无法转换类型'System.Linq.Expressions.UnaryExpression“对象键入'System.Linq.Expressions.MemberExpression”

问题描述

我创建了C＃方法>获取方法名

 公共字符串GetCorrectPropertyName< T>（表达式来; Func键< T，串>>表达式）
 {
回报率（（MemberExpression）expression.Body）.Member.Name; //故障点
} 
  

和调用它作为

 字符串lcl_name = FALSE; 
公共字符串名称
 {
 {返回lcl_name; } 
组
 {
 lcl_name =价值; 
 OnPropertyChanged（GetCorrectPropertyName< ThisClassName>（X => x.Name））; 
} 
} 
  

这工作正常，如果属性是字符串，并为所有其他类型给出了这样的例外：

1. I changed string to object in method signature, but then it fails again.
2. I changed calling from x => x.PropertyName to x => Convert.ToString(x.PropertyName) and it still fails

Where am I wrong?

解决方案

You need a separate line to extract the Member where the input expression is a Unary Expression.

Just converted this from VB.Net, so might be slightly off - let me know if I need to make any minor tweaks:

public string GetCorrectPropertyName<T>(Expression<Func<T, Object>> expression)
{
    if (expression.Body is MemberExpression) {
        return ((MemberExpression)expression.Body).Member.Name;
    }
    else {
        var op = ((UnaryExpression)expression.Body).Operand;
        return ((MemberExpression)op).Member.Name;
    }                
}

The VB version is:

Public Shared Function GetCorrectPropertyName(Of T) _
             (ByVal expression As Expression(Of Func(Of T, Object))) As String
    If TypeOf expression.Body Is MemberExpression Then
        Return DirectCast(expression.Body, MemberExpression).Member.Name
    Else
        Dim op = (CType(expression.Body, UnaryExpression).Operand)
        Return DirectCast(op, MemberExpression).Member.Name
    End If
End Function

Note that the input expression does not return string necessarily - that constrains you to only reading properties that return strings.

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