Resolve DesignMode for a User Control

• Download source code - 388 B

Introduction

This is a fast, reliable method to determine if you are currently in Design Mode.

Background

Background is the usual for this one - I needed to do certain things with my custom control in design mode. Noting fairly quickly that the DesignMode property was not reliable, I did the usual searches, and came up with a number of methods (including Mika Wendelius' [^] article here[^]). The possibilities were:

• Mika's solution using reflection to get the DesignMode property of all controls in the path up to and including the host form. Although this method is reliable, using reflection means that (a) The application requires Full Trust, and (b) all the checks and balances that go along with reflection usage are unnecessarily slow.
• Checking the process name, i.e.,
  C#

  System.Diagnostics.Process.GetCurrentProcess().ProcessName == "devenv"

  As with the reflection method, this requires Full Trust to work, and is even slower.
• Checking the LicenseManager.UsageMode property. This is very fast, but it turns out that it is not 100% reliable. If the LicenseManager cannot find a CurrentContext value, then it returns LicenseUsageMode.Runtime regardless of the actual mode.
• Checking the Site.DesignMode property for each control in the tree, up to and including the host form. This is pretty much the same as Mika's solution, except the Site.DesignMode property is not protected, so reflection is not required. The only time hit on this method is the traversing of the control's parents until it finds one that is set, or it reaches the end.

It also should be noted that once a module if found to be in design mode or not, the mode does not change. As such, once the mode has been determined, any subsequent calls should just return the previous result, rather than going through the process all over again.

The final result I came up with is:

static class DesignModeExtension {
	static bool? _isinDesignMode = null;

	public static bool IsInDesignMode(this Control control) {
		if (!_isinDesignMode.HasValue) {
			_isinDesignMode = (LicenseManager.UsageMode == LicenseUsageMode.Designtime);
			while (!_isinDesignMode.Value && control != null) {
				_isinDesignMode = control.Site?.DesignMode ?? false;
				control = control.Parent;
			}
		}
		return _isinDesignMode.Value;
	}
}

Firstly, I check whether the mode has already been determined. If it hasn't, I proceed to determine it.

The determination starts with the fastest method, albeit unreliable. However, it is only the "false" return value that is unreliable. If this test returns true, then there is no need to traverse the controls to see if they are in design mode. Finally, if needed, I traverse the control's parents until I either find one that confirms I am in design mode, or I reach the end, in which case I can be certain that the application is not in design mode. I then save the final result before returning it to the caller.

Using the Code

The attached source is not in any project - it is simply a .cs file containing the definition. To install it, simply add this file to your project.

Using the extension is as simple as if (this.IsInDesignMode()). This can be called from anywhere within a control's scope.