C# Convert dynamic string to existing Class [duplicate]

Question

Within a windows app, using C#, I have a reporting module that will be reliant upon classes to populate the reports. However there will be many reports and I do not want to have to code for each one.

The flow will be as such: Within the report editor, the report will be assigned a class (i.e. "Applications") as a string. When the user selected the report to run, the code will acquire the data from a SQL query. The code will take the data and find out which class to place the data into. Then the report will take the class and populate the report with the data from the class.

Here is my dilemna, how do I make the code dynamic so that the code will convert the assigned class into the proper Class Object?

Example in mind:

gVar = Report;
(gVar.ReportClass)oClass = new gVar.ReportClass;

Answer 1

Use Type.GetType (specifically one of the overloads (e.g., Type.GetType(string)) that takes a string parameter) to load the instance of Type for the appropriate class, and then use Activator.CreateInstance or Type.GetConstructor on that instance of Type to instantiate an instance.

So, something like

Type type = Type.GetType(assemblyQualifiedName);
object instance = Activator.CreateInstance(type);

Note that you must pass the assembly qualified name unless the type is in mscorlib or the currently executing assembly.

Additionally, Activator.CreateInstance assumes the existence of a default constructor. If there is not a default constructor, or you need to pass some parameters to the constructor, you will have to use an overload of Activator.CreateInstance that lets you specify the constructor parameters, or Type.GetConstructor to load the appropriate constructor.

Answer 2

You can use reflection to do it. If you give them all some similar base class or interface, you can do something like:

myBaseReport report = (myBaseReport)System.Activator.CreateInstance("MyAssemblyName", myClassStringWithFullNameSpace).Unwrap();

This will go into the assembly named and load the class directly. The class string is the full name of the type in question, so something like MyGlobalNamespace.MyCustomNameSpace.MySpecificType. This will allow you to create the specific type of report and put it into the base class type or interface type.

Answer 3

It's a little unclear exactly what you're asking for here. Based on what I"m reading, though, you have a string that contains a type name and you want to instantiate a class based on that? You can use reflection to do this...

Type type = Type.GetType(strTypeName);
object oClass = Activator.CreateInstance(type);

Answer 4

You'll be fine using implicit operators:

• http://www.codeproject.com/KB/cs/Csharp_implicit_operator.aspx

That sounds good for your needs, because it allows you to do something like:

Orange orange = new Orange();
Apple apple = (Apple)orange;

Or:

string appleJson = "{ Weight: '2kg' }";
Apple apple = appleJson;

An implicit operator will deserialize that apple-JSON-serialized string into a regular Apple-typed object.

I don't know if this is what you're looking for, and I hope no one will be voting down if this is a C# feature that's available.

EDITED: I misunderstood the question. Thanks to commenters, even who down-voted my answer, because I was wrong.

EDIT 2:

Taking others Activator/Reflection approach - which seems to be the right one for the author of current question -, and reading his other question about "how to fill then the properties of obtained report instance", I want to suggest some solution.

You can define some attribute like "ReportPropertyAttribute" with no properties, default constructor, and inspect with reflection for properties that are marked with suggested attribute.

Or you can define some configuration file or configuration section (regular .NET configuration API), so you can define "known report types" and "which properties are arguments or parameters of some report type".

I hope this is in the line of your needs!