2010-02-04

DesignMode in Visual Studio, inheritance, process name and a work around

The text and code below is only tested for Winform. WPF might behave differently; hopefully behaves differently.

I won't go into any details on why the ISite.DesignMode is good and sometimes even crucial to have. It is much better done in the link at the bottom.

First out there is unfortunately a caveat with DesignMode, it doesn't work with inherited forms and user controls. This is a problem since I always inherit from the base form in my projects and tell others to do the same. It also doesn't work inside the form's or the user control's constructor and then by any method that is called by the constructor. Long call chains to might make this hard to track down.
Secondly there is another way to check for design mode and that is to check for the LicenseManager.UsageMode but this in turn doesn't work in event handlers.
Thirdly one can set a flag in the base Form and base UserControl. But this doesn't solve the problem since we cannot be sure with what to set this value.
Fourthly is a workaround where one can check for the name of the process itself which is Visual Studio's process name (devenv) in case of design mode. This process name might change in future releases of Visual Studio and is also different for other IDEs.
Fifthly is other process information like the name of the module and stuff. Check into the Process and you'll see that the app is called MyApp.vshost.exe while being debugged.

The fourth solution (processname=devenv) seems to be the most viable but I believe there is something useful in the fifth (other process information). There must be a way to notice that the name of all your code doesn't match the name of the running environment; namespace, assembly name, whatever. I still haven't figured out how though.

Below is some code to copy-paste.
It is not 100% correct though since the DesignMode property isn't virtual. This might end with some really tough-to-track-down bugs where one iterates the forms but don't get the overloaded DesignMode flag. The code also doesn't promise to work forever since there is a magic string naming the name of the Visual Studio process.


public partial class MyAppForm : System.Windows.Forms.Form
{
protected new bool DesignMode
{
get
{
return HelperMethods.IsDesignMode(this);
}
}
}

public partial class MyAppUserControl : UserControl
{
protected new bool DesignMode
{
get
{
return HelperMethods.IsDesignMode(this);
}
}
}

class HelperMethods
{
public static bool IsDesignMode(System.ComponentModel.Component x)
{
var site = x as System.ComponentModel.ISite;
return
( null == site ? false : site.DesignMode ) ||
System.ComponentModel.LicenseManager.UsageMode == System.ComponentModel.LicenseUsageMode.Designtime ||
System.Diagnostics.Process.GetCurrentProcess().ProcessName == "devenv";
}
}
The code above is also in pastebin for easier copy-paste.
A good article is here: http://dotnetfacts.blogspot.com/2009/01/identifying-run-time-and-design-mode.html
There is a description of how to debug this here: http://brennan.offwhite.net/blog/2006/08/30/design-time-debugging-aspnet-20-in-visual-studio-2005/

1 comment:

踢人 said...

要保持更新呦,加油!!!期待你的新文章!!! ........................................