Convert, e.g., string "System.Drawing.Colors.Red" into true data type?

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Ken Overton - 30 Jan 2005 12:53 GMT

Obviously the system does this for deserialization. So how can I do it
for arbitrary classes (not just enums)? Does this require generating a
temporary assembly and compiling it?

-- kov

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Mattias Sj?gren - 30 Jan 2005 19:54 GMT

Ken,

>Obviously the system does this for deserialization. So how can I do it
>for arbitrary classes (not just enums)?

Type.GetType() or Assembly.GetType(). Since there can be multiple
types with the same name in different assemblies, you need to specify
which asembly to look in one way or another.

>Does this require generating a temporary assembly and compiling it?

No

Mattias

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Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
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Ken Overton - 30 Jan 2005 21:13 GMT

Mattias Sjögren wrote:

>>Obviously the system does this for deserialization. So how can I do it
>>for arbitrary classes (not just enums)?
>
> Type.GetType() or Assembly.GetType(). Since there can be multiple
> types with the same name in different assemblies, you need to specify
> which asembly to look in one way or another.

Sorry, I guess I'm a bit dense. I understand that
Type.GetType("System.Drawing.Color") will give me a Type object with all
the info about that class, but how can I use a Type object to actually
*create an instance* of that class? In my example above I suppose I
could get the PropertyInfo for the static property
System.Drawing.Colors.Red, but I'm not sure that is a generic solution
for all constant expressions of all types. I'm looking for a generic
solution to produce an instance of a constant given that constant
expression as a string and the type, like for example:

Class String Constant expression string
============ ======
"System.Drawing.Color" "Red"
"System.Int32" "0x0f"
"MyOwnClass.PiDouble" "3.14"
etc.

As far as I can see, if you want to call a method/property on an
instance via reflection, the instance has to already be created. I
suppose I could make my own factory to parse expressions and figure out
how to create them, it just seems like .NET already has that somewhere.
Either that or I have a poor understanding of the problem, which could
very well be.

-- kov

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Nathan Baulch - 31 Jan 2005 00:17 GMT

> Sorry, I guess I'm a bit dense. I understand that
> Type.GetType("System.Drawing.Color") will give me a Type object with
> all the info about that class, but how can I use a Type object to
> actually *create an instance* of that class?

Your best bet is to use a TypeConverter.
You'll need to apply the TypeConverterAttribute to your custom classes if
you want them to work with this approach.
The following code demonstrates a few different examples.

Type[] types = new Type[] {
typeof(Int32),
typeof(Color),
typeof(DayOfWeek),
typeof(DateTime),
typeof(MyClass)
};
string[] values = new string[] {
"13",
"Red",
"Saturday",
"2005-05-05",
"abc123"
};
for(int i = 0; i < types.Length; i++) {
object o = TypeDescriptor.GetConverter(
types[i]).ConvertFrom(values[i]);
Console.WriteLine("{0}\t{1}", o.GetType(), o);
}

Nathan

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Ken Overton - 31 Jan 2005 00:14 GMT

> Your best bet is to use a TypeConverter.
> You'll need to apply the TypeConverterAttribute to your custom classes if
> you want them to work with this approach.

Thank you, Nathan, that looks like it's exactly what I was missing.

Cheers,

-- kov

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Convert, e.g., string "System.Drawing.Colors.Red" into true data type?

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