Python for Bioinformatics: respondsToSelector

Monday, July 28, 2008

respondsToSelector

On p. 108, Hillegass mentions the respondToSelector method in NSObject. He says that an object calls this method on its delegate before sending it a message. Here is a simple illustration (no delegate yet). We don't do anything in the nib for this one. We just get an instance of MyReceiver, and through go_(), we ask whether it responds to the selector for a method. Here is the code:

class PyInvokeAppDelegate(NSObject):
    def awakeFromNib(self):
        self.myReceiver = MyReceiver.alloc().init()
        self.go_(self)
    
    def go_(self,sender):
        NSLog("go_ %s" % sender.description())
        flag = self.myReceiver.respondsToSelector_(
            "absentMethod:")
        NSLog("go_ returning %s" % flag)
        
class MyReceiver(NSObject):
    def respondsToSelector_(self, s):
        NSLog("Receiver respondsToSelector_ %s" % s)
        super(MyReceiver,self).respondsToSelector_(s)

and the (edited) console log:

go_ < PyInvokeAppDelegate: 0x1f1dd80>
Receiver respondsToSelector_ absentMethod:
go_ returning None