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Binder

public class Binder
extends Object implements IBinder

java.lang.Object
   ↳ android.os.Binder


Base class for a remotable object, the core part of a lightweight remote procedure call mechanism defined by IBinder. This class is an implementation of IBinder that provides standard local implementation of such an object.

Most developers will not implement this class directly, instead using the aidl tool to describe the desired interface, having it generate the appropriate Binder subclass. You can, however, derive directly from Binder to implement your own custom RPC protocol or simply instantiate a raw Binder object directly to use as a token that can be shared across processes.

This class is just a basic IPC primitive; it has no impact on an application's lifecycle, and is valid only as long as the process that created it continues to run. To use this correctly, you must be doing so within the context of a top-level application component (a Service, Activity, or ContentProvider) that lets the system know your process should remain running.

You must keep in mind the situations in which your process could go away, and thus require that you later re-create a new Binder and re-attach it when the process starts again. For example, if you are using this within an Activity, your activity's process may be killed any time the activity is not started; if the activity is later re-created you will need to create a new Binder and hand it back to the correct place again; you need to be aware that your process may be started for another reason (for example to receive a broadcast) that will not involve re-creating the activity and thus run its code to create a new Binder.

See also:

Summary

Inherited constants

Public constructors

Binder()

Default constructor initializes the object.

Public methods

void attachInterface(IInterface owner, String descriptor)

Convenience method for associating a specific interface with the Binder.

static final long clearCallingIdentity()

Reset the identity of the incoming IPC on the current thread.

void dump(FileDescriptor fd, String[] args)

Implemented to call the more convenient version dump(FileDescriptor, PrintWriter, String[]).

void dumpAsync(FileDescriptor fd, String[] args)

Like dump(FileDescriptor, String[]), but ensures the target executes asynchronously.

static final void flushPendingCommands()

Flush any Binder commands pending in the current thread to the kernel driver.

static final int getCallingPid()

Return the ID of the process that sent you the current transaction that is being processed.

static final int getCallingUid()

Return the Linux uid assigned to the process that sent you the current transaction that is being processed.

static final UserHandle getCallingUserHandle()

Return the UserHandle assigned to the process that sent you the current transaction that is being processed.

String getInterfaceDescriptor()

Default implementation returns an empty interface name.

boolean isBinderAlive()

Check to see if the process that the binder is in is still alive. Note that if you're calling on a local binder, this always returns true because your process is alive if you're calling it.

static final void joinThreadPool()

Add the calling thread to the IPC thread pool.

void linkToDeath(IBinder.DeathRecipient recipient, int flags)

Local implementation is a no-op.

boolean pingBinder()

Default implementation always returns true -- if you got here, the object is alive.

IInterface queryLocalInterface(String descriptor)

Use information supplied to attachInterface() to return the associated IInterface if it matches the requested descriptor.

static final void restoreCallingIdentity(long token)

Restore the identity of the incoming IPC on the current thread back to a previously identity that was returned by clearCallingIdentity().

final boolean transact(int code, Parcel data, Parcel reply, int flags)

Default implementation rewinds the parcels and calls onTransact.

boolean unlinkToDeath(IBinder.DeathRecipient recipient, int flags)

Local implementation is a no-op.

Protected methods

void dump(FileDescriptor fd, PrintWriter fout, String[] args)

Print the object's state into the given stream.

boolean onTransact(int code, Parcel data, Parcel reply, int flags)

Default implementation is a stub that returns false.

Inherited methods

Public constructors

Binder

added in API level 1
public Binder ()

Default constructor initializes the object.

Public methods

attachInterface

added in API level 1
public void attachInterface (IInterface owner, 
                String descriptor)

Convenience method for associating a specific interface with the Binder. After calling, queryLocalInterface() will be implemented for you to return the given owner IInterface when the corresponding descriptor is requested.

Parameters
owner IInterface

This value may be null.

descriptor String

This value may be null.

clearCallingIdentity

added in API level 1
public static final long clearCallingIdentity ()

Reset the identity of the incoming IPC on the current thread. This can be useful if, while handling an incoming call, you will be calling on interfaces of other objects that may be local to your process and need to do permission checks on the calls coming into them (so they will check the permission of your own local process, and not whatever process originally called you).

Returns
long Returns an opaque token that can be used to restore the original calling identity by passing it to restoreCallingIdentity(long).

dump

added in API level 3
public void dump (FileDescriptor fd, 
                String[] args)

Implemented to call the more convenient version dump(FileDescriptor, PrintWriter, String[]).

Parameters
fd FileDescriptor: The raw file descriptor that the dump is being sent to.

This value must never be null.

args String: additional arguments to the dump request.

This value may be null.

dumpAsync

added in API level 13
public void dumpAsync (FileDescriptor fd, 
                String[] args)

Like dump(FileDescriptor, String[]), but ensures the target executes asynchronously.

Parameters
fd FileDescriptor: The raw file descriptor that the dump is being sent to.

This value must never be null.

args String: additional arguments to the dump request.

This value may be null.

flushPendingCommands

added in API level 1
public static final void flushPendingCommands ()

Flush any Binder commands pending in the current thread to the kernel driver. This can be useful to call before performing an operation that may block for a long time, to ensure that any pending object references have been released in order to prevent the process from holding on to objects longer than it needs to.

getCallingPid

added in API level 1
public static final int getCallingPid ()

Return the ID of the process that sent you the current transaction that is being processed. This pid can be used with higher-level system services to determine its identity and check permissions. If the current thread is not currently executing an incoming transaction, then its own pid is returned.

