DEAL John M [mailto:[EMAIL PROTECTED]] wrote:
> I don't quite buy into the "designer attempts to instantiate
> the Page class... and of course it can't instantiate an
> *abstract* class" aspect of it. The point is the page that
> is being designed is a concrete version of the abstract class
> and it is that concrete class that should be being
> instantiated (no different than at runtime). I could buy if
> it complained that I hadn't implemented an abstract method in
> my concrete class, but not that the designer should be trying
> to instantiate the abstract itself (what would be the point
> of inheritance if you never got to the concrete class?). I'm
> really not trying to be difficult, I just don't see why the
> designer would ever try and instantiate the abstract class.
Ok... lemme break this down for ya a bit. Here's what I've come to
understand while diving into the guts of this stuff for fun. When designing
a WebForm, it instantiates the base Page class, *not* the Page class being
designed. So when this happens in your scenario you get:
System.Runtime.Serialization.SerializationException: Type Abstract
at
Microsoft.VSDesigner.WebForms.RootCodeDomSerializer.Deserialize(IDesignerSer
ializationManager manager, Object codeObject)
at Microsoft.VisualStudio.Designer.Serialization.CodeDomLoader.Load()
at
Microsoft.VisualStudio.Designer.Serialization.BaseDesignerLoader.Load()
Specifically, this comes from the following IL:
<codeSnippet language="C#">
IL_0160: callvirt instance string
[System]System.CodeDom.CodeTypeReference::get_BaseType()
IL_0165: stelem.ref
IL_0166: ldloc.s V_8
IL_0168: call string Microsoft.VSDesigner.SR::GetString(string,
object[])
IL_016d: newobj instance void
[mscorlib]System.Runtime.Serialization.SerializationException::.ctor(string)
IL_0172: throw
IL_0173: ldloc.s V_7
IL_0175: callvirt instance bool [mscorlib]System.Type::get_IsAbstract()
IL_017a: brfalse.s IL_01a1
IL_017c: ldstr "WFD_TypeAbstract"
IL_0181: ldc.i4.1
IL_0182: newarr [mscorlib]System.Object
IL_0187: stloc.s V_8
IL_0189: ldloc.s V_8
IL_018b: ldc.i4.0
IL_018c: ldloc.s V_7
IL_018e: callvirt instance string [mscorlib]System.Type::get_FullName()
IL_0193: stelem.ref
IL_0194: ldloc.s V_8
IL_0196: call string Microsoft.VSDesigner.SR::GetString(string,
object[])
IL_019b: newobj instance void
[mscorlib]System.Runtime.Serialization.SerializationException::.ctor(string)
IL_01a0: throw
</codeSnippet>
Basically, IL_0160 get's the base type of the page class in preparation to
instantiate it for help with design. However, you see at IL_0175 the check
to make sure it's not abstract. Since your base class is abstract, you get
the error you're seeing. Otherwise IL_017a breaks to IL_01a1 which
eventually leads to instantiating the base class and continues forward with
design.
HTH,
Drew
.NET MVP
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