Develop Reference

How to save game data to the cloud using gdx-gamesvcs?

I want to implement Google Play Games Services in my game on the libgdx engine. I tried using gdx-gamesvcs for this. But I am having trouble saving data. I understood from the example that one value is being saved, not the entire state of the game. So I decided to check it out: save and load one value using gsClient.loadGameState and gsClient.saveGameState. I deliberately deleted the game data from the device. But as a result, not only the test value changed, but many others as well. I thought that the state of the entire game is being saved, but the values ​​obtained do not fit into the logic of the game and could not be obtained in it.
How should I use this tool and is it worth it at all, or is it better to use what libgdx itself offers?
Here is a piece of code:
if (gsClient.isSessionActive()) {
try {
gsClient.saveGameState("data", intToByteArray(testValue), 0, null);
} catch (UnsupportedOperationException unsupportedOperationException) {
}
if (gsClient.isSessionActive()) {
try {
gsClient.loadGameState("data", new ILoadGameStateResponseListener() {
#Override
public void gsGameStateLoaded(byte[] gameState) {
if (gameState != null) {
setTestValue(bytesToInt(gameState));
}
}
});
} catch (UnsupportedOperationException unsupportedOperationException) {
}
}
UPD
Yes, saving occurs both to the cloud and to the device, for saving to the device I use Preferences. I have a Google account login button in the game, it works, I have repeatedly seen this standard bar of my account level, which appears at the top when I log in. Everything is set up in the developer console too, I have an id for achievements and leaderboards. In code, I work with the client like this (In the create() method):
public IGameServiceClient gsClient;
if (gsClient == null) {
gsClient = new MockGameServiceClient(1) {
#Override
protected Array<ILeaderBoardEntry> getLeaderboardEntries() {
return null;
}
#Override
protected Array<String> getGameStates() {
return null;
}
#Override
protected byte[] getGameState() {
return new byte[0];
}
#Override
protected Array<IAchievement> getAchievements() {
return null;
}
#Override
protected String getPlayerName() {
return null;
}
};
}
gsClient.setListener(this);
gsClient.resumeSession();
Next is loading.
The exception is not caught, I removed it and everything works as before.

Well, libgdx offers no built-in cloud-save, it is hard to use it for that. :-)
You should in any case save to local AND to cloud, as the cloud is not very fast to load its state.
I can see no problem in your code besides the fact that you swallow an UnsupportedOperationException that is thrown if you did not activate cloud save feature. So the interesting question is: what happens if you don't swallow the exception, and did you intialize GpgsClient with cloud save enabled? Are you really logged in to Gpgs, and is the feature also activated in your developer console?

The main problem was that gameState was null, this arose due to the fact that you had to wait 24 hours after enabling the save function in the developer console, and the advice on clearing the memory of google play games on the test device did not help. After a while gameState began to pass the existing values, but I started having problems with the graphics flow, probably due to the asynchronous loading.

