C#ICollection<T>接口简介

public interface ICollection<T> : IEnumerable<T>, 
	IEnumerable

Type Parameters

T

The type of the elements in the collection.

The ICollection(Of T) type exposes the following members.

Properties

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	Name	Description
	Count	Gets the number of elements contained in the ICollection(Of T).
	IsReadOnly	Gets a value indicating whether the ICollection(Of T) is read-only.

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Methods

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	Name	Description
	Add	Adds an item to the ICollection(Of T).
	Clear	Removes all items from the ICollection(Of T).
	Contains	Determines whether the ICollection(Of T) contains a specific value.
	CopyTo	Copies the elements of the ICollection(Of T) to an Array, starting at a particular Array index.
	GetEnumerator	Returns an enumerator that iterates through a collection. (Inherited from IEnumerable.)
	GetEnumerator	Returns an enumerator that iterates through the collection. (Inherited from IEnumerable(Of T).)
	Remove	Removes the first occurrence of a specific object from the ICollection(Of T).

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Extension Methods

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	Name	Description
	Aggregate(Of T)(Func(Of T, T, T))	Overloaded. Applies an accumulator function over a sequence. (Defined by Enumerable.)
	Aggregate(Of T, TAccumulate)(TAccumulate, Func(Of TAccumulate, T, TAccumulate))	Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value. (Defined by Enumerable.)
	Aggregate(Of T, TAccumulate, TResult)(TAccumulate, Func(Of TAccumulate, T, TAccumulate), Func(Of TAccumulate, TResult))	Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value, and the specified function is used to select the result value. (Defined by Enumerable.)
	All(Of T)	Determines whether all elements of a sequence satisfy a condition. (Defined by Enumerable.)
	Any(Of T)	Overloaded. Determines whether a sequence contains any elements. (Defined by Enumerable.)
	Any(Of T)(Func(Of T, Boolean))	Overloaded. Determines whether any element of a sequence satisfies a condition. (Defined by Enumerable.)
	AsEnumerable(Of T)	Returns the input typed as IEnumerable(Of T). (Defined by Enumerable.)
	AsParallel	Overloaded. Enables parallelization of a query. (Defined by ParallelEnumerable.)
	AsParallel(Of T)	Overloaded. Enables parallelization of a query. (Defined by ParallelEnumerable.)
	AsQueryable	Overloaded. Converts an IEnumerable to an IQueryable. (Defined by Queryable.)
	AsQueryable(Of T)	Overloaded. Converts a generic IEnumerable(Of T) to a generic IQueryable(Of T). (Defined by Queryable.)
	Average(Of T)(Func(Of T, Decimal))	Overloaded. Computes the average of a sequence of Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average(Of T)(Func(Of T, Nullable(Of Decimal)))	Overloaded. Computes the average of a sequence of nullable Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average(Of T)(Func(Of T, Double))	Overloaded. Computes the average of a sequence of Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average(Of T)(Func(Of T, Nullable(Of Double)))	Overloaded. Computes the average of a sequence of nullable Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average(Of T)(Func(Of T, Int32))	Overloaded. Computes the average of a sequence of Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average(Of T)(Func(Of T, Nullable(Of Int32)))	Overloaded. Computes the average of a sequence of nullable Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average(Of T)(Func(Of T, Int64))	Overloaded. Computes the average of a sequence of Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average(Of T)(Func(Of T, Nullable(Of Int64)))	Overloaded. Computes the average of a sequence of nullable Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average(Of T)(Func(Of T, Single))	Overloaded. Computes the average of a sequence of Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average(Of T)(Func(Of T, Nullable(Of Single)))	Overloaded. Computes the average of a sequence of nullable Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Cast(Of TResult)	Casts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
	Concat(Of T)	Concatenates two sequences. (Defined by Enumerable.)
	Contains(Of T)(T)	Overloaded. Determines whether a sequence contains a specified element by using the default equality comparer. (Defined by Enumerable.)
	Contains(Of T)(T, IEqualityComparer(Of T))	Overloaded. Determines whether a sequence contains a specified element by using a specified IEqualityComparer(Of T). (Defined by Enumerable.)
