How to use performSelector withObject afterDelay with primitive types in Cocoa

Question

The NSObject method performSelector withObject afterDelay  allows me to invoke a method on the object with an object argument after a certain time  It cannot be used for methods with a non-object argument  e g  ints  floats  structs  non-object pointers  etc     What is the simplest way to achieve the same thing with a method with a non-object argument  I know that for regular performSelector withObject   the solution is to use NSInvocation  which by the way is really complicated   But I don t know how to handle the  delay  part   Thanks

User · Answer

I find that the quickest  but somewhat dirty  way to do this is by invoking objc msgSend directly  However  it s dangerous to invoke it directly because you need to read the documentation and make sure that you re using the correct variant for the type of return value and because objc msgSend is defined as vararg for compiler convenience but is actually implemented as fast assembly glue  Here s some code used to call a delegate method - delegate integerDidChange   that takes a single integer argument    import  lt objc message h gt    SEL theSelector    selector integerDidChange    if   self delegate respondsToSelector theSelector         typedef void   IntegerDidChangeFuncPtrType  id  SEL  NSInteger       IntegerDidChangeFuncPtrType MyFunction    IntegerDidChangeFuncPtrType objc msgSend      MyFunction self delegate  theSelector  theIntegerThatChanged       This first saves the selector since we re going to refer to it multiple times and it would be easy to create a typo  It then verifies that the delegate actually responds to the selector - it might be an optional protocol  It then creates a function pointer type that specifies the actual signature of the selector  Keep in mind that all Objective-C messages have two hidden first arguments  the object being messaged and the selector being sent  Then we create a function pointer of the appropriate type and set it to point to the underlying objc msgSend function  Keep in mind that if the return value is a float or struct  you need to use a different variant of objc msgSend  Finally  send the message using the same machinery that Objective-C uses under the sheets

User · Answer

You Could just use NSTimer to call a selector    NSTimer timerWithTimeInterval 1 0 target self selector  selector yourMethod   userInfo nil repeats NO

User · Answer

PerformSelector WithObject always takes an object  so in order to pass arguments like int double float etc      You can use something like this     NSNumber is an object         self performSelector  selector setUserAlphaNumber   withObject   NSNumber numberWithFloat  1 0f      afterDelay 1 5        - void  setUserAlphaNumber   NSNumber   number         txtUsername setAlpha   number floatValue             Same way you can use  NSNumber numberWithInt   etc     and in the receiving method you can convert the number into your format as  number int  or  number double

User · Answer

Blocks are the way to go  You can have complex parameters  type safety  and it s a lot simpler and safer than most of the old answers here  For example  you could just write    MONBlock performBlock    obj setFrame SOMETHING    afterDelay 2     Blocks allow you to capture arbitrary parameter lists  reference objects and variables   Backing Implementation  basic     interface MONBlock   NSObject     void performBlock  void      pBlock afterDelay  NSTimeInterval pDelay    end   implementation MONBlock     void imp performBlock  void      pBlock    pBlock          void performBlock  void      pBlock afterDelay  NSTimeInterval pDelay      self performSelector  selector imp performBlock                withObject  pBlock copy               afterDelay pDelay       end   Example   int main int argc  const char   argv        autoreleasepool       block bool didPrint   false    int pi   3     close enough  p     MONBlock performBlock   NSLog   Hello  World  pi is  i   pi   didPrint   true   afterDelay 2      while   didPrint        NSRunLoop currentRunLoop runUntilDate  NSDate dateWithTimeInterval 0 1 sinceDate NSDate date           NSLog    Bye  World          return 0      Also see Michael s answer   1  for another example

User · Answer

I would always recomend that you use NSMutableArray as the object to pass on  This is because you can then pass several objects  like the button pressed and other values  NSNumber  NSInteger and NSString are just containers of some value  Make sure that when you get the object from the array that you refer to to a correct container type  You need to pass on NS containers  There you may test the value  Remember that containers use isEqual when values are compared    define DELAY TIME 5  - void changePlayerGameOnes  UIButton  sender      NSNumber  nextPlayer    NSNumber numberWithInt  gdata currentPlayer intValue  1        NSMutableArray  array     NSMutableArray alloc initWithObjects sender  nil        array addObject nextPlayer        self performSelector  selector next   withObject array afterDelay DELAY TIME     - void next  NSMutableArray  nextPlayer      if gdata    nil     if game choose next player         self nextPlayer  nextPlayer objectAtIndex 1  button  nextPlayer objectAtIndex 0

User · Answer

Pehaps   ok  very likely  I m missing something  but why not just create an object type  say NSNumber  as a container to your non-object type variable  such as CGFloat   CGFloat myFloat   2 0   NSNumber  myNumber    NSNumber numberWithFloat myFloat     self performSelector  selector MyCalculatorMethod   withObject myNumber afterDelay 5 0

User · Answer

DO NOT USE THIS ANSWER  I HAVE ONLY LEFT IT FOR HISTORICAL PURPOSES  SEE THE COMMENTS BELOW   There is a simple trick if it is a BOOL parameter   Pass nil for NO and self for YES  nil is cast to the BOOL value of NO  self is cast to the BOOL value of YES   This approach breaks down if it is anything other than a BOOL parameter   Assuming self is a UIView     nil will be cast to NO when the selector is performed  self performSelector  selector setHidden   withObject nil afterDelay 5 0      self will be cast to YES when the selector is performed  self performSelector  selector setHidden   withObject self afterDelay 10 0

User · Answer

Here is what I used to call something I couldn t change using NSInvocation   SEL theSelector   NSSelectorFromString   setOrientation animated     NSInvocation  anInvocation    NSInvocation             invocationWithMethodSignature               MPMoviePlayerController instanceMethodSignatureForSelector theSelector      anInvocation setSelector theSelector    anInvocation setTarget theMovie   UIInterfaceOrientation val   UIInterfaceOrientationPortrait  BOOL anim   NO   anInvocation setArgument  amp val atIndex 2    anInvocation setArgument  amp anim atIndex 3     anInvocation performSelector  selector invoke  withObject nil afterDelay 1

User · Answer

Calling performSelector with an NSNumber or other NSValue will not work  Instead of using the value of the NSValue NSNumber  it will effectively cast the pointer to an int  float  or whatever and use that   But the solution is simple and obvious  Create the NSInvocation and call   invocation performSelector  selector invoke  withObject nil afterDelay delay

User · Answer

I know this is an old question but if you are building iOS SDK 4  then you can use blocks to do this with very little effort and make it more readable   double delayInSeconds   2 0  int primitiveValue   500  dispatch time t popTime   dispatch time DISPATCH TIME NOW   int64 t  delayInSeconds   NSEC PER SEC    dispatch after popTime  dispatch get main queue      void        self doSomethingWithPrimitive primitiveValue

User · Answer

Just wrap the float  boolean  int or similar in an NSNumber   For structs  I don t know of a handy solution  but you could make a separate ObjC class that owns such a struct

User · Answer

I also wanted to do this  but with a method that receives a BOOL parameter  Wrapping the bool value with NSNumber  FAILED TO PASS THE VALUE  I have no idea why   So I ended up doing a simple hack  I put the required parameter in another dummy function and call that function using the performSelector  where withObject   nil    self performSelector  selector dummyCaller   withObject nil afterDelay 5 0    - void dummyCaller     self myFunction YES

User · Answer

Perhaps NSValue  just make sure your pointers are still valid after the delay  ie  no objects allocated on stack

[objective-c] How to use performSelector:withObject:afterDelay: with primitive types in Cocoa?

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