How To Obtain Type for Generic Conversion

[Charles Law]

I want to do something like this:

obj = CType(value, Value.Type)

Well, not exactly, but I think that captures the essence. I realise it won't
work as I have written it, and it looks a bit like a nebulous statement, but
I am looking for a generic way to convert a variable of unknown type to its
actual type.

Perhaps a better example would be

Enum MyEnum As Byte
AnElement
AnotherElement
End Enum

Dim e As MyEnum
Dim obj as Object

e = AnotherElement

obj = CType(e, Byte)

The thing is, I don't know, until runtime what the underlying type is.

Any thoughts?

TIA

Charles

[Cor Ligthert]

Hi Charles,

Can you not do something with overloaded functions: That much types are not
there and maybe even less when you know what you use.

function charles(byval item as integer) as integer
end function

function charles(byval item as string) as string
end function

I did not try it, just something that came up and maybe it helps you.

Cor

[Charles Law]

Hi Cor

I think, from what you are suggesting, that the compiler would have to know
at compile time what the type was, so that it could use the correct
overloaded function. In fact, the type won't be known until runtime.

What I am actually doing, is using reflection to translate a structure into
a byte array. As I iterate through the structure - which I am passed at
runtime - each element may have a different type, and I wish to convert each
type into the correct number of bytes for its internal storage.

Charles
"Cor Ligthert" <no**********@planet.nl> wrote in message
news:%2****************@TK2MSFTNGP11.phx.gbl...

Hi Charles,

Can you not do something with overloaded functions: That much types are not there and maybe even less when you know what you use.

function charles(byval item as integer) as integer
end function

function charles(byval item as string) as string
end function

I did not try it, just something that came up and maybe it helps you.

Cor

[Jay B. Harlow [MVP - Outlook]]

Charles,
Have you tried:

Dim e As MyEnum = MyEnum.AnotherElement
Dim obj as Object

Dim theType As Type = GetType(Byte)

obj = Convert.ChangeType(value, theType)

Hope this helps
Jay

"Charles Law" <bl***@nowhere.com> wrote in message
news:%2****************@TK2MSFTNGP10.phx.gbl...

I want to do something like this:

obj = CType(value, Value.Type)

Well, not exactly, but I think that captures the essence. I realise it won't work as I have written it, and it looks a bit like a nebulous statement, but I am looking for a generic way to convert a variable of unknown type to its actual type.

Perhaps a better example would be

Enum MyEnum As Byte
AnElement
AnotherElement
End Enum

Dim e As MyEnum
Dim obj as Object

e = AnotherElement

obj = CType(e, Byte)

The thing is, I don't know, until runtime what the underlying type is.

Any thoughts?

TIA

Charles

[Charles Law]

Hi Jay

Thanks. I have tried it now, but it seems to work only for byte types.
Anything larger throws an exception "Value was either too large or too small
for an unsigned byte".

The code I currently have is below:

<code>
Public Shared Function ToByteArray(ByVal MyStruct As Object) As Byte()

' Convert a structure into a byte array

Dim al As ArrayList

Dim Fields As FieldInfo()

Try
Fields = MyStruct.GetType.GetFields

al = New ArrayList

For Each fld As FieldInfo In Fields
If fld.FieldType.Equals(GetType(Byte)) Then
' Add byte to array list
al.Add(CByte(fld.GetValue(MyStruct)))

ElseIf fld.FieldType.Equals(GetType(Int16)) Then
' Add 16-bit value to array list
Dim i16 As Int16

i16 = CType(fld.GetValue(MyStruct), Int16)

' Little-endian
al.Add(CByte(i16 And &HFF))
al.Add(CByte((i16 And &HFF00) >> 8))

' Big-endian
'al.Add(CByte(i16 >> 8))
'al.Add(CByte(i16 And &HFF))

ElseIf fld.FieldType.Equals(GetType(SomeEnumeratedValue))
Then
' This is coded as a byte
al.Add(CByte(fld.GetValue(MyStruct)))

ElseIf fld.FieldType.Equals(GetType(SomethingElse)) Then
' This is coded as a byte
al.Add(CByte(fld.GetValue(MyStruct)))

Else
Throw New Exception("Cannot convert type " &
fld.FieldType.ToString)
End If
Next fld

Catch ex As Exception
Throw

End Try

Return DirectCast(al.ToArray(GetType(Byte)), Byte())

End Function
</code>

As you will see, there is the potential for a lot of If .. Then ... Elses. I
am looking for a generic way to convert to save all the typing and
duplication. Any thoughts?

