Use of FlagsAttribute

[Randy]

I can't seem to find a clear example on how to use the FlagsAttribute. In
my example below shouldn't both message boxes show? Instead no messagebox
displays. I know that .NET will auto-number enum's when omitted.

<Flags()> Public Enum Permission
Read
Write
Delete
Rename
Copy
Move
End Enum

Private p As Permission
p = Permission.Copy And Permission.Read

If p = Permission.Copy Then
MessageBox.Show ("Copy")
End If

If p = Permission.Copy And p = Permission.Read Then
MessageBox.Show ("Copy & Read")
End If

[Daniel Pratt]

Re: Use of FlagsAttribute

Hi Randy
"Randy" <randy@penHATES PAMsoft.com> wrote in message
news:OFCJzq0jDH A.392@TK2MSFTNG P11.phx.gbl...[color=blue]
> I can't seem to find a clear example on how to use the FlagsAttribute. In
> my example below shouldn't both message boxes show? Instead no messagebox
> displays. I know that .NET will auto-number enum's when omitted.[/color]
<snip>

If you don't specify values for your enum fields, they will be assigned
values in a straight sequence (1,2,3,4, etc...). If you want a "flagged"
enum you need to specify values that correspond to individual bit positions
(1,2,4,16, etc.):

<Flags()> Public Enum Permission
Read = 1
Write = 2
Delete = 4
Rename = 16
Copy = 32
Move = 64
End Enum

Hope that helps.

Regards,
Dan

p.s. *Should* the compiler be smart enough to auto-assign values correctly
if the "Flags" attribute is present? I think so.

[Jay B. Harlow [MVP - Outlook]]

Re: Use of FlagsAttribute

Randy,
In addition to Daniel's suggestion of giving values to the Enum values.

<Flags()> Public Enum Permission
Read = 1
Write = 2
Delete = 4
Rename = 16
Copy = 32
Move = 64
End Enum

To combine the values you need to use Or.
[color=blue]
> Private p As Permission[/color]
p = Permission.Copy Or Permission.Read

Then you need to 'mask' the value and see if its not zero.

If (p and Permission.Copy ) <> 0 Then[color=blue]
> MessageBox.Show ("Copy")
> End If[/color]

You can check for not zero or both values combined:
If (p and Permission.Copy Or Permission.Read ) = (Permission.Cop y Or
Permission.Read ) Then[color=blue]
> MessageBox.Show ("Copy & Read")
> End If[/color]

Sometimes when dealing with combined values, such as Read & Copy above, I
will define a constant that represents the two values combined

Const ReadAndCopy As Permission = Permission.Copy Or Permission.Read
If (p and ReadAndCopy ) = ReadAndCopy Then[color=blue]
> MessageBox.Show ("Copy & Read")
> End If[/color]

Other times I will setup a function to check the masked values:

Private Function CheckMask(ByVal value As Permission, ByVal mask As
Permission)
Return (value And mask) = value
End Function

If CheckMask(p, Permission.Copy Or Permission.Read ) Then[color=blue]
> MessageBox.Show ("Copy & Read")
> End If[/color]

I will use the mask & value method when I want to check that out of Copy &
Read only Copy is set.

If (p and Permission.Copy Or Permission.Read ) = Permission.Copy Then
MessageBox.Show ("Of Copy & Read, only Copy set")
End If

When you think about it, one would expect And would be used to combine the
value (set theory). However enums are implemented as integers and boolean
theory is how they are worked with...

Hope this helps
Jay

"Randy" <randy@penHATES PAMsoft.com> wrote in message
news:OFCJzq0jDH A.392@TK2MSFTNG P11.phx.gbl...[color=blue]
> I can't seem to find a clear example on how to use the FlagsAttribute. In
> my example below shouldn't both message boxes show? Instead no messagebox
> displays. I know that .NET will auto-number enum's when omitted.
>
> <Flags()> Public Enum Permission
> Read
> Write
> Delete
> Rename
> Copy
> Move
> End Enum
>
> Private p As Permission
> p = Permission.Copy And Permission.Read
>
> If p = Permission.Copy Then
> MessageBox.Show ("Copy")
> End If
>
> If p = Permission.Copy And p = Permission.Read Then
> MessageBox.Show ("Copy & Read")
> End If
>
>[/color]

[Jay B. Harlow [MVP - Outlook]]

Re: Use of FlagsAttribute

Randy,
In addition to Daniel's suggestion of giving values to the Enum values.

