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// By default, the data field is empty, so check for null.

Console.WriteLine("\n-> Custom Data:");

if (e.Data != null)

{

foreach (DictionaryEntry de in e.Data)

Console.WriteLine("-> {0}: {1}", de.Key, de.Value);

}

}

With this, we would now find the update shown in Figure 7-4.

Figure 7-4.

Obtaining programmer-defined data

The Data property is very useful in that it allows us to pack in custom information regarding the

error at hand without requiring us to build a brand-new class type extending the Exception base

class (which, prior to .NET 2.0, was our only option!). As helpful as the Data property may be, how-

ever, it is still common for .NET developers to build strongly typed exception classes, which account

for custom data using strongly typed properties.

This approach allows the caller to catch a specific Exception-derived type, rather than having

to dig into a data collection to obtain additional details. To understand how to do so, we need to

examine the distinction between system-level and application-level exceptions.