pass parameters when calling function in objective c

Question

I am in the early stages exposed to Objective-c. I have a question is, with one function call like this, the parameters will be passed on like.

time_call = [[NSDate date] timeIntervalSince1970];
[Services get_time:self :@selector(callBackTime:)];

This is the function called

-(void) callBackTime:(NSString *)result 
{
    NSLog(@"result: %@", result);
}

I don't understand result parameter passed to the function type as in the other what was called

I apologize for not stating explicitly question. But here is the original function in Class Service

+(void) get_time:(id)delegate :(SEL)selector
{
    NSLog(@"get time call"); 
}

Here [Services get_time:self :@selector(callBackTime:)]; you are calling the get_time method. Show the code written inside the get_time method. — Midhun MP
– Midhun MP, Commented Jan 15, 2014 at 6:53
I know that the function callBackTime is called. But I don't understand result parameter passed to the function type as in the other what was called — bachle26
– bachle26, Commented Jan 15, 2014 at 6:55

CRD · Accepted Answer · 2014-01-15 09:07:26Z

1

It is unclear what you are not understanding, I suspect English is not your first language - which is OK! Here is a guess in the hope it helps.

Your original get_time:: method in Services does not use its arguments, and as such will never call callBackTime:, so maybe this is why you say you "don't understand result parameter" - without a call no value is obviously passed for this parameter.

Consider this alternate definition of get_time::

+(void) get_time:(id)delegate :(SEL)selector
{
    [delegate performSelector:selector withObject:[NSDate date]]; 
}

Now the method uses its two parameters to invoke the passed method (selector) on the passed object (delegate) - the method requires one parameter and this is supplied ([NSDate date] - the current date & time, picked as your method is called get_time).

If you run this your callBackTime: method should NSLog() the current date.

Hopefully that helps you understand where result comes from - get_time needs to supply it.

HTH

Addendum

I missed that callBackTime: is declared to accept an NSString * and my example passes an NSDate *. The code will work due to Objective-C's lose typing, but to be correct either callBackTime: should take an id or my sample should pass an NSString, e.g. [[NSDate date] description] would do.

edited Jan 15, 2014 at 9:07

answered Jan 15, 2014 at 7:30

CRD

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2 Comments

bachle26 Over a year ago

sorry for my question was not clear. My english is not good, but google translate does not seem very efficient. I mean, I do not understand when callBackTime function is called, then the parameters passed to its NSString what type. I do not see it being passed on.

CRD Over a year ago

In your original code the callBackTime: method was never called, the selector for the method was passed to get_time:: - passing a selector does not call the method. In my example the method is called and passed a value for its result parameter. callBackTime: "passes on" the value of its parameter to NSLog(), it doesn't pass it on to anything else. Does that help?

KudoCC · Accepted Answer · 2014-01-15 07:12:09Z

1

When you want to send a method to an object. You need two object , one is the object(receiver) the other is selector which describe what the message is. Maybe you need parameters if the selector has.

Here :

time_call = [[NSDate date] timeIntervalSince1970];
[Services get_time:self :@selector(callBackTime:)];

+(void) get_time:(id)delegate :(SEL)selector {
    NSLog(@"get time call"); 
}

delegate is the self(receiver) and selector is @selector(callBackTime:). So in get_time it can send message to delegate like this:

[delegate performSelector:selector withObject:result] ;

answered Jan 15, 2014 at 7:12

KudoCC

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Comments

Joshua · Accepted Answer · 2014-01-15 07:12:09Z

1

If your asking how to pass an object from the class Services maybe you can try something like this:

-(void)callBackTime:(NSString *)result{
    NSLog(@">> %@",result);
}

+(void) get_time:(id)delegate :(SEL)selector {
    if([delegate respondsToSelector:selector]){
        //pass the object here using the selector you have
        [delegate performSelector:selector withObject:@"theObject"];
    }
}

answered Jan 15, 2014 at 7:12

Joshua

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Comments

Bug · Accepted Answer · 2014-01-15 06:56:46Z

0

Here you can pass perameter like that

This is what you are doing

 [Services get_time:self :@selector(callBackTime:)];

This is what you have to do for passing parameter

    [Services get_time:self :@selector(callBackTime:yourResultString)];

answered Jan 15, 2014 at 6:56

Bug

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