<Flags()> Public Enum Permission
Read = 1
Write = 2
Delete = 4
Rename = 16
Copy = 32
Move = 64
End Enum

To combine the values you need to use Or.
[color=blue]
> Private p As Permission[/color]
p = Permission.Copy Or Permission.Read

Then you need to 'mask' the value and see if its not zero.

If (p and Permission.Copy ) <> 0 Then[color=blue]
> MessageBox.Show ("Copy")
> End If[/color]

You can check for not zero or both values combined:
If (p and Permission.Copy Or Permission.Read ) = (Permission.Cop y Or
Permission.Read ) Then[color=blue]
> MessageBox.Show ("Copy & Read")
> End If[/color]

Sometimes when dealing with combined values, such as Read & Copy above, I
will define a constant that represents the two values combined

Const ReadAndCopy As Permission = Permission.Copy Or Permission.Read
If (p and ReadAndCopy ) = ReadAndCopy Then[color=blue]
> MessageBox.Show ("Copy & Read")
> End If[/color]

Other times I will setup a function to check the masked values:

Private Function CheckMask(ByVal value As Permission, ByVal mask As
Permission)
Return (value And mask) = value
End Function

If CheckMask(p, Permission.Copy Or Permission.Read ) Then[color=blue]
> MessageBox.Show ("Copy & Read")
> End If[/color]

I will use the mask & value method when I want to check that out of Copy &
Read only Copy is set.

If (p and Permission.Copy Or Permission.Read ) = Permission.Copy Then
MessageBox.Show ("Of Copy & Read, only Copy set")
End If

When you think about it, one would expect And would be used to combine the
value (set theory). However enums are implemented as integers and boolean
theory is how they are worked with...

Hope this helps
Jay

"Randy" <randy@penHATES PAMsoft.com> wrote in message
news:OFCJzq0jDH A.392@TK2MSFTNG P11.phx.gbl...[color=blue]
> I can't seem to find a clear example on how to use the FlagsAttribute. In
> my example below shouldn't both message boxes show? Instead no messagebox
> displays. I know that .NET will auto-number enum's when omitted.
>
> <Flags()> Public Enum Permission
> Read
> Write
> Delete
> Rename
> Copy
> Move
> End Enum
>
> Private p As Permission
> p = Permission.Copy And Permission.Read
>
> If p = Permission.Copy Then
> MessageBox.Show ("Copy")
> End If
>
> If p = Permission.Copy And p = Permission.Read Then
> MessageBox.Show ("Copy & Read")
> End If
>
>[/color]

[Mr.Tickle]

Re: Use of FlagsAttribute

This is something I find that .NET messed up.


if I specify the [Flags] attribute, why should I have to set the enum values
in powers of 2? Why cant the enum be smart enough to see that attribute and
set them accordingly. What is the benifit of the Flags attribute then? Its
lost. Pointless.





