就是runtime。Objective-C的訊息傳遞和訊息機制也就不多說了，今天主要說的是動態方法，也就是函式的呼叫。
二、相關的幾個函式
下面一張圖詳細的概括了每個函式呼叫的先後以及執行的前提
- 1.物件在收到無法解讀的訊息後，首先會呼叫所屬類的 ***objc
+ (BOOL)resolveInstanceMethod:(SEL)sel
這個方法在執行時，沒有找到SEL的IMP時就會執行。這個函式是給類利用class_addMethod新增函式的機會。根據文件，如果實現了新增函式程式碼則返回YES，未實現返回NO。
舉個例子，新建了一個工程，首先我在ViewController這個類中執行doSomething1這個方法，程式碼如下
//
// ViewController.m
// RuntimeTest1
//
// Created by HenryCheng on 15/12/24.
// Copyright © 2015年 www.igancao.com All rights reserved.
//
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
[self performSelector:@selector(doSomething)];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end ```
執行結果
複製程式碼2015-12-24 10:35:37.726 RuntimeTest1[1877:337842] -[ViewController doSomething]: unrecognized selector sent to instance 0x7fe9f3736680 2015-12-24 10:35:37.729 RuntimeTest1[1877:337842] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController doSomething]: unrecognized selector sent to instance 0x7fe9f3736680' ***** First throw call stack:**
不出意外，程式崩潰，因為沒有找到`doSomething`這個方法，下面我們在裡面實現 `+ (BOOL)resolveInstanceMethod:(SEL)sel`這個方法，並且判斷如果`SEL` 是`doSomething`那就輸出`add method here`
複製程式碼// // ViewController.m // RuntimeTest1 // // Created by HenryCheng on 15/12/24. // Copyright © 2015年 www.igancao.com All rights reserved. //
#import "ViewController.h"
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad { [super viewDidLoad]; [self performSelector:@selector(doSomething)];
}
- (BOOL)resolveInstanceMethod:(SEL)sel { if (sel == @selector(doSomething)) { NSLog(@"add method here"); return YES; } return [super resolveInstanceMethod:sel]; }
- (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated. }
@end```
繼續執行，然後看到log
**2015-12-24 10:47:24.687 RuntimeTest1[2007:382077] add method here**
**2015-12-24 10:47:24.687 RuntimeTest1[2007:382077] -[ViewController doSomething]: unrecognized selector sent to instance 0x7f9568c331f0**
**2015-12-24 10:47:24.690 RuntimeTest1[2007:382077] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController doSomething]: unrecognized selector sent to instance 0x7f9568c331f0'**
***** First throw call stack:**
複製程式碼可以看到程式依然是崩潰了，但是我們可以看到輸出了add method here，這說明我們 + (BOOL)resolveInstanceMethod:(SEL)sel這個方法執行了，並進入了判斷，所以，在這兒，我們可以做一下操作，使這個方法得到響應，不至於走到最後- (void)doesNotRecognizeSelector:(SEL)aSelector這個方法中而崩掉了，接下來，我們繼續操作，如下
//
// ViewController.m
// RuntimeTest1
//
// Created by HenryCheng on 15/12/24.
// Copyright © 2015年 www.igancao.com All rights reserved.
//
#import "ViewController.h"
#import <objc/runtime.h>
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
[self performSelector:@selector(doSomething)];
}
+ (BOOL)resolveInstanceMethod:(SEL)sel {
if (sel == @selector(doSomething)) {
NSLog(@"add method here");
class_addMethod([self class], sel, (IMP)dynamicMethodIMP, "v@:");
return YES;
}
return [super resolveInstanceMethod:sel];
}
void dynamicMethodIMP (id self, SEL _cmd) {
NSLog(@"doSomething SEL");
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
複製程式碼匯入了<objc/runtime.h>並且在+ (BOOL)resolveInstanceMethod:(SEL)sel中執行了class_addMethod這個方法，然後定義了一個void dynamicMethodIMP (id self, SEL _cmd)這個函式，執行工程，看log
**2015-12-24 11:45:11.934 RuntimeTest1[2284:478571] add method here**
**2015-12-24 11:45:11.934 RuntimeTest1[2284:478571] doSomething SEL**
複製程式碼這時候我們發現，程式並沒有崩潰，而且還輸出了doSomething SEL，這時候就說明我們已經通過runtime成功的向我們這個類中新增了一個方法。關於class_addMethod這個方法，是這樣定義的
OBJC_EXPORT BOOL class_addMethod(Class cls, SEL name, IMP imp, const char *types)
複製程式碼cls在這個類中新增方法，也就是方法所新增的類name方法名，這個可以隨便起的imp實現這個方法的函式types定義該數返回值型別和引數型別的字串，這裡比如"v@:"，其中v就是void，帶表返回型別就是空，@代表引數，這裡指的是id(self)，這裡:指的是方法SEL(_cmd)，比如我再定義一個函式
int newMethod (id self, SEL _cmd, NSString *str) {
return 100;
}
複製程式碼那麼新增這個函式的方法就應該是
ass_addMethod([self class], @selector(newMethod), (IMP)newMethod, "i@:@");
- 2.如果在
+ (BOOL)resolveInstanceMethod:(SEL)sel中沒有找到或者新增方法
訊息繼續往下傳遞到- (id)forwardingTargetForSelector:(SEL)aSelector看看是不是有物件可以執行這個方法，我們來重新建個工程，然後新建一個叫SecondViewController的類，裡面有一個- (void)secondVCMethod方法，如下
//
// SecondViewController.m
// RuntimeTest2
//
// Created by HenryCheng on 15/12/24.
