Since the methods are instance methods, I don't know what I am talking
about.
I did not intend to imply that you don't know what you are talking
about. I am looking forward to your guidance in the future.
DanH wrote:
"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<s...@samhobbs.org> 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<s...@samhobbs.org> 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
--
Sam Hobbs
Los Angeles, CA
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