(How)
C^# You Are - 28 January 2007

1. What is the IExtenderProvider for?  Answer

   This interface allows a component to extend the list of properties available to other controls in a WinForms application.  For example the ErrorProvider component extends all controls on a form to add several properties.  Each control will display new properties in the property window.  In reality the designer calls methods on the provider component to associate these extended properties to a specific control.

2. How can you add context-sensitive help support to a control?  Answer

   Add a HelpProvider component to the form.  Then use the extended properties to set the help namespace and topic.  At runtime when F1 is pressed the associated help information will be displayed to the user.

3. How can you create docking windows in .NET?  Answer

   Technically you can't.  .NET does not provide any support for docking windows beyond the docking toolstrips.  In order to use docking windows you have to either write your own or use a third-party component.

4. How can you add auto-completion support to a combo box in a WinForms app?  Answer

   Prior to v2 you would have to write the code yourself.  In v2 auto-completion is supported automatically.  The Combobox exposes a property called AutoCompleteSource which allows you to specify what to display in the auto-complete list.  Options include the file system, the IE history or your own custom source.  The AutoCompleteMode property specifies how the auto-completion works such as whether it is displayed as a suggestion or appends the suggestion.  Finally the AutoCompleteCustomSource allows you to specify a custom source.

5. How do you prevent a user from closing a form?  Answer

   This is commonly done in document-managed apps where a user can edit a document and is then prompted to save the document prior to closing.  If the user chooses to cancel the save then the form does not close.  In .NET this can be accomplished by overriding the OnFormClosing method or by handling the FormClosing method.  This method/event allows you to cancel the event (such as if the user cancels the save operation).  For example, the following code will prompt the user to save a document.  If they cancel the save then the form is not closed.

   protected override void OnFormClosing ( FormClosingEventArgs e )
   {
      base.OnFormClosing(e);
   
      if (!e.Cancel && DocumentIsDirty)
      {
         switch(ShowSaveDialog())
         { 
            case DialogResult.Yes : SaveDocument(); break;
            case DialogResult.No : break;
            case DialogResult.Cancel : e.Cancel = true; break;
         };
      };
   }

   Refer to the FAQ section for an issue with how form closing works.  A final note, in v1.x you would use OnClosing and Closing.  This method/event has been deprecated in lieu of the new v2 method/event.