从装饰属性中提取属性数据

Question

有没有什么方法可以只选择properties那些用指定装饰的Attribute并提取Attribute数据......一次通过？

目前我首先进行PropertyInfo过滤，然后获取属性数据：

属性数据：

public class Weight

{

    public string Name { get; set; }

    public double Value { get; set; }

    public Weight(string Name,double Value) {

        this.Name = Name;

        this.Value = Value;

    }

}

属性：

[AttributeUsage(AttributeTargets.Property)]

public class WeightAttribute : Attribute

{

    public WeightAttribute(double val,[CallerMemberName]string Name=null)

    {

        this.Weight = new Weight(Name, val);

    }

    public Weight Weight { get; set; }

}

提取器：

private static IReadOnlyList<Weight> ExtractWeights(Type type)

{

    var properties = type.GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.DeclaredOnly)

        .Where(x => x.GetCustomAttribute<WeightAttribute>() != null);

    var weights = properties

        .Select(x => x.GetCustomAttribute<WeightAttribute>().Weight)

        .ToArray();

    return weights;

}

正如您在我的Extractor方法中看到的那样，我首先过滤PropertyInfo[]然后获取数据。还有其他更有效的方法吗？

Answer 1

出于某种原因，当 LINQ 语法实际上非常有用并且使意图非常清晰时，它似乎被避免了。用 LINQ 语法重写，以下适用 @DavidG 的优点。private static IReadOnlyList<Weight> ExtractWeights(Type type){&nbsp; &nbsp; return (from p in type.GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.DeclaredOnly)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; let attr = p.GetCustomAttribute<WeightAttribute>()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; where attr != null&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; select attr.Weight).ToArray();}当查询变得更加复杂时，例如需要测试整个方法签名的这个let（完全公开：我的答案），渐进式过滤很容易遵循，并且沿途发现的事实在子句中高度可见。

Answer 2

通过使用空条件运算符并将空检查作为最后一件事，您可以避免再次获取自定义属性：private static IReadOnlyList<Weight> ExtractWeights(Type type){&nbsp; &nbsp; return type&nbsp; &nbsp; &nbsp; &nbsp; .GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.DeclaredOnly)&nbsp; &nbsp; &nbsp; &nbsp; .Select(x => x.GetCustomAttribute<WeightAttribute>()?.Weight)&nbsp; &nbsp; &nbsp; &nbsp; .Where(x => x!= null)&nbsp; &nbsp; &nbsp; &nbsp; .ToArray();}完整示例：https ://dotnetfiddle.net/fbp50c