Re: Display a bitmap from Win32, unmanaged code?
- From: jiewan@xxxxxxxxxxxxxxxxxxxx ("Jie Wang [MSFT]")
- Date: Thu, 07 May 2009 10:55:04 GMT
| First, related to deleting the underlying bitmap. In the low-level Win32
| code, the bitmap is reused and managed, there. This is code that's been
| around for many years and is stable which is why I don't want to fiddle
with
| it (but I probably will have to in the coming months).
Glad to know that. If the hBitmap will be reused, then we don't need to
delete it after creating the Bitmap object.
| Third, the proposed solution to move the dispose seems a bit fragile.
What
| is needed is a callback or method like is sued for the asynchronous load
for
| a pictureBox. In that way, the control could notify the caller when it's
done
| with the object. What's a bit odd is that it seems as though the
| pictureBox.image call is actually doing things asynchronously, else this
| would not be a problem. Is there a way to know, for sure, that the image
is
| done being displayed so that the data it was copying from can be
discarded?
| It's obvious that the call completing is not an indication that it's save
to
| dispose it.
The only time to Dispose the image is the when it is no longer needed. By
that, I mean at the time there is no reference that will use the image
again.
If the image is still be displayed in the PictureBox, then the PictureBox
holds a reference to it, when the OnPaint event happens, the PictureBox
needs the image to redraw itself.
So I think the best safe time to Dispose the old image is right after the
new image is assigned to the PictureBox.
Image old = this.theImage.Image;
this.theImage.Image = theBitmap;
if (old != null) old.Dispose();
I should have added this in my previous post.
Image.Dispose() for your reference:
http://msdn.microsoft.com/en-us/library/8th8381z.aspx
Note the Remarks section.
Hope this helps.
Best regards,
Jie Wang (jiewan@xxxxxxxxxxxxxxxxxxxx, remove 'online.')
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