Charles
"Jay B. Harlow [MVP - Outlook]" <Ja************@msn.com> wrote in message
news:OJ*************@TK2MSFTNGP11.phx.gbl...

Charles,
Have you tried:

Dim e As MyEnum = MyEnum.AnotherElement
Dim obj as Object

Dim theType As Type = GetType(Byte)

obj = Convert.ChangeType(value, theType)

Hope this helps
Jay

"Charles Law" <bl***@nowhere.com> wrote in message
news:%2****************@TK2MSFTNGP10.phx.gbl...

I want to do something like this:

obj = CType(value, Value.Type)

Well, not exactly, but I think that captures the essence. I realise it

won't

work as I have written it, and it looks a bit like a nebulous statement,

but

I am looking for a generic way to convert a variable of unknown type to

its

actual type.

Perhaps a better example would be

Enum MyEnum As Byte
AnElement
AnotherElement
End Enum

Dim e As MyEnum
Dim obj as Object

e = AnotherElement

obj = CType(e, Byte)

The thing is, I don't know, until runtime what the underlying type is.

Any thoughts?

TIA

Charles

[Jay B. Harlow [MVP - Outlook]]

Charles,

Thanks. I have tried it now, but it seems to work only for byte types.
Anything larger throws an exception "Value was either too large or too small for an unsigned byte".
The code I gave IS for byte types! Notice the GetType(Byte) in there, you
would need to change GetType(Byte) to the specific type you are interested
in (for example FieldInfo.FieldType). Remember an Enum can be Byte, Short,
Integer or Long.

Dim theType As Type = GetType(Byte) ' convert to byte Dim theType As Type = GetType(Integer) ' convert to integer
Dim theType As Type = GetType(String) ' convert to string
Dim theType As Type = GetType(Double) ' convert to double obj = Convert.ChangeType(value, theType)
Unfortunately it does not really make sense to convert an integer to an
integer, as I don't see that really buys you anything!

What are you really attempting to do???

Have you looked at BinarySerialization?
I would use a MemoryStream & BinaryWriter if I really needed to implement
the ToByteArray routine. Something like:

' Convert a structure into a byte array
Public Shared Function ToByteArray(ByVal MyStruct As Object) As Byte()
Dim stream As New MemoryStream
Dim writer As New BinaryWriter(stream)
Dim fields() As FieldInfo = MyStruct.GetType().GetFields()
For Each fld As FieldInfo In fields
If fld.FieldType Is GetType(Byte) Then
writer.Write(DirectCast(fld.GetValue(MyStruct), Byte))
ElseIf fld.FieldType Is GetType(Short) Then
writer.Write(DirectCast(fld.GetValue(MyStruct), Short))
ElseIf fld.FieldType Is GetType(Integer) Then
writer.Write(DirectCast(fld.GetValue(MyStruct), Integer))
ElseIf fld.FieldType Is GetType(String) Then
writer.Write(DirectCast(fld.GetValue(MyStruct), String))
ElseIf fld.FieldType.IsEnum Then
' find the underlying type of enum and write that.
Else
' get all the fields on the Structure or Class fields
writer.Write(ToByteArray(fld.GetValue(MyStruct)))
End If
Next fld

Return stream.GetBuffer()
End Function

Alternatively you can use BitConverter.GetBytes to get an array of bytes
given a value.

Note both BinaryWriter & GetBytes don't allow you to work with an object
variable directly.

Hope this helps
Jay
"Charles Law" <bl***@nowhere.com> wrote in message
news:OZ**************@TK2MSFTNGP11.phx.gbl... Hi Jay

Thanks. I have tried it now, but it seems to work only for byte types.
Anything larger throws an exception "Value was either too large or too small for an unsigned byte".

