Handler
open class Handler
| kotlin.Any | |
| ↳ | android.os.Handler |
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(java.lang.Runnable,long), #postDelayed, sendEmptyMessage, sendMessage, sendMessageAtTime, and sendMessageDelayed methods. The post versions allow you to enqueue Runnable objects to be called by the message queue when they are received; the sendMessage 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 post or sendMessage 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.
Summary
| Nested classes | |
|---|---|
| abstract |
Callback interface you can use when instantiating a Handler to avoid having to implement your own subclass of Handler. |
| Public constructors | |
|---|---|
Handler()Default constructor associates this handler with the |
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Handler(callback: Handler.Callback?)Constructor associates this handler with the |
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Use the provided |
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Handler(looper: Looper, callback: Handler.Callback?)Use the provided |
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| Public methods | |
|---|---|
| open static Handler |
createAsync(looper: Looper)Create a new Handler whose posted messages and runnables are not subject to synchronization barriers such as display vsync. |
| open static Handler |
createAsync(looper: Looper, callback: Handler.Callback)Create a new Handler whose posted messages and runnables are not subject to synchronization barriers such as display vsync. |
| open Unit |
dispatchMessage(msg: Message)Handle system messages here. |
| Unit | |
| Looper | |
| open String |
getMessageName(message: Message)Returns a string representing the name of the specified message. |
| open Unit |
handleMessage(msg: Message)Subclasses must implement this to receive messages. |
| Boolean |
hasCallbacks(r: Runnable)Check if there are any pending posts of messages with callback r in the message queue. |
| Boolean |
hasMessages(what: Int)Check if there are any pending posts of messages with code 'what' in the message queue. |
| Boolean |
hasMessages(what: Int, object: Any?)Check if there are any pending posts of messages with code 'what' and whose obj is 'object' in the message queue. |
| Message |
Returns a new |
| Message |
obtainMessage(what: Int)Same as |
| Message |
obtainMessage(what: Int, obj: Any?)Same as |
| Message |
obtainMessage(what: Int, arg1: Int, arg2: Int)Same as |
| Message |
obtainMessage(what: Int, arg1: Int, arg2: Int, obj: Any?)Same as |
| Boolean |
Causes the Runnable r to be added to the message queue. |
| Boolean |
Posts a message to an object that implements Runnable. |
| Boolean |
postAtTime(r: Runnable, uptimeMillis: Long)Causes the Runnable r to be added to the message queue, to be run at a specific time given by uptimeMillis. |
| Boolean |
postAtTime(r: Runnable, token: Any?, uptimeMillis: Long)Causes the Runnable r to be added to the message queue, to be run at a specific time given by uptimeMillis. |
| Boolean |
postDelayed(r: Runnable, delayMillis: Long)Causes the Runnable r to be added to the message queue, to be run after the specified amount of time elapses. |
| Boolean |
postDelayed(r: Runnable, token: Any?, delayMillis: Long)Causes the Runnable r to be added to the message queue, to be run after the specified amount of time elapses. |
| Unit |
Remove any pending posts of Runnable r that are in the message queue. |
| Unit |
removeCallbacks(r: Runnable, token: Any?)Remove any pending posts of Runnable r with Object token that are in the message queue. |
| Unit |
removeCallbacksAndMessages(token: Any?)Remove any pending posts of callbacks and sent messages whose obj is token. |
| Unit |
removeMessages(what: Int)Remove any pending posts of messages with code 'what' that are in the message queue. |
| Unit |
removeMessages(what: Int, object: Any?)Remove any pending posts of messages with code 'what' and whose obj is 'object' that are in the message queue. |
| Boolean |
sendEmptyMessage(what: Int)Sends a Message containing only the what value. |
| Boolean |
sendEmptyMessageAtTime(what: Int, uptimeMillis: Long)Sends a Message containing only the what value, to be delivered at a specific time. |
| Boolean |
sendEmptyMessageDelayed(what: Int, delayMillis: Long)Sends a Message containing only the what value, to be delivered after the specified amount of time elapses. |
| Boolean |
sendMessage(msg: Message)Pushes a message onto the end of the message queue after all pending messages before the current time. |
| Boolean |
Enqueue a message at the front of the message queue, to be processed on the next iteration of the message loop. |
| open Boolean |
sendMessageAtTime(msg: Message, uptimeMillis: Long)Enqueue a message into the message queue after all pending messages before the absolute time (in milliseconds) uptimeMillis. |
| Boolean |
sendMessageDelayed(msg: Message, delayMillis: Long)Enqueue a message into the message queue after all pending messages before (current time + delayMillis). |
| open String |
toString() |
Public constructors
Handler
Handler()
Deprecated: Implicitly choosing a Looper during Handler construction can lead to bugs where operations are silently lost (if the Handler is not expecting new tasks and quits), crashes (if a handler is sometimes created on a thread without a Looper active), or race conditions, where the thread a handler is associated with is not what the author anticipated. Instead, use an java.util.concurrent.Executor or specify the Looper explicitly, using Looper#getMainLooper, android.view.View#getHandler, or similar. If the implicit thread local behavior is required for compatibility, use new Handler(Looper.myLooper()) to make it clear to readers.
