Android Service

In the last article we looked at some of the concepts of Service and how to use it. This article focuses on 2 ways to use Service for IPC communication.

IPC communication with AIDL

A, code implementation — remote process Service binding

The above code communicates with the Service in the current process. Now let’s implement how to bind the Service in different processes.

AIDL:Android Interface Definition Language.

Service transfers data across processes using AIDL. The main steps are as follows:

Write AIDL files, AS automatically generated Java classes to implement the proxy for IPC communication
Inherit your own AIDL class and implement the methods inside
Return our implementation class in onBind(), exposing it to the outside world
Objects that need to communicate with a Service are bound to the Service through bindService and receive data in ServiceConnection.

Let’s do this in code:

First we need to create a new Service

public class MyRemoteService extends Service {
	@Nullable
	@Override
	public IBinder onBind(Intent intent) {
  		Log.e("MyRemoteService"."MyRemoteService thread id = " + Thread.currentThread().getId());
    return null; }}Copy the code

In the manifest file, we declare that our Service also specifies the name of the process to run

<service
        android:name=".service.MyRemoteService"
        android:process=":remote" />

Copy the code

Create a new AIDL file for users to transfer data between processes.

AIDL supports the following types: Eight basic data types, String, CharSequence, List, Map, and custom types. Lists, maps, and custom types are explained below.

There will be a default implementation method, just delete, here we create a new file as follows:
```
package xxxx;// The package name where aidl resides
//interface cannot be preceded by modifiers
interface IProcessInfo {
	// All the credit methods you want can be added here
	int getProcessId(a);
}
Copy the code
```

Implement our AIDL class

public class IProcessInfoImpl extends IProcessInfo.Stub {
	@Override
	public int getProcessId(a) throws RemoteException {
  		returnandroid.os.Process.myPid(); }}Copy the code

Return in onBind() of the Service

public class MyRemoteService extends Service {
	IProcessInfoImpl mProcessInfo = new IProcessInfoImpl();
	@Nullable
	@Override
	public IBinder onBind(Intent intent) {
  		Log.e("MyRemoteService"."MyRemoteService thread id = " + Thread.currentThread().getId());
    returnmProcessInfo; }}Copy the code

Binding Service

 mTvRemoteBind.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, MyRemoteService.class); bindService(intent, mRemoteServiceConnection, BIND_AUTO_CREATE); }}); mRemoteServiceConnection =new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {

            Log.e("MainActivity"."MyRemoteService onServiceConnected");
			// Retrieve data from aiDL
            IProcessInfo processInfo = IProcessInfo.Stub.asInterface(service);
            try {
                Log.e("MainActivity"."MyRemoteService process id = " + processInfo.getProcessId());
            } catch(RemoteException e) { e.printStackTrace(); }}@Override
        public void onServiceDisconnected(ComponentName name) {
            Log.e("MainActivity"."MyRemoteService onServiceDisconnected"); }};Copy the code

As long as the binding is successful, the process ID of MyRemoteService will be printed in the log. This completes the process of communicating with the services of different processes.

Two, code operation — call Service of other app

Calling a Service defined by another app has a few subtle differences compared to calling a Service defined by a different app process

The implicit invocation used by bindService() is not appropriate because it needs to be accessed by other apps. Action needs to be defined at Service definition time

We define the following Service in App A of the thread we define:
```
<service android:name=".service.ServerService"> <intent-filter android:name="com.jxx.server.service.bind" /> <category android:name="android.intent.category.DEFAULT" /> </intent-filter> </service>Copy the code
```

We need to do this in App B where we need bindService

First, copy the aidl file defined in A to B. For example, copy the iprocessInfo. aidl file defined above, including the path.

Call Service in B by explicit call

mTvServerBind.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Intent intent = new Intent();
        intent.setAction("com.jxx.server.service.bind");/ / Service action
        intent.setPackage("com.jxx.server");//App A package namebindService(intent, mServerServiceConnection, BIND_AUTO_CREATE); }});Copy the code

Passing of custom objects in AIDL

The main steps are as follows:

To define custom objects, implement the Parcelable interface
Create an AIDL file for a custom object
Reference custom objects in the AIDL file where the data is passed
Copy custom objects and aiDL files to the app that requires bindService, leaving the main path intact

Let’s look at the code:

Define custom objects and implement the Parcelable interface

public class ServerInfo implements Parcelable {

public ServerInfo(a) {

}

String mPackageName;

public String getPackageName(a) {
    return mPackageName;
}

public void setPackageName(String packageName) {
    mPackageName = packageName;
}

protected ServerInfo(Parcel in) {
    mPackageName = in.readString();
}

public static final Creator<ServerInfo> CREATOR = new Creator<ServerInfo>() {
    @Override
    public ServerInfo createFromParcel(Parcel in) {
        return new ServerInfo(in);
    }

    @Override
    public ServerInfo[] newArray(int size) {
        return newServerInfo[size]; }};@Override
public int describeContents(a) {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeString(mPackageName);
}

You need to add this method yourself when using out or inout modifiers
public void readFromParcel(Parcel dest) { mPackageName = dest.readString(); }}Copy the code

Create an AIDL file for a custom object

package com.jxx.server.aidl;
// Note that parcelable is lowercase
parcelable ServerInfo;
Copy the code

Reference custom objects

package com.jxx.server.aidl;
// Even in the same package, here also need to guide the package
import com.jxx.server.aidl.ServerInfo;
interface IServerServiceInfo {
	ServerInfo getServerInfo(a);
	void setServerInfo(inout ServerInfo serverinfo);
}
Copy the code

