Question

我在一些代码中创建了这个表达式：

t => (t.SomeProperty As Object)

现在我试图通过这个小片段获取属性名称（SomeProperty）（长时间从互联网上获取）：

    public static PropertyInfo GetPropertyInfo<TSource, TProperty>
        (TSource source, Expression<Func<TSource, TProperty>> propertyLambda) {
        var type = typeof(TSource);

        var member = propertyLambda.Body as MemberExpression;
        if (member == null)
            throw new ArgumentException($"Expression '{propertyLambda}' refers to a method, not a property.");

        var propInfo = member.Member as PropertyInfo;
        if (propInfo == null)
            throw new ArgumentException($"Expression '{propertyLambda}' refers to a field, not a property.");

        if (type != propInfo.ReflectedType && !type.IsSubclassOf(propInfo.ReflectedType))
            throw new ArgumentException($"Expresion '{propertyLambda}' refers to a property that is not from type {type}.");

        return propInfo;
    }

但是如您所知，propertyLambda.Body as MemberExpression始终为空，因此：t => (t.Some1 As Object)不是属性引用。在这种情况下，有没有办法获得属性名称？

Answer 1

C＃as运算符转换为Expression.TypeAs，C＃转换运算符转换为Expression.Convert或Expression.ConvertChecked。如您所见，它们都是UnaryExpression类型，因此您可以使用Operand属性提取操作数表达式。你可以在一个循环中做到这一点，以支持多个演员阵容。

付诸行动，替换

var member = propertyLambda.Body as MemberExpression;

与

var operand = propertyLambda.Body;
while (operand.NodeType == ExpressionType.TypeAs || operand.NodeType == ExpressionType.Convert || operand.NodeType == ExpressionType.ConvertChecked)
    operand = ((UnaryExpression)operand).Operand;
var member = operand as MemberExpression;

Answer 2

在您的情况下，您需要查看作为强制转换的一元表达式的操作数。

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">

<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<input type="text"  title="Your name" id="name">
<button type="button" id="submit">Submit</button>

为了使程序更安全，您应该检查您的propertyLamba。类似的东西：

((propertyLamdba.Body as UnaryExpression).Operand as MemberExpression).Member

Answer 3

我建议这样做：

PropertyInfo info = t.GetType().GetProperty("SomeProperty",
    BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
// Use these binding flags to get a member of any visibility.

它为给定名称的属性返回PropertyInfo。

如果您不想明确处理名称，请使用nameof(t.SomeProperty)。

您可能还会发现方法.GetProperties对于获取特定类型的所有属性非常有用。

表达式`t =＆gt; （t.SomeProperty As Object）`指的是方法，而不是属性

3 个答案: