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Added in API level 1

Message

public final class Message
extends Object implements Parcelable

java.lang.Object
   ↳ android.os.Message


Defines a message containing a description and arbitrary data object that can be sent to a Handler. This object contains two extra int fields and an extra object field that allow you to not do allocations in many cases.

While the constructor of Message is public, the best way to get one of these is to call Message.obtain() or one of the Handler.obtainMessage() methods, which will pull them from a pool of recycled objects.

Summary

Inherited constants

From interface android.os.Parcelable

Fields

public static final Creator<Message> CREATOR

public int arg1

arg1 and arg2 are lower-cost alternatives to using setData() if you only need to store a few integer values.

public int arg2

arg1 and arg2 are lower-cost alternatives to using setData() if you only need to store a few integer values.

public Object obj

An arbitrary object to send to the recipient.

public Messenger replyTo

Optional Messenger where replies to this message can be sent.

public int sendingUid

Optional field indicating the uid that sent the message.

public int what

User-defined message code so that the recipient can identify what this message is about.

Public constructors

Message()

Constructor (but the preferred way to get a Message is to call Message.obtain()).

Public methods

void copyFrom(Message o)

Make this message like o.

int describeContents()

Describe the kinds of special objects contained in this Parcelable instance's marshaled representation.

Runnable getCallback()

Retrieve callback object that will execute when this message is handled.

Bundle getData()

Obtains a Bundle of arbitrary data associated with this event, lazily creating it if necessary.

Handler getTarget()

Retrieve the a Handler implementation that will receive this message.

long getWhen()

Return the targeted delivery time of this message, in milliseconds.

boolean isAsynchronous()

Returns true if the message is asynchronous, meaning that it is not subject to Looper synchronization barriers.

static Message obtain(Handler h)

Same as obtain(), but sets the value for the target member on the Message returned.

static Message obtain(Handler h, int what)

Same as obtain(), but sets the values for both target and what members on the Message.

static Message obtain(Handler h, Runnable callback)

Same as obtain(Handler), but assigns a callback Runnable on the Message that is returned.

static Message obtain(Message orig)

Same as obtain(), but copies the values of an existing message (including its target) into the new one.

static Message obtain(Handler h, int what, int arg1, int arg2, Object obj)

Same as obtain(), but sets the values of the target, what, arg1, arg2, and obj members.

static Message obtain(Handler h, int what, int arg1, int arg2)

Same as obtain(), but sets the values of the target, what, arg1, and arg2 members.

static Message obtain(Handler h, int what, Object obj)

Same as obtain(), but sets the values of the target, what, and obj members.

static Message obtain()

Return a new Message instance from the global pool.

Bundle peekData()

Like getData(), but does not lazily create the Bundle.

void recycle()

Return a Message instance to the global pool.

void sendToTarget()

Sends this Message to the Handler specified by getTarget().

void setAsynchronous(boolean async)

Sets whether the message is asynchronous, meaning that it is not subject to Looper synchronization barriers.

void setData(Bundle data)

Sets a Bundle of arbitrary data values.

void setTarget(Handler target)
String toString()

Returns a string representation of the object.

void writeToParcel(Parcel dest, int flags)

Flatten this object in to a Parcel.

Inherited methods

From class java.lang.Object
From interface android.os.Parcelable

Fields

CREATOR

Added in API level 1
Creator<Message> CREATOR

arg1

Added in API level 1
int arg1

arg1 and arg2 are lower-cost alternatives to using setData() if you only need to store a few integer values.

arg2

Added in API level 1
int arg2

arg1 and arg2 are lower-cost alternatives to using setData() if you only need to store a few integer values.

obj

Added in API level 1
Object obj

An arbitrary object to send to the recipient. When using Messenger to send the message across processes this can only be non-null if it contains a Parcelable of a framework class (not one implemented by the application). For other data transfer use setData(Bundle).

Note that Parcelable objects here are not supported prior to the FROYO release.

replyTo

Added in API level 1
Messenger replyTo

Optional Messenger where replies to this message can be sent. The semantics of exactly how this is used are up to the sender and receiver.

sendingUid

Added in API level 21
int sendingUid

Optional field indicating the uid that sent the message. This is only valid for messages posted by a Messenger; otherwise, it will be -1.

what

Added in API level 1
int what

User-defined message code so that the recipient can identify what this message is about. Each Handler has its own name-space for message codes, so you do not need to worry about yours conflicting with other handlers.

Public constructors

Message

Added in API level 1
Message ()

Constructor (but the preferred way to get a Message is to call Message.obtain()).

Public methods

copyFrom

Added in API level 1
void copyFrom (Message o)

Make this message like o. Performs a shallow copy of the data field. Does not copy the linked list fields, nor the timestamp or target/callback of the original message.

Parameters
o Message

describeContents

Added in API level 1
int describeContents ()

Describe the kinds of special objects contained in this Parcelable instance's marshaled representation. For example, if the object will include a file descriptor in the output of writeToParcel(Parcel, int), the return value of this method must include the CONTENTS_FILE_DESCRIPTOR bit.

Returns
int a bitmask indicating the set of special object types marshaled by this Parcelable object instance.

getCallback

Added in API level 1
Runnable getCallback ()

Retrieve callback object that will execute when this message is handled. This object must implement Runnable. This is called by the target Handler that is receiving this Message to dispatch it. If not set, the message will be dispatched to the receiving Handler's handleMessage(Message).

