c# - What is, and how do I determine the cause of this strange exception with drawing a Rectangle? -

i'm trying draw rectangle in onpaint method of custom control. it's not don't know how, it's i'm trying time (as opposed creating new pen everytime onpaint called).

using system; using system.collections.generic; using system.componentmodel; using system.data; using system.drawing; using system.linq; using system.text; using system.threading.tasks; using system.windows.forms;  namespace somenamespace {     public partial class window : form     {         #region designer properties         [browsable(true), displayname("formbordercolor"), category("appearance")]         public color formbordercolor { get; set; }          [browsable(true), displayname("formborderthickness"), category("appearance")]         public float formborderthickness { get; set; }          #endregion          private pen formborderpen;         private brush formborderbrush;         private rectangle formborderrectangle;          public window()         {             initializecomponent();              this.doublebuffered = true;              this.setstyle(controlstyles.optimizeddoublebuffer, true);             this.setstyle(controlstyles.userpaint, true);             this.setstyle(controlstyles.allpaintinginwmpaint, true);             this.setstyle(controlstyles.resizeredraw, true);              this.setstyle(controlstyles.containercontrol, true);             this.setstyle(controlstyles.selectable, true);              // initialize border properties             formborderbrush = new solidbrush(formbordercolor);             formborderpen = new pen(formborderbrush, formborderthickness);             formborderrectangle = new rectangle(0, 0, this.width - (int)formborderthickness, this.height - (int)formborderthickness);         }          protected override void onpaint(painteventargs paint)         {             switch(this.formborderstyle)             {                 // if formborderstyle set none, can either                 // draw our own custom border, or no border @ all.                 case formborderstyle.none:                     // draw form border if necessary.                     console.writeline(formbordercolor);                     console.writeline(formborderthickness);                      console.writeline(formborderbrush);                     console.writeline(formborderpen);                     console.writeline(formborderrectangle);                      if(formborderthickness >= 1)                     {                         console.writeline("hooray?");                         paint.graphics.drawrectangle(formborderpen, formborderrectangle);                     }                     else                     {                         console.writeline("can't draw border.");                     }                     break;                 default:                     break;             }              base.onpaint(paint);         }     } } 

... but, i've getting bunch of exceptions , believe it's because values not being set when i'm expecting them set. don't know else set values.

i'm going take wild stab in dark here, , assume these exceptions being thrown because values these objects being set in constructor, however, don't know else set these values. , i've seen on msdn, thought setting values in right place.

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customendcap exception:

'formborderpen.customendcap' threw exception of type 'system.argumentexception'

customstartcap exception:

'formborderpen.customstartcap' threw exception of type 'system.argumentexception'

dashpattern exception:

'formborderpen.dashpattern' threw exception of type 'system.outofmemoryexception'

what don't understand is, why getting these exceptions? i'm not playing around caps or dashpatterns. , why pen , brushes empty when manually setting them?

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your pen size 0 formborderthickness, cause of problems seeing.

also, shouldn't use form's constructor if reference properties width or height since dimensions haven't been determined yet. should use onload override that.

i create pens , dispose of them in paint event, keep them local in scope. same thing rectangle.