No line is drawn from the code

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1.00/5 (1 vote)

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Hi there,

Why doesn't a Line get drawn on the screen with below code???

C#

//Declaration
public Graphics obj_Graphics;
private Bitmap obj_Bitmap;

//Coding
        obj_Bitmap = new Bitmap(1000, 1000);
        obj_Graphics = Graphics.FromImage(obj_Bitmap);
        obj_Graphics.DrawLine(new Pen(new SolidBrush(Color.Black), 5), 100, 500, 400, 500);

Thanks in advance...

Posted 1-May-11 20:56pm

aswathy.s.88

Updated 1-May-11 21:00pm

jim lahey

v2

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Sergey Alexandrovich Kryukov 2-May-11 3:26am

ASP.NET?!
--SA

2 solutions

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E.F. Nijboer · Answer 1 · 2011-05-01T21:11:00

Solution 1

You are using some objects you declared yourself. These are in memory but not on screen. Have a look at the link for a simple example how to do it when working with forms:
http://www.geekpedia.com/tutorial50_Drawing-with-Csharp.html[^]

If you want to use the created content on your web page, have a look at this link:
http://msdn.microsoft.com/en-us/library/system.web.httpresponse.outputstream.aspx[^]

Good luck!

Posted 1-May-11 21:11pm

E.F. Nijboer

Updated 2-May-11 0:41am

v2

Comments

Sergey Alexandrovich Kryukov 2-May-11 3:25am

ASP.NET?!
--SA

E.F. Nijboer 2-May-11 4:31am

The link to the example isn't quite correct on that but the reason the line isn't visible still is the same I guess. Drawing to a Graphics object won't automatically display on screen.

Sergey Alexandrovich Kryukov 2-May-11 4:38am

Yes of course. It's about drawing in Paint or OnPaint and Invalidate. But it has nothing to do with ASP.NET, which makes the whole question incorrect. It's either ASP.NET or System.Drawing, not both. See our discussion with Griff.
--SA

E.F. Nijboer 2-May-11 6:04am

The question isn't very clear as is already mentioned. It is of course possible to create images on the fly for use in a page by saving it to the response.outputStream.

Sergey Alexandrovich Kryukov 2-May-11 6:32am

Or gosh, you're absolutely right! I somehow missed the fact the OP draws on Bitmap, probably because as I was mislead by the words "drawn on screen". And this is pretty usual technique, this is how complex mathematical expressions are rendered on the fly in the Web site.

Certainly, my 5. (I would mention it in the body of your answer.)
And thanks for finally explaining this to me.
--SA

E.F. Nijboer 2-May-11 6:42am

Thanks! Also added a link to msdn with information to the answer.

Sergey Alexandrovich Kryukov 2-May-11 7:14am

Another 5! Oops... Does not up-vote by another 5, pity... :-)
--SA

OriginalGriff · Answer 2 · 2011-05-01T21:15:00

Solution 2

Because you are not drawing on the screen, you are drawing on a bitmap:

obj_Graphics = Graphics.FromImage(obj_Bitmap);

If you want to draw it i=on teh screen, then handle the Paint event for your form, or a panel on your form and use the Graphics object you are handled in the EventArgs parameter:

e.Graphics.DrawLine(new Pen(new SolidBrush(Color.Black), 5), 100, 500, 400, 500);

Posted 1-May-11 21:15pm

OriginalGriff

Comments

Sergey Alexandrovich Kryukov 2-May-11 3:26am

ASP.NET?!
--SA

OriginalGriff 2-May-11 4:09am

Hadn't noticed that - I assumed the OP was forms based from the "get drawn on the screen" part.
ASP.NET could be just buzzword frenzy - either that or we need more code.

Sergey Alexandrovich Kryukov 2-May-11 4:34am

It it is just a buzzword, the correct answer should be "stop messing up unrelated things, first tell me what do you want". This is not just the formality (who knows?), there are real examples of messing up things. For example, recently one patient asked how to use Windows.Forms.Form in the ASP.NET Page (!!!). I had to explain that there is a client part and the server, and "Who will look at this form?", etc...
--SA

OriginalGriff 2-May-11 4:43am

And I had one the other way this morning: http://www.codeproject.com/Answers/189811/how-to-use-javascript-in-Csharp-NET-window-applica.aspx
You do have to wonder what they teach them sometimes.

Sergey Alexandrovich Kryukov 2-May-11 5:20am

Yes, funny (I voted 5 for that answer). Fantasy is unlimited...
--SA

Sergey Alexandrovich Kryukov 2-May-11 6:35am

Wait a second! I completely missed the fact that OP and you are drawing in a bitmap which can be sent in the response to the client. E.F. just explained it to me.
--SA

OriginalGriff 2-May-11 6:37am

Don't look at me! I'm drawing on the Graphics object of the PaintEventArgs! :laugh:

Sergey Alexandrovich Kryukov 2-May-11 7:07am

Interesting idea. Where do you get it? :-) :-)
--SA