// Copyright © 2015年 www.igancao.com All rights reserved.
//
#import "SecondViewController.h"
@interface SecondViewController ()
@end
@implementation SecondViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
}
- (void)secondVCMethod {
NSLog(@"This is secondVC method !");
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
/*
#pragma mark - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
// Get the new view controller using [segue destinationViewController].
// Pass the selected object to the new view controller.
}
*/
@end
複製程式碼工程結構應該是這樣的
ViewController中呼叫- (void)secondVCMethod這個方法，我們知道ViewController和SecondViewController並無繼承關係，按照正常的步驟去做程式肯定會因為在ViewController找不到- (void)secondVCMethod這個方法而直接崩潰的
//
// ViewController.m
// RuntimeTest2
//
// Created by HenryCheng on 15/12/24.
// Copyright © 2015年 www.igancao.com All rights reserved.
//
#import "ViewController.h"
#import <objc/runtime.h>
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
[self performSelector:@selector(secondVCMethod)];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
複製程式碼執行結果
**2015-12-24 13:54:44.314 RuntimeTest2[3164:835814] -[ViewController secondVCMethod]: unrecognized selector sent to instance 0x7fc3a8535c10**
**2015-12-24 13:54:44.317 RuntimeTest2[3164:835814] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController secondVCMethod]: unrecognized selector sent to instance 0x7fc3a8535c10'**
***** First throw call stack:**
複製程式碼現在我們來處理一下這個訊息，如下
//
// ViewController.m
// RuntimeTest2
//
// Created by HenryCheng on 15/12/24.
// Copyright © 2015年 www.igancao.com All rights reserved.
//
#import "ViewController.h"
#import <objc/runtime.h>
@interface ViewController ()
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
[self performSelector:@selector(secondVCMethod)];
}
- (id)forwardingTargetForSelector:(SEL)aSelector {
Class class = NSClassFromString(@"SecondViewController");
UIViewController *vc = class.new;
if (aSelector == NSSelectorFromString(@"secondVCMethod")) {
NSLog(@"secondVC do this !");
return vc;
}
return nil;
}
+ (BOOL)resolveInstanceMethod:(SEL)sel {
return [super resolveInstanceMethod:sel];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
複製程式碼執行結果
**2015-12-24 14:00:34.168 RuntimeTest2[3284:870957] secondVC do this !**
**2015-12-24 14:00:34.169 RuntimeTest2[3284:870957] This is secondVC method !**
複製程式碼我們會發現- (void)secondVCMethod這個方法執行了，程式也並沒有崩潰，原因就是在這一步
- (id)forwardingTargetForSelector:(SEL)aSelector {
Class class = NSClassFromString(@"SecondViewController");
UIViewController *vc = class.new;
if (aSelector == NSSelectorFromString(@"secondVCMethod")) {
NSLog(@"secondVC do this !");
return vc;
}
return nil;
}
複製程式碼在沒有找到- (void)secondVCMethod這個方法的時候，訊息繼續傳遞，直到- (id)forwardingTargetForSelector:(SEL)aSelector，然後我在裡面建立了一個SecondViewController的物件，並且判斷如果有這個方法，就返回SecondViewController的物件。這個函式就是訊息的轉發，在這兒我們成功的把訊息傳給了SecondViewController，然後讓它來執行，所以就執行了那個方法。同時，也相當於完成了一個多繼承！
三、最後一點
當然，還有好幾個函式，在上面那張圖裡面已經清晰的表達了，有興趣的可以自己試試，看看訊息的傳遞順序到底是怎麼樣的。上面提到的這些只是runtime的冰山一角，runtime黑魔法的強大遠不止於此，比如方法的調配（Method Swizzling）等，在專案實戰中還是很有用的，後面有時間會再介紹.
參考