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VB.NET Discussion Thread
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Feb 13th, 2009

Help understanding code snippet

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Hi all, here is a code snippet I'm having trouble understanding.

VB.NET Syntax (Toggle Plain Text)
public notinheritable class myClass
 
------Public Delegate Sub mySubDelegate()
 
------Public Sub mySub(ByVal Text As String)
 
-----------------If Me.InvokeRequired Then
 
------------------------Dim SI As New mySubDelegate(AddressOf mySub)
 
------------------------Me.Invoke(SI, New Object() {Text})
 
-----------------Else
 
------------------------ Text = "Something"
 
-----------------End If
 
------End Sub
 
End class
public notinheritable class myClass

------Public Delegate Sub mySubDelegate()

------Public Sub mySub(ByVal Text As String)

-----------------If Me.InvokeRequired Then

------------------------Dim SI As New mySubDelegate(AddressOf mySub)

------------------------Me.Invoke(SI, New Object() {Text})

-----------------Else

------------------------ Text = "Something"

-----------------End If

------End Sub

End class

Assume that for the execution of mySub, that an invoke is required. So the IF condition should be satisfied. Why doesn't this code execute the ELSE section as well? My expectation was that the line: Me.Invoke(SI, New Object() {Text}) would cause the program to execute the Else section as well. Can anybody help me understand why it doesn't? Thanks.

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TriceD

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Feb 13th, 2009

Re: Help understanding code snippet

First of all - if you surround your code with "" then people will respond quicker.

Secondly,
in an if statement you follow this line of resaoning

if condition is met then perform the routine then go directly to "end if" do not pass go and do not collect $200. If the condition isn't met and there is an else, then everything that doesn't meet your condition gets the else. Let's say you can only choose chocolate or vanilla ice cream. It would be

VB.NET Syntax (Toggle Plain Text)
if iceCream = chocolate
     give user chocolate (then you head to the end if)
else
     give user vanilla (then head to the end if)
end if
if iceCream = chocolate
     give user chocolate (then you head to the end if)
else
     give user vanilla (then head to the end if)
end if

Last edited by rapture; Feb 13th, 2009 at 4:42 pm.

rapture

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Feb 18th, 2009

Re: Help understanding code snippet

Click to Expand / Collapse Quote originally posted by rapture ...

First of all - if you surround your code with "" then people will respond quicker.

OK, thanks.

Quote ...

Secondly,
in an if statement you follow this line of resaoning

if condition is met then perform the routine then go directly to "end if" do not pass go and do not collect $200. If the condition isn't met and there is an else, then everything that doesn't meet your condition gets the else. Let's say you can only choose chocolate or vanilla ice cream. It would be
VB.NET Syntax (Toggle Plain Text)
if iceCream = chocolate
     give user chocolate (then you head to the end if)
else
     give user vanilla (then head to the end if)
end if
if iceCream = chocolate give user chocolate (then you head to the end if) else give user vanilla (then head to the end if) end if

Thanks for the explanation, but my problem doesn't lie in understanding how IF-ELSE conditions are executed, but rather in the specific code found in this particular IF-ELSE statement.

According to my understanding, which, mind you, is shaky at best, since I'm a vb.net newb, on the line:

VB.NET Syntax (Toggle Plain Text)
Dim SI As New mySubDelegate(AddressOf mySub)
Dim SI As New mySubDelegate(AddressOf mySub)

,

SI is declared as a delegate, pointing to the mySub method. So when it's called on the line:

VB.NET Syntax (Toggle Plain Text)
Me.Invoke(SI, New Object() {Text})
Me.Invoke(SI, New Object() {Text})

,

it calls the mySub method a second time. This second time, according to my understanding, doesn't need an invoke. So in effect, the mySub() method should be called twice. Once, when an invoke is required causing the IF part to be executed, and once when an invoke is not required, causing the ELSE part to be executed.

What I'd like to find out is why the line:

VB.NET Syntax (Toggle Plain Text)
Me.Invoke(SI, New Object() {Text})
Me.Invoke(SI, New Object() {Text})

doesn't cause an invoke to not be required, thus causing the ELSE part to be executed.

Last edited by TriceD; Feb 18th, 2009 at 7:20 am.

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