How to return a strongly typed array from the ToArray method by using Visual C# (312390)

SUMMARY

This step-by-step article shows you how to use Visual C# to return a strongly typed array from the ToArray(type) method.

The parameter-less ToArray method of the ArrayList class returns an array of type Object. You cannot use the parameter-less implementation of ToArray to cast the Object array to an array of your type. For example, if you add a number of Customer objects to an ArrayList, the underlying list is not made a Customer array. This causes the following statement to fail with the System.InvalidCastException exception:

Customer [] customer = (Customer[])myArrayList.ToArray();
				

To return a strongly typed array, use the overloaded ToArray method that accepts an object type as a parameter. For example, the following statement succeeds:

Customer [] customer = (Customer[])myArrayList.ToArray(typeof(Customer));
				

NOTE: C# disallows an implicit cast, so you must explicitly cast the result of the ToArray method.

IMPORTANT: All elements of the ArrayList must be of the same object type. The ToArray method fails if you attempt to cast an ArrayList of heterogeneous objects to a specific type.

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Step-by-Step Example

1. Start a new Console Application project in Visual C# .NET or in Microsoft Visual C# 2005.
2. Replace the code in Class1.cs with the following code.
   
   Note In Visual Studio 2005, the default file is Program.cs.

   using System;
   using System.Collections;
    
     class Class1
     {
       
       [STAThread]
       static void Main(string[] args)
       {
         
           customer c = new customer();
           c.cname = "anonymous";
           
           ArrayList al=new ArrayList();
           al.Add(c);
           object[] cArray = al.ToArray();
           //Display the type of the ArrayList.
           Console.WriteLine(cArray.GetType());
           
           //Uncomment the next line to reproduce the InvalidCastException.
           //customer[] custArray = (customer[])(al.ToArray());
           
           //Comment the next line to reproduce the InvalidCastException.  
           customer[] custArray = (customer[])al.ToArray(typeof(customer));
   
           Console.WriteLine(custArray.GetType());
          
       }
     }
     class customer
     {
       public string cname;
     }
   
   					

3. Press the CTRL+F5 key combination to build and run the project. (CTRL+F5 allows the Console window to remain open.)
4. To reproduce the InvalidCastException exception, follow the two commenting instructions in the sample code. back to the top