	Count(Of T)	Overloaded. Returns the number of elements in a sequence. (Defined by Enumerable.)
	Count(Of T)(Func(Of T, Boolean))	Overloaded. Returns a number that represents how many elements in the specified sequence satisfy a condition. (Defined by Enumerable.)
	DefaultIfEmpty(Of T)	Overloaded. Returns the elements of the specified sequence or the type parameter's default value in a singleton collection if the sequence is empty. (Defined by Enumerable.)
	DefaultIfEmpty(Of T)(T)	Overloaded. Returns the elements of the specified sequence or the specified value in a singleton collection if the sequence is empty. (Defined by Enumerable.)
	Distinct(Of T)	Overloaded. Returns distinct elements from a sequence by using the default equality comparer to compare values. (Defined by Enumerable.)
	Distinct(Of T)(IEqualityComparer(Of T))	Overloaded. Returns distinct elements from a sequence by using a specified IEqualityComparer(Of T) to compare values. (Defined by Enumerable.)
	ElementAt(Of T)	Returns the element at a specified index in a sequence. (Defined by Enumerable.)
	ElementAtOrDefault(Of T)	Returns the element at a specified index in a sequence or a default value if the index is out of range. (Defined by Enumerable.)
	Except(Of T)(IEnumerable(Of T))	Overloaded. Produces the set difference of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.)
	Except(Of T)(IEnumerable(Of T), IEqualityComparer(Of T))	Overloaded. Produces the set difference of two sequences by using the specified IEqualityComparer(Of T) to compare values. (Defined by Enumerable.)
	First(Of T)	Overloaded. Returns the first element of a sequence. (Defined by Enumerable.)
	First(Of T)(Func(Of T, Boolean))	Overloaded. Returns the first element in a sequence that satisfies a specified condition. (Defined by Enumerable.)
	FirstOrDefault(Of T)	Overloaded. Returns the first element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.)
	FirstOrDefault(Of T)(Func(Of T, Boolean))	Overloaded. Returns the first element of the sequence that satisfies a condition or a default value if no such element is found. (Defined by Enumerable.)
	GroupBy(Of T, TKey)(Func(Of T, TKey))	Overloaded. Groups the elements of a sequence according to a specified key selector function. (Defined by Enumerable.)
	GroupBy(Of T, TKey)(Func(Of T, TKey), IEqualityComparer(Of TKey))	Overloaded. Groups the elements of a sequence according to a specified key selector function and compares the keys by using a specified comparer. (Defined by Enumerable.)
	GroupBy(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement))	Overloaded. Groups the elements of a sequence according to a specified key selector function and projects the elements for each group by using a specified function. (Defined by Enumerable.)
	GroupBy(Of T, TKey, TResult)(Func(Of T, TKey), Func(Of TKey, IEnumerable(Of T), TResult))	Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. (Defined by Enumerable.)
	GroupBy(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement), IEqualityComparer(Of TKey))	Overloaded. Groups the elements of a sequence according to a key selector function. The keys are compared by using a comparer and each group's elements are projected by using a specified function. (Defined by Enumerable.)
	GroupBy(Of T, TKey, TResult)(Func(Of T, TKey), Func(Of TKey, IEnumerable(Of T), TResult), IEqualityComparer(Of TKey))	Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. The keys are compared by using a specified comparer. (Defined by Enumerable.)
	GroupBy(Of T, TKey, TElement, TResult)(Func(Of T, TKey), Func(Of T, TElement), Func(Of TKey, IEnumerable(Of TElement), TResult))	Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. The elements of each group are projected by using a specified function. (Defined by Enumerable.)
	GroupBy(Of T, TKey, TElement, TResult)(Func(Of T, TKey), Func(Of T, TElement), Func(Of TKey, IEnumerable(Of TElement), TResult), IEqualityComparer(Of TKey))	Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function. (Defined by Enumerable.)
	GroupJoin(Of T, TInner, TKey, TResult)(IEnumerable(Of TInner), Func(Of T, TKey), Func(Of TInner, TKey), Func(Of T, IEnumerable(Of TInner), TResult))	Overloaded. Correlates the elements of two sequences based on equality of keys and groups the results. The default equality comparer is used to compare keys. (Defined by Enumerable.)
	GroupJoin(Of T, TInner, TKey, TResult)(IEnumerable(Of TInner), Func(Of T, TKey), Func(Of TInner, TKey), Func(Of T, IEnumerable(Of TInner), TResult), IEqualityComparer(Of TKey))	Overloaded. Correlates the elements of two sequences based on key equality and groups the results. A specified IEqualityComparer(Of T) is used to compare keys. (Defined by Enumerable.)
