C# 3.0 Cookbook, 3rd Edition

3.11. Determining a Variable's Type with the is Operator

Problem

A method exists that creates an object from one of several types of classes. This object is then returned as a generic object type. Based on the type of object that was initially created in the method, you want to branch to different logic.

Solution

Use the is operator. This operator returns a Boolean true or false, indicating whether the cast is legal, but the cast never actually occurs.

	    public class Point2D {...}
	    public class Point3D {...}
	    public class ExPoint2D : Point2D {...}
	    public class ExPoint3D : Point3D {...}

Next, you have a method that accepts an integer value, and based on this value, one of the four specific point types is returned:

	    public object CreatePoint(PointTypeEnum pointType)
	    {
	        switch (pointType)
	        {
	            case PointTypeEnum.Point2D:
	                return (new Point2D( ));
	            case PointTypeEnum.Point3D:
	                return (new Point3D( ));
	            case PointTypeEnum.ExPoint2D:
	                return (new ExPoint2D( ));
	            case PointTypeEnum.ExPoint3D:
	                return (new ExPoint3D( ));
	            default:
	                return (null);
	        }
	    }

where the PointTypeEnum is defined as:

	    public enum PointTypeEnum
	    {
	        Point2D, Point3D, ExPoint2D, ExPoint3D
	    }

Finally, you have a method that calls the CreatePoint method. This method handles the point object type returned from the CreatePoint method based on the actual point object returned:

 public void CreateAndHandlePoint( ) { // Create a new point object and return it. object retObj = CreatePoint(PointTypeEnum.Point2D); // Handle the point object based on its actual ...