Sticky Windows - How to make your (top-level) forms to stick one to the other or to the screen

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Introduction

Delphi has a nice way of displaying its forms: all forms are (by default) top-level forms. This makes it easy to develop applications that are not restricted to the "MainFrame" client area but to the all screen, without having to have your application maximized. However, visually organizing such windows is sometimes hard for the end-user if he wants to maximize the visible area and minimize the window overlaps.

The class presented here tries to overcome this "arrangement" issue helping the end-user better organize their forms by sticking them one to the other and/or to the screen when moved or resized. (Code also takes care of correct sticking in multi screen environments but I did not manage to test it.)

Using the Code

The class inherits from System.Windows.Forms.NativeWindow, thus no inheritance is required in order to make your class Stick able.

In order to make your top-windows stick-able, all you have to do is declare a member variable of type StickyWindow and initialize it in your form:

private Blue.Windows.StickyWindow stickyWindow;
[...]
public 
Form2() // your constructor

{
stickyWindow = new 
Blue.Windows.StickyWindow ( this );
}

Now you have a form that will automatically stick on resize or move to all other forms that use the StickyWindow class and to the screen margins;

Customizations

There are few options you can customize about a Sticky Window:

1. public bool StickOnMove

   Allows the form to try to stick when the form is moved.

2. public bool StickOnResize

   Allows the form to try to stick when the form is resized.

3. public bool StickToOther

   Allows the form to try to stick to other stick-able forms.

4. public bool StickToScreen

   Allows the form to try to stick to the screen margins.

5. public int StickGap

   Distance in pixels between two forms or a form and the screen where the sticking should start.

6. public static void RegisterExternalReferenceForm( Form externalForm )

   Registers an external form (not StickyWindow form) in the list of forms that StickyWindows can stick to.

   E.g.: If you don't want your MainFrame to be stick-able but you want child forms to try to stick to it, than you will register your MainFrame with RegisterExternalReferenceForm so that other forms will try to stick to it.

7. public static void UnregisterExternalReferenceForm ( Form externalForm )

   Same as RegisterExternalReferenceForm but it un-registers the form.

These are all the defined possible customizations of the StickyWindow.

Implementation Details

The idea behind the implementation is to filter the NC (NonClient) messages from the Form's message queue and do the own Moving/Resizing of the form by overriding the WndProc of the NativeWindow.

When a WM_NCLBUTTONDOWN is received for the Form, the StickyWindow checks the required operation (Move/Resize) and starts the algorithm for the requested operation.

While mouse is moved, the algorithm computes the new Form's position/size and then tries to compute the distance to the closest Form or screen border. If the shortest distance is smaller than the StickGap, the form will be moved/resized to touch the margins of the form/screen, thus sticking taking place.

While resize takes place, the form will take care not to shrink below Form.MinimumSize or SystemInformation.MinWindowTrackSize or to grow above Form.MaximumSize or SystemInformation.MaxWindowTrackSize.

Credits

• The main credits go to WinAmp's team who made the idea of sticking windows popular.
• The second credits go to Infopulse, the place where I've developed the first StickyWindows implementation in C++.

History

• 09.Feb.2004: version 1.0

  First released version.

Copyright

You can use these sources for absolutely free.