Create instance using a string instead class name

Question

I want to instance a class depending on a combobox selection. Let say I have the following classes and interface:

Public Interface Sports
Sub description()
End Interface

Public Class Football : Implements Sports
Public Sub description() Implements Sports.description
    MsgBox("Football")
End Sub
End Class

Public Class Hockey : Implements Sports
Public Sub description() Implements Sports.description
    MsgBox("Hockey")
End Sub
End Class

One solution for my client looks like:

    Dim test As Sports

if combobox.selectedtext = "Football" then
test = New Football
else
test = New Hockey
end if

test.description()

With many subclasses this can be quite long, so I was thinking about a way to instance the chosen class depending on the selected text. I know this looks stupid, but something like:

Dim text As String = ComboBox1.SelectedText
test = New "test"

Is it possible to instance a class depending on an assigned string?

Philip Pittle · Accepted Answer · 2014-07-29 21:11:57Z

1

You can use the Activator.CreateIntance method to create a new instance.

This method requires a Type be passed in, so if you only have the string, you'll need to combine the method with Type.GetType:

Activator.CreateInstance(Type.GetType(ComboBox1.SelectedText))

You'll then need to cast the returned Object to Sports if you want to assign it to your variable.

Note: The ComboBox will need to list the full type name (name and namespace) otherwise Type.GetType will not work.

answered Jul 29, 2014 at 21:11

Philip Pittle

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Ryan Emerle · Accepted Answer · 2014-07-29 21:21:53Z

1

You can dynamically instantiate a type based on its unqualified name by searching for the type:

// Find the type by unqualified name
var locatedType = Assembly.GetExecutingAssembly()
                          .GetTypes()
                          .FirstOrDefault( type => type.Name == "Football" );

// Create an instance of the type if we found one
Sports sportsInstance = null;
if( locatedType != null ){
    sportsInstance = (Sports)Activator.CreateInstance( locatedType );
}

This will search the current assembly for a type matching the name "Football" and instantiate it if it was found.

answered Jul 29, 2014 at 21:21

Ryan Emerle

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