Handler Class

Definition

Namespace:

Android.OS

Assembly:

Mono.Android.dll

A Handler allows you to send and process Message and Runnable objects associated with a thread's MessageQueue.

[Android.Runtime.Register("android/os/Handler", DoNotGenerateAcw=true)]
public class Handler : Java.Lang.Object

[<Android.Runtime.Register("android/os/Handler", DoNotGenerateAcw=true)>]
type Handler = class
    inherit Object

Inheritance

Object

Object

Handler

Derived

Android.Content.AsyncQueryHandler

Android.Content.AsyncQueryHandler.WorkerHandler

Android.Webkit.HttpAuthHandler

Android.Webkit.SslErrorHandler

Attributes

RegisterAttribute

Remarks

A Handler allows you to send and process Message and Runnable objects associated with a thread's MessageQueue. Each Handler instance is associated with a single thread and that thread's message queue. When you create a new Handler it is bound to a Looper. It will deliver messages and runnables to that Looper's message queue and execute them on that Looper's thread.

There are two main uses for a Handler: (1) to schedule messages and runnables to be executed at some point in the future; and (2) to enqueue an action to be performed on a different thread than your own.

Scheduling messages is accomplished with the #post, #postAtTime(Runnable, long), #postDelayed, #sendEmptyMessage, #sendMessage, #sendMessageAtTime, and #sendMessageDelayed methods. The <em>post</em> versions allow you to enqueue Runnable objects to be called by the message queue when they are received; the <em>sendMessage</em> versions allow you to enqueue a Message object containing a bundle of data that will be processed by the Handler's #handleMessage method (requiring that you implement a subclass of Handler).

When posting or sending to a Handler, you can either allow the item to be processed as soon as the message queue is ready to do so, or specify a delay before it gets processed or absolute time for it to be processed. The latter two allow you to implement timeouts, ticks, and other timing-based behavior.

When a process is created for your application, its main thread is dedicated to running a message queue that takes care of managing the top-level application objects (activities, broadcast receivers, etc) and any windows they create. You can create your own threads, and communicate back with the main application thread through a Handler. This is done by calling the same <em>post</em> or <em>sendMessage</em> methods as before, but from your new thread. The given Runnable or Message will then be scheduled in the Handler's message queue and processed when appropriate.

Java documentation for android.os.Handler.

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.

Constructors

Handler()	Default constructor associates this handler with the Looper for the current thread.
Handler(Action<Message>)
Handler(Handler+ICallback)	Constructor associates this handler with the Looper for the current thread and takes a callback interface in which you can handle messages.
Handler(IntPtr, JniHandleOwnership)	A constructor used when creating managed representations of JNI objects; called by the runtime.
Handler(Looper, Handler+ICallback)	Use the provided Looper instead of the default one and take a callback interface in which to handle messages.
Handler(Looper)	Use the provided Looper instead of the default one.

Properties

Class	Returns the runtime class of this Object. (Inherited from Object)
Handle	The handle to the underlying Android instance. (Inherited from Object)
JniIdentityHashCode	(Inherited from Object)
JniPeerMembers
Looper
PeerReference	(Inherited from Object)
ThresholdClass	This API supports the Mono for Android infrastructure and is not intended to be used directly from your code.
ThresholdType	This API supports the Mono for Android infrastructure and is not intended to be used directly from your code.

