Статья
11/18/2011

Queryable.SkipWhile<TSource> Method (IQueryable<TSource>, Expression<Func<TSource, Int32, Boolean>>)

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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.

Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function SkipWhile(Of TSource) ( _
    source As IQueryable(Of TSource), _
    predicate As Expression(Of Func(Of TSource, Integer, Boolean)) _
) As IQueryable(Of TSource)

public static IQueryable<TSource> SkipWhile<TSource>(
    this IQueryable<TSource> source,
    Expression<Func<TSource, int, bool>> predicate
)

Type Parameters

TSource
The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable<TSource>
An IQueryable<T> to return elements from.

predicate
Type: System.Linq.Expressions.Expression<Func<TSource, Int32, Boolean>>
A function to test each element for a condition; the second parameter of this function represents the index of the source element.

Return Value

Type: System.Linq.IQueryable<TSource>
An IQueryable<T> that contains elements from source starting at the first element in the linear series that does not pass the test specified by predicate.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<TSource>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception	Condition
ArgumentNullException	source or predicate is nulla null reference (Nothing in Visual Basic).

Remarks

This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T, TResult> types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

The SkipWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource, Int32, Boolean>>) method generates a MethodCallExpression that represents calling SkipWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource, Int32, Boolean>>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling SkipWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource, Int32, Boolean>>) depends on the implementation of the type of the source parameter. The expected behavior is that it applies predicate to each element in source until it finds an element for which predicate returns false. That element and all the remaining elements are returned. The index of each source element is provided as the second argument to predicate.

Examples

The following code example demonstrates how to use SkipWhile<TSource>(IQueryable<TSource>, Expression<Func<TSource, Int32, Boolean>>) to skip elements of an array as long as a condition that depends on the element's index is true.

      Dim amounts() As Integer = {5000, 2500, 9000, 8000, _
                          6500, 4000, 1500, 5500}

      ' Skip over amounts in the array until the first amount
      ' that is less than or equal to the product of its
      ' index in the array and 1000. Take the remaining items.
      Dim query = amounts.AsQueryable() _
          .SkipWhile(Function(amount, index) amount > index * 1000)

      Dim output As New System.Text.StringBuilder
      For Each amount As Integer In query
         output.AppendLine(amount)
      Next

      ' Display the output.
      outputBlock.Text &= output.ToString() & vbCrLf

      ' This code produces the following output:

      ' 4000
      ' 1500
      ' 5500

         int[] amounts = { 5000, 2500, 9000, 8000, 
                                6500, 4000, 1500, 5500 };

         // Skip over amounts in the array until the first amount
         // that is less than or equal to the product of its
         // index in the array and 1000. Take the remaining items.
         IEnumerable<int> query =
             amounts.AsQueryable()
             .SkipWhile((amount, index) => amount > index * 1000);

         foreach (int amount in query)
            outputBlock.Text += amount + "\n";

         /*
             This code produces the following output:

             4000
             1500
             5500
         */

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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