MouseWheel Events

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bern11 - 19 Feb 2007 03:42 GMT

I have an panel containing an image which creates scrollbars if the
image is too large for the panel. MouseWheel events automatically
scroll the scroll-bars. How do I intercept the mouse-wheel and make it
perform another function? I added a delegate mousewheel handler, but
now I get both events (panel scroll plus intended new function). I want
to switch between functions based on a flag.

I've already sub-classed the panel to gain access to other properties,
should I simply over-ride the mousewheel event and call the base event
based on a flag setting? Seems kindof the hard way....

PS. I also just noticed I never set the autoscroll property to true,
but the autoscrollbar behaviour seems to be enabled when I set the
autoscrollminsize property. Is this supposed to happen or did I just
get lucky and my code might not always work.

PPS. Why doesn't MouseWheel event show up in the designer? I had to
type the whole thing in, delegate declaration and all.

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Oliver Sturm - 21 Feb 2007 10:27 GMT

Hello bern11,

>I've already sub-classed the panel to gain access to other properties,
>should I simply over-ride the mousewheel event and call the base event
>based on a flag setting? Seems kindof the hard way....

Well, this seems kind of the right way to me though :-) Hard way? Well,
you're doing something non-standard, so you first have to find a way to
get rid of the standard behaviour, and stealing away the event is often a
good way of doing that.

>PS. I also just noticed I never set the autoscroll property to true, but
>the autoscrollbar behaviour seems to be enabled when I set the
>autoscrollminsize property. Is this supposed to happen or did I just get
>lucky and my code might not always work.

Have a look at Reflector - it shows you that the setter for the
AutoScrollMinSize property looks like this:

set
{
if (value != this.userAutoScrollMinSize)
{
this.userAutoScrollMinSize = value;
this.AutoScroll = true;
base.PerformLayout();
}
}

So, it definitely looks like the programmer wanted AutoScroll to be set to
true in this case.

>PPS. Why doesn't MouseWheel event show up in the designer? I had to type
>the whole thing in, delegate declaration and all.

Because it's marked [Browsable(false)] on the Control (once more, see
Reflector). Oh, why did they do that? I don't know. Maybe it's a mistake,
or they had a genuine reason not to expose the event - I couldn't find
much useful info about this.

Oliver Sturm

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MouseWheel Events

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