Unity ads returns INVALID_ARGUMENT

I've integrated UnityAds on my Android app (that is not published yet).
I get app id and placement id from database on my server.
App id and placement id are correct, I've copied and pasted about 30 times for be sure of it.
So, when I try to get an ad in test mode, it give me the INVALID_ARGUMENT error.
Here an explaination of the error code by Unity, but as you can see it is a little generic.
I have an object that simply represents an ad service (like admob, FAN, inmobi etc)
In this case the object is called advert, and here it's how I show an ad with Unity:
protected void showUnity(){
UnityAds.initialize(this, advert.getApiKey(), true); //advert.getApiKey() returns the app id
UnityAds.addListener(new IUnityAdsListener() {
#Override
public void onUnityAdsReady(String s) {
Log.i(TAG, "onUnityAdsReady "+s);
if(s.equals(advert.getUnitId()) && !unityReady)
UnityAds.show(ActivityAd.this, advert.getUnitId()); //advert.getUnitId() returns the placement id
}
#Override
public void onUnityAdsStart(String s) {
Log.i(TAG, "onUnityAdsStart "+s);
unityReady = true;
}
#Override
public void onUnityAdsFinish(String s, UnityAds.FinishState finishState) {
if (finishState.compareTo(UnityAds.FinishState.COMPLETED) == 0) {
onAdReward(); //my callback for reward
} else if (finishState.compareTo(UnityAds.FinishState.SKIPPED) == 0) {
onAdClosed(); //my callback for ad close
} else if (finishState.compareTo(UnityAds.FinishState.ERROR) == 0) {
onAdError(finishState.toString()); //my callback for errors
}
}
#Override
public void onUnityAdsError(UnityAds.UnityAdsError unityAdsError, String s) {
onAdError(unityAdsError.toString()); //my callback for errors, here results INVALID_ARGUMENT error
}
});
}
Does anyone know what is wrong? Thanks in advance

If you check the callback closely the onUnityAdsError has 2 params, first provides the error code and the second param provides you information about what went wrong.
#Override
public void onUnityAdsError(UnityAds.UnityAdsError unityAdsError, String reason) {
onAdError(unityAdsError.toString()); //my callback for errors, here results INVALID_ARGUMENT error
}
So just check the reason and you should be able to find out what is going wrong in your integration.

Here are some methods which you can follow to solve this INVALID_ARGUMENT problem
1. Make sure you are implementing the right Initialization code in your app. There are 2 types of Initialization.
Only Unity ads Initialization
Mediation Initialization
and both methods have their own banner, interstitial, and rewarded ad code.
2. Make sure you enable test mode as Boolean. (i.e: private Boolean testMode = true;) (make sure to do false this before publish on store)
3. You can add your mobile phone as a test device to get test ads on your phone forcefully. for this, you have to first copy the Ad ID of your device. For that, go to your mobile settings > Google > Ads > This device's advertising ID. copy that ID and go to unity dashboard > Monetization > Testing > Add Test Device. Add your device Ads ID here with any name, and now you will be able to see test ads on the device.

