How to replicate the ItemDrag event

[Tom P.]

I have a bunch of colors as preferences in my application (Title
color, text color, border color, etc...). I'd like the option to copy
a color from one parameter to another by dragging the first color and
dropping it in the second color parameters space.
My question is how do I replicate the ItemDrag event that starts the
whole thing off? I'm stuck using either Buttons or PictureBoxes (due
to the need to display the selected color to the user). So how do I
replicate the ItemDrag event in an object that doesn't support it?

Tom P.

[Pavel Minaev]

On Aug 1, 4:04*pm, "Tom P." <[e-mail]:

I have a bunch of colors as preferences in my application (Title
color, text color, border color, etc...). I'd like the option to copy
a color from one parameter to another by dragging the first color and
dropping it in the second color parameters space.
My question is how do I replicate the ItemDrag event that starts the
whole thing off? I'm stuck using either Buttons or PictureBoxes (due
to the need to display the selected color to the user). So how do I
replicate the ItemDrag event in an object that doesn't support it?

I'm not sure what you mean by "replicating ItemDrag". ItemDrag is a
special event for controls which are containers of items (which are
not controls), and you have to detect dragging of a particular item.
For plain controls, you can just use MouseDown/MouseMove as usual -
basically, you should detect that user has pressed the mouse button
down, and has moved the mouse while still holding the button so that
the distance passed by mouse cursor is larger than
SystemInformation.DragSize. At that moment, you can invoke DoDragDrop,
and the rest is all the same.

[Tom P.]

On Aug 1, 7:43*am, Pavel Minaev <[e-mail]:

On Aug 1, 4:04*pm, "Tom P." <[e-mail]:

I have a bunch of colors as preferences in my application (Title
color, text color, border color, etc...). I'd like the option to copy
a color from one parameter to another by dragging the first color and
dropping it in the second color parameters space.
My question is how do I replicate the ItemDrag event that starts the
whole thing off? I'm stuck using either Buttons or PictureBoxes (due
to the need to display the selected color to the user). So how do I
replicate the ItemDrag event in an object that doesn't support it?

I'm not sure what you mean by "replicating ItemDrag". ItemDrag is a
special event for controls which are containers of items (which are
not controls), and you have to detect dragging of a particular item.
For plain controls, you can just use MouseDown/MouseMove as usual -
basically, you should detect that user has pressed the mouse button
down, and has moved the mouse while still holding the button so that
the distance passed by mouse cursor is larger than
SystemInformation.DragSize. At that moment, you can invoke DoDragDrop,
and the rest is all the same.

The steps you outlined are what I meant. I didn't realise I could
invoke DoDragDrop when not in a dragdrop event, I'll have to see if
there's enough information at that time. Now to figure out how to tell
if the mouse has moved farther than DragSize (Basically how to compare
a linear measurement to a co-ordinate measurement).

But thanks for the DoDragDrop tip. I just didn't realize.

Tom P.

[Pavel Minaev]

On Aug 1, 4:54*pm, "Tom P." <[e-mail]:

The steps you outlined are what I meant. I didn't realise I could
invoke DoDragDrop when not in a dragdrop event, I'll have to see if
there's enough information at that time. Now to figure out how to tell
if the mouse has moved farther than DragSize (Basically how to compare
a linear measurement to a co-ordinate measurement).

DragSize is actually an instance of struct Size, so it defines Width
and Height of the drag rectangle - if horizontal mouse delta is larger
than Width, or if vertical delta is larger than Height, then it's time
to start dragging.

[Tom P.]

On Aug 1, 8:56*am, Pavel Minaev <[e-mail]:

DragSize is actually an instance of struct Size, so it defines Width
and Height of the drag rectangle - if horizontal mouse delta is larger
than Width, or if vertical delta is larger than Height, then it's time
to start dragging.

I got it!

Thanks for the help. I had to do a (old.X - new.X >= DragSize.Width)
|| (old.Y - new.Y >= DragSize.Height).

And the dragdrop was exciting. (I am posting it for those looking to
figure this bloody technology out. It was hard enough to find I hope
this helps others.)

Once you have established that you are dragging (see above) you do the
following:

DataObject tempDataObject = new DataObject(this.BackColor);
DoDragDrop(tempDataObject, DragDropEffects.Copy);

This creates a DataObject and stores the data you want to pass to the
drop target in it (in my case a Color object). This is the only method
that you look at from the "draggers" point of view. The other events
are fired by the Drop target (don't forget the drop target could be
the same as the object that started the drag so it might look
confusing).

Then, in the DragEnter and DragOver events you check your object and
make sure you are accepting the data that is being dragged by checking
the DataFormats like so...

List<stringlstTest;

lstTest = new List<string>(drgevent.Data.GetFormats());

if (lstTest.Contains("FileDrop"))
{
//If you want to do different things based on different keys then
check those too..
if ((drgevent.KeyState & 8) == 8)
{
drgevent.Effect = DragDropEffects.Copy;
}
else
{
drgevent.Effect = DragDropEffects.Move;
}

}

Then, in the DragDrop event you get the object out of the DragObject
structure...

List<stringItemFormats;

ItemFormats = new List<string>(drgevent.Data.GetFormats());

if (ItemFormats.Contains("System.Drawing.Color"))
{
this.BackColor = (Color)drgevent.Data.GetData(typeof(Color));
}
Then process the data any way you feel you need to.

Hope this helps others.
Tom P.

[Pavel Minaev]

On Aug 1, 9:11*pm, "Tom P." <[e-mail]:

if (ItemFormats.Contains("System.Drawing.Color"))
{
* * *this.BackColor = (Color)drgevent.Data.GetData(typeof(Color));

}

Note that IDataObject.GetData() returns null if such type was not
found, so you typically just ask for the type and check for null - no
need to do GetFormats()/Contains(). If you need to check whether the
data is of a given format without retrieving it,
IDataObject.GetDataPresent() is probably still more efficient.