Returns
int

getCallingUid

added in API level 1
public static final int getCallingUid ()

Return the Linux uid assigned to the process that sent you the current transaction that is being processed. This uid can be used with higher-level system services to determine its identity and check permissions. If the current thread is not currently executing an incoming transaction, then its own uid is returned.

Returns
int

getCallingUserHandle

added in API level 17
public static final UserHandle getCallingUserHandle ()

Return the UserHandle assigned to the process that sent you the current transaction that is being processed. This is the user of the caller. It is distinct from getCallingUid() in that a particular user will have multiple distinct apps running under it each with their own uid. If the current thread is not currently executing an incoming transaction, then its own UserHandle is returned.

Returns
UserHandle

This value will never be null.

getInterfaceDescriptor

added in API level 1
public String getInterfaceDescriptor ()

Default implementation returns an empty interface name.

Returns
String

This value may be null.

isBinderAlive

added in API level 1
public boolean isBinderAlive ()

Check to see if the process that the binder is in is still alive. Note that if you're calling on a local binder, this always returns true because your process is alive if you're calling it.

Returns
boolean false if the process is not alive. Note that if it returns true, the process may have died while the call is returning.

joinThreadPool

added in API level 1
public static final void joinThreadPool ()

Add the calling thread to the IPC thread pool. This function does not return until the current process is exiting.

linkToDeath

added in API level 1
public void linkToDeath (IBinder.DeathRecipient recipient, 
                int flags)

Local implementation is a no-op.

Parameters
recipient IBinder.DeathRecipient

This value must never be null.

flags int

pingBinder

added in API level 1
public boolean pingBinder ()

Default implementation always returns true -- if you got here, the object is alive.

Returns
boolean Returns false if the hosting process is gone, otherwise the result (always by default true) returned by the pingBinder() implementation on the other side.

queryLocalInterface

added in API level 1
public IInterface queryLocalInterface (String descriptor)

Use information supplied to attachInterface() to return the associated IInterface if it matches the requested descriptor.

Parameters
descriptor String

This value must never be null.

Returns
IInterface

This value may be null.

restoreCallingIdentity

added in API level 1
public static final void restoreCallingIdentity (long token)

Restore the identity of the incoming IPC on the current thread back to a previously identity that was returned by clearCallingIdentity().

Parameters
token long: The opaque token that was previously returned by clearCallingIdentity().

transact

added in API level 1
public final boolean transact (int code, 
                Parcel data, 
                Parcel reply, 
                int flags)

Default implementation rewinds the parcels and calls onTransact. On the remote side, transact calls into the binder to do the IPC.

Parameters
code int: The action to perform. This should be a number between IBinder.FIRST_CALL_TRANSACTION and IBinder.LAST_CALL_TRANSACTION.

data Parcel: Marshalled data to send to the target. Must not be null. If you are not sending any data, you must create an empty Parcel that is given here.

reply Parcel: Marshalled data to be received from the target. May be null if you are not interested in the return value.

flags int: Additional operation flags. Either 0 for a normal RPC, or IBinder.FLAG_ONEWAY for a one-way RPC.

Returns
boolean Returns the result from Binder.onTransact(int, Parcel, Parcel, int). A successful call generally returns true; false generally means the transaction code was not understood.

Throws
RemoteException

unlinkToDeath

added in API level 1
public boolean unlinkToDeath (IBinder.DeathRecipient recipient, 
                int flags)

Local implementation is a no-op.

Parameters
recipient IBinder.DeathRecipient

This value must never be null.

flags int

Returns
boolean true if the recipient is successfully unlinked, assuring you that its DeathRecipient.binderDied() method will not be called; false if the target IBinder has already died, meaning the method has been (or soon will be) called.

Protected methods

dump

added in API level 1
protected void dump (FileDescriptor fd, 
                PrintWriter fout, 
                String[] args)

Print the object's state into the given stream.

Parameters
fd FileDescriptor: The raw file descriptor that the dump is being sent to.

This value must never be null.

fout PrintWriter: The file to which you should dump your state. This will be closed for you after you return.

This value must never be null.

args String: additional arguments to the dump request.

This value may be null.

onTransact

added in API level 1
protected boolean onTransact (int code, 
                Parcel data, 
                Parcel reply, 
                int flags)

Default implementation is a stub that returns false. You will want to override this to do the appropriate unmarshalling of transactions.

If you want to call this, call transact().

Implementations that are returning a result should generally use Parcel.writeNoException and Parcel.writeException to propagate exceptions back to the caller.

Parameters
code int: The action to perform. This should be a number between IBinder.FIRST_CALL_TRANSACTION and IBinder.LAST_CALL_TRANSACTION.

data Parcel: Marshalled data being received from the caller.

This value must never be null.

reply Parcel: If the caller is expecting a result back, it should be marshalled in to here.

This value may be null.

flags int: Additional operation flags. Either 0 for a normal RPC, or IBinder.FLAG_ONEWAY for a one-way RPC.

Returns
boolean Return true on a successful call; returning false is generally used to indicate that you did not understand the transaction code.

Throws
RemoteException