Matlab & Java: Execute matlab asynchronously

so, here is my today problem:
First of all, please note that I do NOT have the Matlab parallel toolbox available.
I am running java code witch interact with Matlab. Sometime Matlab directly call some java functions, sometimes it is the opposite. In this case, we use a notification system which comes from here:
http://undocumentedmatlab.com/blog/matlab-callbacks-for-java-events
We then address the notification in proper callbacks.
Here is a simple use case:
My user select a configuration file using the java interface, loaded into Matlab.
Using an interface listener, we notify Matlab that the configuration file has been selected, it then run a certain number of functions that will analyzes the file
Once the analysis is done, it is pushed into the java runtime, which will populate interface tables with the result. This step involve that matlab will call a java function.
Finally, java request the interface to be switched to an arbitrary decided tab.
This is the order of which things would happen in an ideal world, however, here is the code of the listener actionPerformed method:
#Override
public void actionPerformed(ActionEvent arg0) {
Model wModel = controller.getModel();
Window wWindow = controller.getWindow();
MatlabStructure wStructure = new MatlabStructure();
if(null != wModel) {
wModel.readMatlabData(wStructure);
wModel.notifyMatlab(wStructure, MatlabAction.UpdateCircuit);
}
if(null != wWindow) {
wWindow.getTabContainer().setSelectedComponent(wWindow.getInfosPannel());
}
}
What happen here, is that, when the notifyMatlab method is called, the code does not wait for it to be completed before it continues. So what happen is that the method complete and switch to an empty interface page (setSelectedComponent), and then the component is filled with values.
What I would like to, is for java to wait that my notifyMatlab returns a "I have completed !!" signal, and then pursue. Which involves asynchrounous code since Matlab will code java methods during its execution too ...
So far here is what I tried:
In the MatlabEventObject class, I added an isAcknowledge member, so now the class (which I originaly found in the above link), look like this (I removed all unchanged code from the original class):
public class MatlabEventObject extends java.util.EventObject {
private static final long serialVersionUID = 1L;
private boolean isAcknowledged = false;
public void onNotificationReceived() {
if (source instanceof MatlabEvent) {
System.out.println("Catched a MatlabEvent Pokemon !");
MatlabEvent wSource = (MatlabEvent) source;
wSource.onNotificationReceived();
}
}
public boolean isAcknowledged() {
return isAcknowledged;
}
public void acknowledge() {
isAcknowledged = true;
}
}
In the MatlabEvent class, I have added a future task which goal is to wait for acknowledgement, the methods now look like this:
public class MatlabEvent {
private Vector<IMatlabListener> data = new Vector<IMatlabListener>();
private Vector<MatlabEventObject> matlabEvents = new Vector<MatlabEventObject>();
public void notifyMatlab(final Object obj, final MatlabAction action) {
final Vector<IMatlabListener> dataCopy;
matlabEvents.clear();
synchronized (this) {
dataCopy = new Vector<IMatlabListener>(data);
}
for (int i = 0; i < dataCopy.size(); i++) {
matlabEvents.add(new MatlabEventObject(this, obj, action));
((IMatlabListener) dataCopy.elementAt(i)).testEvent(matlabEvents.get(i));
}
}
public void onNotificationReceived() {
ExecutorService service = Executors.newSingleThreadExecutor();
long timeout = 15;
System.out.println("Executing runnable.");
Runnable r = new Runnable() {
#Override
public void run() {
waitForAcknowledgement(matlabEvents);
}
};
try {
Future<?> task = service.submit(r);
task.get(timeout, TimeUnit.SECONDS);
System.out.println("Notification acknowledged.");
} catch (Exception e) {
e.printStackTrace();
}
}
private void waitForAcknowledgement(final Vector<MatlabEventObject> matlabEvents) {
boolean allEventsAcknowledged = false;
while(!allEventsAcknowledged) {
allEventsAcknowledged = true;
for(MatlabEventObject eventObject : matlabEvents) {
if(!eventObject.isAcknowledged()) {
allEventsAcknowledged = false;
}
break;
}
}
}
}
What happen is that I discover that Matlab actually WAIT for the java code to be completed. So my waitForAcknowledgement method always wait until it timeouts.
In addition, I must say that I have very little knowledge in parallel computing, but I think our java is single thread, so having java waiting for matlab code to complete while matlab is issuing calls to java functions may be an issue. But I can't be sure : ]
If you have any idea on how to solve this issue in a robust way, it will be much much appreciated.

