Question

I’m developing an Android application and I have a problem running a new thread in background.

I make a class with this code:

public class Downloader implements Runnable {

private Vector <DownloadRequest>messages = new Vector<DownloadRequest>(); 
static final int MAXQUEUE = 5; 
ApiRequest mApi;


public void run() { 
    try { 
        while ( true ) { 
            getMessage(); 
        } 
    }  
    catch( ErrorException e ) { } 
} 
private synchronized void getMessage() throws ErrorException{ 
    try {
        notify(); 
        Log.d("DOWNLOADER", "empiezo a coger los mensajes");
        while ( messages.size() == 0 ) 
            wait(); 
        DownloadRequest dr = messages.firstElement(); 
        mApi.setMethod(dr.getRequest());
        try {
            mApi.executeRequest();
        } catch (ErrorException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        Object o = dr.getObject();
        o.notify();
        return;
    }catch(InterruptedException e) {
        throw new ErrorException();

    }

The purpose is wait for receive a new message and call the api.

This object is running in a new thread in this Activity

 public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.view);
    mDownloader = new Downloader(new ApiRequest());
    Thread thread = new Thread(mDownloader);
    thread.start();
    DownloadRequest dr = new DownloadRequest(this,TRIPS_METHOD);
    try {
        mDownloader.putMessage(dr);

But when thread.start() is called the UI remains blocked. I thinks this shouldn’t happen because is a new thread.

Can anyone help me?

Thanks

Answer 1

You are much better served using pre-established classes for this. In Android, AsyncTask handles both the background thread pool and the work queue. If you absolutely feel you have to fork your own thread, use a LinkedBlockingQueue instead of attempting to synchronize access to a Vector. There are a couple of books on Java concurrency available if you wish to read more on the subject.