	Intersect(Of T)(IEnumerable(Of T))	Overloaded. Produces the set intersection of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.)
	Intersect(Of T)(IEnumerable(Of T), IEqualityComparer(Of T))	Overloaded. Produces the set intersection of two sequences by using the specified IEqualityComparer(Of T) to compare values. (Defined by Enumerable.)
	Join(Of T, TInner, TKey, TResult)(IEnumerable(Of TInner), Func(Of T, TKey), Func(Of TInner, TKey), Func(Of T, TInner, TResult))	Overloaded. Correlates the elements of two sequences based on matching keys. The default equality comparer is used to compare keys. (Defined by Enumerable.)
	Join(Of T, TInner, TKey, TResult)(IEnumerable(Of TInner), Func(Of T, TKey), Func(Of TInner, TKey), Func(Of T, TInner, TResult), IEqualityComparer(Of TKey))	Overloaded. Correlates the elements of two sequences based on matching keys. A specified IEqualityComparer(Of T) is used to compare keys. (Defined by Enumerable.)
	Last(Of T)	Overloaded. Returns the last element of a sequence. (Defined by Enumerable.)
	Last(Of T)(Func(Of T, Boolean))	Overloaded. Returns the last element of a sequence that satisfies a specified condition. (Defined by Enumerable.)
	LastOrDefault(Of T)	Overloaded. Returns the last element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.)
	LastOrDefault(Of T)(Func(Of T, Boolean))	Overloaded. Returns the last element of a sequence that satisfies a condition or a default value if no such element is found. (Defined by Enumerable.)
	LongCount(Of T)	Overloaded. Returns an Int64 that represents the total number of elements in a sequence. (Defined by Enumerable.)
	LongCount(Of T)(Func(Of T, Boolean))	Overloaded. Returns an Int64 that represents how many elements in a sequence satisfy a condition. (Defined by Enumerable.)
	Max(Of T)	Overloaded. Returns the maximum value in a generic sequence. (Defined by Enumerable.)
	Max(Of T)(Func(Of T, Decimal))	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Decimal value. (Defined by Enumerable.)
	Max(Of T)(Func(Of T, Nullable(Of Decimal)))	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Decimal value. (Defined by Enumerable.)
	Max(Of T)(Func(Of T, Double))	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Double value. (Defined by Enumerable.)
	Max(Of T)(Func(Of T, Nullable(Of Double)))	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Double value. (Defined by Enumerable.)
	Max(Of T)(Func(Of T, Int32))	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int32 value. (Defined by Enumerable.)
	Max(Of T)(Func(Of T, Nullable(Of Int32)))	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int32 value. (Defined by Enumerable.)
	Max(Of T)(Func(Of T, Int64))	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int64 value. (Defined by Enumerable.)
	Max(Of T)(Func(Of T, Nullable(Of Int64)))	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int64 value. (Defined by Enumerable.)
	Max(Of T)(Func(Of T, Single))	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Single value. (Defined by Enumerable.)
	Max(Of T)(Func(Of T, Nullable(Of Single)))	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Single value. (Defined by Enumerable.)
	Max(Of T, TResult)(Func(Of T, TResult))	Overloaded. Invokes a transform function on each element of a generic sequence and returns the maximum resulting value. (Defined by Enumerable.)
	Min(Of T)	Overloaded. Returns the minimum value in a generic sequence. (Defined by Enumerable.)
	Min(Of T)(Func(Of T, Decimal))	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Decimal value. (Defined by Enumerable.)
	Min(Of T)(Func(Of T, Nullable(Of Decimal)))	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Decimal value. (Defined by Enumerable.)
	Min(Of T)(Func(Of T, Double))	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Double value. (Defined by Enumerable.)
	Min(Of T)(Func(Of T, Nullable(Of Double)))	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Double value. (Defined by Enumerable.)
	Min(Of T)(Func(Of T, Int32))	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int32 value. (Defined by Enumerable.)
	Min(Of T)(Func(Of T, Nullable(Of Int32)))	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int32 value. (Defined by Enumerable.)
	Min(Of T)(Func(Of T, Int64))	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int64 value. (Defined by Enumerable.)
	Min(Of T)(Func(Of T, Nullable(Of Int64)))	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int64 value. (Defined by Enumerable.)
