C＃-加载继承的类

Question

I have a class called FieldDesc .

public class FieldDesc {
    public FieldDesc() {
    }
}

I also have another class that inherits from FieldDesc called StandardHoursByCommunitySvcType .

public class StandardHoursByCommunitySvcType: FieldDesc {
    public StandardHoursByCommunitySvcType() {
    }
}

In my control I have -

FieldDesc aTable;
aTable = new FieldDesc();

String TableName = "StandardHoursByCommunitySvcType";

What do I have to do to get aTable to know that it is an object of type StandardHoursByCommunitySvcType ?

Answer 1

Your question is unclear. Are you trying to declare aTable as a StandardHoursByCommunitySvcType or trying to determine if it has been declared as one?

If you're trying to declare:

FieldDesc aTable;
aTable = new StandardHoursByCommunitySvcType();

That'll work as long as StandardHoursByCommunitySvcType inherits from FieldDesc

If you're trying to determine type:

if(aTable is StandardHoursByCommunitySvcType)
{
    //Do something
}

Answer 2

You can use is operator to find this out

if(someObject is StandardHoursByCommunitySvcType )
    {
       //it means is is object of StandardHoursByCommunitySvcType  type
    }

Answer 3

If you have the two classes

public class FieldDesc
{
    public FieldDesc()
    {
    }

    public void A()
    {
    }

    public virtual void V()
    {
        Console.WriteLine("V from FieldDesc");
    }
}

public class StandardHoursByCommunitySvcType : FieldDesc
{
    public StandardHoursByCommunitySvcType()
    {
    }

    public void B()
    {
    }

    public overrides void V()
    {
        Console.WriteLine("V from StandardHoursByCommunitySvcType");
    }
}

You can do this

FieldDesc fd = new StandardHoursByCommunitySvcType();
StandardHoursByCommunitySvcType svc = new StandardHoursByCommunitySvcType();

fd.A(); // OK
fd.B(); // Fails (does not compile)
((StandardHoursByCommunitySvcType)fd).B(); // OK
fd.V(); // OK, prints "V from StandardHoursByCommunitySvcType"

svc.A(); // OK
svc.B(); // OK
svc.V(); // OK, prints "V from StandardHoursByCommunitySvcType"

The derived class is assignment compatible to the base class; however, accessed through a variable typed as the base class you will only see the the members of the base class.