KeyedCollection<TKey, TItem> Class
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Provides the abstract base class for a collection whose keys are embedded in the values.
Inheritance Hierarchy
System.Object
System.Collections.ObjectModel.Collection<TItem>
System.Collections.ObjectModel.KeyedCollection<TKey, TItem>
System.Collections.Generic.KeyedByTypeCollection<TItem>
System.ServiceModel.Description.MessagePartDescriptionCollection
Namespace: System.Collections.ObjectModel
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
<DebuggerDisplayAttribute("Count = {Count}")> _
<DefaultMemberAttribute("Item")> _
<ComVisibleAttribute(False)> _
Public MustInherit Class KeyedCollection(Of TKey, TItem) _
Inherits Collection(Of TItem)
[DebuggerDisplayAttribute("Count = {Count}")]
[DefaultMemberAttribute("Item")]
[ComVisibleAttribute(false)]
public abstract class KeyedCollection<TKey, TItem> : Collection<TItem>
Type Parameters
- TKey
The type of keys in the collection.
- TItem
The type of items in the collection.
The KeyedCollection<TKey, TItem> type exposes the following members.
Constructors
| Name | Description | |
|---|---|---|
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KeyedCollection<TKey, TItem>() | Initializes a new instance of the KeyedCollection<TKey, TItem> class that uses the default equality comparer. |
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KeyedCollection<TKey, TItem>(IEqualityComparer<TKey>) | Initializes a new instance of the KeyedCollection<TKey, TItem> class that uses the specified equality comparer. |
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KeyedCollection<TKey, TItem>(IEqualityComparer<TKey>, Int32) | Initializes a new instance of the KeyedCollection<TKey, TItem> class that uses the specified equality comparer and creates a lookup dictionary when the specified threshold is exceeded. |
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Properties
| Name | Description | |
|---|---|---|
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Comparer | Gets the generic equality comparer that is used to determine equality of keys in the collection. |
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Count | Gets the number of elements actually contained in the Collection<T>. (Inherited from Collection<T>.) |
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Dictionary | Gets the lookup dictionary of the KeyedCollection<TKey, TItem>. |
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Item[TKey] | Gets the element with the specified key. |
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Item[Int32] | Gets or sets the element at the specified index. (Inherited from Collection<T>.) |
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Items | Gets a IList<T> wrapper around the Collection<T>. (Inherited from Collection<T>.) |
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Methods
| Name | Description | |
|---|---|---|
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Add | Adds an object to the end of the Collection<T>. (Inherited from Collection<T>.) |
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ChangeItemKey | Changes the key associated with the specified element in the lookup dictionary. |
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Clear | Removes all elements from the Collection<T>. (Inherited from Collection<T>.) |
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ClearItems | Removes all elements from the KeyedCollection<TKey, TItem>. (Overrides Collection<T>.ClearItems().) |
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Contains(T) | Determines whether an element is in the Collection<T>. (Inherited from Collection<T>.) |
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Contains(TKey) | Determines whether the collection contains an element with the specified key. |
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CopyTo | Copies the entire Collection<T> to a compatible one-dimensional Array, starting at the specified index of the target array. (Inherited from Collection<T>.) |
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Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
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Finalize | Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.) |
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GetEnumerator | Returns an enumerator that iterates through the Collection<T>. (Inherited from Collection<T>.) |
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GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
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GetKeyForItem | When implemented in a derived class, extracts the key from the specified element. |
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GetType | Gets the Type of the current instance. (Inherited from Object.) |
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IndexOf | Searches for the specified object and returns the zero-based index of the first occurrence within the entire Collection<T>. (Inherited from Collection<T>.) |
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Insert | Inserts an element into the Collection<T> at the specified index. (Inherited from Collection<T>.) |
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InsertItem | Inserts an element into the KeyedCollection<TKey, TItem> at the specified index. (Overrides Collection<T>.InsertItem(Int32, T).) |
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MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
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Remove(T) | Removes the first occurrence of a specific object from the Collection<T>. (Inherited from Collection<T>.) |