Methods

Clone()	Creates and returns a copy of this object. (Inherited from Object)
CreateAsync(Looper, Handler+ICallback)	Create a new Handler whose posted messages and runnables are not subject to synchronization barriers such as display vsync.
CreateAsync(Looper)	Create a new Handler whose posted messages and runnables are not subject to synchronization barriers such as display vsync.
DispatchMessage(Message)	Handle system messages here.
Dispose()	(Inherited from Object)
Dispose(Boolean)	(Inherited from Object)
Dump(IPrinter, String)
DumpAsync(IPrinter, String)
Equals(Object)	Indicates whether some other object is "equal to" this one. (Inherited from Object)
GetHashCode()	Returns a hash code value for the object. (Inherited from Object)
GetMessageName(Message)	Returns a string representing the name of the specified message.
HandleMessage(Message)	Subclasses must implement this to receive messages.
HasCallbacks(IRunnable)	Check if there are any pending posts of messages with callback r in the message queue.
HasMessages(Int32, Object)	Check if there are any pending posts of messages with code 'what' and whose obj is 'object' in the message queue.
HasMessages(Int32)	Check if there are any pending posts of messages with code 'what' in the message queue.
JavaFinalize()	Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. (Inherited from Object)
Notify()	Wakes up a single thread that is waiting on this object's monitor. (Inherited from Object)
NotifyAll()	Wakes up all threads that are waiting on this object's monitor. (Inherited from Object)
ObtainMessage()	Returns a new android.os.Message Message from the global message pool.
ObtainMessage(Int32, Int32, Int32, Object)	Same as #obtainMessage(), except that it also sets the what, obj, arg1,and arg2 values on the returned Message.
ObtainMessage(Int32, Int32, Int32)	Same as #obtainMessage(), except that it also sets the what, arg1 and arg2 members of the returned Message.
ObtainMessage(Int32, Object)	Same as #obtainMessage(), except that it also sets the what and obj members of the returned Message.
ObtainMessage(Int32)	Same as #obtainMessage(), except that it also sets the what member of the returned Message.
Post(Action)
Post(IRunnable)	Causes the Runnable r to be added to the message queue.
PostAtFrontOfQueue(Action)
PostAtFrontOfQueue(IRunnable)	Posts a message to an object that implements Runnable.
PostAtTime(Action, Int64)
PostAtTime(Action, Object, Int64)
PostAtTime(IRunnable, Int64)	Causes the Runnable r to be added to the message queue, to be run at a specific time given by <var>uptimeMillis</var>.
PostAtTime(IRunnable, Object, Int64)	Causes the Runnable r to be added to the message queue, to be run at a specific time given by <var>uptimeMillis</var>.
PostDelayed(Action, Int64)
PostDelayed(IRunnable, Int64)	Causes the Runnable r to be added to the message queue, to be run after the specified amount of time elapses.
PostDelayed(IRunnable, Object, Int64)	Causes the Runnable r to be added to the message queue, to be run after the specified amount of time elapses.
RemoveCallbacks(Action, Object)
RemoveCallbacks(Action)
RemoveCallbacks(IRunnable, Object)	Remove any pending posts of Runnable <var>r</var> with Object <var>token</var> that are in the message queue.
RemoveCallbacks(IRunnable)	Remove any pending posts of Runnable r that are in the message queue.
RemoveCallbacksAndMessages(Object)	Remove any pending posts of callbacks and sent messages whose <var>obj</var> is <var>token</var>.
RemoveMessages(Int32, Object)	Remove any pending posts of messages with code 'what' and whose obj is 'object' that are in the message queue.
RemoveMessages(Int32)	Remove any pending posts of messages with code 'what' that are in the message queue.
SendEmptyMessage(Int32)	Sends a Message containing only the what value.
SendEmptyMessageAtTime(Int32, Int64)	Sends a Message containing only the what value, to be delivered at a specific time.
SendEmptyMessageDelayed(Int32, Int64)	Sends a Message containing only the what value, to be delivered after the specified amount of time elapses.
SendMessage(Message)	Pushes a message onto the end of the message queue after all pending messages before the current time.
SendMessageAtFrontOfQueue(Message)	Enqueue a message at the front of the message queue, to be processed on the next iteration of the message loop.
SendMessageAtTime(Message, Int64)	Enqueue a message into the message queue after all pending messages before the absolute time (in milliseconds) <var>uptimeMillis</var>.
SendMessageDelayed(Message, Int64)	Enqueue a message into the message queue after all pending messages before (current time + delayMillis).
SetHandle(IntPtr, JniHandleOwnership)	Sets the Handle property. (Inherited from Object)
ToArray<T>()	(Inherited from Object)
ToString()	Returns a string representation of the object. (Inherited from Object)
UnregisterFromRuntime()	(Inherited from Object)
Wait()	Causes the current thread to wait until it is awakened, typically by being <em>notified</em> or <em>interrupted</em>. (Inherited from Object)
Wait(Int64, Int32)	Causes the current thread to wait until it is awakened, typically by being <em>notified</em> or <em>interrupted</em>, or until a certain amount of real time has elapsed. (Inherited from Object)
Wait(Int64)	Causes the current thread to wait until it is awakened, typically by being <em>notified</em> or <em>interrupted</em>, or until a certain amount of real time has elapsed. (Inherited from Object)

Explicit Interface Implementations

IJavaPeerable.Disposed()	(Inherited from Object)
IJavaPeerable.DisposeUnlessReferenced()	(Inherited from Object)
IJavaPeerable.Finalized()	(Inherited from Object)
IJavaPeerable.JniManagedPeerState	(Inherited from Object)
IJavaPeerable.SetJniIdentityHashCode(Int32)	(Inherited from Object)
IJavaPeerable.SetJniManagedPeerState(JniManagedPeerStates)	(Inherited from Object)
IJavaPeerable.SetPeerReference(JniObjectReference)	(Inherited from Object)

Extension Methods

JavaCast<TResult>(IJavaObject)	Performs an Android runtime-checked type conversion.
JavaCast<TResult>(IJavaObject)
GetJniTypeName(IJavaPeerable)