Expression.Empty 方法

定義

建立具有 Void 類型的空運算式。Creates an empty expression that has Void type.

public:
 static System::Linq::Expressions::DefaultExpression ^ Empty();
public static System.Linq.Expressions.DefaultExpression Empty ();
static member Empty : unit -> System.Linq.Expressions.DefaultExpression
Public Shared Function Empty () As DefaultExpression

傳回

DefaultExpression

DefaultExpression,其 NodeType 屬性等於 Default,且 Type 屬性設為 VoidA DefaultExpression that has the NodeType property equal to Default and the Type property set to Void.

範例

下列程式碼範例會示範如何建立空的運算式,並將它加入至區塊運算式。The following code example shows how to create an empty expression and add it to a block expression.

// Add the following directive to your file:
// using System.Linq.Expressions;

// This statement creates an empty expression.
DefaultExpression emptyExpr = Expression.Empty();

// The empty expression can be used where an expression is expected, but no action is desired.
// For example, you can use the empty expression as the last expression in the block expression.
// In this case the block expression's return value is void.
var emptyBlock = Expression.Block(emptyExpr);

' Add the following directive to your file:
' Imports System.Linq.Expressions 

' This statement creates an empty expression.
Dim emptyExpr As DefaultExpression = Expression.Empty()

' An empty expression can be used where an expression is expected but no action is desired.
' For example, you can use an empty expression as the last expression in a block expression.
' In this case, the block expression's return value is void.
Dim emptyBlock = Expression.Block(emptyExpr)

備註

在預期運算式但不需要任何動作的情況下,可以使用空的運算式。An empty expression can be used where an expression is expected but no action is desired. 例如,您可以使用空的運算式做為區塊運算式中的最後一個運算式。For example, you can use an empty expression as the last expression in a block expression. 在此情況下,區塊運算式的傳回值是 void。In this case, the block expression's return value is void.

適用於