Asp.Net Programming :: Check if is nothing


	Check if is nothing Hello, I have the following: If MyTag Is Nothing Then ... End If I am getting an error. MyTag is of type HtmlTextWriterTag Private MyTag As HtmlTextWriterTag How can I check if a value was given to MyTag or not? Thanks, Miguel If IsNothing(MyTag) Then . . . End If "shapper" <mdmo@gmail.com> wrote in message news:1180533002.009408.274210@u30g2000hsc.googlegroups.com... - Hide quoted text - > Hello, > I have the following: > If MyTag Is Nothing Then > ... > End If > I am getting an error. > MyTag is of type HtmlTextWriterTag > Private MyTag As HtmlTextWriterTag > How can I check if a value was given to MyTag or not? > Thanks, > Miguel Use "x = Nothing" for value types and "x Is Nothing" for reference types. This will return true if x is set to it's default value. (a further complication is that you can use both for strings, but that's a story for another day). -- David Anton www.tangiblesoftwaresolutions.com Instant C#: VB to C# converter Instant VB: C# to VB converter C++ to C# Converter: converts C++ to C# Instant C++: converts C# or VB to C++/CLI - Hide quoted text - "shapper" wrote: > Hello, > I have the following: > If MyTag Is Nothing Then > ... > End If > I am getting an error. > MyTag is of type HtmlTextWriterTag > Private MyTag As HtmlTextWriterTag > How can I check if a value was given to MyTag or not? > Thanks, > Miguel That's just another form of "MyTag Is Nothing", which won't work for value types. -- David Anton www.tangiblesoftwaresolutions.com Instant C#: VB to C# converter Instant VB: C# to VB converter C++ to C# Converter: converts C++ to C# Instant C++: converts C# or VB to C++/CLI - Hide quoted text - "Scott M." wrote: > If IsNothing(MyTag) Then > . . . > End If > "shapper" <mdmo@gmail.com> wrote in message > news:1180533002.009408.274210@u30g2000hsc.googlegroups.com... > > Hello, > > I have the following: > > If MyTag Is Nothing Then > > ... > > End If > > I am getting an error. > > MyTag is of type HtmlTextWriterTag > > Private MyTag As HtmlTextWriterTag > > How can I check if a value was given to MyTag or not? > > Thanks, > > Miguel On May 30, 3:08 pm, David Anton <DavidAn@discussions.microsoft.com> wrote: - Hide quoted text - > That's just another form of "MyTag Is Nothing", which won't work for value > types. > -- > David Antonwww.tangiblesoftwaresolutions.com > Instant C#: VB to C# converter > Instant VB: C# to VB converter > C++ to C# Converter: converts C++ to C# > Instant C++: converts C# or VB to C++/CLI > "Scott M." wrote: > > If IsNothing(MyTag) Then > > . . . > > End If > > "shapper" <mdmo@gmail.com> wrote in message > >news:1180533002.009408.274210@u30g2000hsc.googlegroups.com... > > > Hello, > > > I have the following: > > > If MyTag Is Nothing Then > > > ... > > > End If > > > I am getting an error. > > > MyTag is of type HtmlTextWriterTag > > > Private MyTag As HtmlTextWriterTag > > > How can I check if a value was given to MyTag or not? > > > Thanks, > > > Miguel David, I got lost. You mean I should use: If MyTag = Nothing Then ... Is that right? Thanks, Miguel -----------------------------------------------Reply----------------------------------------------- Exactly. This will work for variable of any value type, including enums. -- David Anton www.tangiblesoftwaresolutions.com Instant C#: VB to C# converter Instant VB: C# to VB converter C++ to C# Converter: converts C++ to C# Instant C++: converts C# or VB to C++/CLI - Hide quoted text - "shapper" wrote: > On May 30, 3:08 pm, David Anton <DavidAn@discussions.microsoft.com> > wrote: > > That's just another form of "MyTag Is Nothing", which won't work for value > > types. > > -- > > David Antonwww.tangiblesoftwaresolutions.com > > Instant C#: VB to C# converter > > Instant VB: C# to VB converter > > C++ to C# Converter: converts C++ to C# > > Instant C++: converts C# or VB to C++/CLI > > "Scott M." wrote: > > > If IsNothing(MyTag) Then > > > . . . > > > End If > > > "shapper" <mdmo@gmail.com> wrote in message > > >news:1180533002.009408.274210@u30g2000hsc.googlegroups.com... > > > > Hello, > > > > I have the following: > > > > If MyTag Is Nothing Then > > > > ... > > > > End If > > > > I am getting an error. > > > > MyTag is of type HtmlTextWriterTag > > > > Private MyTag As HtmlTextWriterTag > > > > How can I check if a value was given to MyTag or not? > > > > Thanks, > > > > Miguel > David, > I got lost. You mean I should use: > If MyTag = Nothing Then ... > Is that right? > Thanks, > Miguel - Hide quoted text - shapper wrote: > Hello, > I have the following: > If MyTag Is Nothing Then > ... > End If > I am getting an error. > MyTag is of type HtmlTextWriterTag > Private MyTag As HtmlTextWriterTag > How can I check if a value was given to MyTag or not? > Thanks, > Miguel HtmlTextWriterTag is an enumeration, so the value can never be Nothing. A value type always has a value, so you can never check if it has been given a value or not. The default value of a HtmlTextWriterTag variable is HtmlTextWriterTag.Unknown. This is the value that the variable will have if it has not been assigned any value. -- Gran Andersson _____ http://www.guffa.com -----------------------------------------------Reply----------------------------------------------- In VB, "Nothing" is always a shortcut to the default value of a type, whether the type is a ref type or value type. You