Default constructor associates this handler with the Looper for the current thread. If this thread does not have a looper, this handler won't be able to receive messages so an exception is thrown.
Handler
Handler(callback: Handler.Callback?)
Deprecated: Implicitly choosing a Looper during Handler construction can lead to bugs where operations are silently lost (if the Handler is not expecting new tasks and quits), crashes (if a handler is sometimes created on a thread without a Looper active), or race conditions, where the thread a handler is associated with is not what the author anticipated. Instead, use an java.util.concurrent.Executor or specify the Looper explicitly, using Looper#getMainLooper, android.view.View#getHandler, or similar. If the implicit thread local behavior is required for compatibility, use new Handler(Looper.myLooper(), callback) to make it clear to readers.
Constructor associates this handler with the Looper for the current thread and takes a callback interface in which you can handle messages. If this thread does not have a looper, this handler won't be able to receive messages so an exception is thrown.
| Parameters | |
|---|---|
callback |
Handler.Callback?: The callback interface in which to handle messages, or null. |
Handler
Handler(looper: Looper)
Use the provided Looper instead of the default one.
| Parameters | |
|---|---|
looper |
Looper: The looper, must not be null. |
Handler
Handler(
looper: Looper,
callback: Handler.Callback?)
Use the provided Looper instead of the default one and take a callback interface in which to handle messages.
| Parameters | |
|---|---|
looper |
Looper: The looper, must not be null. |
callback |
Handler.Callback?: The callback interface in which to handle messages, or null. |
Public methods
createAsync
open static fun createAsync(looper: Looper): Handler
Create a new Handler whose posted messages and runnables are not subject to synchronization barriers such as display vsync.
Messages sent to an async handler are guaranteed to be ordered with respect to one another, but not necessarily with respect to messages from other Handlers.
| Parameters | |
|---|---|
looper |
Looper: the Looper that the new Handler should be bound to This value cannot be null. |
| Return | |
|---|---|
Handler |
a new async Handler instance This value cannot be null. |
See Also
createAsync
open static fun createAsync(
looper: Looper,
callback: Handler.Callback
): Handler
Create a new Handler whose posted messages and runnables are not subject to synchronization barriers such as display vsync.
Messages sent to an async handler are guaranteed to be ordered with respect to one another, but not necessarily with respect to messages from other Handlers.
| Parameters | |
|---|---|
looper |
Looper: the Looper that the new Handler should be bound to This value cannot be null. |
callback |
Handler.Callback: This value cannot be null. |
| Return | |
|---|---|
Handler |
a new async Handler instance This value cannot be null. |
See Also
dispatchMessage
open fun dispatchMessage(msg: Message): Unit
Handle system messages here.
