ExpressionBuilder.GetCodeExpression 方法

定义

命名空间:
System.Web.Compilation
程序集:
System.Web.dll

在派生类中重写时，返回在页面执行期间用于获取计算表达式的代码。

public:
 abstract System::CodeDom::CodeExpression ^ GetCodeExpression(System::Web::UI::BoundPropertyEntry ^ entry, System::Object ^ parsedData, System::Web::Compilation::ExpressionBuilderContext ^ context);
public abstract System.CodeDom.CodeExpression GetCodeExpression(System.Web.UI.BoundPropertyEntry entry, object parsedData, System.Web.Compilation.ExpressionBuilderContext context);
abstract member GetCodeExpression : System.Web.UI.BoundPropertyEntry * obj * System.Web.Compilation.ExpressionBuilderContext -> System.CodeDom.CodeExpression
Public MustOverride Function GetCodeExpression (entry As BoundPropertyEntry, parsedData As Object, context As ExpressionBuilderContext) As CodeExpression

参数

entry
BoundPropertyEntry

表示表达式绑定到的属性的相关信息的对象。

parsedData
Object

包含由 ParseExpression(String, Type, ExpressionBuilderContext). 返回的已分析数据的对象。

context
ExpressionBuilderContext

表达式计算的上下文信息。

返回

CodeExpression

用于属性分配的 A CodeExpression 。

示例

下面的代码示例演示如何通过重写GetCodeExpression方法返回CodeExpression对象。

public override CodeExpression GetCodeExpression(BoundPropertyEntry entry, 
object parsedData, ExpressionBuilderContext context)
{
    Type type1 = entry.DeclaringType;
    PropertyDescriptor descriptor1 = TypeDescriptor.GetProperties(type1)[entry.PropertyInfo.Name];
    CodeExpression[] expressionArray1 = new CodeExpression[3];
    expressionArray1[0] = new CodePrimitiveExpression(entry.Expression.Trim());
    expressionArray1[1] = new CodeTypeOfExpression(type1);
    expressionArray1[2] = new CodePrimitiveExpression(entry.Name);
    return new CodeCastExpression(descriptor1.PropertyType, new CodeMethodInvokeExpression(new 
   CodeTypeReferenceExpression(base.GetType()), "GetEvalData", expressionArray1));
}

Public Overrides Function GetCodeExpression(ByVal entry _
   As BoundPropertyEntry, ByVal parsedData As Object, ByVal context _
   As ExpressionBuilderContext) As CodeExpression
    Dim type1 As Type = entry.DeclaringType
    Dim descriptor1 As PropertyDescriptor = _
       TypeDescriptor.GetProperties(type1)(entry.PropertyInfo.Name)
    Dim expressionArray1(2) As CodeExpression
    expressionArray1(0) = New CodePrimitiveExpression(entry.Expression.Trim())
    expressionArray1(1) = New CodeTypeOfExpression(type1)
    expressionArray1(2) = New CodePrimitiveExpression(entry.Name)
    Return New CodeCastExpression(descriptor1.PropertyType, _
       New CodeMethodInvokeExpression(New CodeTypeReferenceExpression _
       (MyBase.GetType()), "GetEvalData", expressionArray1))
End Function

注解

继承自类的 ExpressionBuilder 类必须实现 GetCodeExpression 抽象方法。

实施者说明

如果实现自定义表达式生成器，则必须为控件属性执行正确的类型转换，并在对象中 CodeExpression 返回强制转换操作。

适用于