Synchronizing the Active State of multiple forms

• Download demo and source code - 35 Kb

Introduction

This article is an adapted port to C# of my other article. The code of this article implements some forms that synchronize the active state with the owner form.

Features implemented:

• Forms that can synchronize the active state with a owner form;
• Forms that automatically hide when the application is deactivated and when the owner form is minimized or hidden;
• Forms that are automatically disabled when owner form is disabled.

Usage

I will base these examples in the source-code of the demo application included in this article.

1. Add a reference to the assembly Rgl.Windows.Forms.dll in your solution.

2. If you are implementing a dialog box or frame window derive your class from Rgl.Windows.Forms.Form, or else, derive your class from Rgl.Windows.Forms.FloatingForm (i.e. if your form will be a toolbar or a toolwindow).

   public class Form1 : Rgl.Windows.Forms.Form

   or

   public class FloatingForm1 : Rgl.Windows.Forms.FloatingForm

Reference

For sample usage refer to the demo application and source-code.

Properties

• ForceActive (Read-Only)
  Is true when this Form is being draw in the active state.
• SyncActive (Read-Write)
  Is true if this Form will synchronize the active state with owner Form.
• KeepAllwaysVisible (Read-Write)
  Is true if this Form will stay visible when application is deactivated.

Helper methods

• SetVisible
  Call this to change the visible state of this form. Sometimes we cannot use the Visible property of the Form because when we set it to true the Form is also activated; by using this method we can specify if we want to activate the form or not.

Virtual methods (to override if needed)

• OnForceActiveChanged
  Called when the ForceActive property is changed.
• OnCreateFloatingForms
  Called when this Form is being created.
  If you want to create and display some floating forms at the creation time of this Form you should create them in this method and not in the OnLoad method or event handler (read more about this in the BaseForm.cs file).

Under the hood

The key for synchronizing the active state of a form lies on the WM_NCACTIVATE message. By handling or sending this message we can force the painting of a form in the active or inactive state.

The automated hiding of a form is archived by handling the WM_ACTIVATEAPP message.

The other two important messages that need to be handled are WM_ACTIVATE and WM_SHOWWINDOW (handled by overriding OnVisibleChanged); you can find information about them in the source code and in the MSDN library.

To finish, I just want to say that when implementing this assembly I have run into some "strange" problems, read all about them in the source-code.

History

• 14 mar 2002
  • first public version.

Do you have any question or comments? Contact me!