JADE ContractNet and GUI problems

I have some problems with use of ContractNet (Interaction Protocol) and GUI with the use of JADE multiagent framework.
In particular, in the override of handlePropose method.
I know that my problem comes from the use of a GUI. Let me explain:
My agent (Initiator) uses a first GUI and, after a click, the
conversation begins with a second agent (Responder). According to the
Protocol, the Initiator has thus sent a CFP to Responder. The agent
Responder responds with a PROPOSE that contains different data.
Since here, everything ok. Now...
I wish that the agent Initiator, BEFORE returning a reply, may examine
the data ... ie publish them on a JTable, for the user! The user will
examine the proposal via GUI and will choose if to accept or not, by
click on a button.
If accept, the Initiator send ACCEPT_PROPOSAL.
If not accept, the Initiator send REJECT_PROPOSAL.
This should be done in the method handleProposal. This is my code:
#Override
protected void handlePropose(final ACLMessage propose, final Vector acceptances) {
try {
System.out.println("Agent "+getLocalName()
+": receive PROPOSE from "+propose.getSender().getLocalName());
final ACLMessage reply = propose.createReply();
Vector<Goods> goods = (Vector<Goods>) propose.getContentObject();
// the JTable's GUI for visualize the list of data:
final GoodsChoiceBox gcb = new GoodsChoiceBox(propose.getSender().getName(), goods);
// the problem:
gcb.getExecuteJButton().addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
reply.setPerformative(ACLMessage.ACCEPT_PROPOSAL);
System.out.println("Agent "+getLocalName()+": send ACCEPT PROPOSAL ");
acceptances.addElement(reply);
}
});
// similar case, but for REJECT:
// gcb.getAbortJButton().addActionListener(... bla bla
gcb.setVisible(true);
} catch (UnreadableException e){
e.printStackTrace();
}
}
..... But, obviously, does not work.
In the Initiator agent, the ContractNet behaviour is aborted... so also handleInform, handleRefuse and handleFailure (for handle the answers) do not work.
The Initiator's principal GUI is blocked. And other problems...
Instead, if I do this (WITHOUT JButton, another GUI and ActionListener):
#Override
protected void handlePropose(final ACLMessage propose, final Vector acceptances) {
try {
System.out.println("Agent "+getLocalName()
+": received PROPOSE from "+propose.getSender().getLocalName());
final ACLMessage reply = propose.createReply();
Vector<Goods> goods = (Vector<Goods>) propose.getContentObject();
// the JTable's GUI for visualize the list of data:
final GoodsChoiceBox gcb = new GoodsChoiceBox(propose.getSender().getName(), goods);
reply.setPerformative(ACLMessage.ACCEPT_PROPOSAL);
System.out.println("Agente "+getLocalName()+": ACCEPT PROPOSAL di "+propose.getSender().getLocalName());
acceptances.addElement(reply);
} catch (UnreadableException e){
e.printStackTrace();
}
}
.... works.
I know that the problem is the ActionListener and its multithread nature.
But I need the GUI there.
How can I fix?

