Assembly: System (in System.dll)
This class is recommended for cases where the number of elements in a dictionary is unknown. It takes advantage of the improved performance of a ListDictionary with small collections, and offers the flexibility of switching to a Hashtable which handles larger collections better than ListDictionary.
If the initial size of the collection is greater than the optimal size for a ListDictionary, the collection is stored in a Hashtable to avoid the overhead of copying elements from the ListDictionary to a Hashtable.
The constructor accepts a Boolean parameter that allows the user to specify whether the collection ignores the case when comparing strings. If the collection is case-sensitive, it uses the key's implementations of Object.GetHashCode and Object.Equals. If the collection is case-insensitive, it performs a simple ordinal case-insensitive comparison, which obeys the casing rules of the invariant culture only. By default, the collection is case-sensitive. For more information on the invariant culture, see System.Globalization.CultureInfo.
A key cannot be a null reference (Nothing in Visual Basic), but a value can.
[Visual Basic, C#]
The foreach statement of the C# language (for each in Visual Basic) requires the type of each element in the collection. Since each element of the is a key/value pair, the element type is not the type of the key or the type of the value. Instead, the element type is DictionaryEntry. For example:
[Visual Basic, C#]
The foreach statement is a wrapper around the enumerator, which only allows reading from, not writing to, the collection.
Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows CE Platform Note: All keys added to a case-insensitive must have string values.
Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
This implementation does not provide a synchronized (thread safe) wrapper for a , but derived classes can create their own synchronized versions of the using the SyncRoot property.
Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.