VB.NET: Related "If/ElseIf" statements should not have the same condition

A chain of If/ElseIf statements is evaluated from top to bottom. At most, only one branch will be executed: the first one with a condition that evaluates to True.

Therefore, duplicating a condition automatically leads to dead code. Usually, this is due to a copy/paste error. At best, it's simply dead code and at worst, it's a bug that is likely to induce further bugs as the code is maintained, and obviously it could lead to unexpected behavior.

Noncompliant Code Example

If param = 1 Then
  OpenWindow()
ElseIf param = 2 Then
  CloseWindow()
ElseIf param = 1 Then ' Noncompliant
  MoveWindowToTheBackground()
End If

Compliant Solution

If param = 1 Then
  OpenWindow()
ElseIf param = 2 Then
  CloseWindow()
ElseIf param = 3 Then
  MoveWindowToTheBackground()
End If