Articolo
11/18/2011

Queryable.OfType<TResult> Method

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Filters the elements of an IQueryable based on a specified type.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function OfType(Of TResult) ( _
    source As IQueryable _
) As IQueryable(Of TResult)

public static IQueryable<TResult> OfType<TResult>(
    this IQueryable source
)

Type Parameters

TResult
The type to filter the elements of the sequence on.

Parameters

source
Type: System.Linq.IQueryable
An IQueryable whose elements to filter.

Return Value

Type: System.Linq.IQueryable<TResult>
A collection that contains the elements from source that have type TResult.

Usage Note

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

Exceptions

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

Remarks

The OfType method generates a MethodCallExpression that represents calling OfType 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 OfType depends on the implementation of the type of the source parameter. The expected behavior is that it filters out any elements in source that are not of type TResult.

Examples

The following code example demonstrates how to use OfType to filter out elements that are not of type PropertyInfo from a list of elements of type MemberInfo.

      ' Create a list of MemberInfo objects.
      Dim members As List(Of System.Reflection.MemberInfo) = GetType(String).GetMembers().ToList()

      ' Return only those items that can be cast to type PropertyInfo.
      Dim propertiesOnly As IQueryable(Of System.Reflection.PropertyInfo) = _
              members.AsQueryable().OfType(Of System.Reflection.PropertyInfo)()

      Dim output As New System.Text.StringBuilder
      output.AppendLine("Members of type 'PropertyInfo' are:")
      For Each pi As System.Reflection.PropertyInfo In propertiesOnly
         output.AppendLine(pi.Name)
      Next

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

      ' This code produces the following output:

      ' Members of type 'PropertyInfo' are:
      ' Chars
      ' Length

         // Create a list of MemberInfo objects.
         List<System.Reflection.MemberInfo> members = typeof(String).GetMembers().ToList();

         // Return only those items that can be cast to type PropertyInfo.
         IQueryable<System.Reflection.PropertyInfo> propertiesOnly =
             members.AsQueryable().OfType<System.Reflection.PropertyInfo>();

         outputBlock.Text += "Members of type 'PropertyInfo' are:" + "\n";
         foreach (System.Reflection.PropertyInfo pi in propertiesOnly)
            outputBlock.Text += pi.Name + "\n";

         /*
             This code produces the following output:

             Members of type 'PropertyInfo' are:
             Chars
             Length
         */

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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