Android Process Communication

Source: Internet
Author: User

Android Process Communication

I. Concepts

Android uses different components [activity, Service
] To indicate the communication between processes!
The core mechanism of inter-component communication is intent.
You can enable an activity or service through intent, whether the activity or service belongs to the current application
Or other applications!

Intent contains two parts:
1. Purpose [action]
2. content [category, data] partitioned data
Or content data

Intent type:
1. explicitly -- directly specify the Message destination, which is only suitable for communication between different components in the same process
Intent (this, target. Class)
2. Implicit registration in androidmainifest. XML, which is generally used for cross-process communication
Intent (string

II. Implementation-intent simple inter-process communication

Explicit intent is relatively simple!

How to Implement implicit intent?
In the androidmanifest. xml file
1. A <activity> includes:
Zero or more <intent-filter>

It is mainly used as the matching standard. Whether the matching is successful depends on three tags: <action>, <Category>, and <DATA>.

2. A <intent-filter> includes:
One or more

Zero or multiple <Category>

Specify the classification feature of <activity>
<Category android
: Name = "android. Intent. Category. launcher"
-- This <activity> indicates that the project is running.
First Interface

Android: Name = "android. Intent. Category. Home"
-- This <activity> can be used as the launcher, that is, the system
Operation Interface

Android: Name = "android. Intent. Category. Default"
-- Default

Zero or one <DATA>

Specifies the type of data carried, which is described using the MIME type description.
<Data Android: mimetype = "Video/MPEG"
Video/MPEG: Specifies the video whose encoding format is MPEG.
You can also use the wildcard "Video/*" to indicate the types of video files in any format;

You can use
Android: mimetype = "Vnd. Android. cursor. DIR/vnd. myq. Note"
The queried data is composed of multiple records.
Android: mimetype = "Vnd. Android. cursor. Item/vnd. myq. Note"
The queried data is a single record.
Set above
, Rewrite SQLite
GetType (URI) of openhelper
Uri) Method
@ Override
Public String GetType (URI ){
Final int
Match = surimatcher. Match (URI );
Switch (MATCH)
Case Notes
Case live_folder_notes:
"Vnd. Android. cursor. DIR/vnd. myq. Note ";

Case notes_id:
"Vnd. Android. cursor. Item/vnd. myq. Note ";

Throw new
Illegalargumentexception ("invalid URI:" + URI)

The data URI consists of four parts: Scheme: // host: Port/path.
Android: Scheme = "http: // localhost: 8080/test. jsp

3. Processing description of Multiple matching results corresponding to an intent
An intent has multiple matching processing components. What should the system do?
Component Types of response messages:
1) if it is a service, these services can start and process messages.
2) If it is activity, a dialog box will pop up for the user to select.

4. Security Issues
If components of different processes can communicate with each other through implicit messages, the program
Isn't it safe to easily call other programs or components of some sensitive programs in the system?
In fact, Android has a unified, complete, and lightweight security policy model in terms of security.

To put it simply, it is about permission settings.
We can define the permission by ourselves and set the permission in the required component. To create this component, you must configure the permission. Otherwise, the access will fail!

1. Define permission
Android: Name = "android. permission-group.MYQ_INFO"/>
Android: Name = "com. myq. Android. Permission. datetime_service"
Android: permissiongroup = "android. permission-group.MYQ_INFO"
Android: protectionlevel = "normal"

2. Configure permission
<Service android: Name = ". datetimeservice"
Android: Permission = "com. myq. Android. Permission. datetime_service">
Android: Name = "com. myq. Android. multiprocesstest. datetimeservice_action"

3. Use Permission
Android: Name = "com. myq. Android. Permission. datetime_service"/>

Iii. IPC Mechanism

With the message-based intra-process or inter-process communication model of intent, we can enable a service through intent and jump to another one through intent.
Activity, whether the preceding service or activity is in the current process or other processes, that is, whether the current application or the service or
Activity, which can communicate with each other through the message mechanism!

However, one drawback of inter-process communication through the message mechanism is that if the interaction between our activity and service is not enabled simply by the activity
Service operations, but to send some control requests at any time, you must ensure that the activity can be connected to the service at any time during the service operation.

