EventHandling problem : Java has solution but what about Microsoft???

[Herfried K. Wagner [MVP]]

I have added few of the events in some control, example code is:
btnControl.GotFocus +=new EventHandler(EventHandlingMethod);
btnControl.Click +=new EventHandler(EventHandlingMethod);
lblControl.Click +=new EventHandler(EventHandlingMethod);

private void EventHandlingMethod(object sender, EventArgs e)
{
.......
}

btnControl = Button object, lblControl = Lable object

Now the problem is: I am adding the same event handler method in all events
for btnControl and lblControl too.

now in EventHandlingMethod method, i can find which control is using sender
but now if i want to put some switch cases in the method for Event Name then
I have no any such information in the eventargs or anyother way....
=======

I am curious which sense handling different events of different controls in
the same event handler would make. Instead, add separate event handlers for
all event types, not just delegate types. This means separate handlers for
controls' 'Click' and 'GotFocus' events.

 

[Larry Lard]

(some newsgroups trimmed - this really wasn't appropriate for all the
listed groups)

Hi,
I have added few of the events in some control, example code is:
btnControl.GotFocus +=new EventHandler(EventHandlingMethod);
btnControl.Click +=new EventHandler(EventHandlingMethod);
lblControl.Click +=new EventHandler(EventHandlingMethod);

private void EventHandlingMethod(object sender, EventArgs e)
{
.......
}

btnControl = Button object, lblControl = Lable object

Now the problem is: I am adding the same event handler method in all events for btnControl and lblControl too.

now in EventHandlingMethod method, i can find which control is using sender but now if i want to put some switch cases in the method for Event Name then I have no any such information in the eventargs or anyother way....

Can someone help/guide me to get the event name?

Is it possible? if yes then how? If no, then any work around?

Your design is bad. Methods should do one thing. If you actually want
the same thing to happen on GotFocus and on Click, fine. If you want
*different* things to happen, use *different* procedures. If there is
some common and some different functionality, put the common
functionality in a separate procedure called from both event handlers.

You shouldn't treat event handlers like a substitute for a Windows
message loop, that has to handle everything that can possible happen.
The GotFocus event handler should do what is required on GotFocus; the
Click event handler should do what is required on Click; and so on.

 

[Marina]

If you need to do different things depending on the event, why not have different event handlers? You can place common code into a method that both event handlers can call.

I understand what you are saying, but it just doesn't seem like a big deal. It is very easy to work around, and most of the time it is not even an issue because you either need different code in the handler anyway, or the events have different signatures, etc.
Hi,
I have added few of the events in some control, example code is:
btnControl.GotFocus +=new EventHandler(EventHandlingMethod);
btnControl.Click +=new EventHandler(EventHandlingMethod);
lblControl.Click +=new EventHandler(EventHandlingMethod);

private void EventHandlingMethod(object sender, EventArgs e)
{
.......
}

btnControl = Button object, lblControl = Lable object

Now the problem is: I am adding the same event handler method in all events for btnControl and lblControl too.

now in EventHandlingMethod method, i can find which control is using sender but now if i want to put some switch cases in the method for Event Name then I have no any such information in the eventargs or anyother way....

Can someone help/guide me to get the event name?

Is it possible? if yes then how? If no, then any work around?

Thanks in Advance

Regards,
Mahesh Devjibhai Dhola

 

[Mahesh Devjibhai Dhola [MVP]]

Hi,
I have added few of the events in some control, example code is:
btnControl.GotFocus +=new EventHandler(EventHandlingMethod);
btnControl.Click +=new EventHandler(EventHandlingMethod);
lblControl.Click +=new EventHandler(EventHandlingMethod);

private void EventHandlingMethod(object sender, EventArgs e)
{
.......
}

btnControl = Button object, lblControl = Lable object

Now the problem is: I am adding the same event handler method in all events for btnControl and lblControl too.

now in EventHandlingMethod method, i can find which control is using sender but now if i want to put some switch cases in the method for Event Name then I have no any such information in the eventargs or anyother way....

Can someone help/guide me to get the event name?

Is it possible? if yes then how? If no, then any work around?

Thanks in Advance

Regards,
Mahesh Devjibhai Dhola

 

[Andrew Robinson]

Mahesh ,

I agree with what Herfried and Marina have written with regards to different
controls of different types.

The one place where I do find it useful to use a single event handler for
multiple controls is with Button Controls. Take a look at the Button Command
event. You can pass different CommandName and CommandArgument strings for
each button while using the same Button Command event handler.

