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Android.OS.BinderConsts Class

Base interface for a remotable object, the core part of a lightweight remote procedure call mechanism designed for high performance when performing in-process and cross-process calls.

See Also: BinderConsts

Syntax

[Android.Runtime.Register("android/os/IBinder")]
public abstract class BinderConsts

Remarks

Base interface for a remotable object, the core part of a lightweight remote procedure call mechanism designed for high performance when performing in-process and cross-process calls. This interface describes the abstract protocol for interacting with a remotable object. Do not implement this interface directly, instead extend from Binder.

The key IBinder API is BinderConsts.transact(int, android.os.Parcel, android.os.Parcel, int) matched by Binder.OnTransact(Int32,Parcel,Parcel,Parcel). These methods allow you to send a call to an IBinder object and receive a call coming in to a Binder object, respectively. This transaction API is synchronous, such that a call to BinderConsts.transact(int, android.os.Parcel, android.os.Parcel, int) does not return until the target has returned from Binder.OnTransact(Int32,Parcel,Parcel,Parcel); this is the expected behavior when calling an object that exists in the local process, and the underlying inter-process communication (IPC) mechanism ensures that these same semantics apply when going across processes.

The data sent through transact() is a Parcel, a generic buffer of data that also maintains some meta-data about its contents. The meta data is used to manage IBinder object references in the buffer, so that those references can be maintained as the buffer moves across processes. This mechanism ensures that when an IBinder is written into a Parcel and sent to another process, if that other process sends a reference to that same IBinder back to the original process, then the original process will receive the same IBinder object back. These semantics allow IBinder/Binder objects to be used as a unique identity (to serve as a token or for other purposes) that can be managed across processes.

The system maintains a pool of transaction threads in each process that it runs in. These threads are used to dispatch all IPCs coming in from other processes. For example, when an IPC is made from process A to process B, the calling thread in A blocks in transact() as it sends the transaction to process B. The next available pool thread in B receives the incoming transaction, calls Binder.onTransact() on the target object, and replies with the result Parcel. Upon receiving its result, the thread in process A returns to allow its execution to continue. In effect, other processes appear to use as additional threads that you did not create executing in your own process.

The Binder system also supports recursion across processes. For example if process A performs a transaction to process B, and process B while handling that transaction calls transact() on an IBinder that is implemented in A, then the thread in A that is currently waiting for the original transaction to finish will take care of calling Binder.onTransact() on the object being called by B. This ensures that the recursion semantics when calling remote binder object are the same as when calling local objects.

When working with remote objects, you often want to find out when they are no longer valid. There are three ways this can be determined:

See Also

[Android Documentation]

Requirements

Namespace: Android.OS
Assembly: Mono.Android (in Mono.Android.dll)
Assembly Versions: 0.0.0.0
Since: Added in API level 1

The members of Android.OS.BinderConsts are listed below.

See Also: Object

Public Fields

const
DumpTransactionInt32 (1598311760). IBinder protocol transaction code: dump internal state.
const
FirstCallTransactionInt32 (1). The first transaction code available for user commands.
const
FlagOnewayTransactionFlags (1). Flag to BinderConsts.transact(int, android.os.Parcel, android.os.Parcel, int): this is a one-way call, meaning that the caller returns immediately, without waiting for a result from the callee.
const
InterfaceTransactionInt32 (1598968902). IBinder protocol transaction code: interrogate the recipient side of the transaction for its canonical interface descriptor.
const
LastCallTransactionInt32 (16777215). The last transaction code available for user commands.
const
LikeTransactionInt32 (1598835019). IBinder protocol transaction code: tell an app asynchronously that the caller likes it.
const
PingTransactionInt32 (1599098439). IBinder protocol transaction code: pingBinder().
const
TweetTransactionInt32 (1599362900). IBinder protocol transaction code: send a tweet to the target object.