: Playing music
The playing service in the background often runs independently, so that you can hear music when using other program interfaces. At the same time, this background playing service also defines a control interface, such as playing, pause, fast forward, and other methods. At any time, the playing program interface can be connected to the playing service, and then control it through this set of control interface methods.

The above requirement cannot be met only by enabling the service through intent! Therefore, the relatively bulky IPC Mechanism of Android emerged, but its appearance only applies
Communication between activity and service is similar to remote method call, which is like access in C/S mode. By defining the aidl interface file to define an IPC Interface
Interface, the server implements the IPC interface, and the client calls the local proxy of the IPC interface.

Since IPC calls are synchronous, if an IPC service takes more than several milliseconds
Otherwise, the IPC call will suspend the application.
This causes the interface to lose response. In
In this case, consider a single thread to process IPC access.

The IPC between two processes looks like a process entering another process to execute code
Then return with the execution result.

The IPC Mechanism encourages us to "use existing functions whenever possible"
, Using IPC and programs that contain existing functions to collaborate to complete a complete project

IPC implementation Demo:

Package --
Com. myq. Android. multiprocesstest

1. The aidl file is stored in the package,
The file name is:

Idatetimeservice. aidl
File Content:

Com. myq. Android. multiprocesstest;
Interface idatetimeservice
Getcurrentdatetime (in string format)

If the configuration is correct, a Java file with the same name will be generated under Gen.
// Stub class we need to implement
Android. OS. iinterface
Public static abstract class

Extends Android. OS. Binder
Com. myq. Android. multiprocesstest. idatetimeservice
// Obtain
Instance method asinterface
Static com. myq. Android. multiprocesstest. idatetimeservice
(Android. OS. ibinder
// Our own business method, which needs to be implemented
Java. Lang. StringGetcurrentdatetime
(Java. Lang. string format)
Android. OS. RemoteException;

2. Implement idatetimeservice. stub in Service
Com. myq. Android. multiprocesstest;
Java. Text. simpledateformat;
Import java. util. date;
Android. App. Service;
Import Android. content. intent;
Android. OS. ibinder;
Import Android. OS. RemoteException;
Android. util. log;

Public class datetimeservice extends Service

Public static final string datetime_service_action =
"Com. myq. Android. multiprocesstest. datetimeservice_action ";

Static final string tag = "-------- datetimeservice -------"

Private simpledateformat SDF;

Private Final
Idatetimeservice. Stub stub = new idatetimeservice. Stub ()

String getcurrentdatetime (string format) throws RemoteException {
Getcurrentdatetimestring (format );

Private synchronized
String getcurrentdatetimestring (string format)
SDF = new
Simpledateformat (format );
Final string temp = SDF. Format (new date ())
Log. I (TAG, "getcurrentdatetimestring --" + thread. currentthread () + "--" +
Temp );
Return temp;

Public ibinder onbind (intent arg0)

Log. I (TAG, "onbind --" + thread. currentthread ());

3. client code implementation
Private serviceconnection mserviceconn =
New serviceconnection ()

Public void
Onserviceconnected (componentname name, ibinder Service ){
= Idatetimeservice. stub. asinterface (service );

Public void
Onservicedisconnected (componentname name ){
Mdatetimeservice = NULL

Many materials on the Internet
There is no specific description of aidl that involves IPC calls!
In essence, it is because both the server and client have the same aidl file. It must be located under the same package, that is, the package name and drug are the same, and then can be accessed through proxy correctly, otherwise, an error occurs when the aidl file of the client and server is in a different package.

The aidl model is as follows:

| <-------------------- Aidl ----------------------> |
Client --> proxy ---------- parcel data packet --------
Stub <--- Server
Thus proxy + parcel + stub constitute aidl.
However, the proxy runs in the client process, while the stub runs in the server process.
When you access the server through aidl, the client will block the proxy. After the server completes processing, the proxy will be notified to return.

Iv. Attachment and description

The attachment is the demo I used for testing. The system I used is ubuntu9 and android2.2.
Basic functions:
The current system time can be output according to different output formats selected by the user.
Running sequence:
First run the server: multiprocesstest
Run the client: multiprocesstestclient.

The aidl file on the server and client must be in the same package; otherwise, an error occurs.
Implement security issues and control permissions-define, configure, and use
Asynchronous processing -- Handler

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