Notice the set method here, which uses inout, there are three modifiers

-out: The modification of the server is synchronized to the client, but the object obtained by the server may be empty. -inout: the modification is synchronizedCopy the code

When using out and inout, add readFromParcel(Parcel Dest) manually in addition to Parcelable

Copy custom objects and aiDL files into the referenced App.

reference

mServerServiceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            IServerServiceInfo serverServiceInfo = IServerServiceInfo.Stub.asInterface(service);
            try {
                ServerInfo serviceInfo = serverServiceInfo.getServerInfo();
                Log.e("MainActivity"."ServerService packageName = " + serviceInfo.getPackageName());
            } catch(RemoteException e) { e.printStackTrace(); }}@Override
        public void onServiceDisconnected(ComponentName name) {
            Log.e("MainActivity"."ServerService onServiceDisconnected"); }};Copy the code

The objects referenced in a List or Map should also be custom objects that meet the above requirements, or any of several other data types.

Use Messenger for IPC communication

Here’s how it works:

Create a new Messenger object on the Server in response to the Client’s registration and pass it in onBind()
In the ServiceConnection on the Client side, the Messenger object passed from the Server side is saved
At the same time, the Client also creates a Messenger object and registers it with the Server through the Messenger transferred from the Server to maintain communication.
As long as the Client keeps the Messenger object on the Server, it can still communicate with the Server, regardless of whether the unbindService() operation is performed.

First, server-side code

public class MessengerService extends Service {

    static final int MSG_REGISTER_CLIENT = 1;
    static final int MSG_UNREGISTER_CLIENT = 2;
    static final int MSG_SET_VALUE = 3;

    // This is used by the client to receive parameters
    static final int MSG_CLIENT_SET_VALUE = 4;

    static class ServiceHandler extends Handler {

        private final List<Messenger> mMessengerList = new ArrayList<>();

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_REGISTER_CLIENT:
                    mMessengerList.add(msg.replyTo);
                    break;
                case MSG_UNREGISTER_CLIENT:
                    mMessengerList.remove(msg.replyTo);
                    break;
                case MSG_SET_VALUE:
                    int value = msg.arg1;
                    for (Messenger messenger : mMessengerList) {
                        try {
                            messenger.send(Message.obtain(null, MSG_CLIENT_SET_VALUE, value, 0));
                        } catch(RemoteException e) { e.printStackTrace(); }}break;
                default:
                    super.handleMessage(msg); }}}private Messenger mMessenger = new Messenger(new ServiceHandler());

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        returnmMessenger.getBinder(); }}Copy the code

Second, the Client code

public class MessengerClientActivity extends AppCompatActivity {
  // These types need to correspond to the Server side
    static final int MSG_REGISTER_CLIENT = 1;
    static final int MSG_UNREGISTER_CLIENT = 2;
    static final int MSG_SET_VALUE = 3;
    static final int MSG_CLIENT_SET_VALUE = 4;

    class ClientHandler extends Handler {

        @Override
        public void handleMessage(Message msg) {

            if (msg.what == MSG_CLIENT_SET_VALUE) {
                mTvValue.setText(msg.arg1 + "");
            } else {
                super.handleMessage(msg);
            }
        }
    }

    TextView mTvServerBind;
    TextView mTvServerUnbind;
    TextView mTvValue;
    TextView mTvSend;

    ServiceConnection mServerServiceConnection;
    Messenger mServerMessenger;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_messenger);

        mTvServerBind = findViewById(R.id.tv_server_bind);
        mTvServerUnbind = findViewById(R.id.tv_server_unbind);
        mTvValue = findViewById(R.id.tv_value);
        mTvSend = findViewById(R.id.tv_send);

        mTvServerBind.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.setAction("jxx.com.server.service.messenger");
                intent.setPackage("jxx.com.server"); bindService(intent, mServerServiceConnection, BIND_AUTO_CREATE); }}); mTvServerUnbind.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Even if we unbindService, as long as we still have the mServerMessenger object,
                // We can continue to communicate with the ServerunbindService(mServerServiceConnection); }}); mTvSend.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(mServerMessenger ! =null) {
                    try {
                        // Test if you can set the data
                        Message test = Message.obtain(null, MSG_SET_VALUE, new Random().nextInt(100), 0);
                        mServerMessenger.send(test);
                    } catch(RemoteException e) { e.printStackTrace(); }}}}); mServerServiceConnection =new ServiceConnection() {
            @Override
            public void onServiceConnected(ComponentName name, IBinder service) {
                // Messenger on the server
                mServerMessenger = new Messenger(service);

                // Now start building the messenger client uses to send and receive messages
                Messenger clientMessenger = new Messenger(new ClientHandler());

                try {
                    // Register the client with the server
                    Message register = Message.obtain(null, MSG_REGISTER_CLIENT);
                    register.replyTo = clientMessenger;// This is the registered operation. We can see the object being fetched in the Server code above
                    mServerMessenger.send(register);

                    Toast.makeText(MessengerClientActivity.this."Binding successful", Toast.LENGTH_SHORT).show();

                } catch(RemoteException e) { e.printStackTrace(); }}@Override
            public void onServiceDisconnected(ComponentName name) {}}; }Copy the code

IPC communication with AIDL

A, code implementation — remote process Service binding

Two, code operation — call Service of other app

Passing of custom objects in AIDL

Use Messenger for IPC communication

First, server-side code

Second, the Client code

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