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POUsing VB.NET object initializers in a factory pattern
 

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  1. POUsing VB.NET object initializers in a factory pattern
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    <p>I have written a base class from which I wish to derive several child classes (in this case Windows Form classes), and I'm using a Factory pattern in order to maintain a collection of the child instances, so that a form can only have one instance per primary key value (sort of a mash-up of Factory and Singleton patterns.)</p> <p>I'm using the following code in the base form class:</p> <pre><code>Public Class PKSingletonForm Inherits Form Protected _PKValue As Int32 = 0 Protected _strFormKey As String = "" Protected Shared _dictForms As New Dictionary(Of String, PKSingletonForm) Public Shared Function GetForm(Of T As {PKSingletonForm, New})(Optional ByVal PKValue As Int32 = 0) As T '** Create the key string based on form type and PK. Dim strFormKey As String = GetType(T).Name &amp; "::" &amp; PKValue.ToString '** If a valid instance of the form with that key doesn't exist in the collection, then create it. If (Not _dictForms.ContainsKey(strFormKey)) OrElse (_dictForms(strFormKey) Is Nothing) OrElse (_dictForms(strFormKey).IsDisposed) Then _dictForms(strFormKey) = New T() _dictForms(strFormKey)._PKValue = PKValue _dictForms(strFormKey)._strFormKey = strFormKey End If Return DirectCast(_dictForms(strFormKey), T) End Function End Class </code></pre> <p>The idea is to create a child form (called UserInfoForm, for example) that inherits from the base form, and create an instance of it for user #42 as follows:</p> <pre><code>Dim formCurrentUser = PKSingletonForm.GetForm(of UserInfoForm)(42) </code></pre> <p>All this works as intended.</p> <p>However, the UserInfoForm now has some properties I wish to set, and I would like to set them using Object Initializers, as opposed to after the form is created by the factory, like so:</p> <pre><code>Dim formCurrentUser As New UserInfoForm With { .ShowDeleteButton = False, .ShowRoleTabs = False } </code></pre> <p>Is there any way to combine these two methods, so I've got the factory as well as the initializer?</p> <p>I'm not looking for:</p> <pre><code>Dim formCurrentUser = PKSingletonForm.GetForm(of UserInfoForm)(42) formCurrentUser.ShowDeleteButton = False formCurrentUser.ShowRoleTabs = False </code></pre> <p>...because the base class also has a ShowForm() method that takes additional base form parameters, wraps the GetForm() function, and shows the form.</p>
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    1. USPeter Mortensen
    1. USMCattle
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    1. COI don't understand. Why does your `ShowForm()` method mean you can't set the properties the usual way?
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      1. POUsing VB.NET object initializers in a factory pattern
      1. USsvick
    2. COThe ShowForm() was a shared method that was calling GetForm() internally, setting some layout parameters (MDI Parent and whatnot), then calling Me.Show(). It would be called in place of GetForm(), but it turned out that we'd almost always want to call ShowForm().
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      1. USMCattle
    3. COWe've re-engineered it to simplify ShowForm(), which I'll post as the answer below. I'm still curious as to how to combine Object Initializers with a factory constructor, though.
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