"Jay B. Harlow [MVP - Outlook]" <Jay_Harlow@ema il.msn.com> wrote in message
news:OyZU0V6jDH A.684@TK2MSFTNG P09.phx.gbl...[color=blue]
> Randy,
> In addition to Daniel's suggestion of giving values to the Enum values.
>
> <Flags()> Public Enum Permission
> Read = 1
> Write = 2
> Delete = 4
> Rename = 16
> Copy = 32
> Move = 64
> End Enum
>
> To combine the values you need to use Or.
>[color=green]
> > Private p As Permission[/color]
> p = Permission.Copy Or Permission.Read
>
> Then you need to 'mask' the value and see if its not zero.
>
> If (p and Permission.Copy ) <> 0 Then[color=green]
> > MessageBox.Show ("Copy")
> > End If[/color]
>
> You can check for not zero or both values combined:
> If (p and Permission.Copy Or Permission.Read ) = (Permission.Cop y Or
> Permission.Read ) Then[color=green]
> > MessageBox.Show ("Copy & Read")
> > End If[/color]
>
> Sometimes when dealing with combined values, such as Read & Copy above, I
> will define a constant that represents the two values combined
>
> Const ReadAndCopy As Permission = Permission.Copy Or Permission.Read
> If (p and ReadAndCopy ) = ReadAndCopy Then[color=green]
> > MessageBox.Show ("Copy & Read")
> > End If[/color]
>
> Other times I will setup a function to check the masked values:
>
> Private Function CheckMask(ByVal value As Permission, ByVal mask As
> Permission)
> Return (value And mask) = value
> End Function
>
> If CheckMask(p, Permission.Copy Or Permission.Read ) Then[color=green]
> > MessageBox.Show ("Copy & Read")
> > End If[/color]
>
> I will use the mask & value method when I want to check that out of Copy &
> Read only Copy is set.
>
> If (p and Permission.Copy Or Permission.Read ) = Permission.Copy Then
> MessageBox.Show ("Of Copy & Read, only Copy set")
> End If
>
> When you think about it, one would expect And would be used to combine the
> value (set theory). However enums are implemented as integers and boolean
> theory is how they are worked with...
>
> Hope this helps
> Jay
>
> "Randy" <randy@penHATES PAMsoft.com> wrote in message
> news:OFCJzq0jDH A.392@TK2MSFTNG P11.phx.gbl...[color=green]
> > I can't seem to find a clear example on how to use the FlagsAttribute.[/color][/color]
In[color=blue][color=green]
> > my example below shouldn't both message boxes show? Instead no[/color][/color]
messagebox[color=blue][color=green]
> > displays. I know that .NET will auto-number enum's when omitted.
> >
> > <Flags()> Public Enum Permission
> > Read
> > Write
> > Delete
> > Rename
> > Copy
> > Move
> > End Enum
> >
> > Private p As Permission
> > p = Permission.Copy And Permission.Read
> >
> > If p = Permission.Copy Then
> > MessageBox.Show ("Copy")
> > End If
> >
> > If p = Permission.Copy And p = Permission.Read Then
> > MessageBox.Show ("Copy & Read")
> > End If
> >
> >[/color]
>
>[/color]

[Mr.Tickle]

Re: Use of FlagsAttribute

This is something I find that .NET messed up.


if I specify the [Flags] attribute, why should I have to set the enum values
in powers of 2? Why cant the enum be smart enough to see that attribute and
set them accordingly. What is the benifit of the Flags attribute then? Its
lost. Pointless.





