CODEWITHSUNDEEP
androidandroid-service
stud91
stud91

Reputation: 1854

Android service causes a singleton's instance variable to be null

I have class called ClientManager where i load the dictionary from the server. Once the dictionary is loaded a Service is started (which runs in its own process) that will use the data from this dictionary. However, when i access the dictionary through the class singleton it is null. Dictionary object resides in class DataManager. Please see the code below:

ClientManager.java

DataManager mDataManager = DataManager.getInstance();

public void apiCompleted(ApiResult apiResult){
    ....
    DataDictionary dataDict = (DataDictionary) apiResult.valueObject;
    //dictionary loads OK from server since i can see the contents by iterating through it

    mDataManager.addDictionary(dataDict);
    if (!serviceRunning(MyService.class)){
        Intent intent = new Intent(mContext, MyService.class);
        mContext.startService(intent);
    }

MyService.java

public class MyService extends Service {
...
DataManager mDataManager;
@Override
public void onCreate(){
  mDataManager = DataManager.getInstance();

  if(!mDataManager.containsDataDictionary()){
        //toast dictionary is null
  }


}

DataManager.java

public class DataManager {

 private static DataManager instance = null;
 private DataDictionary mDataDictionary = null;

 public static DataManager getInstance(){
    if (instance == null){
        instance = new DataManager();
    }
  return instance;
 }

public boolean containsDataDictionary() {
    if ( m_dataDictionary == null ){
        return false;
    }
    return true;
 }

public DataDictionary getDataDictionary() {
    return mDataDictionary;
}     

public void addDataDictionary(DataDictionary p_dataDictionary) {
    mDataDictionary = p_dataDictionary;
}      
}

Upvotes: 0

Views: 434

Answers (3)

RajeshVijayakumar
RajeshVijayakumar

Reputation: 10622

The Singleton Pattern is allowed to share data within the application not between applications. Any instances of an app its lifespan is restricted within scope of the app life. It seems that you are trying to extend the scope of singleton object outside the app, which is not possible at all..

Note : Each process runs in own VM, so target processes doesn't have singleton instance of source processes.

There are two ways of communication for an app...

1) Active Communication (IPC) : When both source and target app is running (i.e.. processes) you need source/sender should act as a server and target/receiver should act as a client and both should communicate with Remote Object which both side has same remote object signature.Example : AIDL implementation....

2) Passive Communication (Accessing Source's Resource) : When Source is not alive and target is trying to access the data of source which is stored in any kind of storage can be accessed via Intents/Content Provider.

If you want to share data between process then you go with AIDL implementation only...

Upvotes: 0

mach
mach

Reputation: 8395

Data sharing between processes are done through Intents or ContentProviders.

If the data is only shared within your application package you may also use SQLite or SharedPreferences but both these uses non-volatile memory and are significantly slower than data sharing through IPC.

Upvotes: 0

JHH
JHH

Reputation: 9285

You said it yourself: "which runs in its own process"

Each process has its own VM. You cannot access variables etc from one process to another.

The obvious question to follow up this would be, do you absolutely need to run the service in its own process?

Upvotes: 1

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