Objective-C Calling selectors with multiple arguments

Question

In MyClass m  I ve defined  -  void  myTest   NSString    withAString      NSLog   hi       withAString       and the appropriate declaration in MyClass h   Later I want to call   self performSelector  selector mytest withAString   withObject  mystring     in MyClass m but I get an error similar to   Terminating app due to uncaught exception  NSInvalidArgumentException   reason     - MyClass myTest withAtring    unrecognized selector sent to instance 0xe421f0   I tried a simpler case with a selector that took no arguments that printed a string to console and that worked just fine  What s wrong with the code and how can I fix it  Thanks

User · Answer

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Think the class should be defined as   -  void  myTestWithSomeString  NSString    astring      NSLog   hi   s   astring       You only have a single parameter so you should only have a single    You might want to consider using    in your NSLog also  - it is just a good habit to get into - will then write out any object - not just strings

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Your method signature is   -  void  myTest  NSString      withAString happens to be the parameter  the name is misleading  it looks like it is part of the selector s signature    If you call the function in this manner    self performSelector  selector myTest   withObject myString     It will work   But  as the other posters have suggested  you may want to rename the method   -  void myTestWithAString  NSString  aString    And call    self performSelector  selector myTestWithAString   withObject myString

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Shane Arney  performSelector withObject withObject    You might also want to mention that this method is only for passing maximum 2 arguments  and it cannot be delayed   such as performSelector withObject afterDelay     kinda weird that apple only supports 2 objects to be send and didnt make it more generic

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Your code has two problems  One was identified and answered  but the other wasn t  The first was that your selector was missing the name of its parameter  However  even when you fix that  the line will still raise an exception  assuming your revised method signature still includes more than one argument   Let s say your revised method is declared as   - void myTestWithString  NSString   sourceString comparedTo  NSString   testString     Creating selectors for methods that take multiple arguments is perfectly valid  e g   selector myTestWithString comparedTo       However  the performSelector method only allows you to pass one value to myTest  which unfortunately has more than one parameter   It will error out and tell you that you didn t supply enough values   You could always redefine your method to take a collection as it s only parameter   - void myTestWithObjects  NSDictionary   testObjects     However  there is a more elegant solution  that doesn t require refactoring   The answer is to use NSInvocation  along with its setArgument atIndex  and invoke methods   I ve written up an article  including a code example  if you want more details  The focus is on threading  but the basics still apply   Good luck

User · Answer

Your method signature makes no sense  are you sure it isn t a typo  I m not clear how it s even compiling  though perhaps you re getting warnings that you re ignoring   How many parameters do you expect this method to take

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In Objective-C  a selector s signature consists of    The name of the method  in this case it would be  myTest    required  A      colon  following the method name if the method has an input  A name and     for every additional input    Selectors have no knowledge of    The input types The method s return type    Here s a class implementation where performMethodsViaSelectors method performs the other class methods by way of selectors    implementation ClassForSelectors -  void  fooNoInputs       NSLog   Does nothing      -  void  fooOneIput  NSString   first       NSLog   Logs      first     -  void  fooFirstInput  NSString   first secondInput  NSString   second       NSLog   Logs    then      first  second     -  void  performMethodsViaSelectors        self performSelector  selector fooNoInputs         self performSelector  selector fooOneInput   withObject   first         self performSelector  selector fooFirstInput secondInput   withObject   first  withObject   second       end   The method you want to create a selector for has a single input  so you would create a selector for it like so   SEL myTestSelector    selector myTest

[objective-c] Objective-C: Calling selectors with multiple arguments

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