Clear controls does not dispose them - what is the risk?

Question

There are multiple threads(a, b, c etc.) about the fact that Clear() ing items in the .NET component containers does not Dispose them(by calling Dispose(true).

Most frequently, IMHO, the Clear-ed components are not used anymore in the application, so it needs explicitly be Disposed after Clearing them from the parent containers.

Maybe is a good idea that collection's Clear method had a bool parameter dispose that when in true also disposes the collection elements before its removing from the list?

Answer 1

Asking for modifications like this is pointless, the Windows Forms team has been disbanded quite a while ago. It is in maintenance mode, only security issues and OS incompatibilities are considered.

It is otherwise simple enough to create your own method to do this:

  public static class ExtensionMethods {
    public static void Clear(this Control.ControlCollection controls, bool dispose) {
      for (int ix = controls.Count - 1; ix >= 0; --ix) {
        if (dispose) controls[ix].Dispose();
        else controls.RemoveAt(ix);
      }
    }
  }

Now you can write:

  panel1.Controls.Clear(true);

Answer 2

Answering the "what is the risk" question, the risk (or a risk) is running out of window handles, although it can take a while.

I have a "window designer" that generates a window from a script. Each time I change the script, the window is rebuilt (the controls cleared and readded). With a particularly complex window, and using Controls.Clear() each time, after many dozens of refreshes, I will eventually get a "no more window handles" exception and not be able to create any more controls.

Easy enough to replace the Controls.Clear() call with something like:

Controls.Cast<Control>().ForEach(c => c.Dispose());

Answer 3

@Hans Passant answer is good but in case of asynchronous programming you should consider to remove the object before dispose it to avoid some thread to iterate over a disposed object.

More or less something like this:

public static class ExtensionMethods {
  public static void Clear(this Control.ControlCollection controls, bool dispose) {
    for (int ix = controls.Count - 1; ix >= 0; --ix) {
      var tmpObj = controls[ix];
      controls.RemoveAt(ix);
      if (dispose) tmpObj.Dispose();
    }
  }
}