"Jay B. Harlow [MVP - Outlook]" <Jay_Harlow@ema il.msn.com> wrote in message
news:OyZU0V6jDH A.684@TK2MSFTNG P09.phx.gbl...[color=blue]
> Randy,
> In addition to Daniel's suggestion of giving values to the Enum values.
>
> <Flags()> Public Enum Permission
> Read = 1
> Write = 2
> Delete = 4
> Rename = 16
> Copy = 32
> Move = 64
> End Enum
>
> To combine the values you need to use Or.
>[color=green]
> > Private p As Permission[/color]
> p = Permission.Copy Or Permission.Read
>
> Then you need to 'mask' the value and see if its not zero.
>
> If (p and Permission.Copy ) <> 0 Then[color=green]
> > MessageBox.Show ("Copy")
> > End If[/color]
>
> You can check for not zero or both values combined:
> If (p and Permission.Copy Or Permission.Read ) = (Permission.Cop y Or
> Permission.Read ) Then[color=green]
> > MessageBox.Show ("Copy & Read")
> > End If[/color]
>
> Sometimes when dealing with combined values, such as Read & Copy above, I
> will define a constant that represents the two values combined
>
> Const ReadAndCopy As Permission = Permission.Copy Or Permission.Read
> If (p and ReadAndCopy ) = ReadAndCopy Then[color=green]
> > MessageBox.Show ("Copy & Read")
> > End If[/color]
>
> Other times I will setup a function to check the masked values:
>
> Private Function CheckMask(ByVal value As Permission, ByVal mask As
> Permission)
> Return (value And mask) = value
> End Function
>
> If CheckMask(p, Permission.Copy Or Permission.Read ) Then[color=green]
> > MessageBox.Show ("Copy & Read")
> > End If[/color]
>
> I will use the mask & value method when I want to check that out of Copy &
> Read only Copy is set.
>
> If (p and Permission.Copy Or Permission.Read ) = Permission.Copy Then
> MessageBox.Show ("Of Copy & Read, only Copy set")
> End If
>
> When you think about it, one would expect And would be used to combine the
> value (set theory). However enums are implemented as integers and boolean
> theory is how they are worked with...
>
> Hope this helps
> Jay
>
> "Randy" <randy@penHATES PAMsoft.com> wrote in message
> news:OFCJzq0jDH A.392@TK2MSFTNG P11.phx.gbl...[color=green]
> > I can't seem to find a clear example on how to use the FlagsAttribute.[/color][/color]
In[color=blue][color=green]
> > my example below shouldn't both message boxes show? Instead no[/color][/color]
messagebox[color=blue][color=green]
> > displays. I know that .NET will auto-number enum's when omitted.
> >
> > <Flags()> Public Enum Permission
> > Read
> > Write
> > Delete
> > Rename
> > Copy
> > Move
> > End Enum
> >
> > Private p As Permission
> > p = Permission.Copy And Permission.Read
> >
> > If p = Permission.Copy Then
> > MessageBox.Show ("Copy")
> > End If
> >
> > If p = Permission.Copy And p = Permission.Read Then
> > MessageBox.Show ("Copy & Read")
> > End If
> >
> >[/color]
>
>[/color]

[Jay B. Harlow [MVP - Outlook]]

Re: Use of FlagsAttribute

Mr.Tickle,
I won't disagree with you in that the compiler should figure out to use
Powers of two when you apply the Flags attribute and do not explicitly list
the values.
[color=blue]
> What is the benifit of the Flags attribute then?[/color]
The attribute controls the default behavior of the Enum.ToString method.

For example:

Private p As Permission
p = Permission.Copy Or Permission.Read

Debug.WriteLine (p, "Permission ")

If Permission has the Flags attribute, then "Permission : Copy, Read" will be
printed, without the Flags attribute 33 will be printed. You can use one of
the Overloaded Enum.ToString methods to control this...

