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

问题描述

我在C＃中创建了一个方法>获取方法名

I created a method in C# to get methodname

public string GetCorrectPropertyName<T>(Expression<Func<T, string>> expression)
{
   return ((MemberExpression)expression.Body).Member.Name; // Failure Point
}

并将其称为

string lcl_name = false;
public string Name
{
get { return lcl_name ; }
set 
    {
        lcl_name = value;
        OnPropertyChanged(GetCorrectPropertyName<ThisClassName>(x => x.Name));
}
}

如果属性是字符串，并且所有其他类型给出了这个例外：

This works fine if property is string and for all other types gives this exception:

1. 我在方法签名中将字符串更改为对象，但是再次失败。 / li>
   
2. 我从 x => x.PropertyName to x => Convert.ToString（x.PropertyName）并且仍然失败

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

我错了什么？ >

Where am I wrong?

推荐答案

您需要单独的一行来提取输入表达式是Unary Expression的Member。

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

刚刚从VB.Net转换了这个，所以可能会稍微关闭 - 让我知道如果我需要做任何微调：

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;
    }                
}

VB版本是：

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

请注意，输入表达式不会返回字符串 - 限制您只读取返回字符串的属性。

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

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