Question

I have the following

Public Structure Foo
   dim i as integer
End Structure

Public Class Bar

Public Property MyFoo as Foo
Get
   return Foo
End Get
Set(ByVal value as Foo)
   foo  = value
End Set

dim foo as Foo    
End Class

Public Class Other

   Public Sub SomeFunc()    
     dim B as New Bar()    
     B.MyFoo = new Foo()    
     B.MyFoo.i = 14 'Expression is a value and therefore cannot be the target of an assignment ???    
   End Sub
End Class

My question is, why can I not assign to i through my property in the Bar class? What have I done wrong?

Answer 1

The answer is found here, it says the following:

' Assume this code runs inside Form1.
Dim exitButton As New System.Windows.Forms.Button()
exitButton.Text = "Exit this form"
exitButton.Location.X = 140
' The preceding line is an ERROR because of no storage for Location.

The last statement of the preceding
example fails because it creates only
a temporary allocation for the Point
structure returned by the Location
property. A structure is a value type,
and the temporary structure is not
retained after the statement runs. The
problem is resolved by declaring and
using a variable for Location, which
creates a more permanent allocation
for the Point structure. The following
example shows code that can replace
the last statement of the preceding
example.

This is because the struct is only a temporary variable. So the solution is to create a new struct of the type you need, assign it all it’s internal variables and then assign that struct to the struct property of the class.