Hope this helps
Jay

"Mr.Tickle" <MrTickle@mrmen .com> wrote in message
news:%23BVPI69j DHA.2528@TK2MSF TNGP12.phx.gbl. ..[color=blue]
> This is something I find that .NET messed up.
>
>
> if I specify the [Flags] attribute, why should I have to set the enum[/color]
values[color=blue]
> in powers of 2? Why cant the enum be smart enough to see that attribute[/color]
and[color=blue]
> set them accordingly. What is the benifit of the Flags attribute then?[/color]
Its[color=blue]
> lost. Pointless.
>
>
>
>
>
> "Jay B. Harlow [MVP - Outlook]" <Jay_Harlow@ema il.msn.com> wrote in[/color]
message[color=blue]
> news:OyZU0V6jDH A.684@TK2MSFTNG P09.phx.gbl...[color=green]
> > Randy,
> > In addition to Daniel's suggestion of giving values to the Enum values.
> >
> > <Flags()> Public Enum Permission
> > Read = 1
> > Write = 2
> > Delete = 4
> > Rename = 16
> > Copy = 32
> > Move = 64
> > End Enum
> >
> > To combine the values you need to use Or.
> >[color=darkred]
> > > Private p As Permission[/color]
> > p = Permission.Copy Or Permission.Read
> >
> > Then you need to 'mask' the value and see if its not zero.
> >
> > If (p and Permission.Copy ) <> 0 Then[color=darkred]
> > > MessageBox.Show ("Copy")
> > > End If[/color]
> >
> > You can check for not zero or both values combined:
> > If (p and Permission.Copy Or Permission.Read ) = (Permission.Cop y Or
> > Permission.Read ) Then[color=darkred]
> > > MessageBox.Show ("Copy & Read")
> > > End If[/color]
> >
> > Sometimes when dealing with combined values, such as Read & Copy above,[/color][/color]
I[color=blue][color=green]
> > will define a constant that represents the two values combined
> >
> > Const ReadAndCopy As Permission = Permission.Copy Or Permission.Read
> > If (p and ReadAndCopy ) = ReadAndCopy Then[color=darkred]
> > > MessageBox.Show ("Copy & Read")
> > > End If[/color]
> >
> > Other times I will setup a function to check the masked values:
> >
> > Private Function CheckMask(ByVal value As Permission, ByVal mask As
> > Permission)
> > Return (value And mask) = value
> > End Function
> >
> > If CheckMask(p, Permission.Copy Or Permission.Read ) Then[color=darkred]
> > > MessageBox.Show ("Copy & Read")
> > > End If[/color]
> >
> > I will use the mask & value method when I want to check that out of Copy[/color][/color]
&[color=blue][color=green]
> > Read only Copy is set.
> >
> > If (p and Permission.Copy Or Permission.Read ) = Permission.Copy[/color][/color]
Then[color=blue][color=green]
> > MessageBox.Show ("Of Copy & Read, only Copy set")
> > End If
> >
> > When you think about it, one would expect And would be used to combine[/color][/color]
the[color=blue][color=green]
> > value (set theory). However enums are implemented as integers and[/color][/color]
boolean[color=blue][color=green]
> > theory is how they are worked with...
> >
> > Hope this helps
> > Jay
> >
> > "Randy" <randy@penHATES PAMsoft.com> wrote in message
> > news:OFCJzq0jDH A.392@TK2MSFTNG P11.phx.gbl...[color=darkred]
> > > I can't seem to find a clear example on how to use the FlagsAttribute.[/color][/color]
> In[color=green][color=darkred]
> > > my example below shouldn't both message boxes show? Instead no[/color][/color]
> messagebox[color=green][color=darkred]
> > > displays. I know that .NET will auto-number enum's when omitted.
> > >
> > > <Flags()> Public Enum Permission
> > > Read
> > > Write
> > > Delete
> > > Rename
> > > Copy
> > > Move
> > > End Enum
> > >
> > > Private p As Permission
> > > p = Permission.Copy And Permission.Read
> > >
> > > If p = Permission.Copy Then
> > > MessageBox.Show ("Copy")
> > > End If
> > >
> > > If p = Permission.Copy And p = Permission.Read Then
> > > MessageBox.Show ("Copy & Read")
> > > End If
> > >
> > >[/color]
> >
> >[/color]
>
>[/color]

[Jay B. Harlow [MVP - Outlook]]

Re: Use of FlagsAttribute

Mr.Tickle,
I won't disagree with you in that the compiler should figure out to use
Powers of two when you apply the Flags attribute and do not explicitly list
the values.
[color=blue]
> What is the benifit of the Flags attribute then?[/color]
The attribute controls the default behavior of the Enum.ToString method.

For example:

Private p As Permission
p = Permission.Copy Or Permission.Read

Debug.WriteLine (p, "Permission ")

If Permission has the Flags attribute, then "Permission : Copy, Read" will be
printed, without the Flags attribute 33 will be printed. You can use one of
the Overloaded Enum.ToString methods to control this...