	Min(Of T)(Func(Of T, Single))	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Single value. (Defined by Enumerable.)
	Min(Of T)(Func(Of T, Nullable(Of Single)))	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Single value. (Defined by Enumerable.)
	Min(Of T, TResult)(Func(Of T, TResult))	Overloaded. Invokes a transform function on each element of a generic sequence and returns the minimum resulting value. (Defined by Enumerable.)
	OfType(Of TResult)	Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.)
	OrderBy(Of T, TKey)(Func(Of T, TKey))	Overloaded. Sorts the elements of a sequence in ascending order according to a key. (Defined by Enumerable.)
	OrderBy(Of T, TKey)(Func(Of T, TKey), IComparer(Of TKey))	Overloaded. Sorts the elements of a sequence in ascending order by using a specified comparer. (Defined by Enumerable.)
	OrderByDescending(Of T, TKey)(Func(Of T, TKey))	Overloaded. Sorts the elements of a sequence in descending order according to a key. (Defined by Enumerable.)
	OrderByDescending(Of T, TKey)(Func(Of T, TKey), IComparer(Of TKey))	Overloaded. Sorts the elements of a sequence in descending order by using a specified comparer. (Defined by Enumerable.)
	Reverse(Of T)	Inverts the order of the elements in a sequence. (Defined by Enumerable.)
	Select(Of T, TResult)(Func(Of T, TResult))	Overloaded. Projects each element of a sequence into a new form. (Defined by Enumerable.)
	Select(Of T, TResult)(Func(Of T, Int32, TResult))	Overloaded. Projects each element of a sequence into a new form by incorporating the element's index. (Defined by Enumerable.)
	SelectMany(Of T, TResult)(Func(Of T, IEnumerable(Of TResult)))	Overloaded. Projects each element of a sequence to an IEnumerable(Of T) and flattens the resulting sequences into one sequence. (Defined by Enumerable.)
	SelectMany(Of T, TResult)(Func(Of T, Int32, IEnumerable(Of TResult)))	Overloaded. Projects each element of a sequence to an IEnumerable(Of T), and flattens the resulting sequences into one sequence. The index of each source element is used in the projected form of that element. (Defined by Enumerable.)
	SelectMany(Of T, TCollection, TResult)(Func(Of T, Int32, IEnumerable(Of TCollection)), Func(Of T, TCollection, TResult))	Overloaded. Projects each element of a sequence to an IEnumerable(Of T), flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. The index of each source element is used in the intermediate projected form of that element. (Defined by Enumerable.)
	SelectMany(Of T, TCollection, TResult)(Func(Of T, IEnumerable(Of TCollection)), Func(Of T, TCollection, TResult))	Overloaded. Projects each element of a sequence to an IEnumerable(Of T), flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. (Defined by Enumerable.)
	SequenceEqual(Of T)(IEnumerable(Of T))	Overloaded. Determines whether two sequences are equal by comparing the elements by using the default equality comparer for their type. (Defined by Enumerable.)
	SequenceEqual(Of T)(IEnumerable(Of T), IEqualityComparer(Of T))	Overloaded. Determines whether two sequences are equal by comparing their elements by using a specified IEqualityComparer(Of T). (Defined by Enumerable.)
	Single(Of T)	Overloaded. Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence. (Defined by Enumerable.)
	Single(Of T)(Func(Of T, Boolean))	Overloaded. Returns the only element of a sequence that satisfies a specified condition, and throws an exception if more than one such element exists. (Defined by Enumerable.)
	SingleOrDefault(Of T)	Overloaded. Returns the only element of a sequence, or a default value if the sequence is empty; this method throws an exception if there is more than one element in the sequence. (Defined by Enumerable.)
	SingleOrDefault(Of T)(Func(Of T, Boolean))	Overloaded. Returns the only element of a sequence that satisfies a specified condition or a default value if no such element exists; this method throws an exception if more than one element satisfies the condition. (Defined by Enumerable.)
	Skip(Of T)	Bypasses a specified number of elements in a sequence and then returns the remaining elements. (Defined by Enumerable.)
	SkipWhile(Of T)(Func(Of T, Boolean))	Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. (Defined by Enumerable.)
	SkipWhile(Of T)(Func(Of T, Int32, Boolean))	Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. The element's index is used in the logic of the predicate function. (Defined by Enumerable.)
