继承的 WeakReference 在 Silverlight 中抛出 ReflectionTypeLoadException答案

【问题标题】：Inherited WeakReference throwing ReflectionTypeLoadException in Silverlight继承的 WeakReference 在 Silverlight 中抛出 ReflectionTypeLoadException
【发布时间】：2010-07-12 20:21:36
【问题描述】：

我正在尝试在我的 Silverlight 应用程序中使用类型安全的 WeakReference。我正在遵循这个网站上的食谱：http://ondevelopment.blogspot.com/2008/01/generic-weak-reference.html 仅使用 System.WeakReference 并省略引用序列化的内容。

当我尝试运行它时，它会抛出一个 ReflectionTypeLoadException，并显示以下消息：

"{System.TypeLoadException: 覆盖成员时违反继承安全规则：'Coatue.Silverlight.Shared.Cache.WeakReference`1..ctor()'。覆盖方法的安全可访问性必须与方法的安全可访问性相匹配被覆盖。}"

有什么建议吗？

编辑：这是我正在使用的代码：

using System;

namespace Frank
{
    public class WeakReference<T>
        : WeakReference where T : class
    {
        public WeakReference(T target)
            : base(target) { }

        public WeakReference(T target, bool trackResurrection)
            : base(target, trackResurrection) { }

        protected WeakReference() : base() { }

        public new T Target
        {
            get
            {
                return (T)base.Target;
            }
            set
            {
                base.Target = value;
            }
        }
    }
}

【问题讨论】：

你能发布你的 WeakReference 类的代码吗？

标签： c# silverlight weak-references

【解决方案1】：

正如 Thomas 提到的，您不能从 silverlight 中的弱引用继承，但可以将其包装：

using System;

namespace Frank
{
    public class WeakReference<T> where T : class
    {
        private readonly WeakReference inner;

        public WeakReference(T target)
            : this(target, false)
        { }

        public WeakReference(T target, bool trackResurrection)
        {
            if(target == null) throw new ArgumentNullException("target");
            this.inner = new WeakReference(target, trackResurrection);
        }

        public T Target
        {
            get
            {
                return (T)this.inner.Target;
            }
            set
            {
                this.inner.Target = value;
            }
        }

        public bool IsAlive {
            get {
                 return this.inner.IsAlive;
            }
        }
    }
}

【讨论】：

简单高效的解决方法，+1。但是，我认为您还需要一个 IsAlive 属性；）
请注意，您在堆上创建了两个引用对象，而不是在这里创建一个。

【解决方案2】：

WeakReference 类有继承需求，Silverlight 运行时没有必要的权限。所以你不能在 Silverlight 中继承 WeakReference...

[SecurityPermissionAttribute(SecurityAction.InheritanceDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]

【讨论】：

【解决方案3】：

using System;

namespace Harmony.Ria
{
    public class WeakReference<T>
        where T : class
    {
        private WeakReference inner;

        /// <summary>
        /// Initializes a new instance of the System.WeakReference class, referencing 
        /// the specified object.
        /// </summary>
        /// <param name="target">The object to track or null.</param>
        public WeakReference(T target)
            : this(target, false)
        { }

        /// <summary>
        /// Initializes a new instance of the System.WeakReference class, referencing
        /// the specified object and using the specified resurrection tracking.
        /// </summary>
        /// <param name="target">An object to track.</param>
        /// <param name="trackResurrection">Indicates when to stop tracking the object. 
        /// If true, the object is tracked after finalization; if false, the object is 
        /// only tracked until finalization.</param>
        public WeakReference(T target, bool trackResurrection)
        {
            if (target == null) throw new ArgumentNullException("target");
            this.inner = new WeakReference((object)target, trackResurrection);
        }

        /// <summary>
        /// Gets or sets the object (the target) referenced by the current 
        /// System.WeakReference object.
        /// </summary>
        public T Target { get { return (T)this.inner.Target; } set { this.inner.Target = value; } }

        /// <summary>
        /// Gets an indication whether the object referenced by the current 
        /// System.WeakReference object has been garbage collected.
        /// </summary>
        public bool IsAlive { get { return this.inner.IsAlive; } }

        /// <summary>  
        /// Casts an object of the type T to a weak reference  
        /// of T.  
        /// </summary>  
        public static implicit operator WeakReference<T>(T target)
        {
            if (target == null)
            {
                throw new ArgumentNullException("target");
            }
            return new WeakReference<T>(target);
        }

        /// <summary>  
        /// Casts a weak reference to an object of the type the  
        /// reference represents.  
        /// </summary>  
        public static implicit operator T(WeakReference<T> reference)
        {
            if (reference != null)
            {
                return reference.Target;
            }
            else
            {
                return null;
            }
        }
    }
}

【讨论】：