| Parameters | |
|---|---|
msg |
Message: This value cannot be null. |
dump
fun dump(
pw: Printer,
prefix: String
): Unit
| Parameters | |
|---|---|
pw |
Printer: This value cannot be null. |
prefix |
String: This value cannot be null. |
getMessageName
open fun getMessageName(message: Message): String
Returns a string representing the name of the specified message. The default implementation will either return the class name of the message callback if any, or the hexadecimal representation of the message "what" field.
| Parameters | |
|---|---|
message |
Message: The message whose name is being queried This value cannot be null. |
| Return | |
|---|---|
String |
This value cannot be null. |
handleMessage
open fun handleMessage(msg: Message): Unit
Subclasses must implement this to receive messages.
| Parameters | |
|---|---|
msg |
Message: This value cannot be null. |
hasCallbacks
fun hasCallbacks(r: Runnable): Boolean
Check if there are any pending posts of messages with callback r in the message queue.
| Parameters | |
|---|---|
r |
Runnable: This value cannot be null. |
hasMessages
fun hasMessages(what: Int): Boolean
Check if there are any pending posts of messages with code 'what' in the message queue.
hasMessages
fun hasMessages(
what: Int,
object: Any?
): Boolean
Check if there are any pending posts of messages with code 'what' and whose obj is 'object' in the message queue.
| Parameters | |
|---|---|
object |
Any?: This value may be null. |
obtainMessage
fun obtainMessage(): Message
Returns a new Message from the global message pool. More efficient than creating and allocating new instances. The retrieved message has its handler set to this instance (Message.target == this). If you don't want that facility, just call Message.obtain() instead.
| Return | |
|---|---|
Message |
This value cannot be null. |
obtainMessage
fun obtainMessage(what: Int): Message
Same as obtainMessage(), except that it also sets the what member of the returned Message.
| Parameters | |
|---|---|
what |
Int: Value to assign to the returned Message.what field. |
| Return | |
|---|---|
Message |
A Message from the global message pool. This value cannot be null. |
obtainMessage
fun obtainMessage(
what: Int,
obj: Any?
): Message
Same as obtainMessage(), except that it also sets the what and obj members of the returned Message.
| Parameters | |
|---|---|
what |
Int: Value to assign to the returned Message.what field. |
obj |
Any?: Value to assign to the returned Message.obj field. This value may be null. |
| Return | |
|---|---|
Message |
A Message from the global message pool. This value cannot be null. |
obtainMessage
fun obtainMessage(
what: Int,
arg1: Int,
arg2: Int
): Message
Same as obtainMessage(), except that it also sets the what, arg1 and arg2 members of the returned Message.
| Parameters | |
|---|---|
what |
Int: Value to assign to the returned Message.what field. |
arg1 |
Int: Value to assign to the returned Message.arg1 field. |
arg2 |
Int: Value to assign to the returned Message.arg2 field. |
| Return | |
|---|---|
Message |
A Message from the global message pool. This value cannot be null. |
obtainMessage
fun obtainMessage(
what: Int,
arg1: Int,
arg2: Int,
obj: Any?
): Message
Same as obtainMessage(), except that it also sets the what, obj, arg1,and arg2 values on the returned Message.
| Parameters | |
|---|---|
what |
Int: Value to assign to the returned Message.what field. |
arg1 |
Int: Value to assign to the returned Message.arg1 field. |
arg2 |
Int: Value to assign to the returned Message.arg2 field. |
obj |
Any?: Value to assign to the returned Message.obj field. This value may be null. |
| Return | |
|---|---|
Message |
A Message from the global message pool. This value cannot be null. |
post
fun post(r: Runnable): Boolean
Causes the Runnable r to be added to the message queue. The runnable will be run on the thread to which this handler is attached.
| Parameters | |
|---|---|
r |
Runnable: The Runnable that will be executed. This value cannot be null. |
| Return | |
|---|---|
Boolean |
Returns true if the Runnable was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. |
postAtFrontOfQueue
fun postAtFrontOfQueue(r: Runnable): Boolean
Posts a message to an object that implements Runnable. Causes the Runnable r to executed on the next iteration through the message queue. The runnable will be run on the thread to which this handler is attached. This method is only for use in very special circumstances -- it can easily starve the message queue, cause ordering problems, or have other unexpected side-effects.
