SEL performSelector和arguments

Question

看起来应该有一种简单的方法来调用带有一些参数的选择器,只要你拥有一个SEL对象.我似乎找不到正确的语法.

-(MyClass*) init: (SEL)sel owner:(NSObject*) parent
{
   int i =10;
   [parent performSelector:sel:i  ];
}

Answer 1

看一下NSObject文档.在这种情况下:

[parent performSelector:sel withObject:[NSNumber numberWithInt:i]];

(注意此方法实际上列在NSObject协议文档中).由于-[NSObject performSelector:withObject:]需要一个object参数,你必须在父类的类中编写一个包装器

-(void)myMethodForNumber:(NSNumber*)number {
    [self myMethod:[number intValue]];
}

取消装箱NSNumber.

如果您确实想要调用直接接受非对象参数的方法(例如,您无法控制被调用者源并且不想添加类别),则可以使用NSInvocation:

NSInvocation *inv = [NSInvocation invocationWithMethodSignature:[parent methodSignatureForSelector:sel]];
[inv setSelector:sel];
[inv setTarget:parent];
[inv setArgument:&i atIndex:2]; //arguments 0 and 1 are self and _cmd respectively, automatically set by NSInvocation
[inv invoke];

另外,您的方法看起来像一个init方法,但不遵循Objective-C的正确初始化模式.您需要调用超类初始值设定项,并且需要测试nil该调用的结果,并且必须从初始化方法返回self.在所有情况下,Objective-C初始化方法应如下所示:

-(id)myInitMethod {
    self = [super init];
    if(self != nil) {
      //perform initialization of self
    }

    return self;
}

您的方法(如果它是一个init方法)将如下所示:

-(id) init: (SEL)sel owner:(NSObject*) parent
{
   self = [super init];
   if(self != nil) {
       int i = 10;
       NSInvocation *inv = [NSInvocation invocationWithMethodSignature:[parent methodSignatureForSelector:sel]];
       [inv setSelector:sel];
       [inv setTarget:parent];
       [inv setArgument:&i atIndex:2]; //arguments 0 and 1 are self and _cmd respectively, automatically set by NSInvocation
       [inv invoke];
   }

    return self;
}

为了更具风格的Objective-C,我也会重命名初始化器-(id)initWithSelector:owner:.

Answer 2

Barry Wark说的很棒..我刚刚修改了懒惰程序员的讨论

-(void)myMethodWith:(int)number andBOOL:(BOOL) someBool andStr:(NSString *)str{
    NSLog(@"%d %d %@",number,someBool,str);
}

-(void) testMethod{
    SEL sel = @selector(myMethodWith:andBOOL:andStr:);
    int i = 10;
    BOOL bol = YES;
    NSString *str = @"hey baby !";
    NSInvocation *inv = [NSInvocation invocationWithMethodSignature:[self methodSignatureForSelector:sel]];
    [inv setSelector:sel];
    [inv setTarget:self];
    [inv setArgument:&i atIndex:2]; //arguments 0 and 1 are self and _cmd respectively, automatically set by NSInvocation
    [inv setArgument:&bol atIndex:3];
    [inv setArgument:&str atIndex:4];
    [inv invoke];
}