Articolo
11/18/2011

MemberInitExpression Class

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

Represents calling a constructor and initializing one or more members of the new object.

Inheritance Hierarchy

System.Object
System.Linq.Expressions.Expression
System.Linq.Expressions.MemberInitExpression

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

Syntax

'Declaration
Public NotInheritable Class MemberInitExpression _
    Inherits Expression

public sealed class MemberInitExpression : Expression

The MemberInitExpression type exposes the following members.

Properties

	Name	Description
	Bindings	Gets the bindings that describe how to initialize the members of the newly created object.
	CanReduce	Gets a value that indicates whether the expression tree node can be reduced. (Overrides Expression.CanReduce.)
	NewExpression	Gets the expression that represents the constructor call.
	NodeType	Returns the node type of this Expression. Extension nodes should return Extension when overriding this method. (Overrides Expression.NodeType.) In Silverlight for Windows Phone Windows Phone OS 7.1, this member is inherited from Expression.NodeType. In XNA Framework Windows Phone OS 7.0, this member is inherited from Expression.NodeType.
	Type	Gets the static type of the expression that this Expression represents. (Overrides Expression.Type.) In Silverlight for Windows Phone Windows Phone OS 7.1, this member is inherited from Expression.Type. In XNA Framework Windows Phone OS 7.0, this member is inherited from Expression.Type.

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Methods

	Name	Description
	Accept	Dispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall. (Inherited from Expression.)
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	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.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	Reduce	Reduces the MemberInitExpression to a simpler expression. (Overrides Expression.Reduce().)
	ReduceAndCheck	Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression.)
	ReduceExtensions	Reduces the expression to a known node type (that is not an Extension node) or just returns the expression if it is already a known type. (Inherited from Expression.)
	ToString	Returns a textual representation of the Expression. (Inherited from Expression.)
	Update	Creates a new expression that is like this one, but using the supplied children. If all of the children are the same, it will return this expression.
	VisitChildren	Reduces the node and then calls the visitor delegate on the reduced expression. The method throws an exception if the node is not reducible. (Inherited from Expression.)

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Remarks

Use the MemberInit factory methods to create a MemberInitExpression.

The value of the NodeType property of a MemberInitExpression is MemberInit.

Examples

The following example creates a MemberInitExpression that represents the initialization of two members of a new object.

Class Animal
   Public Species As String
   Public Age As Integer
End Class

Shared Sub CreateMemberInitExpression()
   Dim newAnimal As System.Linq.Expressions.NewExpression = _
       System.Linq.Expressions.Expression.[New](Type.GetType("SilverlightApplication.MemberInitExample+Animal"))
   Dim speciesMember As System.Reflection.MemberInfo = _
       Type.GetType("SilverlightApplication.MemberInitExample+Animal").GetMember("Species")(0)
   Dim ageMember As System.Reflection.MemberInfo = _
       Type.GetType("SilverlightApplication.MemberInitExample+Animal").GetMember("Age")(0)
   ' Create a MemberBinding object for each member
   ' that you want to initialize.
   Dim speciesMemberBinding As System.Linq.Expressions.MemberBinding = _
       System.Linq.Expressions.Expression.Bind( _
           speciesMember, _
           System.Linq.Expressions.Expression.Constant("horse"))
   Dim ageMemberBinding As System.Linq.Expressions.MemberBinding = _
       System.Linq.Expressions.Expression.Bind( _
           ageMember, _
           System.Linq.Expressions.Expression.Constant(12))

   ' Create a MemberInitExpression that represents initializing
   ' two members of the 'Animal' class.
   Dim memberInitExpression As System.Linq.Expressions.MemberInitExpression = _
       System.Linq.Expressions.Expression.MemberInit( _
           newAnimal, _
           speciesMemberBinding, _
           ageMemberBinding)

   outputBlock.Text &= memberInitExpression.ToString() & vbCrLf

   ' This code produces the following output:
   '
   ' new Animal() {Species = "horse", Age = 12}
End Sub

class Animal
{
   public string Species { get; set; }
   public int Age { get; set; }
}

public static void CreateMemberInitExpression(System.Windows.Controls.TextBlock outputBlock)
{
   System.Linq.Expressions.NewExpression newAnimal =
       System.Linq.Expressions.Expression.New(typeof(Animal));

   System.Reflection.MemberInfo speciesMember =
       typeof(Animal).GetMember("Species")[0];
   System.Reflection.MemberInfo ageMember =
       typeof(Animal).GetMember("Age")[0];

   // Create a MemberBinding object for each member
   // that you want to initialize.
   System.Linq.Expressions.MemberBinding speciesMemberBinding =
       System.Linq.Expressions.Expression.Bind(
           speciesMember,
           System.Linq.Expressions.Expression.Constant("horse"));
   System.Linq.Expressions.MemberBinding ageMemberBinding =
       System.Linq.Expressions.Expression.Bind(
           ageMember,
           System.Linq.Expressions.Expression.Constant(12));

   // Create a MemberInitExpression that represents initializing
   // two members of the 'Animal' class.
   System.Linq.Expressions.MemberInitExpression memberInitExpression =
       System.Linq.Expressions.Expression.MemberInit(
           newAnimal,
           speciesMemberBinding,
           ageMemberBinding);

   outputBlock.Text += memberInitExpression.ToString() + "\n";

   // This code produces the following output:
   //
   // new Animal() {Species = "horse", Age = 12}
}

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: 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.

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