switch

[shapper]

Hello,

I have the following:

public Style GetStyle(Type type) {
switch (type) {
case typeof(MenuItem);
return MenuItemStyle();
default:
return null;
};
}

I get the error:
A value of an integral type expected

Can't I use a switch to check a type. This one had me confused.

Thanks,
Miguel

 

[Family Tree Mike]

Hello,

I have the following:

public Style GetStyle(Type type) {
switch (type) {
case typeof(MenuItem);
return MenuItemStyle();
default:
return null;
};
}

I get the error:
A value of an integral type expected

Can't I use a switch to check a type. This one had me confused.

Thanks,
Miguel

You would need to switch on the type name. You have to use a string or
an integer type in a switch statement.

 

[Arne Vajhøj]

I have the following:

public Style GetStyle(Type type) {
switch (type) {
case typeof(MenuItem);
return MenuItemStyle();
default:
return null;
};
}

I get the error:
A value of an integral type expected

Can't I use a switch to check a type.

No.

Integer types (including enum) and string only.

Not any class like Type.

Arne

 

[Peter Duniho]

Hello,

I have the following:

public Style GetStyle(Type type) {
switch (type) {
case typeof(MenuItem);
return MenuItemStyle();
default:
return null;
};
}

I get the error:
A value of an integral type expected

Can't I use a switch to check a type. This one had me confused.

As Mike and Arne point out, no...System.Type is not a valid type for use
in a switch.

Mike's suggestion of using the type name could work for you.
Alternatively, if there's a very small number of System.Type values you
want to handle, you could just write a series of if/else statements. If
there are too many choices for that to be maintainable in your opinion,
another alternative is to create a Dictionary<System.Type, Func<Style>>,
and then initialize the dictionary with delegates that do the right
thing. For example:

initialize in an appropriate place:

Dictionary<System.Type, Func<Style>> mptypestyle =
new Dictionary<System.Type, Func<Style>>();

mptypestyle.Add(typeof(MenuItem), () => MenuItemStyle());
// add others as necessary...

then elsewhere:

public Style GetStyle(Type type)
{
Style style;

if (mptypestyle.TryGetValue(type, out style))
{
return style;
}

return null;
}

Pete

 

[shapper]

As Mike and Arne point out, no...System.Type is not a valid type for use
in a switch.

Mike's suggestion of using the type name could work for you.
Alternatively, if there's a very small number of System.Type values you
want to handle, you could just write a series of if/else statements.  If
there are too many choices for that to be maintainable in your opinion,
another alternative is to create a Dictionary<System.Type, Func<Style>>,
and then initialize the dictionary with delegates that do the right
thing.  For example:

initialize in an appropriate place:

     Dictionary<System.Type, Func<Style>> mptypestyle =
         new Dictionary<System.Type, Func<Style>>();

     mptypestyle.Add(typeof(MenuItem), () => MenuItemStyle());
     // add others as necessary...

then elsewhere:

     public Style GetStyle(Type type)
     {
         Style style;

         if (mptypestyle.TryGetValue(type, out style))
         {
             return style;
         }

         return null;
     }

Pete

Hi Pete,

I was trying to do something similar to your suggestion but I wasn't
able to associate each type with a method. Only with a function.

With your approach I am having an error (sorry am I not familiar with
Func):
cannot convert from 'out System.Windows.Style' to 'out
System.Func<System.Windows.Style>'

I did the change:

Func<Style> style;
if (_types.TryGetValue(type, out style)) {
return style;
}

But now I get:
Cannot implicitly convert type 'System.Func<System.Windows.Style>' to
'System.Windows.Style'

How to solve this?

Following your suggestion of using Func I am using the following:

public class StyleFactory {

private Dictionary<Type, Func<Style>> _types = new
Dictionary<Type, Func<Style>>();

public StyleFactory() {
_types.Add(typeof(Menu), () => MenuStyle());
_types.Add(typeof(MenuItem), () => MenuItemStyle());
} // StyleFactory

public Style GetStyle<T>() {
return (Style)GetStyle(typeof(T));
} // GetStyle

public Style GetStyle(Type type) {

Func<Style> style;
if (_types.TryGetValue(type, out style)) {
return style;
}
return null;

} // GetStyle

Thanks,
Miguel





I had done before something similar to what you did but returning a
class based on a interface.
In this case I wasn't able to use that approach.

 

[Peter Duniho]

[...]
But now I get:
Cannot implicitly convert type 'System.Func<System.Windows.Style>' to
'System.Windows.Style'

How to solve this?

By fixing the typographical error in my original suggestion (this is why
it's helpful to really _understand_ the language, rather than just
blindly copying random code snippets people may post...then you can fix
the errors in the snippets yourself ):

public Style GetStyle(Type type)
{
Func<Style> funcStyle;

if (_types.TryGetValue(type, out funcStyle))
{
return funcStyle();
}

return null;
}

Pete

 

[shapper]

[...]
But now I get:
Cannot implicitly convert type 'System.Func<System.Windows.Style>' to
'System.Windows.Style'

How to solve this?

By fixing the typographical error in my original suggestion (this is why
it's helpful to really _understand_ the language, rather than just
blindly copying random code snippets people may post...then you can fix
the errors in the snippets yourself ):

     public Style GetStyle(Type type)
     {
         Func<Style> funcStyle;

         if (_types.TryGetValue(type, out funcStyle))
         {
             return funcStyle();
         }

         return null;
     }

Pete

I was able to solve it in the meanwhile.
As I said I never used Func ... I have been reading about it on the
last hour.

Thanks,
Miguel

 

[Arne Vajhøj]

No.

Integer types (including enum) and string only.

Not any class like Type.

Besides: switching on type look like a problem in
the OO design.

The classes should implement an interface or extend
an abstract class that has a method that does whatever
is needed.

Arne