The code I currently have is below:

<code>
Public Shared Function ToByteArray(ByVal MyStruct As Object) As Byte()

' Convert a structure into a byte array

Dim al As ArrayList

Dim Fields As FieldInfo()

Try
Fields = MyStruct.GetType.GetFields

al = New ArrayList

For Each fld As FieldInfo In Fields
If fld.FieldType.Equals(GetType(Byte)) Then
' Add byte to array list
al.Add(CByte(fld.GetValue(MyStruct)))

ElseIf fld.FieldType.Equals(GetType(Int16)) Then
' Add 16-bit value to array list
Dim i16 As Int16

i16 = CType(fld.GetValue(MyStruct), Int16)

' Little-endian
al.Add(CByte(i16 And &HFF))
al.Add(CByte((i16 And &HFF00) >> 8))

' Big-endian
'al.Add(CByte(i16 >> 8))
'al.Add(CByte(i16 And &HFF))

ElseIf fld.FieldType.Equals(GetType(SomeEnumeratedValue))
Then
' This is coded as a byte
al.Add(CByte(fld.GetValue(MyStruct)))

ElseIf fld.FieldType.Equals(GetType(SomethingElse)) Then
' This is coded as a byte
al.Add(CByte(fld.GetValue(MyStruct)))

Else
Throw New Exception("Cannot convert type " &
fld.FieldType.ToString)
End If
Next fld

Catch ex As Exception
Throw

End Try

Return DirectCast(al.ToArray(GetType(Byte)), Byte())

End Function
</code>

As you will see, there is the potential for a lot of If .. Then ... Elses. I am looking for a generic way to convert to save all the typing and
duplication. Any thoughts?

Charles
"Jay B. Harlow [MVP - Outlook]" <Ja************@msn.com> wrote in message
news:OJ*************@TK2MSFTNGP11.phx.gbl...

Charles,
Have you tried:

Dim e As MyEnum = MyEnum.AnotherElement
Dim obj as Object

Dim theType As Type = GetType(Byte)

obj = Convert.ChangeType(value, theType)

Hope this helps
Jay

"Charles Law" <bl***@nowhere.com> wrote in message
news:%2****************@TK2MSFTNGP10.phx.gbl...

I want to do something like this:

obj = CType(value, Value.Type)

Well, not exactly, but I think that captures the essence. I realise it

won't

work as I have written it, and it looks a bit like a nebulous

statement, but

I am looking for a generic way to convert a variable of unknown type

to its

actual type.

Perhaps a better example would be

Enum MyEnum As Byte
AnElement
AnotherElement
End Enum

Dim e As MyEnum
Dim obj as Object

e = AnotherElement

obj = CType(e, Byte)

The thing is, I don't know, until runtime what the underlying type is.

Any thoughts?

TIA

Charles

[Charles Law]

Hi Jay

I have several structures that represent message packets. I want to be able
to take any one of these structures and convert it into a byte array so I
can send it down the line. Thus, I would have a single routine that could
take any of these structures and send it.

I don't want to have a series of If.... Thens because the structure could
contain a more complex type. I am only interested in the byte-by-byte
representation of the data in the structure. It is perhaps complicated by
the fact that multi-byte types need to be sent little-endian.

Charles
"Jay B. Harlow [MVP - Outlook]" <Ja************@msn.com> wrote in message
news:uB**************@TK2MSFTNGP12.phx.gbl...

Charles,

Thanks. I have tried it now, but it seems to work only for byte types.
Anything larger throws an exception "Value was either too large or too small

for an unsigned byte".

The code I gave IS for byte types! Notice the GetType(Byte) in there, you
would need to change GetType(Byte) to the specific type you are interested
in (for example FieldInfo.FieldType). Remember an Enum can be Byte, Short,
Integer or Long.

Dim theType As Type = GetType(Byte) ' convert to byte Dim theType As Type = GetType(Integer) ' convert to integer
Dim theType As Type = GetType(String) ' convert to string
Dim theType As Type = GetType(Double) ' convert to double obj = Convert.ChangeType(value, theType)
Unfortunately it does not really make sense to convert an integer to an
integer, as I don't see that really buys you anything!

What are you really attempting to do???

