Creating a selector from a method name with parameters

Question

I have a code sample that gets a SEL 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 mymethod to another object  say myDelegate   I have tried   SEL callback    selector myDelegate  mymethod parameter2     but it won t compile

User · Answer

Beyond what s been said already about selectors  you may want to look at the NSInvocation class   An NSInvocation is an Objective-C message rendered static  that is  it is an action turned into an object  NSInvocation objects are used to store and forward messages between objects and between applications  primarily by NSTimer objects and the distributed objects system  An NSInvocation object contains all the elements of an Objective-C message  a target  a selector  arguments  and the return value  Each of these elements can be set directly  and the return value is set automatically when the NSInvocation object is dispatched   Keep in mind that while it s useful in certain situations  you don t use NSInvocation in a normal day of coding  If you re just trying to get two objects to talk to each other  consider defining an informal or formal delegate protocol  or passing a selector and target object as has already been mentioned

User · Answer

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   - void methodWithNoParameters  SEL noParameterSelector    selector methodWithNoParameters    - void methodWithOneParameter  id parameter  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   - void someMethod  NSTimer  timer    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  - void myTimerCallback  NSTimer  timer          do some computations     if  timerShouldEnd            timer invalidate             end          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

User · Answer

You can t pass a parameter in a  selector     It looks like you re trying to implement a callback   The best way to do that would be something like this    object setCallbackObject self withSelector  selector myMethod       Then in your object s setCallbackObject withSelector  method  you can call your callback method   - void setCallbackObject  id anObject withSelector  SEL selector        anObject performSelector selector

User · Answer

You can t pass a parameter in a  selector     It looks like you re trying to implement a callback   The best way to do that would be something like this    object setCallbackObject self withSelector  selector myMethod       Then in your object s setCallbackObject withSelector  method  you can call your callback method   - void setCallbackObject  id anObject withSelector  SEL selector        anObject performSelector selector

User · Answer

Beyond what s been said already about selectors  you may want to look at the NSInvocation class   An NSInvocation is an Objective-C message rendered static  that is  it is an action turned into an object  NSInvocation objects are used to store and forward messages between objects and between applications  primarily by NSTimer objects and the distributed objects system  An NSInvocation object contains all the elements of an Objective-C message  a target  a selector  arguments  and the return value  Each of these elements can be set directly  and the return value is set automatically when the NSInvocation object is dispatched   Keep in mind that while it s useful in certain situations  you don t use NSInvocation in a normal day of coding  If you re just trying to get two objects to talk to each other  consider defining an informal or formal delegate protocol  or passing a selector and target object as has already been mentioned

User · Answer

You can t pass a parameter in a  selector     It looks like you re trying to implement a callback   The best way to do that would be something like this    object setCallbackObject self withSelector  selector myMethod       Then in your object s setCallbackObject withSelector  method  you can call your callback method   - void setCallbackObject  id anObject withSelector  SEL selector        anObject performSelector selector

User · Answer

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   - void methodWithNoParameters  SEL noParameterSelector    selector methodWithNoParameters    - void methodWithOneParameter  id parameter  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   - void someMethod  NSTimer  timer    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  - void myTimerCallback  NSTimer  timer          do some computations     if  timerShouldEnd            timer invalidate             end          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

User · Answer

Beyond what s been said already about selectors  you may want to look at the NSInvocation class   An NSInvocation is an Objective-C message rendered static  that is  it is an action turned into an object  NSInvocation objects are used to store and forward messages between objects and between applications  primarily by NSTimer objects and the distributed objects system  An NSInvocation object contains all the elements of an Objective-C message  a target  a selector  arguments  and the return value  Each of these elements can be set directly  and the return value is set automatically when the NSInvocation object is dispatched   Keep in mind that while it s useful in certain situations  you don t use NSInvocation in a normal day of coding  If you re just trying to get two objects to talk to each other  consider defining an informal or formal delegate protocol  or passing a selector and target object as has already been mentioned

User · Answer

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   - void methodWithNoParameters  SEL noParameterSelector    selector methodWithNoParameters    - void methodWithOneParameter  id parameter  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   - void someMethod  NSTimer  timer    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  - void myTimerCallback  NSTimer  timer          do some computations     if  timerShouldEnd            timer invalidate             end          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

User · Answer

Beyond what s been said already about selectors  you may want to look at the NSInvocation class   An NSInvocation is an Objective-C message rendered static  that is  it is an action turned into an object  NSInvocation objects are used to store and forward messages between objects and between applications  primarily by NSTimer objects and the distributed objects system  An NSInvocation object contains all the elements of an Objective-C message  a target  a selector  arguments  and the return value  Each of these elements can be set directly  and the return value is set automatically when the NSInvocation object is dispatched   Keep in mind that while it s useful in certain situations  you don t use NSInvocation in a normal day of coding  If you re just trying to get two objects to talk to each other  consider defining an informal or formal delegate protocol  or passing a selector and target object as has already been mentioned

User · Answer

You can t pass a parameter in a  selector     It looks like you re trying to implement a callback   The best way to do that would be something like this    object setCallbackObject self withSelector  selector myMethod       Then in your object s setCallbackObject withSelector  method  you can call your callback method   - void setCallbackObject  id anObject withSelector  SEL selector        anObject performSelector selector

User · Answer

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   - void methodWithNoParameters  SEL noParameterSelector    selector methodWithNoParameters    - void methodWithOneParameter  id parameter  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   - void someMethod  NSTimer  timer    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  - void myTimerCallback  NSTimer  timer          do some computations     if  timerShouldEnd            timer invalidate             end          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

[objective-c] Creating a selector from a method name with parameters

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