有没有办法强制编译器限制自定义属性的使用，使其仅用于特定的 property 类型，如 int、short、string（所有原始类型）？
类似于 AttributeUsageAttribute 的 ValidOn-AttributeTargets 枚举。
不，基本上你不能。您可以将其限制为
structclassinterfaceTypeDescriptor您可以运行此单元测试来检查它。
首先声明验证属性PropertyType：
[AttributeUsage(AttributeTargets.Class)]
// [JetBrains.Annotations.BaseTypeRequired(typeof(Attribute))] uncomment if you use JetBrains.Annotations
public class PropertyTypeAttribute : Attribute
{
public Type[] Types { get; private set; }
public PropertyTypeAttribute(params Type[] types)
{
Types = types;
}
}
创建单元测试：
[TestClass]
public class TestPropertyType
{
public static Type GetNullableUnderlying(Type nullableType)
{
return Nullable.GetUnderlyingType(nullableType) ?? nullableType;
}
[TestMethod]
public void Test_PropertyType()
{
var allTypes = AppDomain.CurrentDomain.GetAssemblies().SelectMany(a => a.GetTypes());
var allPropertyInfos = allTypes.SelectMany(a => a.GetProperties()).ToArray();
foreach (var propertyInfo in allPropertyInfos)
{
var propertyType = GetNullableUnderlying(propertyInfo.PropertyType);
foreach (var attribute in propertyInfo.GetCustomAttributes(true))
{
var attributes = attribute.GetType().GetCustomAttributes(true).OfType<PropertyTypeAttribute>();
foreach (var propertyTypeAttr in attributes)
if (!propertyTypeAttr.Types.Contains(propertyType))
throw new Exception(string.Format(
"Property '{0}.{1}' has invalid type: '{2}'. Allowed types for attribute '{3}': {4}",
propertyInfo.DeclaringType,
propertyInfo.Name,
propertyInfo.PropertyType,
attribute.GetType(),
string.Join(",", propertyTypeAttr.Types.Select(x => "'" + x.ToString() + "'"))));
}
}
}
}
您的属性，例如仅允许小数属性类型：
[AttributeUsage(AttributeTargets.Property)]
[PropertyType(typeof(decimal))]
public class PriceAttribute : Attribute
{
}
示例模型：
public class TestModel
{
[Price]
public decimal Price1 { get; set; } // ok
[Price]
public double Price2 { get; set; } // error
}
如果属性放置在不是字符串列表的属性/字段上，下面的代码将返回错误。
行
if (!(value is List<string> list))[AttributeUsage(AttributeTargets.Property |
AttributeTargets.Field, AllowMultiple = false)]
public sealed class RequiredStringListAttribute : ValidationAttribute
{
protected override ValidationResult IsValid(object value, ValidationContext context)
{
if (!(value is List<string> list))
return new ValidationResult($"The required attrribute must be of type List<string>");
bool valid = false;
foreach (var item in list)
{
if (!string.IsNullOrWhiteSpace(item))
valid = true;
}
return valid
? ValidationResult.Success
: new ValidationResult($"This field is required"); ;
}
}
您可以自己编写代码来强制正确使用属性类，但这已经是您能做的了。
我这样做的方式如下：
[AttributeUsage(AttributeTargets.Property)]
public class SomeValidationAttribute : ValidationAttribute
{
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
if (value is not string stringToValidate)
{
throw new AttributeValueIsNotStringException(validationContext.DisplayName, validationContext.ObjectType.Name);
}
// validationContext.DisplayName is name of property, where validation attribut was used.
// validationContext.ObjectType.Name is name of class, in which the property is placed to instantly identify, where is the error.
//Some validation here.
return ValidationResult.Success;
}
}
异常看起来像这样：
public class AttributeValueIsNotStringException : Exception
{
public AttributeValueIsNotStringException(string propertyName, string className) : base(CreateMessage(propertyName, className))
{
}
private static string CreateMessage(string propertyName, string className)
{
return $"Validation attribute cannot be used for property: \"{propertyName}\" in class: \"{className}\" because it's type is not string. Use it only for string properties.";
}
}
对于原始类型和密封类型，你很不幸。
但是，您确实可以通过将属性声明为具有受保护或内部可见性的内部类，将属性的使用（和可见性）限制为类型层次结构。
当然，这里存在各种限制和极端情况，但是这是可能的，并且可能适用于各种用例。
内部可见性可以允许您从其他程序集访问这些字段（如果您使这些字段对这些程序集可见）。
这里是一个简单的自动验证时属性绑定属性的示例。在 Unity 2023.1.12f1 中测试。
using System;
using System.Reflection;
using UnityEngine;
namespace Tiger.Attributes
{
public class AutoBehaviour : MonoBehaviour
{
[AttributeUsage(AttributeTargets.Field)]
protected class AutoAttribute : PropertyAttribute { }
private void OnValidate()
{
var object_fields = GetType().GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
foreach (var field_info in object_fields)
{
if (Attribute.GetCustomAttribute(field_info, typeof(AutoAttribute)) is not AutoAttribute) continue;
var value = GetComponent(field_info.FieldType);
field_info.SetValue(this, value);
}
}
}
}
用法很简单，例如，如果您将此脚本组件附加到 Cube 原始游戏对象，它将自动查找并序列化适当的组件。
using Tiger.Attributes;
using UnityEngine;
namespace Jovian
{
public class TestBehaviour : AutoBehaviour
{
[Auto] public MeshFilter meshFilter;
[Auto] public MeshRenderer meshRenderer;
// Start is called before the first frame update
private void Start()
{
}
// Update is called once per frame
private void Update()
{
}
}
}