So I Tried Graphics Tonight For The First Time
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While Pete had explained that dispose should be used, he hadn't explained why, or how to best do it. I felt it worth a (slightly) more detailed response. The only problem with drawing in the Click event for learning purposes is that it can confuse more than elucidate - look at the number of "I drew it and it disappeared" questions we get. Starting off with drawing into the Paint event, with an existing Graphics context just makes it a bit easier for beginners. They can them be introduced to the concept of graphics contexts for other objects. :-D
I have learnt that you can not make someone love you, all you can do is stalk them and hope they panic and give in. Apathy Error: Don't bother striking any key.
He wasn't talking about me. He said wise. ;) Good explanation though and you might want to consider posting it as a tip/trick so that it can be easily linked to in response to other questions.
"WPF has many lovers. It's a veritable porn star!" - Josh Smith
As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.
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Hey Luc, Is there any Graphics Library available for .Net which does more than what GDI+ does? I mean something that takes care of some advanced functions like layering? I have an interest in printing multiple png images with transparency, being able to drag and drop them. Also, having multiple layers like in Adobe Photoshop? Ofcourse I mean open source/free. Som
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I'm not experienced with any additional library, I tend to write the code I use myself. Mostly from reading forums like this one, I must warn you transparancy is a bit tricky in Windows. You may want to look to some of the graphics articles at CodeProject; and then there is GIMP which could inspire you. :)
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read formatted code with indentation, so please use PRE tags for code snippets.
I'm not participating in frackin' Q&A, so if you want my opinion, ask away in a real forum (or on my profile page).
GIMP is what drove me to try drawing in Windows. :-O
"A Journey of a Thousand Rest Stops Begins with a Single Movement"
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naah.. the hardest part is to fight flickering ;) when anything u do in windows doesn't work :D
The hardest part was keeping them where I want them as the underlying control scrolls, horizontally and vertically. :sigh:
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Then don't stop; the first line is the hardest :laugh:
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read formatted code with indentation, so please use PRE tags for code snippets.
I'm not participating in frackin' Q&A, so if you want my opinion, ask away in a real forum (or on my profile page).
Just don't go one toke over the line.
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This gets a little complex, but: The Graphics object is a limited resource, which contains unmanaged memory. What that means is that it uses memory which is not on the normal C# heap, or the stack - it is in a different area completely, and the .NET garbage collector will not process it. When your method ends, the last reference to the object is destroyed, so it becomes available to be garbage collected - which is fine. But, the GC will only try to dispose of it when it runs short of managed memory - which could be in a few weeks time, you just don't know! In the meantime, all that unused, unmanaged memory is sitting there, being wasted. If you manually call Dispose() on your object when you are finished with it, the resources are released immediately, and all is well. The easiest way to do this is to wrap you object in a
usingblock:using(Graphics g = CreateGraphics())
{
... use the Graphics object
}The system will then call Dispose at the end. I probably haven't explained this too well, but if you look in any reasonable book on C#, it will talk about it in loads more detail! BTW: I wouldn't do the drawing in the Button.Click event - do it in the Form.Paint event - which supplies you with a graphics context in e.Graphics - and use the Button.Click to set any parameters (such as where you want it, what color, etc.) then call Invalidate() to force a re-draw.
I have learnt that you can not make someone love you, all you can do is stalk them and hope they panic and give in. Apathy Error: Don't bother striking any key.
I'm not sure it's a big deal. This seems to work fine:
private void button1_Click(object sender, EventArgs e)
{
Random rnd = new Random((int)(DateTime.Now.Ticks % int.MaxValue));
for (int i = 0; i < 100000; i++)
{
Graphics g = this.CreateGraphics();
g.DrawEllipse(Pens.Blue, new Rectangle(rnd.Next(0, 50),
rnd.Next(0, 50), rnd.Next(55, 100), rnd.Next(55, 100)));
}
}I'm sure it's not a bad idea to manually dispose of the Graphics object, but I'm not sure it's entirely necessary to make sure one does so.
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I'm not sure it's a big deal. This seems to work fine:
private void button1_Click(object sender, EventArgs e)
{
Random rnd = new Random((int)(DateTime.Now.Ticks % int.MaxValue));
for (int i = 0; i < 100000; i++)
{
Graphics g = this.CreateGraphics();
g.DrawEllipse(Pens.Blue, new Rectangle(rnd.Next(0, 50),
rnd.Next(0, 50), rnd.Next(55, 100), rnd.Next(55, 100)));
}
}I'm sure it's not a bad idea to manually dispose of the Graphics object, but I'm not sure it's entirely necessary to make sure one does so.
Don't forget that the Graphics object (along with Pens, Brushes, etc.) do not just allocate unmanaged memory - they also allocate GDI handles, which are a limited system resource. If you do not release them, there is no guarantee that your software will continue to work in all environments. Using Dispose on all applicable objects is considered good practice because it does reduce the chances of unpredictable failures now or in the future. On a side note: If your code executed only once a second, it would execute 100000 Graphics object creations in just over a day. How long would it last before it started to get problems? I dunno; that is the fun of memory leaks!
I have learnt that you can not make someone love you, all you can do is stalk them and hope they panic and give in. Apathy Error: Don't bother striking any key.
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Don't forget that the Graphics object (along with Pens, Brushes, etc.) do not just allocate unmanaged memory - they also allocate GDI handles, which are a limited system resource. If you do not release them, there is no guarantee that your software will continue to work in all environments. Using Dispose on all applicable objects is considered good practice because it does reduce the chances of unpredictable failures now or in the future. On a side note: If your code executed only once a second, it would execute 100000 Graphics object creations in just over a day. How long would it last before it started to get problems? I dunno; that is the fun of memory leaks!
I have learnt that you can not make someone love you, all you can do is stalk them and hope they panic and give in. Apathy Error: Don't bother striking any key.
OriginalGriff wrote:
If your code executed only once a second, it would execute 100000 Graphics object creations in just over a day.
Did you see the for loop? That's how many it creates per button click. There was not much of an increase in memory usage.
OriginalGriff wrote:
they also allocate GDI handles, which are a limited system resource
That might be a valid concern.
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OriginalGriff wrote:
If your code executed only once a second, it would execute 100000 Graphics object creations in just over a day.
Did you see the for loop? That's how many it creates per button click. There was not much of an increase in memory usage.
OriginalGriff wrote:
they also allocate GDI handles, which are a limited system resource
That might be a valid concern.
aspdotnetdev wrote:
Did you see the for loop?
I did - but I've only had one cup of coffee this morning, and explained what I meant badly. What I meant was: In the real world, your code would not necessarily sit on a button click, but would react to what else is going on. If you had your drawing code in a method that was executed frequently (by a timer update, or other external event) then at a rate of one execution per second, 100000 Graphics object creations would happen in just over a day.
I have learnt that you can not make someone love you, all you can do is stalk them and hope they panic and give in. Apathy Error: Don't bother striking any key.
