"I apologize that I don't know what the Java term is that corresponds with the C++ term static"
The Java term is "static". Both setOnClickListener and the listener's method onClick are instance methods, not static ones. The argument to setOnClickListener is the reference of (pointer to) the object instance that implements onClick. In some cases it's convenient for that to be the current class, but in other cases not. "this" has no special significance in the setOnClickListener invocation -- no different from any other reference that might be supplied. It simply refers to the current instance in cases where that's the way the programmer wants to do it. I've been programming in C++ for 14 years. Was the lead designer/ developer for the Java implementation in IBM iSeries (which was written in C++). I kinda know both languages pretty well. On Jul 18, 7:51 pm, Sam Hobbs <[email protected]> wrote: > Except the original question is about "this" and why it works to use it > as an argument. My comments explain why the this is missing when an > event handler is called. > > I apologize that I don't know what the Java term is that corresponds > with the C++ term static, but in C++ the this pointer is the only > difference between a static and a non-static function. Providing the > this pointer in C++ as an argument for a static function allows the > event handler to do everything that a non-static function does except > the static function must use the this pointer to qualify references to > the class. > > Perhaps I misunderstand what you are saying; are you saying that it is > possible to pass something else in the argument other than the this > reference? If so then that is not inconsistent with what I said or meant > to say, but the question was about the this reference. > > > > DanH wrote: > > Well, that's not exactly it. The pointer is needed in > > setOnClickListener to distinguish that specific instance of the > > listener class from the thousand other possible instances in the > > machine. You'll find the analogous pointer in C++ based systems, eg. > > > And note that it need not be "this". One might very well do: > > > MyListenerClass listener = new MyListenerClass(<some args>); > > someWidget.setOnClickListener(listener); > > > On Jul 18, 4:53 pm, Sam Hobbs<[email protected]> wrote: > >> I am new to Java, but since Justin says that the this reference is > >> essentially the same as in C++ and C# I hope my comments are helpful. > > >> I think one point that was not made clear is that the operating system > >> (Android, Linux or whatever) is not written in Java but if it was > >> written in Java it would need to call event handlers in a manner that is > >> independent of the language. So when Android calls the > >> setOnClickListener event handler, it does not have a this reference and > >> could not call the event handler with this even if it knew what this is. > >> So it is quite common to pass the this as an argument so the event > >> handler can access the other members of it's class. > > >> Keith Roberts wrote: > >>> Hey all, > > >>> I know that the keyword "this" refers to an instance variable or can > >>> invoke a constructor, but I don't understand how passing "this" as the > >>> arg for setOnClickListener () works?Could someone explain? > > >>> Thanks, > > >>> keith > > >> -- > >> Sam Hobbs > >> Los Angeles, CA > > -- > Sam Hobbs > Los Angeles, CA -- You received this message because you are subscribed to the Google Groups "Android Beginners" group. NEW! Try asking and tagging your question on Stack Overflow at http://stackoverflow.com/questions/tagged/android To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-beginners?hl=en