	Sum(Of T)(Func(Of T, Decimal))	Overloaded. Computes the sum of the sequence of Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum(Of T)(Func(Of T, Nullable(Of Decimal)))	Overloaded. Computes the sum of the sequence of nullable Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum(Of T)(Func(Of T, Double))	Overloaded. Computes the sum of the sequence of Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum(Of T)(Func(Of T, Nullable(Of Double)))	Overloaded. Computes the sum of the sequence of nullable Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum(Of T)(Func(Of T, Int32))	Overloaded. Computes the sum of the sequence of Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum(Of T)(Func(Of T, Nullable(Of Int32)))	Overloaded. Computes the sum of the sequence of nullable Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum(Of T)(Func(Of T, Int64))	Overloaded. Computes the sum of the sequence of Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum(Of T)(Func(Of T, Nullable(Of Int64)))	Overloaded. Computes the sum of the sequence of nullable Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum(Of T)(Func(Of T, Single))	Overloaded. Computes the sum of the sequence of Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum(Of T)(Func(Of T, Nullable(Of Single)))	Overloaded. Computes the sum of the sequence of nullable Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Take(Of T)	Returns a specified number of contiguous elements from the start of a sequence. (Defined by Enumerable.)
	TakeWhile(Of T)(Func(Of T, Boolean))	Overloaded. Returns elements from a sequence as long as a specified condition is true. (Defined by Enumerable.)
	TakeWhile(Of T)(Func(Of T, Int32, Boolean))	Overloaded. Returns elements from a sequence as long as a specified condition is true. The element's index is used in the logic of the predicate function. (Defined by Enumerable.)
	ToArray(Of T)	Creates an array from a IEnumerable(Of T). (Defined by Enumerable.)
	ToDictionary(Of T, TKey)(Func(Of T, TKey))	Overloaded. Creates a Dictionary(Of TKey, TValue) from an IEnumerable(Of T) according to a specified key selector function. (Defined by Enumerable.)
	ToDictionary(Of T, TKey)(Func(Of T, TKey), IEqualityComparer(Of TKey))	Overloaded. Creates a Dictionary(Of TKey, TValue) from an IEnumerable(Of T) according to a specified key selector function and key comparer. (Defined by Enumerable.)
	ToDictionary(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement))	Overloaded. Creates a Dictionary(Of TKey, TValue) from an IEnumerable(Of T) according to specified key selector and element selector functions. (Defined by Enumerable.)
	ToDictionary(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement), IEqualityComparer(Of TKey))	Overloaded. Creates a Dictionary(Of TKey, TValue) from an IEnumerable(Of T) according to a specified key selector function, a comparer, and an element selector function. (Defined by Enumerable.)
	ToList(Of T)	Creates a List(Of T) from an IEnumerable(Of T). (Defined by Enumerable.)
	ToLookup(Of T, TKey)(Func(Of T, TKey))	Overloaded. Creates a Lookup(Of TKey, TElement) from an IEnumerable(Of T) according to a specified key selector function. (Defined by Enumerable.)
	ToLookup(Of T, TKey)(Func(Of T, TKey), IEqualityComparer(Of TKey))	Overloaded. Creates a Lookup(Of TKey, TElement) from an IEnumerable(Of T) according to a specified key selector function and key comparer. (Defined by Enumerable.)
	ToLookup(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement))	Overloaded. Creates a Lookup(Of TKey, TElement) from an IEnumerable(Of T) according to specified key selector and element selector functions. (Defined by Enumerable.)
	ToLookup(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement), IEqualityComparer(Of TKey))	Overloaded. Creates a Lookup(Of TKey, TElement) from an IEnumerable(Of T) according to a specified key selector function, a comparer and an element selector function. (Defined by Enumerable.)
	Union(Of T)(IEnumerable(Of T))	Overloaded. Produces the set union of two sequences by using the default equality comparer. (Defined by Enumerable.)
	Union(Of T)(IEnumerable(Of T), IEqualityComparer(Of T))	Overloaded. Produces the set union of two sequences by using a specified IEqualityComparer(Of T). (Defined by Enumerable.)
	Where(Of T)(Func(Of T, Boolean))	Overloaded. Filters a sequence of values based on a predicate. (Defined by Enumerable.)
	Where(Of T)(Func(Of T, Int32, Boolean))	Overloaded. Filters a sequence of values based on a predicate. Each element's index is used in the logic of the predicate function. (Defined by Enumerable.)
	Zip(Of T, TSecond, TResult)	Applies a specified function to the corresponding elements of two sequences, producing a sequence of the results. (Defined by Enumerable.)