This works with traditional Button controls as well as Link Buttons and
Image Buttons.

--

Andrew Robinson
www.binaryocean.com
www.bellinghamdotnet.org


Hi,
I have added few of the events in some control, example code is:
btnControl.GotFocus +=new EventHandler(EventHandlingMethod);
btnControl.Click +=new EventHandler(EventHandlingMethod);
lblControl.Click +=new EventHandler(EventHandlingMethod);
private void EventHandlingMethod(object sender, EventArgs e)
{
.......
}
btnControl = Button object, lblControl = Lable object
Now the problem is: I am adding the same event handler method in all events
for btnControl and lblControl too.
now in EventHandlingMethod method, i can find which control is using sender
but now if i want to put some switch cases in the method for Event Name then
I have no any such information in the eventargs or anyother way....
Can someone help/guide me to get the event name?
Is it possible? if yes then how? If no, then any work around?
Thanks in Advance
Regards,
Mahesh Devjibhai Dhola

 

[Mahesh Devjibhai Dhola [MVP]]

Dear,
The Microsoft Event handling framework allows me to do this what you suggest
but some time, its possible to have such requirement so its not the matter
of sense but its my need so if you can suggest me the woraround for my
prolme then it will be helpful to me.

 

[Mahesh Devjibhai Dhola [MVP]]

Dear,
Your design is good or bad, it depends on requirement.
I know what is good and bad design for my situation. I am creating my own
framework and thats why i need such help.
This is very simple and general need to have "Event name" in some cases. I
am surprised that all Event has common property and thats Event name and
EventArgs is simply derived from Object class, instead it should have
atleast name property.
So, please dont concentrate on design and if possible, help me to find out
the answer. That is my need and anyhow i want to solve it.

Thanking you all for your kind support.

(some newsgroups trimmed - this really wasn't appropriate for all the
listed groups)

sender but now if i want to put some switch cases in the method for Event
Name then I have no any such information in the eventargs or anyother
way....

 

[Mahesh Devjibhai Dhola [MVP]]

Dear,
I am creating my own framework and its not centric to Buttton or some
control only. It will be applicable to all the events of all the controls.
So i need one common place which will be a common event handler method for
all and from that method my framework will work ahead by checking the sender
control and event name and i am doing lot other things at event time and i
will need more info than just sender and eventargs so i need to have such
method and switch case for event names.
For the same type of situation, java allows to have event name but i am
wondering why Microsoft has not such a simple provision in EventArgs??

 

[Herfried K. Wagner [MVP]]

The Microsoft Event handling framework allows me to do this what you
suggest
but some time, its possible to have such requirement so its not the matter
of sense but its my need so if you can suggest me the woraround for my
prolme then it will be helpful to me.

No, I can't suggest a workaround, because each workaround would be an ugly
hack I would not want to see getting into production code.

 

[Patrice]

EventArgs is just the base class for event arguments. You could perhaps
define your own class that would pass the information you need.

I won't discuss this design but it looks like you could also inherits from
those controls and change the On<Event> method ?

 

[Danny Tuppeny]

The Microsoft Event handling framework allows me to do this what you suggest
but some time, its possible to have such requirement so its not the matter
of sense but its my need so if you can suggest me the woraround for my
prolme then it will be helpful to me.

It doesn't make sense, but you could create a method called from all
event handlers, eg.

void GlobalHandler(object sender, string command, EventArgs e)
{
// your code here
}

and hook them up like this:

void button1_click(object sender, EventArgs e)
{
GlobalHandler(sender, "Click", e);
}

But I agree with the other posts - it's stupid. If you're doing the same
thing, you wouldn't need the string. If you're doing different things,
they should be in seperate methods.

 

[jmcgrew]

This design seems strange to me too, but I'll take your word that it
makes sense for your project.