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Remove(TKey) | Removes the element with the specified key from the KeyedCollection<TKey, TItem>. |
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RemoveAt | Removes the element at the specified index of the Collection<T>. (Inherited from Collection<T>.) |
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RemoveItem | Removes the element at the specified index of the KeyedCollection<TKey, TItem>. (Overrides Collection<T>.RemoveItem(Int32).) |
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SetItem | Replaces the item at the specified index with the specified item. (Overrides Collection<T>.SetItem(Int32, T).) |
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ToString | Returns a string that represents the current object. (Inherited from Object.) |
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Explicit Interface Implementations
| Name | Description | |
|---|---|---|
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ICollection.CopyTo | Copies the elements of the ICollection to an Array, starting at a particular Array index. (Inherited from Collection<T>.) |
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ICollection<T>.IsReadOnly | Gets a value indicating whether the ICollection<T> is read-only. (Inherited from Collection<T>.) |
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ICollection.IsSynchronized | Gets a value indicating whether access to the ICollection is synchronized (thread safe). (Inherited from Collection<T>.) |
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ICollection.SyncRoot | Gets an object that can be used to synchronize access to the ICollection. (Inherited from Collection<T>.) |
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IEnumerable.GetEnumerator | Returns an enumerator that iterates through a collection. (Inherited from Collection<T>.) |
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IList.Add | Adds an item to the IList. (Inherited from Collection<T>.) |
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IList.Contains | Determines whether the IList contains a specific value. (Inherited from Collection<T>.) |
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IList.IndexOf | Determines the index of a specific item in the IList. (Inherited from Collection<T>.) |
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IList.Insert | Inserts an item into the IList at the specified index. (Inherited from Collection<T>.) |
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IList.IsFixedSize | Gets a value indicating whether the IList has a fixed size. (Inherited from Collection<T>.) |
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IList.IsReadOnly | Gets a value indicating whether the IList is read-only. (Inherited from Collection<T>.) |
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IList.Item | Gets or sets the element at the specified index. (Inherited from Collection<T>.) |
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IList.Remove | Removes the first occurrence of a specific object from the IList. (Inherited from Collection<T>.) |
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Remarks
The KeyedCollection<TKey, TItem> class provides both O(1) indexed retrieval and keyed retrieval that approaches O(1). It is an abstract type (MustInherit in Visual Basic), or more accurately an infinite set of abstract types, because each of its constructed generic types is an abstract base class. To use KeyedCollection<TKey, TItem>, derive your collection type from the appropriate constructed type.
The KeyedCollection<TKey, TItem> class is a hybrid between a collection based on the IList<T> generic interface and a collection based on the IDictionary<TKey, TValue> generic interface. Like collections based on the IList<T> generic interface, KeyedCollection<TKey, TItem> is an indexed list of items. Like collections based on the IDictionary<TKey, TValue> generic interface, KeyedCollection<TKey, TItem> has a key associated with each element.
Unlike dictionaries, an element of KeyedCollection<TKey, TItem> is not a key/value pair; instead, the entire element is the value and the key is embedded within the value. For example, an element of a collection derived from KeyedCollection<String,String> (KeyedCollection(Of String, String) in Visual Basic) might be "John Doe Jr." where the value is "John Doe Jr." and the key is "Doe"; or a collection of employee records containing integer keys could be derived from KeyedCollection<int,Employee>. The abstract (MustOverride in Visual Basic) GetKeyForItem method extracts the key from the element.
By default, the KeyedCollection<TKey, TItem> includes a lookup dictionary. When an item is added to the KeyedCollection<TKey, TItem>, the item's key is extracted once and saved in the lookup dictionary for faster searches. This behavior is overridden by specifying a dictionary creation threshold when you create the KeyedCollection<TKey, TItem>. The lookup dictionary is created the first time the number of elements exceeds that threshold. If you specify –1 as the threshold, the lookup dictionary is never created.
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When the internal lookup dictionary is used, it contains references to all the items in the collection if TItem is a reference type, or copies of all the items in the collection if TItem is a value type. Thus, using the lookup dictionary may not be appropriate if TItem is a value type. |
Every key in a KeyedCollection<TKey, TItem> must be unique. A key cannot be nulla null reference (Nothing in Visual Basic).
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
Thread Safety
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.