CODEWITHSUNDEEP
vb.netstringcastinginteger
CJ7
CJ7

Reputation: 23275

How to cast from Object to Integer in VB.NET?

How should I cast from an Object to an Integer in VB.NET?

When I do:

Dim intMyInteger as Integer = TryCast(MyObject, Integer)

it says:

TryCast operand must be reference type, but Integer is a value type.

Upvotes: 19

Views: 49681

Answers (4)

Abacus
Abacus

Reputation: 2109

The equivalent for TryCast is CType. Both will do a type conversion if it is possible. By contrast, DirectCast will only convert the type if it is that type already.

To illustrate, you can use CType to convert a String, or Short, or Double, to an Integer. DirectCast will generally give you a syntax/compile error if you do that; but if you try to go around the error by using type Object (this is called "boxing" and "unboxing"), it will throw an exception at run-time.

    Dim OnePointTwo As Object = "1.2"
    Try
        Dim temp = CType(OnePointTwo, Integer)
        Console.WriteLine("CType converted to: " & temp.ToString & " (type: " & temp.GetType.ToString & ")")
    Catch ex As Exception
        Console.WriteLine("CType threw exception")
    End Try
    Try
        Dim temp = DirectCast(OnePointTwo, Integer)
        Console.WriteLine("DirectCast converted to: " & temp.ToString & " (type: " & temp.GetType.ToString & ")")
    Catch ex As Exception
        Console.WriteLine("DirectCast threw exception")
    End Try

This will output:

    CType converted to: 1 (type: System.Int32)
    DirectCast threw exception

So to most closely follow the TryCast semantics, I suggest using a function like this:

Shared Function TryCastInteger(value As Object) As Integer?
    Try
        If IsNumeric(value) Then
            Return CType(value, Integer)
        Else
            Return Nothing
        End If
    Catch ex As Exception
        Return Nothing
    End Try
End Function

And to illustrate its effect:

Shared Sub TestTryCastInteger()
    Dim temp As Integer?

    Dim OnePointTwo As Object = "1.2"
    temp = TryCastInteger(OnePointTwo)
    If temp Is Nothing Then
        Console.WriteLine("Could not convert to Integer")
    Else
        Console.WriteLine("TryCastInteger converted to: " & temp.ToString & " (type: " & temp.GetType.ToString & ")")
    End If

    Dim NotANumber As Object = "bob's your uncle"
    temp = TryCastInteger(NotANumber)
    If temp Is Nothing Then
        Console.WriteLine("Could not convert to Integer")
    Else
        Console.WriteLine("TryCastInteger converted to: " & temp.ToString & " (type: " & temp.GetType.ToString & ")")
    End If
End Sub

Running TestTryCastInteger() will output:

    TryCastInteger converted to: 1 (type: System.Int32)
    Could not convert to Integer

There also is such a thing as a null/Nothing Integer, or any other static type, called a "nullable" type, see Variable declaration question mark for some more information. But that does not really make it a "reference" type either.

Upvotes: 2

CoOl
CoOl

Reputation: 2797

You can use this:

Dim intMyInteger as Integer

Integer.TryParse(MyObject, intMyInteger)

Upvotes: 5

Jonathon Reinhart
Jonathon Reinhart

Reputation: 137398

TryCast is the equivalent of C#'s as operator. It is a "safe cast" operator that doesn't throw an exception if the cast fails. Instead, it returns Nothing (null in C#). The problem is, you can't assign Nothing (null) (a reference type) to an Integer (a value type). There is no such thing as an Integer null/Nothing.

Instead, you can use TypeOf and Is:

If TypeOf MyObject Is Integer Then
    intMyInteger = DirectCast(MyObject, Integer)
Else
    intMyInteger = 0
End If

This tests to see if the runtime type of MyObject is Integer. See the MSDN documentation on the TypeOf operator for more details.

You could also write it like this:

Dim myInt As Integer = If(TypeOf myObj Is Integer, DirectCast(myObj,Integer), 0)

Furthermore, if an integer with a default value (like 0) is not suitable, you could consider a Nullable(Of Integer) type.

Upvotes: 34

Swordblaster
Swordblaster

Reputation: 356

Use Directcast and catch InvalidCastException

Upvotes: 3

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