How to read class Properties without instantiation?-CodePudding

How can i read all class Properties, without having an instantiated object of this Class nor hard-coding the name of the class itself? The name of the class is dynamically, stored as a string in a variable.

(As classes are added independentely of the developer of the function above, the code of the function won't be extended by "switch-case" for every new Class)

Unfortunately, the following Code...

// first part ist just to explan and won't be available in the code... the content of modelClass will unknown
MyModel mod = new();
string modelClass = mod.GetType().ToString();
//
Console.WriteLine("Class of Model is: {0}", modelClass );
PropertyInfo[] myPropertyInfo;
myPropertyInfo = Type.GetType(modelClass).GetProperties();

throws an ...

fail: Microsoft.AspNetCore.Components.Server.Circuits.CircuitHost[111]
      Unhandled exception in circuit 'Vir-nbPwhGHcOpSjnVvTlz4-11RtlEirY2qypkNIPw8'.
      System.NullReferenceException: Object reference not set to an instance of an object.

The Console Output confirms, the right Class has been used. But i am confused, as i thought GetProperties() doesn't need an concrete Object.

Using the Object directly, works without problem

myPropertyInfo = mod.GetType().GetProperties();

Also typeof() seems close to what i'm looking for. But it looks as i can't pass a Variable which contains the String of the desired Class. Then, typeof() determines the type of the Variable i pass

CodePudding user response：

I would bet that Type.GetType(modelClass) returns null. If we look in the documentation we find this description of the return value:

The type with the specified name, if found; otherwise, null.

So we know modelClass does not contain a valid type name.

This becomes even more clear when we look at modelClass = mod.GetType().ToString();. .ToString() converts the object to a string, it does not return the name of the type. If you want the name of the type, use mod.GetType().FullName

I would suggest reading eric lipperts article on how to debug small programs. Because this should be fairly easy to debug by just placing a breakpoint and checking variables.

CodePudding user response：

Your problem is that Type.ToString() just returns the types (short) name without qualifiers. So in your case just "MyModel". However Type.GetType() needs an assembly-qualfied name. Otherwise it just returns null because the type wans't found. From the docs for the string-parameter for Type.GetType:

The assembly-qualified name of the type to get. See AssemblyQualifiedName. If the type is in the currently executing assembly or in mscorlib.dll/System.Private.CoreLib.dll, it is sufficient to supply the type name qualified by its namespace.

When on the other hand you have a concrete instance and call GetType on that, you never get null, as every object has a type.