Calling a rectangle, simple c# question

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3.50/5 (2 votes)

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System.Drawing.Graphics graphicsObj;
graphicsObj = this.CreateGraphics();
Pen myPen = new Pen(System.Drawing.Color.Black, 5);
Rectangle myRectangle = new Rectangle(20, 200, 40, 80);
graphicsObj.DrawRectangle(myPen, myRectangle);

I created that rectangle in a method called draw1();
I have another method called draw2();..
How can I refer to that same rectangle in draw1(); to change it's background colour? (I know how to change the background colour, I just need to call it in method 2).. Like an instantiation kind of thing.

Posted 10-Feb-11 4:00am

LighthouseCall

Updated 10-Feb-11 4:03am

Manas Bhardwaj

v2

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3 solutions

Solution 2

Then just promote your rectangle to a member variable instead of local variable.

Rectangle _rect = new Rectangle(20, 200, 40, 80);
void Draw1()
{
   //use _rect here...
}
void Draw2()
{
   //use _rect here...
}
//use this function to update your rectangle when needed
void UpdateRect()
{
   _rect = new Rectangle(...);
}

Posted 10-Feb-11 4:09am

Olivier Levrey

Updated 10-Feb-11 4:12am

v2

Solution 1

make the return type of method1 as Rectangle[^]

private Rectangle Draw1()
{
	Rectangle _myRect = null;
	//whatever
	return _myRect;
}

Now you can pass it to the method2 to make changes there.

C#

private void Draw2(Rectangle PobjRect)
{
    //whatever
}

Posted 10-Feb-11 4:06am

Manas Bhardwaj

Updated 10-Feb-11 4:57am

v2

Comments

johannesnestler 10-Feb-11 10:29am

this is not the solution for this kind of problem - moving the variable to a higher scope-level is the answer - (Look at Answer2).

Manas Bhardwaj 10-Feb-11 10:59am

It surely is. You can pass the Rectangle object to the method2 to make the changes in it.

I also updated my answer to make it more obvious.

Global variables are never encouraged. If your method can handle it why global variables?

johannesnestler 10-Feb-11 12:14pm

Hi Manas,

I'm suprised by your answer. Of course in a common sense your solution is "correct".
But for this specific problem I have never seen such code - you write your drawing functions like this, returning the drawn objects? If you think about a typical Forms-App where do you define your Rectangle in the first place? Where is the "master" method, managing/dispatching the returned references? In a Form-Constructor - no? in Main method - no? So where? After concidering this (I have ~14 years experience in Windows-GUI programing) it brought me to the upper comment: "This is not the solution for THIS KIND OF PROBLEM".

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Sergey Alexandrovich Kryukov · Accepted Answer · 2011-02-10T04:42:00

Do not create graphics! (This is a rule of thumb, but valid in 99.90% cases.)
This topic was discussed many times. Always use Paint event:

C#

myControl.Paint += delegate(object sender, PaintEventArgs eventArgs) {
   using (Pen myPen = new Pen(System.Drawing.Color.Black, 5)) {
      Rectangle myRectangle = new Rectangle(20, 200, 40, 80);
      eventArgs.Graphics.DrawRectangle(myPen, myRectangle);
      DrawRectangleDetail(eventArgs.Graphics, myRectangle);
      DrawOnTopOfRectangle(eventArgs.Graphics, myRectangle);
      DrawSomethingElse(eventArgs.Graphics);
   } //using: here myPen.Dispose() is called automatically
}; //myControl.Paint

Also, where do you call myPen.Dispose? In the code above it is shown: through the using construct (see comment).

Now, about your methods Draw1, Draw2, etc. Call them all from the handler show above. Make them accepting a Graphics parameter, if you need to re-use already initialized Rectange, add a Rectangle parameter to those which require that. See the calls to Draw... in my sample.

—SA