Expression.Field 方法

public:
 static System::Linq::Expressions::MemberExpression ^ Field(System::Linq::Expressions::Expression ^ expression, System::Reflection::FieldInfo ^ field);

public static System.Linq.Expressions.MemberExpression Field (System.Linq.Expressions.Expression expression, System.Reflection.FieldInfo field);

public static System.Linq.Expressions.MemberExpression Field (System.Linq.Expressions.Expression? expression, System.Reflection.FieldInfo field);

static member Field : System.Linq.Expressions.Expression * System.Reflection.FieldInfo -> System.Linq.Expressions.MemberExpression

Public Shared Function Field (expression As Expression, field As FieldInfo) As MemberExpression

參數

傳回

MemberExpression

MemberExpression，其 NodeType 屬性等於 MemberAccess，且 Expression 和 Member 屬性設定為指定的值。A MemberExpression that has the NodeType property equal to MemberAccess and the Expression and Member properties set to the specified values.

例外狀況

備註

Type產生的屬性等於的 MemberExpression FieldType 屬性 field 。The Type property of the resulting MemberExpression is equal to the FieldType property of field.

public:
 static System::Linq::Expressions::MemberExpression ^ Field(System::Linq::Expressions::Expression ^ expression, System::String ^ fieldName);

public static System.Linq.Expressions.MemberExpression Field (System.Linq.Expressions.Expression expression, string fieldName);

static member Field : System.Linq.Expressions.Expression * string -> System.Linq.Expressions.MemberExpression

Public Shared Function Field (expression As Expression, fieldName As String) As MemberExpression

參數

傳回

MemberExpression

MemberExpression，其 NodeType 屬性等於 MemberAccess、Expression 屬性設定為 expression，且 Member 屬性設定為 FieldInfo，代表 fieldName 所表示的欄位。A MemberExpression that has the NodeType property equal to MemberAccess, the Expression property set to expression, and the Member property set to the FieldInfo that represents the field denoted by fieldName.

例外狀況

範例

下列程式碼範例示範如何建立代表存取欄位的運算式。The following code example shows how to create an expression that represents accessing a field.

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

class TestFieldClass
{
    int sample = 40;
}

static void TestField()
{
    TestFieldClass obj = new TestFieldClass();

    // This expression represents accessing a field.
    // For static fields, the first parameter must be null.
    Expression fieldExpr = Expression.Field(
        Expression.Constant(obj),
        "sample"
    );

    // The following statement first creates an expression tree,
    // then compiles it, and then runs it.
    Console.WriteLine(Expression.Lambda<Func<int>>(fieldExpr).Compile()());
}

// This code example produces the following output:
//
// 40

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

Class TestFieldClass
    Dim sample As Integer = 40
End Class

Sub TestField()

    Dim obj As New TestFieldClass()

    ' This expression represents accessing a field.
    ' For static fields, the first parameter must be Nothing.
    Dim fieldExpr As Expression = Expression.Field(
          Expression.Constant(obj),
          "sample"
      )

    ' The following statement first creates an expression tree,
    ' then compiles it, and then runs it.
    Console.WriteLine(Expression.Lambda(Of Func(Of Integer))(fieldExpr).Compile()())
End Sub

' This code example produces the following output:
'
' 40

備註

Type產生的屬性等於的 MemberExpression FieldType 屬性，其代表所表示 FieldInfo 的欄位 fieldName 。The Type property of the resulting MemberExpression is equal to the FieldType property of the FieldInfo that represents the field denoted by fieldName.

這個方法會搜尋 expression 。具有名稱之欄位的類型及其基底類型 fieldName 。This method searches expression.Type and its base types for a field that has the name fieldName. 公用欄位是針對非公用欄位提供喜好設定。Public fields are given preference over non-public fields. 如果找到相符的欄位，這個方法會將 expression FieldInfo 表示該欄位的傳遞給 Field 。If a matching field is found, this method passes expression and the FieldInfo that represents that field to Field.

public:
 static System::Linq::Expressions::MemberExpression ^ Field(System::Linq::Expressions::Expression ^ expression, Type ^ type, System::String ^ fieldName);

public static System.Linq.Expressions.MemberExpression Field (System.Linq.Expressions.Expression expression, Type type, string fieldName);

public static System.Linq.Expressions.MemberExpression Field (System.Linq.Expressions.Expression? expression, Type type, string fieldName);

static member Field : System.Linq.Expressions.Expression * Type * string -> System.Linq.Expressions.MemberExpression

Public Shared Function Field (expression As Expression, type As Type, fieldName As String) As MemberExpression

參數

傳回

MemberExpression

建立的 MemberExpression。The created MemberExpression.