Question

I’m writing a biorhythm app. To test it i have a form with a Button and a PictureBox. When I click on the button i do

myPictureBox.Image = GetBiorhythm2(); 

Which runs ok for the first time, but on the second click it causes the following exception:

System.ArgumentException: Parameter is not valid.    at System.Drawing.Graphics.CheckErrorStatus    at System.Drawing.Graphics.FillEllipse    at Larifari.Biorhythm.Biorhythm.GetBiorhythm2 in c:\delo\Horoskop\Biorhythm.cs:line 157    at Larifari.test.Button1Click in c:\delo\Horoskop\test.Designer.cs:line 169    at System.Windows.Forms.Control.OnClick    at System.Windows.Forms.Button.OnClick    at System.Windows.Forms.Button.OnMouseUp    at System.Windows.Forms.Control.WmMouseUp    at System.Windows.Forms.Control.WndProc    at System.Windows.Forms.ButtonBase.WndProc    at System.Windows.Forms.Button.WndProc    at ControlNativeWindow.OnMessage    at ControlNativeWindow.WndProc    at System.Windows.Forms.NativeWindow.DebuggableCallback    at ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop    at ThreadContext.RunMessageLoopInner    at ThreadContext.RunMessageLoop    at System.Windows.Forms.Application.Run    at Larifari.test.Main in c:\delo\Horoskop\test.cs:line 20 

the cut-down function which causes the error is :

public static Image GetBiorhythm2() {         Bitmap bmp = new Bitmap(600, 300);         Image img = bmp;         Graphics g = Graphics.FromImage(img);          Brush brush = Brushes.Black;         g.FillEllipse(brush, 3, 3, 2, 2); //Here the exception is thrown on the second call to the function          brush.Dispose(); //If i comment this out, it works ok.          return img;  } 

if I comment-out the brush disposal it works ok, but I am not happy with that and wish to find an alternative solution. Can you help me please ?

Answer 1

It looks like you’re trying to dispose of a static, which causes some problems next time it’s used:

    Brush brush = Brushes.Black;     g.FillEllipse(brush, 3, 3, 2, 2); //Here the exception is thrown on the second call to the function      brush.Dispose(); //If i comment this out, it works ok. 

When you set brush = Brushes.Black, you’re actually setting brush as a reference (or pointer) to the static Brushes.Black. By disposing it, you’re effectively writing:

    Brushes.Black.dispose(); 

When you come back around to use the black brush again, the runtime says you can’t because it’s already been disposed of, and isn’t a valid argument to g.FillEllipse()

A better way to write this might be just simply:

    g.FillEllipse(Brushes.Black, 3, 3, 2, 2); 

Or, if you want to be really complex about it:

    Brush brush = Brushes.Black.Clone();     g.FillEllipse( brush, 3, 3, 2, 2 );     brush.Dispose(); 

Or if you don’t care about things looking wrong, just comment out the brush.Dispose(); line in your original code.