[消息传递之二]－NSMethodSignature练习

墨蓝 2022-08-19 05:53 175阅读 0赞

#import <Foundation/Foundation.h>
    
    @interface MyInvoc : NSObject
    {
         NSString* _name;
    }
    
    -(NSInteger) myLen:(NSString*) aStr;
    
    -(NSMethodSignature*) methodSignatureForSelector:(SEL)aSelector;
    -(void)forwardInvocation:(NSInvocation *)anInvocation;
    @end

#import "MyInvoc.h"
    
    @implementation MyInvoc
    {
        NSMutableDictionary* _dic;
    }
    
    -(id)init
    {
        if (self = [super init]) {
            _name = [[NSString alloc] init];
            _name = @"hello";
            _dic  = [[NSMutableDictionary alloc] init];
        }
        return self;
    }
    
    -(NSInteger) myLen:(NSString *)aStr
    {
        return [aStr length];
    }
    
    -(NSMethodSignature*) methodSignatureForSelector:(SEL)aSelector
    {
        NSMethodSignature* Msignature =[super methodSignatureForSelector:aSelector];
        if (!Msignature) {
            NSString* MethodName = NSStringFromSelector(aSelector);
            if ([MethodName rangeOfString:@"set"].location == 0) {
                Msignature = [NSMethodSignature signatureWithObjCTypes:"v@:@"];
                //v@:@ v:返回值类型void;@ id类型,执行sel的对象;：SEL;@参数
            }
            else
            {
                if ([MethodName compare:@"length"] == NSOrderedSame) {
                     Msignature = [_name methodSignatureForSelector:aSelector];
                }
                else{
                    Msignature =[NSMethodSignature signatureWithObjCTypes:"@@:"];
                //@:返回值类型id;@id类型,执行sel的对象;：SEL;
                }
            }
        }
        return Msignature;
    }
    
    -(void)forwardInvocation:(NSInvocation *)anInvocation
    {
        NSString* MethodName = NSStringFromSelector([anInvocation selector]);
        if ([MethodName rangeOfString:@"set"].location == 0) {
            NSString* key = [[MethodName substringWithRange:NSMakeRange(3, [MethodName length] - 4)] lowercaseString];
            id obj;
            [anInvocation getArgument:&obj atIndex:2];
            [_dic setObject:obj forKey:key];
        }
        else{
           if ([MethodName compare:@"length"] == NSOrderedSame) {
               [anInvocation invokeWithTarget:_name];
           }
            else
           {
               id obj = [_dic objectForKey:MethodName];
               [anInvocation setReturnValue:&obj];
           }
        }
    }
    
    @end

#import "ViewController.h"
    #import "MyInvoc.h"
    
    @interface ViewController ()
    
    @end
    
    @implementation ViewController
    
    - (void)viewDidLoad {
        [super viewDidLoad];
        id m = [[MyInvoc alloc] init];
        //注意点1:执行的方法最好能找到，利用sel声明变量虽然也能用，但有警告。
        [m setName: @"hello"];
        NSLog(@"name is %@, length is %ld",[m name], [m length]);
    }
    
    - (void)didReceiveMemoryWarning {
        [super didReceiveMemoryWarning];
        // Dispose of any resources that can be recreated.
    }
    
    @end

总结

1，sel与nsstring的转换系统提供了两个函数，特别方便。nsstringfromselector,nsselectorfromstring;

2，调用没有找到的函数时才会进入获取签名函数。

3，\[aninvocation invokeWithTarget:\_name\],这里的taget是能够执行这个签名的函数的对象。