BlueDolphin BlueDolphin - 2 months ago 15
Objective-C Question

Creating a selector from a method name with parameters

I have a code sample that gets a

from the current object,

SEL callback = @selector(mymethod:parameter2);

And I have a method like

-(void)mymethod:(id)v1 parameter2;(NSString*)v2 {

Now I need to move
to another object, say

I have tried:

SEL callback = @selector(myDelegate, mymethod:parameter2);

but it won't compile.


SEL is a type that represents a selector in Objective-C. The @selector() keyword returns a SEL that you describe. It's not a function pointer and you can't pass it any objects or references of any kind. For each variable in the selector (method), you have to represent that in the call to @selector. For example:

SEL noParameterSelector = @selector(methodWithNoParameters);

SEL oneParameterSelector = @selector(methodWithOneParameter:); // notice the colon here

-(void)methodWIthTwoParameters:(id)parameterOne and:(id)parameterTwo;
SEL twoParameterSelector = @selector(methodWithTwoParameters:and:); // notice the parameter names are omitted

Selectors are generally passed to delegate methods and to callbacks to specify which method should be called on a specific object during a callback. For instance, when you create a timer, the callback method is specifically defined as:


So when you schedule the timer you would use @selector to specify which method on your object will actually be responsible for the callback:

@implementation MyObject

    // do some computations
    if( timerShouldEnd ) {
      [timer invalidate];


// ...

int main(int argc, const char **argv)
    // do setup stuff
    MyObject* obj = [[MyObject alloc] init];
    SEL mySelector = @selector(myTimerCallback:);
    [NSTimer scheduledTimerWithTimeInterval:30.0 target:obj selector:mySelector userInfo:nil repeats:YES];
    // do some tear-down
    return 0;

In this case you are specifying that the object obj be messaged with myTimerCallback every 30 seconds.