just have to use "Is" with ref types and "=" with value types. This is far more general than the C# "null", which doesn't apply at all to value types. -- David Anton www.tangiblesoftwaresolutions.com Instant C#: VB to C# converter Instant VB: C# to VB converter C++ to C# Converter: converts C++ to C# Instant C++: converts C# or VB to C++/CLI - Hide quoted text - "Gran Andersson" wrote: > shapper wrote: > > Hello, > > I have the following: > > If MyTag Is Nothing Then > > ... > > End If > > I am getting an error. > > MyTag is of type HtmlTextWriterTag > > Private MyTag As HtmlTextWriterTag > > How can I check if a value was given to MyTag or not? > > Thanks, > > Miguel > HtmlTextWriterTag is an enumeration, so the value can never be Nothing. > A value type always has a value, so you can never check if it has been > given a value or not. > The default value of a HtmlTextWriterTag variable is > HtmlTextWriterTag.Unknown. This is the value that the variable will have > if it has not been assigned any value. > -- > Gran Andersson > _____ > http://www.guffa.com > In VB, "Nothing" is always a shortcut to the default value of a type, > whether > the type is a ref type or value type. So, how about this... Dim x As Integer = 0 Will the following produce true? If x = Nothing then .... End If Zero is the default value of an Integer type, yet I have explicitly set its value to zero, so how could I get a true when testing against Nothing? -----------------------------------------------Reply----------------------------------------------- Try it... When x = 0, "x = Nothing" evaluates to 'True' -- David Anton www.tangiblesoftwaresolutions.com Instant C#: VB to C# converter Instant VB: C# to VB converter C++ to C# Converter: converts C++ to C# Instant C++: converts C# or VB to C++/CLI - Hide quoted text - "Scott M." wrote: > > In VB, "Nothing" is always a shortcut to the default value of a type, > > whether > > the type is a ref type or value type. > So, how about this... > Dim x As Integer = 0 > Will the following produce true? > If x = Nothing then > .... > End If > Zero is the default value of an Integer type, yet I have explicitly set its > value to zero, so how could I get a true when testing against Nothing? Well, I'll be! I'm not sure I am comfortable with that behavior though. "David Anton" <DavidAn@discussions.microsoft.com> wrote in message news:7D2FE2C9-6832-4EA8-B935-E19F5FBEE42B@microsoft.com... - Hide quoted text - > Try it... > When x = 0, "x = Nothing" evaluates to 'True' > -- > David Anton > www.tangiblesoftwaresolutions.com > Instant C#: VB to C# converter > Instant VB: C# to VB converter > C++ to C# Converter: converts C++ to C# > Instant C++: converts C# or VB to C++/CLI > "Scott M." wrote: >> > In VB, "Nothing" is always a shortcut to the default value of a type, >> > whether >> > the type is a ref type or value type. >> So, how about this... >> Dim x As Integer = 0 >> Will the following produce true? >> If x = Nothing then >> .... >> End If >> Zero is the default value of an Integer type, yet I have explicitly set >> its >> value to zero, so how could I get a true when testing against Nothing? I could write a book on VB weirdness... The problem is the way VB has developed over the years. It's almost as if the VB design team has simply responded ad-hoc to user requests, no matter how half-baked ("why can't I add parentheses to property calls?" "why can't I omit parentheses on method calls?", "why can't Nothing apply to value types?", "why do I have to declare my variables?", etc.). -- David Anton www.tangiblesoftwaresolutions.com Instant C#: VB to C# converter Instant VB: C# to VB converter C++ to C# Converter: converts C++ to C# Instant C++: converts C# or VB to C++/CLI - Hide quoted text - "Scott M." wrote: > Well, I'll be! > I'm not sure I am comfortable with that behavior though. > "David Anton" <DavidAn@discussions.microsoft.com> wrote in message > news:7D2FE2C9-6832-4EA8-B935-E19F5FBEE42B@microsoft.com... > > Try it... > > When x = 0, "x = Nothing" evaluates to 'True' > > -- > > David Anton > > www.tangiblesoftwaresolutions.com > > Instant C#: VB to C# converter > > Instant VB: C# to VB converter > > C++ to C# Converter: converts C++ to C# > > Instant C++: converts C# or VB to C++/CLI > > "Scott M." wrote: > >> > In VB, "Nothing" is always a shortcut to the default value of a type, > >> > whether > >> > the type is a ref type or value type. > >> So, how about this... > >> Dim x As Integer = 0 > >> Will the following produce true? > >> If x = Nothing then > >> .... > >> End If > >> Zero is the default value of an Integer type, yet I have explicitly set > >> its > >> value to zero, so how could I get a true when testing against Nothing? David Anton wrote: > I could write a book on VB weirdness... > The problem is the way VB has developed over the years. It's almost as if > the VB design team has simply responded ad-hoc to user requests, no matter > how half-baked ("why can't I add parentheses to property calls?" "why can't I > omit parentheses on method calls?", "why can't Nothing apply to value > types?", "why do I have to declare my variables?", etc.). Well, the last one would rather be the other way around, as not declaring the variables was how it was done in BASIC. "Why can't I declare my variables, as you do in a real programming language?" ;) -- Gran Andersson _____ http://www.guffa.com