Package android.os

Class Message

  • All Implemented Interfaces:
    Parcelable
    public final class Message
extends Object
implements Parcelable
    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.

    • Field Detail

      • what

        public 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.

      • arg1

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

      • arg2

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

      • obj

        public 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(android.os.Bundle).

        Note that Parcelable objects here are not supported prior to the android.os.Build.VERSION_CODES#FROYO release.

      • replyTo

        public 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

        public 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.

    • Constructor Detail

      • Message

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

    • Method Detail

      • obtain

        public static Message obtain()
        Return a new Message instance from the global pool. Allows us to avoid allocating new objects in many cases.

      • obtain

        public static Message obtain​(Message orig)
        Same as obtain(), but copies the values of an existing message (including its target) into the new one.
        Parameters:
        orig - Original message to copy.
        Returns:
        A Message object from the global pool.

      • obtain

        public static Message obtain​(Handler h)
        Same as obtain(), but sets the value for the target member on the Message returned.
        Parameters:
        h - Handler to assign to the returned Message object's target member.
        Returns:
        A Message object from the global pool.

      • obtain

        public static Message obtain​(Handler h,
                             Runnable callback)
        Same as obtain(Handler), but assigns a callback Runnable on the Message that is returned.
        Parameters:
        h - Handler to assign to the returned Message object's target member.
        callback - Runnable that will execute when the message is handled.
        Returns:
        A Message object from the global pool.

      • obtain

        public static Message obtain​(Handler h,
                             int what)
        Same as obtain(), but sets the values for both target and what members on the Message.
        Parameters:
        h - Value to assign to the target member.
        what - Value to assign to the what member.
        Returns:
        A Message object from the global pool.

      • obtain

        public static Message obtain​(Handler h,
                             int what,
                             Object obj)
        Same as obtain(), but sets the values of the target, what, and obj members.
        Parameters:
        h - The target value to set.
        what - The what value to set.
        obj - The object method to set.
        Returns:
        A Message object from the global pool.

      • obtain

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

      • obtain

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

      • recycle

        public void recycle()

      • copyFrom

        public 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.

      • getWhen

        public long getWhen()
        Return the targeted delivery time of this message, in milliseconds.

      • setTarget

        public void setTarget​(Handler target)

      • getTarget

        public 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.

      • getCallback

        public 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 {@link Handler#handleMessage(Message Handler.handleMessage())}.

      • getData

        public 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.
        See Also:
        peekData(), setData(Bundle)

      • peekData

        public 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.
        See Also:
        getData(), setData(Bundle)

      • setData

        public 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.
        See Also:
        getData(), peekData()

      • sendToTarget

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

      • isAsynchronous

        public boolean isAsynchronous()
        Returns true if the message is asynchronous, meaning that it is not subject to Looper synchronization barriers.
        Returns:
        True if the message is asynchronous.
        See Also:
        setAsynchronous(boolean)

      • setAsynchronous

        public 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 android.view.View#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 - True if the message is asynchronous.
        See Also:
        isAsynchronous()

      • toString

        public String toString()
        Description copied from class: Object
        Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression: 
           getClass().getName() + '@' + Integer.toHexString(hashCode())

        See Writing a useful toString method if you intend implementing your own toString method.

        Overrides:
        toString in class Object
        Returns:
        a printable representation of this object.

      • describeContents

        public int describeContents()
        Description copied from interface: Parcelable
        Describe the kinds of special objects contained in this Parcelable's marshalled representation.
        Specified by:
        describeContents in interface Parcelable
        Returns:
        a bitmask indicating the set of special object types marshalled by the Parcelable.

      • writeToParcel

        public void writeToParcel​(Parcel dest,
                          int flags)
        Description copied from interface: Parcelable
        Flatten this object in to a Parcel.
        Specified by:
        writeToParcel in interface Parcelable
        Parameters:
        dest - The Parcel in which the object should be written.
        flags - Additional flags about how the object should be written. May be 0 or Parcelable.PARCELABLE_WRITE_RETURN_VALUE.