C# - reference to a variable?

Jakub K. · 2008-02-25T16:05:06

I am learning C# right now, coming from C++, and encountering a problem. I have a Form class that has a bitmap called DrawArea that it draws to the screen OnPaint. Further, I have a Renderer object that stores a reference to that DrawArea so it can draw to it. What I do is I pass the DrawArea to my Renderer, by reference, and set it to Renderer's private variable. Thus, the Renderer has a reference that points to the instance of DrawArea. This, however, is NOT what I want. You see, when my window resize, I delete my DrawArea and recreate it. Hence, when that happens, the Renderer's reference points to a, now obsolete, Bitmap*. Is there any way to have a reference point to an actual variable (other reference), rather than an instance in memory? Or do I need to use the "unsafe" pointers? Also can I return a reference via a function? how? (gah, I really dislike the C#'s referencing model ><) Btw, here's my code: /// <summary> /// This class takes care of rendering out TMEngine components to the screen /// </summary> class Renderer { //========================================================================= // Public //========================================================================= public Renderer(ref Bitmap DrawArea, ref cEntityManager EntityManager, ref cTimer Timer) { _DrawArea = DrawArea; //this doesn't do what I want _rEntityManager = EntityManager; _rTimer = Timer; } public void Update() { Graphics Graph = Graphics.FromImage(_DrawArea); // this throws exception if the DrawArea I passed in constructor gets deleted and re-created Pen MyPen = new Pen(Color.Blue); //yaya I know would be more efficient to story this as private member, but optimizations come later Graph.DrawEllipse(MyPen, 0, 0, 10, 10); MyPen.Dispose(); } //========================================================================= // Private //========================================================================= private Bitmap _DrawArea; private cEntityManager _rEntityManager; private cTimer _rTimer; } *as a sidenote, I get an exception when I try to modify that bitmap after reference - I thoguht C# did auto-garbage collection and would not delete the bitmap as long as I had some reference pointing to it...

For Beginners

Started by Koobazaur February 24, 2008 10:26 PM

11 comments, last by Shiny 16 years, 2 months ago

EdR

117

February 25, 2008 03:42 PM

Quote:Original post by Koobazaur
Sure, maybe C++ is ladden with memory voulnerabilities and unsafe code but, damn, at least when I had ** ppSomething I knew exactly what was going on instead of having to wonder what is referencing what (not to mention extra flexibility).

Keep in mind how long it took you to understand how that worked, though. C# is preposterously easy and very elegant once it clicks; I literally can't write C++ anymore.

http://edropple.com

SnprBoB86

277

February 25, 2008 03:49 PM

Quote:Original post by Koobazaur
at least when I had ** ppSomething I knew exactly what was going on instead of having to wonder what is referencing what (not to mention extra flexibility). And wtf is up with the lack of template, errr, generic specialization? Seriously...

You have nearly the exact same flexibility in C# and you can know "exactly what is going on" with great certainty once you learn the .NET model just as you learned the C++ model.

C# can accomplish non-partial generics specialization through inheritance. For example:

class SpecializedForBar : Foo<Bar>
{
//override virtual members of Foo
}

Brandon Bloomhttp://brandonbloom.name

Shiny

456

February 25, 2008 04:05 PM

       public void Update(){                    Graphics Graph = Graphics.FromImage(_DrawArea); // this throws exception if the DrawArea I passed in constructor gets deleted and re-created    Pen MyPen = new Pen(Color.Blue); //yaya I know would be more efficient to story this as private member, but optimizations come later    Graph.DrawEllipse(MyPen, 0, 0, 10, 10);    MyPen.Dispose();                         }

Just thought I should make a point -- you're clearing up after your pen right here, but not your System.Drawing.Graphics object that you're drawing on -- this is going to be a potential problem later if you're not careful. Anytime you use a graphics object that you didn't get given (i.e., in a paint() method you get given the surface that GDI+ is looking after...) you ought to manually call dispose() so that things don't end up leaking later on :)

This is a fact of life of using GDI+ -- 'tis a C++ library wrapped up in .NET but still must use unmanaged memory for certain stuff (Bitmaps ought to be disposed too, btw).

Anyways, 'twas my two cents. I second the proposition of inheriting from an existing container, too -- save you lots of work. Drawing an Image (system.drawing.image)/Bitmap onto a panel is as easy as grabbing the paint code for said panel and squishing in something along the lines of

Given some PaintEventArgs e -- e.Graphics.DrawImage(Image i);

and voila. DrawImage is overloaded so you can specify things such as height/width/graphics unit etc.

~Shiny

------------'C makes it easy to shoot yourself in the foot. C++ makes it harder, but when you do, it blows away your whole leg.' -Bjarne Stroustrup

C# - reference to a variable?

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