Arguments in @selector

Question

Is there any way that I can pass arguments in selector?

example: I have this method

- (void)myMethod:(NSString*)value1 setValue2:(NSString*)value2{  } 

and I need to call this function through a selector passing two arguments.

[NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(/*my method*/) userInfo:nil repeats:YES]; 

How can I do this?

Answer 1

You could use the NSTimer method:

+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds                                  invocation:(NSInvocation *)invocation                                     repeats:(BOOL)repeats; 

Instead, since an NSInvocation object will allow you to pass arguments; an NSInvocation object is, as the docs define it:

an Objective-C message rendered static, that is, it is an action turned into an object.

Whilst creating an NSTimer object using a selector requires the format of the method being:

- (void)timerFireMethod:(NSTimer*)theTimer 

An NSInvocation allows you to set the target, the selector, and the arguments that you pass in:

SEL selector = @selector(myMethod:setValue2:);  NSMethodSignature *signature = [MyObject instanceMethodSignatureForSelector:selector]; NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature]; [invocation setSelector:selector];  NSString *str1 = @"someString"; NSString *str2 = @"someOtherString";  //The invocation object must retain its arguments [str1 retain]; [str2 retain];  //Set the arguments [invocation setTarget:targetInstance]; [invocation setArgument:&str1 atIndex:2]; [invocation setArgument:&str2 atIndex:3];  [NSTimer scheduledTimerWithTimeInterval:0.1 invocation:invocation repeats:YES]; 

Where MyObject is the class that myMethod:setValue2: is declared and implemented on – instanceMethodSignatureForSelector: is a convenience function declared on NSObject which returns an NSMethodSignature object for you, to be passed to NSInvocation.

Also, to note, with setArgument:atIndex:, the indices for arguments to be passed to the method set as the selector start at index 2. From the docs:

Indices 0 and 1 indicate the hidden arguments self and _cmd, respectively; you should set these values directly with the setTarget: and setSelector: methods. Use indices 2 and greater for the arguments normally passed in a message.

Answer 2

For scheduledTimerWithTimeInterval:, the selector you pass can only have one argument. Further, its one argument must be an NSTimer * object. In other words, the selector must take the following form:

- (void)timerFireMethod:(NSTimer*)theTimer 

What you could do is store the arguments in the userInfo dictionary and call the selector you want from the timer callback:

- (void)startMyTimer {     /* ... Some stuff ... */     [NSTimer scheduledTimerWithTimeInterval:0.1                                       target:self                                     selector:@selector(callMyMethod:)                                     userInfo:[NSDictionary dictionaryWithObjectsAndKeys:someValue,                         @"value1", someOtherValue, @"value2", nil]                                      repeats:YES]; }  - (void)callMyMethod:(NSTimer *)theTimer {     NSString *value1 = [[theTimer userInfo] objectForKey:@"value1"];     NSString *value2 = [[theTimer userInfo] objectForKey:@"value2"];     [self myMethod:value1 setValue2:value2]; }