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Remarks

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The ICollection(Of T) interface is the base interface for classes in the System.Collections.Generic namespace.

The ICollection(Of T) interface extends IEnumerable(Of T); IDictionary(Of TKey, TValue) and IList(Of T) are more specialized interfaces that extend ICollection(Of T). A IDictionary(Of TKey, TValue) implementation is a collection of key/value pairs, like the Dictionary(Of TKey, TValue) class. A IList(Of T) implementation is a collection of values, and its members can be accessed by index, like the List(Of T) class.

If neither the IDictionary(Of TKey, TValue) interface nor the IList(Of T) interface meet the requirements of the required collection, derive the new collection class from the ICollection(Of T) interface instead for more flexibility.

Examples

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The following example implements the ICollection(Of T) interface to create a collection of custom Box objects named BoxCollection. Each Box has height, length, and width properties, which are used to define equality. Equality can be defined as all dimensions being the same or the volume being the same. The Box class implements the IEquatable(Of T) interface to define the default equality as the dimensions being the same.

The BoxCollection class implements the Contains method to use the default equality to determine whether a Box is in the collection. This method is used by the Add method so that each Box added to the collection has a unique set of dimensions. The BoxCollection class also provides an overload of the Contains method that takes a specified EqualityComparer(Of T) object, such as BoxSameDimensions and BoxSameVol classes in the example.

This example also implements an IEnumerator(Of T) interface for the BoxCollection class so that the collection can be enumerated.