Returns
Runnable

getData

Added in API level 1
Bundle getData ()

Obtains a Bundle of arbitrary data associated with this event, lazily creating it if necessary. Set this value by calling setData(Bundle). Note that when transferring data across processes via Messenger, you will need to set your ClassLoader on the Bundle via Bundle.setClassLoader() so that it can instantiate your objects when you retrieve them.

Returns
Bundle

See also:

getTarget

Added in API level 1
Handler getTarget ()

Retrieve the a Handler implementation that will receive this message. The object must implement Handler.handleMessage(). Each Handler has its own name-space for message codes, so you do not need to worry about yours conflicting with other handlers.

Returns
Handler

getWhen

Added in API level 1
long getWhen ()

Return the targeted delivery time of this message, in milliseconds.

Returns
long

isAsynchronous

Added in API level 22
boolean isAsynchronous ()

Returns true if the message is asynchronous, meaning that it is not subject to Looper synchronization barriers.

Returns
boolean True if the message is asynchronous.

See also:

obtain

Added in API level 1
Message obtain (Handler h)

Same as obtain(), but sets the value for the target member on the Message returned.

Parameters
h Handler: Handler to assign to the returned Message object's target member.
Returns
Message A Message object from the global pool.

obtain

Added in API level 1
Message obtain (Handler h, 
                int what)

Same as obtain(), but sets the values for both target and what members on the Message.

Parameters
h Handler: Value to assign to the target member.
what int: Value to assign to the what member.
Returns
Message A Message object from the global pool.

obtain

Added in API level 1
Message obtain (Handler h, 
                Runnable callback)

Same as obtain(Handler), but assigns a callback Runnable on the Message that is returned.

Parameters
h Handler: Handler to assign to the returned Message object's target member.
callback Runnable: Runnable that will execute when the message is handled.
Returns
Message A Message object from the global pool.

obtain

Added in API level 1
Message obtain (Message orig)

Same as obtain(), but copies the values of an existing message (including its target) into the new one.

Parameters
orig Message: Original message to copy.
Returns
Message A Message object from the global pool.

obtain

Added in API level 1
Message obtain (Handler h, 
                int what, 
                int arg1, 
                int arg2, 
                Object obj)

Same as obtain(), but sets the values of the target, what, arg1, arg2, and obj members.

Parameters
h Handler: The target value to set.
what int: The what value to set.
arg1 int: The arg1 value to set.
arg2 int: The arg2 value to set.
obj Object: The obj value to set.
Returns
Message A Message object from the global pool.

obtain

Added in API level 1
Message obtain (Handler h, 
                int what, 
                int arg1, 
                int arg2)

Same as obtain(), but sets the values of the target, what, arg1, and arg2 members.

Parameters
h Handler: The target value to set.
what int: The what value to set.
arg1 int: The arg1 value to set.
arg2 int: The arg2 value to set.
Returns
Message A Message object from the global pool.

obtain

Added in API level 1
Message obtain (Handler h, 
                int what, 
                Object obj)

Same as obtain(), but sets the values of the target, what, and obj members.

Parameters
h Handler: The target value to set.
what int: The what value to set.
obj Object: The object method to set.
Returns
Message A Message object from the global pool.

obtain

Added in API level 1
Message obtain ()

Return a new Message instance from the global pool. Allows us to avoid allocating new objects in many cases.

Returns
Message

peekData

Added in API level 1
Bundle peekData ()

Like getData(), but does not lazily create the Bundle. A null is returned if the Bundle does not already exist. See getData() for further information on this.

Returns
Bundle

See also:

recycle

Added in API level 1
void recycle ()

Return a Message instance to the global pool.

You MUST NOT touch the Message after calling this function because it has effectively been freed. It is an error to recycle a message that is currently enqueued or that is in the process of being delivered to a Handler.

sendToTarget

Added in API level 1
void sendToTarget ()

Sends this Message to the Handler specified by getTarget(). Throws a null pointer exception if this field has not been set.

setAsynchronous

Added in API level 22
void setAsynchronous (boolean async)

Sets whether the message is asynchronous, meaning that it is not subject to Looper synchronization barriers.

Certain operations, such as view invalidation, may introduce synchronization barriers into the Looper's message queue to prevent subsequent messages from being delivered until some condition is met. In the case of view invalidation, messages which are posted after a call to invalidate() are suspended by means of a synchronization barrier until the next frame is ready to be drawn. The synchronization barrier ensures that the invalidation request is completely handled before resuming.

Asynchronous messages are exempt from synchronization barriers. They typically represent interrupts, input events, and other signals that must be handled independently even while other work has been suspended.

Note that asynchronous messages may be delivered out of order with respect to synchronous messages although they are always delivered in order among themselves. If the relative order of these messages matters then they probably should not be asynchronous in the first place. Use with caution.

Parameters
async boolean: True if the message is asynchronous.

See also:

setData

Added in API level 1
void setData (Bundle data)

Sets a Bundle of arbitrary data values. Use arg1 and arg2 members as a lower cost way to send a few simple integer values, if you can.

Parameters
data Bundle

See also:

setTarget

Added in API level 1
void setTarget (Handler target)

Parameters
target Handler

toString

Added in API level 1
String toString ()

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())
 

Returns
String a string representation of the object.

writeToParcel

Added in API level 1
void writeToParcel (Parcel dest, 
                int flags)

Flatten this object in to a Parcel.

Parameters
dest Parcel: The Parcel in which the object should be written.
flags int: Additional flags about how the object should be written. May be 0 or PARCELABLE_WRITE_RETURN_VALUE.
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