Android:Parcelable/Bundle/IBinder

public interface

Parcelable

Class Overview

Interface for classes whose instances can be written to and restored from a Parcel. Classes implementing the Parcelable interface must also have a static field called CREATOR, which is an object implementing the Parcelable.Creator interface.

 

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public final class

Bundle

extends Object
implements Parcelable Cloneable

A mapping from String values to various Parcelable types.

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public interface

IBinder

android.os.IBinder

Class Overview

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 transact() matched by Binder.onTransact(). 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 transact() does not return until the target has returned from Binder.onTransact(); 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.

 

作用：是远程对象、轻量级过程调用机制的核心部分的基本接口。这个接口描述了与远程对象之间进行交互的抽象协议。一般不直接实现IBinder接口，而是实现它的子类：Binder。

IBinder最重要的API是transact()对应的是Binder.onTransact().这些API都是同步的。

 

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.

 

transcat()是通过Parcel传送数据的，在整个进程间交互过程中，Ibinder/Binder对象是始终一致的。

 

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本质上, other processes appear to use as additional threads that you did not create executing in your own process.

 

整个IPC（进程间通信）的过程是这样的：当进程A的调用线程把transaction发送给进程B之后，自身就阻塞在transact()中。进程B中的空闲线程然后接收过来的transaction，并对目标对象调用Binder.onTransact()，并用结果Parcel回复，进程A中的线程收到后，继续从阻塞的地方开始执行。

 

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.

 

Binder系统也支持进程间的递归。

 

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:

• The transact() method will throw a RemoteException exception if you try to call it on an IBinder whose process no longer exists.
• The pingBinder() method can be called, and will return false if the remote process no longer exists.
• The linkToDeath() method can be used to register a IBinder.DeathRecipient with the IBinder, which will be called when its containing process goes away.

常用的成员方法：

public abstract boolean transact (int code, Parcel data, Parcel reply, int flags)

Since: API Level 1

Perform a generic operation with the object.

Parameters

code	The action to perform. This should be a number between FIRST_CALL_TRANSACTION and LAST_CALL_TRANSACTION.
data	Marshalled data to send to the target. Most not be null. If you are not sending any data, you must create an empty Parcel that is given here.
reply	Marshalled data to be received from the target. May be null if you are not interested in the return value.
flags	Additional operation flags. Either 0 for a normal RPC, or FLAG_ONEWAY for a one-way RPC.

Throws

RemoteException

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public class

Binder

extends Object
implements IBinder

Class Overview

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 the standard support creating a 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.

 

Binder主要用于进程间的远程通信调用，而这些通信的核心机制由IBinder来实现。也可以直接从Binder派生出子类，然后实现自己的RPC协议。

 

常用的成员方法：

 

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

Since: API Level 1

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().

Throws

RemoteException