C#

VB

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using System;
using System.Collections;
using System.Collections.Generic;

class Program
{

    static void Main(string[] args)
    {

        BoxCollection bxList = new BoxCollection();

        bxList.Add(new Box(10, 4, 6));
        bxList.Add(new Box(4, 6, 10));
        bxList.Add(new Box(6, 10, 4));
        bxList.Add(new Box(12, 8, 10));

        // Same dimensions. Cannot be added:
        bxList.Add(new Box(10, 4, 6));

        // Test the Remove method.
        PrintResults(bxList);
        Console.WriteLine("Removing 6x10x4");
        bxList.Remove(new Box(6, 10, 4));
        PrintResults(bxList);

        // Test the Contains method.
        Box BoxCheck = new Box(8, 12, 10);
        Console.WriteLine("Contains {0}x{1}x{2} by dimensions: {3}", 
            BoxCheck.Height.ToString(), BoxCheck.Length.ToString(), 
            BoxCheck.Width.ToString(), bxList.Contains(BoxCheck).ToString());

        // Test the Contains method overload with a specified equality comparer.
        Console.WriteLine("Contains {0}x{1}x{2} by volume: {3}", 
            BoxCheck.Height.ToString(), BoxCheck.Length.ToString(), 
            BoxCheck.Width.ToString(), bxList.Contains(BoxCheck, 
            new BoxSameVol()).ToString());

    }
    public static void PrintResults(BoxCollection bxList)
    {
        Console.WriteLine("\nHeight\tLength\tWidth\tHash Code");
        foreach (Box bx in bxList)
        {
            Console.WriteLine("{0}\t{1}\t{2}\t{3}",
                bx.Height.ToString(), bx.Length.ToString(), 
                bx.Width.ToString(), bx.GetHashCode().ToString());
        }

        // Results by manipulating the enumerator directly:

        //IEnumerator enumerator = bxList.GetEnumerator();
        //Console.WriteLine("\nHeight\tLength\tWidth\tHash Code");
        //while (enumerator.MoveNext())
        //{
        //    Box b = (Box)enumerator.Current;
        //    Console.WriteLine("{0}\t{1}\t{2}\t{3}",
        //    b.Height.ToString(), b.Length.ToString(), 
        //    b.Width.ToString(), b.GetHashCode().ToString());
        //}

        Console.WriteLine();
    }

}

public class Box : IEquatable<Box>
{

    public Box(int h, int l, int w)
    {
        this.Height = h;
        this.Length = l;
        this.Width = w;
    }
    public int Height { get; set; }
    public int Length { get; set; }
    public int Width { get; set; }

    // Defines equality using the
    // BoxSameDimensions equality comparer.
    public bool Equals(Box other)
    {
        if (new BoxSameDimensions().Equals(this, other))
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public override bool Equals(object obj)
    {
        return base.Equals(obj);
    }

    public override int GetHashCode()
    {
        return base.GetHashCode();
    }
}

public class BoxCollection : ICollection<Box>
{

    // The generic enumerator obtained from IEnumerator<Box>
    // by GetEnumerator can also be used with the non-generic IEnumerator.
    // To avoid a naming conflict, the non-generic IEnumerable method
    // is explicitly implemented.

    public IEnumerator<Box> GetEnumerator()
    {
        return new BoxEnumerator(this);
    }
    IEnumerator IEnumerable.GetEnumerator()
    {
        return new BoxEnumerator(this);
    }

    // The inner collection to store objects.
    private List<Box> innerCol;

    // For IsReadOnly
    private bool isRO = false;

    public BoxCollection()
    {
        innerCol = new List<Box>();
    }

    // Adds an index to the collection.
    public Box this[int index]
    {
        get { return (Box)innerCol[index]; }
        set { innerCol[index] = value; }
    }