| Parameters | |
|---|---|
r |
Runnable: The Runnable that will be executed. This value cannot be null. |
| Return | |
|---|---|
Boolean |
Returns true if the message was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. |
postAtTime
fun postAtTime(
r: Runnable,
uptimeMillis: Long
): Boolean
Causes the Runnable r to be added to the message queue, to be run at a specific time given by uptimeMillis. The time-base is android.os.SystemClock#uptimeMillis. Time spent in deep sleep will add an additional delay to execution. The runnable will be run on the thread to which this handler is attached.
| Parameters | |
|---|---|
r |
Runnable: The Runnable that will be executed. This value cannot be null. |
uptimeMillis |
Long: The absolute time at which the callback should run, using the android.os.SystemClock#uptimeMillis time-base. |
| Return | |
|---|---|
Boolean |
Returns true if the Runnable was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. Note that a result of true does not mean the Runnable will be processed -- if the looper is quit before the delivery time of the message occurs then the message will be dropped. |
postAtTime
fun postAtTime(
r: Runnable,
token: Any?,
uptimeMillis: Long
): Boolean
Causes the Runnable r to be added to the message queue, to be run at a specific time given by uptimeMillis. The time-base is android.os.SystemClock#uptimeMillis. Time spent in deep sleep will add an additional delay to execution. The runnable will be run on the thread to which this handler is attached.
| Parameters | |
|---|---|
r |
Runnable: The Runnable that will be executed. This value cannot be null. |
token |
Any?: An instance which can be used to cancel r via removeCallbacksAndMessages. This value may be null. |
uptimeMillis |
Long: The absolute time at which the callback should run, using the android.os.SystemClock#uptimeMillis time-base. |
| Return | |
|---|---|
Boolean |
Returns true if the Runnable was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. Note that a result of true does not mean the Runnable will be processed -- if the looper is quit before the delivery time of the message occurs then the message will be dropped. |
See Also
postDelayed
fun postDelayed(
r: Runnable,
delayMillis: Long
): Boolean
Causes the Runnable r to be added to the message queue, to be run after the specified amount of time elapses. The runnable will be run on the thread to which this handler is attached. The time-base is android.os.SystemClock#uptimeMillis. Time spent in deep sleep will add an additional delay to execution.
| Parameters | |
|---|---|
r |
Runnable: The Runnable that will be executed. This value cannot be null. |
delayMillis |
Long: The delay (in milliseconds) until the Runnable will be executed. |
| Return | |
|---|---|
Boolean |
Returns true if the Runnable was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. Note that a result of true does not mean the Runnable will be processed -- if the looper is quit before the delivery time of the message occurs then the message will be dropped. |
postDelayed
fun postDelayed(
r: Runnable,
token: Any?,
delayMillis: Long
): Boolean
Causes the Runnable r to be added to the message queue, to be run after the specified amount of time elapses. The runnable will be run on the thread to which this handler is attached. The time-base is android.os.SystemClock#uptimeMillis. Time spent in deep sleep will add an additional delay to execution.
| Parameters | |
|---|---|
r |
Runnable: The Runnable that will be executed. This value cannot be null. |
token |
Any?: An instance which can be used to cancel r via removeCallbacksAndMessages. This value may be null. |
delayMillis |
Long: The delay (in milliseconds) until the Runnable will be executed. |
| Return | |
|---|---|
Boolean |
Returns true if the Runnable was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. Note that a result of true does not mean the Runnable will be processed -- if the looper is quit before the delivery time of the message occurs then the message will be dropped. |
removeCallbacks
fun removeCallbacks(r: Runnable): Unit
Remove any pending posts of Runnable r that are in the message queue.
| Parameters | |
|---|---|
r |
Runnable: This value cannot be null. |
removeCallbacks
fun removeCallbacks(
r: Runnable,
token: Any?
