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.NET Tip: Type Casting and Comparison Using "as" and "is"

  • September 28, 2007
  • By Jay Miller
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You are probably used to using C-style casts. Look at an example starting with C-style casts and see how using "as" and "is" can help your code. A common situation I run into is working with controls in an ASP.NET DataGrid. Suppose I need to work with the DataGridItem that is the parent of one of the controls in the grid. Using C-style type casting, I would do something like this:

// C-style
try
{
   DataGridItem item = (DataGridItem)mycontrol.Parent;
   if (item.GetType().ToString() == "DataGridItem")
   {
      // Do something interesting here
   }
}
catch (InvalidCastException ex)
{
}

Although this method works, there is a much cleaner way. First, I'll address the type cast and exception handling using "as". With "as", there is no need to check for exceptions Because it will either return the object as the requested type or it will return null. You then can check the value against null to see whether the type conversion was successful.

// Using As
DataGridItem item = mycontrol.Parent as DataGridItem;
if (item != null)
{
   // Do something interesting here
}

This code is much more concise and explicit than when using C-style type casting. Adding the use of "is" in the comparison makes this code more readable and is slightly more efficient than the comparison to null. The end result looks like this:

// Using As and Is
DataGridItem item = mycontrol.Parent as DataGridItem;
if (item is DataGridItem)
{
   // Do something interesting here
}

Compare this with the original version using C-style type casting. I think that you will agree the version using "as" and "is" is easier to understand and maintain because there is no need to worry about invalid cast exceptions.

About the Author

Jay Miller is a Software Engineer with Electronic Tracking Systems, a company dedicated to robbery prevention, apprehension, and recovery based in Carrollton, Texas. Jay has been working with .NET since the release of the first beta and is co-author of Learn Microsoft Visual Basic.Net In a Weekend. Jay can be reached via email at jmiller@sm-ets.com.






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