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Messenger

public final class Messenger
extends Object implements Parcelable

java.lang.Object
   ↳ android.os.Messenger


Reference to a Handler, which others can use to send messages to it. This allows for the implementation of message-based communication across processes, by creating a Messenger pointing to a Handler in one process, and handing that Messenger to another process.

Note: the implementation underneath is just a simple wrapper around a Binder that is used to perform the communication. This means semantically you should treat it as such: this class does not impact process lifecycle management (you must be using some higher-level component to tell the system that your process needs to continue running), the connection will break if your process goes away for any reason, etc.

Summary

Inherited constants

From interface android.os.Parcelable

Fields

public static final Creator<Messenger> CREATOR

Public constructors

Messenger(Handler target)

Create a new Messenger pointing to the given Handler.

Messenger(IBinder target)

Create a Messenger from a raw IBinder, which had previously been retrieved with getBinder().

Public methods

int describeContents()

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

boolean equals(Object otherObj)

Comparison operator on two Messenger objects, such that true is returned then they both point to the same Handler.

IBinder getBinder()

Retrieve the IBinder that this Messenger is using to communicate with its associated Handler.

int hashCode()

Returns a hash code value for the object.

static Messenger readMessengerOrNullFromParcel(Parcel in)

Convenience function for reading either a Messenger or null pointer from a Parcel.

void send(Message message)

Send a Message to this Messenger's Handler.

static void writeMessengerOrNullToParcel(Messenger messenger, Parcel out)

Convenience function for writing either a Messenger or null pointer to a Parcel.

void writeToParcel(Parcel out, 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<Messenger> CREATOR

Public constructors

Messenger

Added in API level 1
Messenger (Handler target)

Create a new Messenger pointing to the given Handler. Any Message objects sent through this Messenger will appear in the Handler as if Handler.sendMessage(Message) had been called directly.

Parameters
target Handler: The Handler that will receive sent messages.

Messenger

Added in API level 1
Messenger (IBinder target)

Create a Messenger from a raw IBinder, which had previously been retrieved with getBinder().

Parameters
target IBinder: The IBinder this Messenger should communicate with.

Public methods

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.

equals

Added in API level 1
boolean equals (Object otherObj)

Comparison operator on two Messenger objects, such that true is returned then they both point to the same Handler.

Parameters
otherObj Object: the reference object with which to compare.
Returns
boolean true if this object is the same as the obj argument; false otherwise.

getBinder

Added in API level 1
IBinder getBinder ()

Retrieve the IBinder that this Messenger is using to communicate with its associated Handler.

Returns
IBinder Returns the IBinder backing this Messenger.

hashCode

Added in API level 1
int hashCode ()

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

The general contract of hashCode is:

  • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
  • If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
  • It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)

Returns
int a hash code value for this object.

readMessengerOrNullFromParcel

Added in API level 1
Messenger readMessengerOrNullFromParcel (Parcel in)

Convenience function for reading either a Messenger or null pointer from a Parcel. You must have previously written the Messenger with writeMessengerOrNullToParcel(Messenger, Parcel).

Parameters
in Parcel: The Parcel containing the written Messenger.
Returns
Messenger Returns the Messenger read from the Parcel, or null if null had been written.

send

Added in API level 1
void send (Message message)

Send a Message to this Messenger's Handler.

Parameters
message Message: The Message to send. Usually retrieved through Message.obtain().
Throws
RemoteException Throws DeadObjectException if the target Handler no longer exists.

writeMessengerOrNullToParcel

Added in API level 1
void writeMessengerOrNullToParcel (Messenger messenger, 
                Parcel out)

Convenience function for writing either a Messenger or null pointer to a Parcel. You must use this with readMessengerOrNullFromParcel(Parcel) for later reading it.

Parameters
messenger Messenger: The Messenger to write, or null.
out Parcel: Where to write the Messenger.

writeToParcel

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

Flatten this object in to a Parcel.

Parameters
out 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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