Not enough memory or not enough pens?

Q1

It looks like you are trying to create too many user interface controls at the same time. Even if the memory remains, you are out of pens. See below for a short but rather technical explanation.

Q4

I understand a user object as any object that is part of a GUI. At least prior to Windows XP, the Windows UI API was in USER.DLL

(one of the core DLLs in Windows). Basically, the user interface consists of "windows". All controls like buttons, text boxes, checkboxes are internally the same, namely "windows". To create them, you must call a Win32 API function CreateWindow

. This function will then return a handle to the created "window" (user interface element or "custom object").

So I am assuming the handle to the user object is the handle returned by this function. (Winforms is based on the old Win32 API and therefore uses a function CreateWindow

.)

Q2

Indeed, you cannot create as many UI controls as you want. All these descriptors received through CreateWindow

must be freed at some point. In Winforms, the easiest and safest way to do this is using a block using

or call Dispose

:

using (MyForm form = new MyForm())
{
    if (form.ShowDialog() == DialogResult.OK) ...
}    

      

        
        
        
      

    

Basically, everything System.Windows.Forms.Control

can be Dispose

d and should be removed. Sometimes this is done automatically for you, but you shouldn't rely on it. Always Dispose

your UI controls when you no longer need them.

Note for Dispose

modal and non-modal forms:

• Modal forms (shown with ShowDialog
  
  ) are not automatically removed. You have to do it yourself as shown in the above code example.
• The modeling forms (shown with Show
  
  ) are automatically deleted for you, since you have no control over it when the user is closed. No need to explicitly call Dispose
  
  !

Q5

Every time you create a UI object, Winforms makes calls internally CreateWindow

. This is how descriptors are allocated. And they are not released until the appropriate call is made DestroyWindow

. In Winforms, this call is triggered by Dispose

any method System.Windows.Forms.Control

. (Note: While I'm still pretty sure of this, I'm actually a little guessing. I may be 100% wrong. Looking at the internals of Winforms with Reflector reveals the truth.)

Q3

Assuming yours is StrategyEditor

creating a massive bunch of UI controls, I don't think you can do much. If you cannot simplify this control (in terms of the number of children to create) then it seems like you are stuck in the situation where you are. You simply cannot create infinitely many user interface controls.

However, you can keep track of how much is being StrategyEditor

opened at any given time (increment the counter on each instance and decrement it each time it is closed), you can keep track of the last one using the FormClosing

/ FormClosed

event of a form or in a Dispose

control method ). Then you can limit the number of open concurrently StrategyEditor

to a fixed number, say 5. If the limit is exceeded, you can throw an exception in the constructor so that no more instances are created. Of course, I can't tell if StrategyForm

the exception will be handled from your constructor StrategyEditor

...

public class StrategyEditor : ...
{
    public StrategyEditor()
    {
        InitializeComponent();

        if (numberOfLiveInstances >= maximumAllowedLiveInstances)
            throw ...;
        // not a nice solution IMHO, but if you've no other choice...
    }
}

      

        
        
        
      

    

Anyway, limiting the number of instances StrategyEditor

seems like a temporary fix to me and won't solve the real problem.