Use Custom Properties in Forms to Standardize & Speed up RAD Article #2 in Series - RAD Tips by Les Smith

You can use Custom Properties and Enums in Window Forms to enforce standards, speed coding, and make your code more readable.  This is the second article in a series of articles on tips for Rapid Application Development in Visual Studio .NET, whether you are developing in VB.NET or C#.  See my first article on Visual Inheritance.

Windows Forms are created with certain base properties.  In .NET (C# and VB.NET), you can add your own properties to your forms.  Using Attributes can cause them to be visible in the Forms Properties box, just like any intrinsic property.  In this article, I will show three custom properties that you might want to add to your forms to standardize event handling functionality in your forms.  The examples that I am using for this article will address three problems that I encounter in almost every Windows Form that has any appreciable logic in it.  I will create the properties and then discuss the reason for them and their usage.

First, I will create three Enums to provide Intellisense, which makes your code much more readable.  By the way, you can place the Enums above the Class definition line and save yourself one level of Intellisense.

Public Enum State       Loading       Loaded       Closing    End Enum    Public Enum Modified       Clean       Dirty    End Enum    Public Enum HandleEvents       [Default]       Busy       Noise    End Enum

Next, I will add three Private variables that will utilize these Enums.

Private _FormState As State    Private _FormChanged As Modified    Private _FormEventHandling As HandleEvents

Next, I will create the Public Properties for these events.

<Browsable(True), _    Description("Tells the Load State of the form")> _    Public Property FormState() As State       Get          Return _FormState       End Get       Set(ByVal Value As State)          _FormState = Value       End Set    End Property    <Browsable(True), _    Description("Tells if control contents have been modified")> _    Public Property FormChanged() As Modified       Get          Return _FormChanged       End Get       Set(ByVal Value As Modified)          _FormChanged = Value       End Set    End Property    <Browsable(True), _    Description("Tells whether to ignore or process events")> _    Public Property FormEventHandling() As HandleEvents       Get          Return _FormEventHandling       End Get       Set(ByVal Value As HandleEvents)          _FormEventHandling = Value       End Set    End Property

As stated previously, there are three specific problems that I normally face in any complex Windows Form.  First, there is almost always some initialization code which must be done when any form is initially loaded, but I do not want to do it but once for each instantiation of the form.  In VB6, I would have set a formLoading variable to True in the Form_Load event, checked it in the Activate event, and if not set, I would perform some initialization and then set the formLoading variable to False so that with any subsequent firing of the Activated event, I would not execute the Initialization code again.  That VB6 type code is shown below:

Private formLoading As Boolean

Private Sub frmDialogTemplate_Load(ByVal sender As Object, _       ByVal e As System.EventArgs) Handles MyBase.Load       formLoading = True    End Sub

Private Sub frmDialogTemplate_Activated(ByVal sender As Object, _       ByVal e As System.EventArgs) Handles MyBase.Activated       If formLoading Then          ' this code will only execute once          ' perform initialization code here,          ' connect to database, load grids, etc.          ' then turn off formLoading so we dont execute again          formLoading = False       End If    End Sub

In VB.NET, I will use new methology, which was available in VB6, but not necessarily pushed.  In the first place, I will encourage you to use the Forms Constructor in my next article on Event Firiing Order.  But, to continue with the illustrationg at hand, here is how I would use the previously created property FormState doing it the .NET way.

Private Sub frmDialogTemplate_Load(ByVal sender As Object, _       ByVal e As System.EventArgs) Handles MyBase.Load       FormState = State.Loading    End Sub    Private Sub frmDialogTemplate_Activated(ByVal sender As Object, _       ByVal e As System.EventArgs) Handles MyBase.Activated       If FormState = State.Loading Then          ' this code will only execute once          ' perform initialization code here,          ' connect to database, load grids, etc.          ' then turn off formLoading so we dont execute again          FormState = State.Loaded       End If    End Sub

You can easily see that the .NET way is more readable, and Intellisense kicks in when I am referencing the FormState property.

Another great thing that you can do with Custom Properties is to make them show up in the Properties Box for the Form.  If you take another look at the Public Properties, you will see that I have added <Browsable(True)> to the definition line of the properties.  This causes the property to be displayed in the Properties Box as shown in Figure 1 below.  Setting the Description attribute causes the description to show in the area below the properties.

There are some useful things to know about the Custom Public Properties.  First, if you do not create a Set Acceptor in the Property Method, the property becomes ReadOnly and you cannot modify it at run-time.  Second, if you omit the Get Acceptor, the property becomes Write Only and you cannot read it a run-time.  

Figure 1 - Custom Properties in Property Box.