): Unit
Remove any pending posts of Runnable r with Object token that are in the message queue. If token is null, all callbacks will be removed.
| Parameters | |
|---|---|
r |
Runnable: This value cannot be null. |
token |
Any?: This value may be null. |
removeCallbacksAndMessages
fun removeCallbacksAndMessages(token: Any?): Unit
Remove any pending posts of callbacks and sent messages whose obj is token. If token is null, all callbacks and messages will be removed.
| Parameters | |
|---|---|
token |
Any?: This value may be null. |
removeMessages
fun removeMessages(what: Int): Unit
Remove any pending posts of messages with code 'what' that are in the message queue.
removeMessages
fun removeMessages(
what: Int,
object: Any?
): Unit
Remove any pending posts of messages with code 'what' and whose obj is 'object' that are in the message queue. If object is null, all messages will be removed.
| Parameters | |
|---|---|
object |
Any?: This value may be null. |
sendEmptyMessage
fun sendEmptyMessage(what: Int): Boolean
Sends a Message containing only the what value.
| Return | |
|---|---|
Boolean |
Returns true if the message was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. |
sendEmptyMessageAtTime
fun sendEmptyMessageAtTime(
what: Int,
uptimeMillis: Long
): Boolean
Sends a Message containing only the what value, to be delivered at a specific time.
| Return | |
|---|---|
Boolean |
Returns true if the message was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. |
sendEmptyMessageDelayed
fun sendEmptyMessageDelayed(
what: Int,
delayMillis: Long
): Boolean
Sends a Message containing only the what value, to be delivered after the specified amount of time elapses.
| Return | |
|---|---|
Boolean |
Returns true if the message was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. |
sendMessage
fun sendMessage(msg: Message): Boolean
Pushes a message onto the end of the message queue after all pending messages before the current time. It will be received in handleMessage, in the thread attached to this handler.
| Parameters | |
|---|---|
msg |
Message: This value cannot be null. |
| Return | |
|---|---|
Boolean |
Returns true if the message was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. |
sendMessageAtFrontOfQueue
fun sendMessageAtFrontOfQueue(msg: Message): Boolean
Enqueue a message at the front of the message queue, to be processed on the next iteration of the message loop. You will receive it in handleMessage, in the thread attached to this handler. This method is only for use in very special circumstances -- it can easily starve the message queue, cause ordering problems, or have other unexpected side-effects.
| Parameters | |
|---|---|
msg |
Message: This value cannot be null. |
| Return | |
|---|---|
Boolean |
Returns true if the message was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. |
sendMessageAtTime
open fun sendMessageAtTime(
msg: Message,
uptimeMillis: Long
): Boolean
Enqueue a message into the message queue after all pending messages before the absolute time (in milliseconds) uptimeMillis. The time-base is android.os.SystemClock#uptimeMillis. Time spent in deep sleep will add an additional delay to execution. You will receive it in handleMessage, in the thread attached to this handler.
| Parameters | |
|---|---|
uptimeMillis |
Long: The absolute time at which the message should be delivered, using the android.os.SystemClock#uptimeMillis time-base. |
msg |
Message: This value cannot be null. |
| Return | |
|---|---|
Boolean |
Returns true if the message was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. Note that a result of true does not mean the message will be processed -- if the looper is quit before the delivery time of the message occurs then the message will be dropped. |
sendMessageDelayed
fun sendMessageDelayed(
msg: Message,
delayMillis: Long
): Boolean
Enqueue a message into the message queue after all pending messages before (current time + delayMillis). You will receive it in handleMessage, in the thread attached to this handler.
| Parameters | |
|---|---|
msg |
Message: This value cannot be null. |
| Return | |
|---|---|
Boolean |
Returns true if the message was successfully placed in to the message queue. Returns false on failure, usually because the looper processing the message queue is exiting. Note that a result of true does not mean the message will be processed -- if the looper is quit before the delivery time of the message occurs then the message will be dropped. |
toString
open fun toString(): String
| Return | |
|---|---|
String |
a string representation of the object. |