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Android Reference

RemoteCallbackList


android.os

Class RemoteCallbackList<E extends IInterface>



  • public class RemoteCallbackList<E extends IInterface>
    extends Object
    Takes care of the grunt work of maintaining a list of remote interfaces, typically for the use of performing callbacks from a Service to its clients. In particular, this:
    • Keeps track of a set of registered IInterface callbacks, taking care to identify them through their underlying unique IBinder (by calling IInterface.asBinder().
    • Attaches a IBinder.DeathRecipient to each registered interface, so that it can be cleaned out of the list if its process goes away.
    • Performs locking of the underlying list of interfaces to deal with multithreaded incoming calls, and a thread-safe way to iterate over a snapshot of the list without holding its lock.

    To use this class, simply create a single instance along with your service, and call its register(E) and unregister(E) methods as client register and unregister with your service. To call back on to the registered clients, use beginBroadcast(), getBroadcastItem(int), and finishBroadcast().

    If a registered callback's process goes away, this class will take care of automatically removing it from the list. If you want to do additional work in this situation, you can create a subclass that implements the onCallbackDied(E) method.

    • Constructor Detail

      • RemoteCallbackList

        public RemoteCallbackList()
    • Method Detail

      • register

        public boolean register(E callback)
        Simple version of RemoteCallbackList#register(E, Object) that does not take a cookie object.
      • register

        public boolean register(E callback,
                       Object cookie)
        Add a new callback to the list. This callback will remain in the list until a corresponding call to unregister(E) or its hosting process goes away. If the callback was already registered (determined by checking to see if the callback.asBinder() object is already in the list), then it will be left as-is. Registrations are not counted; a single call to unregister(E) will remove a callback after any number calls to register it.
        Parameters:
        callback - The callback interface to be added to the list. Must not be null -- passing null here will cause a NullPointerException. Most services will want to check for null before calling this with an object given from a client, so that clients can't crash the service with bad data.
        cookie - Optional additional data to be associated with this callback.
        Returns:
        Returns true if the callback was successfully added to the list. Returns false if it was not added, either because kill() had previously been called or the callback's process has gone away.
        See Also:
        unregister(E), kill(), onCallbackDied(E)
      • unregister

        public boolean unregister(E callback)
        Remove from the list a callback that was previously added with register(E). This uses the callback.asBinder() object to correctly find the previous registration. Registrations are not counted; a single unregister call will remove a callback after any number calls to register(E) for it.
        Parameters:
        callback - The callback to be removed from the list. Passing null here will cause a NullPointerException, so you will generally want to check for null before calling.
        Returns:
        Returns true if the callback was found and unregistered. Returns false if the given callback was not found on the list.
        See Also:
        register(E)
      • kill

        public void kill()
        Disable this callback list. All registered callbacks are unregistered, and the list is disabled so that future calls to register(E) will fail. This should be used when a Service is stopping, to prevent clients from registering callbacks after it is stopped.
        See Also:
        register(E)
      • onCallbackDied

        public void onCallbackDied(E callback)
        Old version of #onCallbackDied(E, Object) that does not provide a cookie.
      • onCallbackDied

        public void onCallbackDied(E callback,
                          Object cookie)
        Called when the process hosting a callback in the list has gone away. The default implementation calls #onCallbackDied(E) for backwards compatibility.
        Parameters:
        callback - The callback whose process has died. Note that, since its process has died, you can not make any calls on to this interface. You can, however, retrieve its IBinder and compare it with another IBinder to see if it is the same object.
        cookie - The cookie object original provided to #register(E, Object).
        See Also:
        register(E)
      • beginBroadcast

        public int beginBroadcast()
        Prepare to start making calls to the currently registered callbacks. This creates a copy of the callback list, which you can retrieve items from using getBroadcastItem(int). Note that only one broadcast can be active at a time, so you must be sure to always call this from the same thread (usually by scheduling with Handler) or do your own synchronization. You must call finishBroadcast() when done.

        A typical loop delivering a broadcast looks like this:

         int i = callbacks.beginBroadcast();
         while (i > 0) {
             i--;
             try {
                 callbacks.getBroadcastItem(i).somethingHappened();
             } catch (RemoteException e) {
                 // The RemoteCallbackList will take care of removing
                 // the dead object for us.
             }
         }
         callbacks.finishBroadcast();
        Returns:
        Returns the number of callbacks in the broadcast, to be used with getBroadcastItem(int) to determine the range of indices you can supply.
        See Also:
        getBroadcastItem(int), finishBroadcast()
      • getBroadcastItem

        public E getBroadcastItem(int index)
        Retrieve an item in the active broadcast that was previously started with beginBroadcast(). This can only be called after the broadcast is started, and its data is no longer valid after calling finishBroadcast().

        Note that it is possible for the process of one of the returned callbacks to go away before you call it, so you will need to catch RemoteException when calling on to the returned object. The callback list itself, however, will take care of unregistering these objects once it detects that it is no longer valid, so you can handle such an exception by simply ignoring it.

        Parameters:
        index - Which of the registered callbacks you would like to retrieve. Ranges from 0 to 1-beginBroadcast().
        Returns:
        Returns the callback interface that you can call. This will always be non-null.
        See Also:
        beginBroadcast()
      • finishBroadcast

        public void finishBroadcast()
        Clean up the state of a broadcast previously initiated by calling beginBroadcast(). This must always be called when you are done with a broadcast.
        See Also:
        beginBroadcast()
      • getRegisteredCallbackCount

        public int getRegisteredCallbackCount()
        Returns the number of registered callbacks. Note that the number of registered callbacks may differ from the value returned by beginBroadcast() since the former returns the number of callbacks registered at the time of the call and the second the number of callback to which the broadcast will be delivered.

        This function is useful to decide whether to schedule a broadcast if this requires doing some work which otherwise would not be performed.

        Returns:
        The size.


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