即使在GC.Collect之后，（Mono C＃）中的WeakReference仍然存活

Question

以下用C＃编写并在Mono Droid上执行的代码无法按预期工作。

    var strongRef = "abc";
    WeakReference weakRef = new WeakReference (strongRef);
    strongRef = null;
    System.GC.Collect (2,GCCollectionMode.Forced);
    System.Diagnostics.Debug.WriteLine ("Target:" + weakRef.Target + " IsAlive:" + weakRef.IsAlive);

预期O / P：目标：null IsAlive：false

实际O / P：目标：abc IsAlive：true