MouseDown, MouseUp, Timing and Threading

[Jeremy Robertson]

I'm working on an application that manages large image files (mulit-page
..Tiff's to be exact some 1000+ pages).

I've written an user control that displays a number of the images as
thumbnails in a scrollable window. The user can select and modify Images
from my thumbnail control. I need to let the user re-arrange the images if
they are out of order. I need the user to be able to click on a thumbnail or
multiple and DRAG them to the correct position, BUT I don't just want
erroneous clicking and barley moving the mouse to do the re-order. On Event
MouseDown I capture the selected image(s) in a array, then pop off a new
thread that waits 1 second before it sets a Bool that allows re-ordering,
and displays a blinky thing to show where the re-order is going to go. On
Event MouseMove I just change the position of the blinkything (if needed) to
reflect the position of where it's going to go. On Event MouseUp if the
timer has gone long enough (one second) and it's in a new position then I
re-order...

Here's my problem. When a user MousesDown, in another part of the app, a
full size-image gets loaded and displayed(only one page); now if I'm loading
a big 300dpi grayscale image, it takes over a second. So on these large
images, when a user MouseDowns, moves the mouse, and then MouseUps in under
the time it takes the large image to load, the MouseUp event doesn't happen
until it loads (which is over a second) so it assumes the user meant to move
no matter what, which really messes things up.

I'm writing this control to be used by others, and telling them to work
around this is unacceptable. Is there a way to have the MouseUp event
handled in separate Thread so that the large processing time doesn't break
my control? or some other ingenious way to do this? :) I understand that the
built-in Drag-Drop events also happen in the same thread so I'm pretty sure
that wouldn't help me, and I don't need to worry about stuff being dragged
into/out of my control.

[Fergus Cooney]

Hi Jeremy,

I'm not sure I fully understand what you are saying - the 'in another part
of the app, a
full size-image gets loaded' part - but I wonder whether it might be easier to
do the image loading in a different thread rather than trying to MouseUp in a
different thread?

Another curiousity - is this large-image loadingh part of your drag-n-drop
rearranging? If not, perhaps you could simply not allow a drag to be initiated
until the load has finshed?

Regards,
Fergus