    // Determines if an item is in the collection
    // by using the BoxSameDimensions equality comparer.
    public bool Contains(Box item)
    {
        bool found = false;

        foreach (Box bx in innerCol)
        {
            // Equality defined by the Box
            // class's implmentation of IEquitable<T>.
            if (bx.Equals(item))
            {
                found = true;
            }
        }

        return found;
    }

    // Determines if an item is in the 
    // collection by using a specified equality comparer.
    public bool Contains(Box item, EqualityComparer<Box> comp)
    {
        bool found = false;

        foreach (Box bx in innerCol)
        {
            if (comp.Equals(bx, item))
            {
                found = true;
            }
        }

        return found;
    }

    // Adds an item if it is not already in the collection
    // as determined by calling the Contains method.
    public void Add(Box item)
    {

        if (!Contains(item))
        {
            innerCol.Add(item);
        }
        else
        {
            Console.WriteLine("A box with {0}x{1}x{2} dimensions was already added to the collection.",
                item.Height.ToString(), item.Length.ToString(), item.Width.ToString());
        }
    }

    public void Clear()
    {
        innerCol.Clear();
    }

    public void CopyTo(Box[] array, int arrayIndex)
    {
        for (int i = 0; i < innerCol.Count; i++)
        {

            array[i] = (Box)innerCol[i];
        }
    }

    public int Count
    {
        get
        {
            return innerCol.Count;
        }
    }

    public bool IsReadOnly
    {
        get { return isRO; }
    }

    public bool Remove(Box item)
    {
        bool result = false;

        // Iterate the inner collection to 
        // find the box to be removed.
        for (int i = 0; i < innerCol.Count; i++)
        {

            Box curBox = (Box)innerCol[i];

            if (new BoxSameDimensions().Equals(curBox, item))
            {
                innerCol.RemoveAt(i);
                result = true;
                break;
            }
        }
        return result;
    }
}


// Defines the enumerator for the Boxes collection.
// (Some prefer this class nested in the collection class.)
public class BoxEnumerator : IEnumerator<Box>
{
    private BoxCollection _collection;
    private int curIndex;
    private Box curBox;


    public BoxEnumerator(BoxCollection collection)
    {
        _collection = collection;
        curIndex = -1;
        curBox = default(Box);

    }

    public bool MoveNext()
    {
        //Avoids going beyond the end of the collection.
        if (++curIndex >= _collection.Count)
        {
            return false;
        }
        else
        {
            // Set current box to next item in collection.
            curBox = _collection[curIndex];
        }
        return true;
    }

    public void Reset() { curIndex = -1; }

    void IDisposable.Dispose() { }

    public Box Current
    {
        get { return curBox; }
    }


    object IEnumerator.Current
    {
        get { return Current; }
    }

}

// Defines two boxes as equal if they have the same dimensions.
public class BoxSameDimensions : EqualityComparer<Box>
{

    public override bool Equals(Box b1, Box b2)
    {
        if (b1.Height == b2.Height && b1.Length == b2.Length
                            && b1.Width == b2.Width)
        {
            return true;
        }
        else
        {
            return false;
        }
    }


    public override int GetHashCode(Box bx)
    {
        int hCode = bx.Height ^ bx.Length ^ bx.Width;
        return hCode.GetHashCode();
    }

}

// Defines two boxes as equal if they have the same volume.
public class BoxSameVol : EqualityComparer<Box>
{

    public override bool Equals(Box b1, Box b2)
    {
        if ((b1.Height * b1.Length * b1.Width) ==
                (b2.Height * b2.Length * b2.Width))
        {
            return true;
        }
        else
        {
            return false;
        }
    }


    public override int GetHashCode(Box bx)
    {
        int hCode = bx.Height ^ bx.Length ^ bx.Width;
        Console.WriteLine("HC: {0}", hCode.GetHashCode());
        return hCode.GetHashCode();
    }
}


/* 
This code example displays the following output:
================================================

A box with 10x4x6 dimensions was already added to the collection.

Height  Length  Width   Hash Code
10      4       6       46104728
4       6       10      12289376
6       10      4       43495525
12      8       10      55915408

Removing 6x10x4

Height  Length  Width   Hash Code
10      4       6       46104728
4       6       10      12289376
12      8       10      55915408

Contains 8x12x10 by dimensions: False
Contains 8x12x10 by volume: True 
 */