Hope this helps
Jay

"Mr.Tickle" <MrTickle@mrmen .com> wrote in message
news:%23BVPI69j DHA.2528@TK2MSF TNGP12.phx.gbl. ..[color=blue]
> This is something I find that .NET messed up.
>
>
> if I specify the [Flags] attribute, why should I have to set the enum[/color]
values[color=blue]
> in powers of 2? Why cant the enum be smart enough to see that attribute[/color]
and[color=blue]
> set them accordingly. What is the benifit of the Flags attribute then?[/color]
Its[color=blue]
> lost. Pointless.
>
>
>
>
>
> "Jay B. Harlow [MVP - Outlook]" <Jay_Harlow@ema il.msn.com> wrote in[/color]
message[color=blue]
> news:OyZU0V6jDH A.684@TK2MSFTNG P09.phx.gbl...[color=green]
> > Randy,
> > In addition to Daniel's suggestion of giving values to the Enum values.
> >
> > <Flags()> Public Enum Permission
> > Read = 1
> > Write = 2
> > Delete = 4
> > Rename = 16
> > Copy = 32
> > Move = 64
> > End Enum
> >
> > To combine the values you need to use Or.
> >[color=darkred]
> > > Private p As Permission[/color]
> > p = Permission.Copy Or Permission.Read
> >
> > Then you need to 'mask' the value and see if its not zero.
> >
> > If (p and Permission.Copy ) <> 0 Then[color=darkred]
> > > MessageBox.Show ("Copy")
> > > End If[/color]
> >
> > You can check for not zero or both values combined:
> > If (p and Permission.Copy Or Permission.Read ) = (Permission.Cop y Or
> > Permission.Read ) Then[color=darkred]
> > > MessageBox.Show ("Copy & Read")
> > > End If[/color]
> >
> > Sometimes when dealing with combined values, such as Read & Copy above,[/color][/color]
I[color=blue][color=green]
> > will define a constant that represents the two values combined
> >
> > Const ReadAndCopy As Permission = Permission.Copy Or Permission.Read
> > If (p and ReadAndCopy ) = ReadAndCopy Then[color=darkred]
> > > MessageBox.Show ("Copy & Read")
> > > End If[/color]
> >
> > Other times I will setup a function to check the masked values:
> >
> > Private Function CheckMask(ByVal value As Permission, ByVal mask As
> > Permission)
> > Return (value And mask) = value
> > End Function
> >
> > If CheckMask(p, Permission.Copy Or Permission.Read ) Then[color=darkred]
> > > MessageBox.Show ("Copy & Read")
> > > End If[/color]
> >
> > I will use the mask & value method when I want to check that out of Copy[/color][/color]
&[color=blue][color=green]
> > Read only Copy is set.
> >
> > If (p and Permission.Copy Or Permission.Read ) = Permission.Copy[/color][/color]
Then[color=blue][color=green]
> > MessageBox.Show ("Of Copy & Read, only Copy set")
> > End If
> >
> > When you think about it, one would expect And would be used to combine[/color][/color]
the[color=blue][color=green]
> > value (set theory). However enums are implemented as integers and[/color][/color]
boolean[color=blue][color=green]
> > theory is how they are worked with...
> >
> > Hope this helps
> > Jay
> >
> > "Randy" <randy@penHATES PAMsoft.com> wrote in message
> > news:OFCJzq0jDH A.392@TK2MSFTNG P11.phx.gbl...[color=darkred]
> > > I can't seem to find a clear example on how to use the FlagsAttribute.[/color][/color]
> In[color=green][color=darkred]
> > > my example below shouldn't both message boxes show? Instead no[/color][/color]
> messagebox[color=green][color=darkred]
> > > displays. I know that .NET will auto-number enum's when omitted.
> > >
> > > <Flags()> Public Enum Permission
> > > Read
> > > Write
> > > Delete
> > > Rename
> > > Copy
> > > Move
> > > End Enum
> > >
> > > Private p As Permission
> > > p = Permission.Copy And Permission.Read
> > >
> > > If p = Permission.Copy Then
> > > MessageBox.Show ("Copy")
> > > End If
> > >
> > > If p = Permission.Copy And p = Permission.Read Then
> > > MessageBox.Show ("Copy & Read")
> > > End If
> > >
> > >[/color]
> >
> >[/color]
>
>[/color]