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Question

c# form inheritance event handlers fire twice

Answer 1

+3 A:

could you add some code of how do you inherit and use buttons? In C# you should not have a such issue, because there is no Handles keyword.

You may, however, add multiple time handlers to the buttons event click like:

parent
    myButton.Click += myClickAction

child
    sameButton.Click += sameClickAction

When inheriting you should not click on the inherited buttons in designer(that will add a new, maybe the same, action on the inherited button)

Add a breackpoint in the twice executed action, when hit consult the CallStack Visual Studio Window in order to see who calls your method twice...

EDIT

Not sure what happens, but try the following:

Replace:

this.btnNext.Click += new System.EventHandler(this.installButton_Click);

with

this.btnNext.Click -= new System.EventHandler(this.installButton_Click);
this.btnNext.Click -= new System.EventHandler(this.installButton_Click);
this.btnNext.Click -= new System.EventHandler(this.installButton_Click);
this.btnNext.Click += new System.EventHandler(this.installButton_Click);

EDIT2

In order to analyze the calls to your method instantly do the following:

Set a Tracepoint in the installButton_Click method:
Edit the tracepoint properties, in order to trace the callstack(or also use just $CALLER - only theprevious function):
In the Output window deactivate(right click) all messages but "Program Output";
Analyze your output in run-time:

alt text

serhio 2010-01-21 16:16:28

added some code, I can't see a repeated handler and a search turned up nothing.

Nathan 2010-01-21 16:32:27

Ok the call stack shows this: MynetInstaller.exe!MynetInstaller.InstallerForm.installButton_Click(object sender = {Text = "Siguiente"}, System.EventArgs e = {X = 60 Y = 9 Button = Left}) Line 226 C#both times, so both times its called by the button with text "Siguiente" (next)?

Nathan 2010-01-21 16:44:54

yes, but see the next caller, who does cal the Button "Siguiente"?...

serhio 2010-01-21 22:07:11

i'm not exactly sure how to see, i've not used this part of VS much, how would I do that? thanks

Nathan 2010-01-22 08:13:47

i get that line above, then[external code]Installer.exe!Installer.Program.Main() Line 21 + 0x1d bytes[external code]And get identical entries both times it is called

Nathan 2010-01-22 08:16:48

Thanks Serhio, It stops when I add that change, but will only run the button once even if you generate a new click event. but a passable work around, does this point to an underlying reason for thie behaviour?

Nathan 2010-01-22 10:17:49

Apparently somewhere in the code you subscribe twice to your event. The multiple `-=` unsubscribe multiple instances, and adds only one, but, normally, you should add a tracepoint(breackpoint with a 'when hit..' condition) and correct the code do not add twice the same handler to this Click event.

serhio 2010-01-22 10:51:47

hmmm would a search have no turned up the second subscription? leaving it 'as is' is a bit annoying as whenever you open the form it raises a warning that the underlying code has been changed and that this could cause problems! How would a breakpoint help? thanks for all your help

Nathan 2010-01-25 11:15:12

you can see my Edit2

serhio 2010-01-25 23:32:35

thats again for your help, i've done as you recommended but they both seem identical?

Nathan 2010-01-26 08:47:14

ok, they are really identical, could you now move the same tracepoint at the `this.btnNext.Click +=` line and paste the trace?

serhio 2010-01-26 09:35:34

done - results added to OP

Nathan 2010-01-26 10:33:14

as you ca see, the difference is in the `InstallerForm.performChecks` function(called in InitializeComponent?). So, perhaps it adds the second time the handler.Its better anyway to move all initialization custom logic (as `performChecks`) from `InitializeComponent` to `OnLoad` or `_Load` in the form.

serhio 2010-01-26 11:09:25

Perfect, i removed those sections and its solved, the code only runs once! Thank you for your help serhio, i owe you one!

Nathan 2010-01-26 11:34:29

you welcome, pleased to help.

serhio 2010-01-26 11:48:25

Answer 2

A:

C# adds event handlers to controls this way.

this.btnMyButton.Click += new System.EventHandler(this.btnMyButton_Click);

Just take a look if you have something like the statement above for your button within the derived form, if so, remove/comment it, since it is adding an additional event handler for that button.

Albert 2010-01-21 16:27:47

I have looked and can't see one, i have also done a search for this.btnMyButton_Click in my project and found a single reference.

Nathan 2010-01-21 16:31:54

search `btnNext.Click` and `btnMyButton_Click` (without `this.`)

serhio 2010-01-21 16:43:17

the only reference is in designer as i've shown above, (one in each of the three different subforms inherited from "rootForm" )

Nathan 2010-01-21 16:49:41

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c# form inheritance event handlers fire twice

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