c# - 通过 lambda 表达式传递属性名称以读取属性值

Question

我找到了这个解决方案:

public static T GetAttributeFrom<T>(this object instance, string propertyName) where T : Attribute
{
    var attrType = typeof(T);
    var property = instance.GetType().GetProperty(propertyName);
    return (T)property .GetCustomAttributes(attrType, false).First();
}

由 jgauffin 编写的代码，来自 How to retrieve Data Annotations from code

我总是这样使用扩展:

foo.GetAttributeFrom<StringLengthAttribute>(nameof(Foo.Bar)).MaximumLength

有没有办法使用 lambda 来传递 propertyName，例如:

foo.GetAttributeFrom<StringLengthAttribute>(f => f.Bar).MaximumLength

提前谢谢您!

Answer 1

您可以将工作拆分为两个函数，以绕过为泛型方法指定所有泛型参数类型限制

public static object[] GetPropertyAttributes<TObject, TProperty>(
    this TObject instance,
    Expression<Func<TObject, TProperty>> propertySelector)
{
    //consider handling exceptions and corner cases
    var propertyName = ((PropertyInfo)((MemberExpression)propertySelector.Body).Member).Name;
    var property = instance.GetType().GetProperty(propertyName);
    return property.GetCustomAttributes(false);
}

public static T GetFirst<T>(this object[] input) where T : Attribute
{
    //consider handling exceptions and corner cases
    return input.OfType<T>().First();
}

然后像这样使用它

foo.GetPropertyAttributes(f => f.Bar)
   .GetFirst<StringLengthAttribute>()
   .MaximumLength;