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Type: ObjectId

The ObjectId type is an object identifier. All of its members are threadsafe.

The ObjectId type has three facets:


  • bool IsAlive { get; } - Gets a value indicating whether the target is still alive (has not been garbage collected).
  • object Target { get; } - Gets the target object. Will return null if the object has been garbage collected.
  • T TargetAs<T>() - Gets the target object, cast to T. Note that this does an explicit cast, not an "as-cast".
  • void Register(Action action) and void Register(Action<ObjectId> action) - Registers the action as a callback.

Creating an ObjectId

ObjectId instances may not be created directly. They are only returned from the ObjectTracker.TrackObject method.

For example:
var target = ...;
var id = ObjectTracker.Default.TrackObject(target);
// "id" is now the object identifier for "target"

Using an ObjectId as a unique identifier

ObjectId instances use reference equality, so they can be compared using either the Equals method or operator==. Every tracked object has exactly one ObjectId instance.

For example:
static object target = ...;

// In thread 1:
var id1 = ObjectTracker.Default.TrackObject(target);

// In thread 2:
var id2 = ObjectTracker.Default.TrackObject(target);

Assert.IsTrue(id1 == id2);

Even though the two ObjectId variables are assigned on different threads, they are the same instance.

Using an ObjectId as a weak reference

Code that has an ObjectId may use the IsAlive and Target properties and the TargetAs method. IsAlive is not commonly used, but TargetAs is useful for getting a strong reference:

ObjectId id = ...;
MyTargetType target = id.TargetAs<MyTargetType>();
if (target == null)
  // Target has been garbage collected.
  // Target is still alive. Use it.

Using an ObjectId to register callbacks

It's possible to register a callback that will (in most cases) be invoked some time after the target is garbage collected. See the registered action documentation for all the details.

ObjectId id = ...;
id.Register(_ =>
  // Be careful in here! See the Registered action documentation...

Last edited Jul 23, 2010 at 8:47 PM by shammah, version 12


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