This seems like a good time to use C# 2.0's anonymous delegates. If
your event handling method doesn't need to have the standard event
signature, you could do something like this...


private void EventHandlingMethod(string eventName, object sender,
EventArgs e)
{
...
}

btnControl.GotFocus += delegate(object s, EventArgs e) {
EventHandlingMethod("GotFocus", s, e); };
btnControl.Click += delegate(object s, EventArgs e) {
EventHandlingMethod("Click", s, e); };


Now, if you do need to use the standard event signature, you could
create a new EventArgs class that includes a name, stuff the event name
in there, and pass that in as the e parameter:


class NamedEventArgs : EventArgs {
NamedEventArgs(string name, EventArgs inner) { ... }
public string Name { get ... }
public EventArgs InnerArgs { get ... }
}

private void EventHandlingMethod(object sender, EventArgs e)
{
string name;
NamedEventArgs nea = e as NamedEventArgs;
if (nea != null) {
name = nea.Name;
e = nea.Inner;
} else {
name = "???";
}
...
}

btnControl.GotFocus += delegate(object s, EventArgs e) {
EventHandlingMethod(s, new NamedEventArgs("GotFocus", e)); };
btnControl.Click += delegate(object s, EventArgs e) {
EventHandlingMethod(s, new NamedEventArgs("Click", e)); };


Jesse

 

[=?ISO-8859-1?Q?Lasse_V=E5gs=E6ther_Karlsen?=]

Dear,
Your design is good or bad, it depends on requirement.

<snip>

If the "good" design needs an ugly hack to implement, it's not a good
design, regardless of how possible it is in other frameworks.

In this case your only option that I know of would be to access the
stack trace of the methods that called you and look at the method names
there. Ie. if you find "OnClick", it's a click event, and so on.

This is an ugly hack, and depending on access permissions the software
is to run under might not be possible anyway.

The data that is sent to the .NET event handlers carry no information
about what event was triggered that ended up in this method call.

I see this case as designing that cars can fly, calling it a good design
and then later on struggle to figure out how on earth this would be
possible.

It isn't.

Change your design.

 

[Danny Tuppeny]

In this case your only option that I know of would be to access the
stack trace of the methods that called you and look at the method names
there. Ie. if you find "OnClick", it's a click event, and so on.

A bit off-topic, but is it possible to programatically get a stack
trace? I've had to do it once (in a test app, so not important how ugly
it was), and resorted to throwing an exception just to get the
StackTrace. I assume there's a nicer away - probably in
System.Diagnostics somwhere?

 

[Stefan Simek]

A bit off-topic, but is it possible to programatically get a stack
trace? I've had to do it once (in a test app, so not important how ugly
it was), and resorted to throwing an exception just to get the
StackTrace. I assume there's a nicer away - probably in
System.Diagnostics somwhere?

There are the System.Diagnostics.StackTrace/StackFrame classes, but
using them is the ugliest hack I can possibly imagine. And it would not
help at all, because you would only get the name of method that fired
the event (in the better case, might be as well the optimizer inlines
the method and you get the method that called the event-firing method),
which, unless you use the OnXxx convention would not help at all. And,
of course, I expect it to be terribly slow.

Just my 2c.

Stefan

 

[Danny Tuppeny]

There are the System.Diagnostics.StackTrace/StackFrame classes, but
using them is the ugliest hack I can possibly imagine. And it would not
help at all, because you would only get the name of method that fired
the event (in the better case, might be as well the optimizer inlines
the method and you get the method that called the event-firing method),
which, unless you use the OnXxx convention would not help at all. And,
of course, I expect it to be terribly slow.

Just my 2c.

Cool. Don't worry, I'm not planning on using it in any "proper"
software, but it might come in handy when writing apps to test apps (if
a test fails, an exception might not be thrown, but it'd be nice to have
the route through the code)

 

[Truong Hong Thi]

Don't worry, I'm not planning on using it in any "proper"

software

It could be useful in some "proper" software. For example, you write a
logging framework that allows outputting of the method/class name in
the logged message. You could use the Stack to get the name of the
method that call the log routine. Without Stack, I don't know any other
way to get the MethodBase representing the caller method.

 

[Mahesh Devjibhai Dhola [MVP]]

Thanks dude,
I am not using .Net 2.0 currently in production environment but i will keep
your solution in my mind.

Thanks for the concern.

 

[John A. Bailo]

You should be looking at multicast delegates as an interface for your
events.

 

[Stefan Simek]

It could be useful in some "proper" software. For example, you write a
logging framework that allows outputting of the method/class name in
the logged message. You could use the Stack to get the name of the
method that call the log routine. Without Stack, I don't know any other
way to get the MethodBase representing the caller method.

Maybe, but there's still the problem I have mentioned in my previous
post. If your calling method gets inlined (I agree it won't happen too
often, at least for non-trivial methods, but who knows how the JIT will
behave in future versions?), you get the caller of the calling method
which can be misleading.