Have you looked at BinarySerialization?
I would use a MemoryStream & BinaryWriter if I really needed to implement
the ToByteArray routine. Something like:

' Convert a structure into a byte array
Public Shared Function ToByteArray(ByVal MyStruct As Object) As Byte()
Dim stream As New MemoryStream
Dim writer As New BinaryWriter(stream)
Dim fields() As FieldInfo = MyStruct.GetType().GetFields()
For Each fld As FieldInfo In fields
If fld.FieldType Is GetType(Byte) Then
writer.Write(DirectCast(fld.GetValue(MyStruct), Byte))
ElseIf fld.FieldType Is GetType(Short) Then
writer.Write(DirectCast(fld.GetValue(MyStruct), Short))
ElseIf fld.FieldType Is GetType(Integer) Then
writer.Write(DirectCast(fld.GetValue(MyStruct), Integer))
ElseIf fld.FieldType Is GetType(String) Then
writer.Write(DirectCast(fld.GetValue(MyStruct), String))
ElseIf fld.FieldType.IsEnum Then
' find the underlying type of enum and write that.
Else
' get all the fields on the Structure or Class fields
writer.Write(ToByteArray(fld.GetValue(MyStruct)))
End If
Next fld

Return stream.GetBuffer()
End Function

Alternatively you can use BitConverter.GetBytes to get an array of bytes
given a value.

Note both BinaryWriter & GetBytes don't allow you to work with an object
variable directly.

Hope this helps
Jay
"Charles Law" <bl***@nowhere.com> wrote in message
news:OZ**************@TK2MSFTNGP11.phx.gbl...

Hi Jay

Thanks. I have tried it now, but it seems to work only for byte types.
Anything larger throws an exception "Value was either too large or too

small

for an unsigned byte".

The code I currently have is below:

<code>
Public Shared Function ToByteArray(ByVal MyStruct As Object) As Byte()
' Convert a structure into a byte array

Dim al As ArrayList

Dim Fields As FieldInfo()

Try
Fields = MyStruct.GetType.GetFields

al = New ArrayList

For Each fld As FieldInfo In Fields
If fld.FieldType.Equals(GetType(Byte)) Then
' Add byte to array list
al.Add(CByte(fld.GetValue(MyStruct)))

ElseIf fld.FieldType.Equals(GetType(Int16)) Then
' Add 16-bit value to array list
Dim i16 As Int16

i16 = CType(fld.GetValue(MyStruct), Int16)

' Little-endian
al.Add(CByte(i16 And &HFF))
al.Add(CByte((i16 And &HFF00) >> 8))

' Big-endian
'al.Add(CByte(i16 >> 8))
'al.Add(CByte(i16 And &HFF))

ElseIf fld.FieldType.Equals(GetType(SomeEnumeratedValue)) Then
' This is coded as a byte
al.Add(CByte(fld.GetValue(MyStruct)))

ElseIf fld.FieldType.Equals(GetType(SomethingElse)) Then
' This is coded as a byte
al.Add(CByte(fld.GetValue(MyStruct)))

Else
Throw New Exception("Cannot convert type " &
fld.FieldType.ToString)
End If
Next fld

Catch ex As Exception
Throw

End Try

Return DirectCast(al.ToArray(GetType(Byte)), Byte())

End Function
</code>

As you will see, there is the potential for a lot of If .. Then ... Elses. I

am looking for a generic way to convert to save all the typing and
duplication. Any thoughts?

Charles
"Jay B. Harlow [MVP - Outlook]" <Ja************@msn.com> wrote in

message news:OJ*************@TK2MSFTNGP11.phx.gbl...

Charles,
Have you tried:

Dim e As MyEnum = MyEnum.AnotherElement
Dim obj as Object

Dim theType As Type = GetType(Byte)

obj = Convert.ChangeType(value, theType)

Hope this helps
Jay

"Charles Law" <bl***@nowhere.com> wrote in message
news:%2****************@TK2MSFTNGP10.phx.gbl...
> I want to do something like this:
>
> obj = CType(value, Value.Type)
>
> Well, not exactly, but I think that captures the essence. I realise it won't
> work as I have written it, and it looks a bit like a nebulous

statement, but
> I am looking for a generic way to convert a variable of unknown type to its
> actual type.
>
> Perhaps a better example would be
>
> Enum MyEnum As Byte
> AnElement
> AnotherElement
> End Enum
>
> Dim e As MyEnum
> Dim obj as Object
>
> e = AnotherElement
>
> obj = CType(e, Byte)
>
> The thing is, I don't know, until runtime what the underlying type is. >
> Any thoughts?
>
> TIA
>
> Charles
>
>