I try to answer myself. I'm not sure it's the best solution, but certainly works.
Note that before coming to this solution I am well documented with the guides and tutorials found (on http://jade.tilab.com/), and confronting myself with other
JADE developers (in mailing lists http://jade.tilab.com/pipermail/jade-develop/)
The answer is complicated, so I'll try to be exhaustive.
In my project I have to deal with two different types of agents.
The ShipperAgent, which represents one shipper: it keeps track of the vehicles owned by the shipper, those available, and the goods "reserved" from it.
The BuyerAgent, which represents customers (or buyers): each customer has a list of goods that want to move from point A to point B.
The two agents are registered to the yellow pages service.
In ShipperAgent, clicking on the "SEARCH" button you start a search: start a Contract Net Interaction Protocol.
Explain the Contract Net Interaction Protocol and my case
In the standard FIPA: http://www.fipa.org/specs/fipa00029/SC00029H.html
In JADE guide can be found here: http://jade.tilab.com/doc/programmersguide.pdf (p. 35)
Further on you will notice the changes that I had to take.
The ShipperAgent sends CFP each BuyerAgent.
Each BuyerAgent:
2.1 if he has goods, send a PROPOSE to ShipperAgent.
2.2 if does not have the goods, send a REFUSE to ShipperAgent. And for buyer, the protocol ends.
Since here is easy. With the sniffer, we can observe:
Now:
The ShipperAgent:
3.1 receives one or more PROPOSE by buyers, and displays (see image below).
3.2 if it receives the REFUSE (or does not receive anything after a certain time), ending communication with those buyer.
Here's how the Shipper graphically displays the proposals:
Now it's up to the user to choose which goods wants and what not.
To achieve this, I had to create some kind of "internal communication" to the agent himself: the GUI (in 3.1), once clicked Execute, sends a message to the agent. It may seem inelegant, but it seems to be the only way to not crash the protocol side ShipperAgent.
The ShipperAgent:
 4.1 if the user has selected one or more goods proposals (and click Execute), sends to the corresponding BuyerAgent an ACCEPT_PROPOSAL, where specific goods that want to (a subset of the previous proposal).
 4.2 if the user does not select any good (or click on Cancel), sends to the corresponding BuyerAgent an REJECT_PROPOSAL. Ends communication to that buyer.
The BuyerAgent:
 5.1 if receives an ACCEPT_PROPOSAL, check that the goods are still available (any other shippers could have them "reserved" in the meanwhile) and, if so, sends an INFORM.
5.2 if receives an ACCEPT_PROPOSAL ma one or more goods are no longer available, sends FAILURE.
 5.3 if it receives an REJECT_PROPOSAL, ends communication with the ShipperAgent.
In brief this (for example):
The code
BuyerAgent.java
I create a dispatcher who is always ready to receive the CFP. As soon as it receives and start protocol, buyer-side: start SearchJobResponder.
/*
* ...
*/
final MessageTemplate template = MessageTemplate.and(
MessageTemplate.MatchProtocol(FIPANames.InteractionProtocol.FIPA_CONTRACT_NET),
MessageTemplate.MatchPerformative(ACLMessage.CFP) );
// SSResponderDispatcher:
SSResponderDispatcher dispatcher = new SSResponderDispatcher(this, template) {
BuyerAgent b = (BuyerAgent) this.myAgent;
protected Behaviour createResponder(ACLMessage initiationMsg) {
// SearchJobResponder for single cfp:
return new SearchJobResponder(b, initiationMsg);
}
};
addBehaviour(dispatcher);
/*
* ...
*/
ShipperAgent.java
Search all buyer, creates a CFP and start the protocol, shipper-side: start SearchJobInitiator.
/*
* ...
*/
ACLMessage cfp = new ACLMessage(ACLMessage.CFP);
AID[] buyerAgents = searchBuyers(); // search all buyerAgents
for (AID buyer : buyerAgents)
cfp.addReceiver(buyer);
addBehaviour(new SearchJobInitiator(this, cfp));
/*
* ...
*/
SearchJobInitiator.java
This was the hard part...
/*
* ...
*/
public class SearchJobInitiator extends ContractNetInitiator {
ShipperAgent shipperAgent;
public SearchJobInitiator(ShipperAgent a, ACLMessage cfp) {
super(a, cfp);
shipperAgent=a;
// Very important:
registerHandleAllResponses(new HandleProposes());
}
#Override
protected Vector<?> prepareCfps(ACLMessage cfp) {
long now = System.currentTimeMillis();
cfp.setConversationId("contractNet-by-"
+shipperAgent.getAID().getLocalName()+now);
cfp.setContent("Fammi delle proposte di lavoro");
/*
* filtering...
*/
cfp.setProtocol(FIPANames.InteractionProtocol.FIPA_CONTRACT_NET);
cfp.setReplyByDate(new Date(now+10000));
//cfp.setReplyWith("cfp"+System.currentTimeMillis()) //useless, is overwrited at the end
return super.prepareCfps(cfp);
}
//inner class for handling a single proposal
public class HandleProposes extends Behaviour {
private static final long serialVersionUID = 1L;
private Vector<ACLMessage> proposes;
private Vector<ACLMessage> acceptances;
private int numberOfProposes;
public void onStart() {
proposes = (Vector<ACLMessage>) getDataStore().get(ALL_RESPONSES_KEY);
acceptances = (Vector<ACLMessage>) getDataStore().get(ALL_ACCEPTANCES_KEY);
numberOfProposes=proposes.size();
for (Iterator I=proposes.iterator(); I.hasNext();) {
ACLMessage propose = (ACLMessage) I.next();
// Very important:
if (propose.getPerformative()==ACLMessage.PROPOSE)
myAgent.addBehaviour(new HandleSinglePropose(propose, acceptances));
else
numberOfProposes--;
}
}
public void action() {
if (!done())
block();
}
public boolean done() {
return (acceptances.size()==numberOfProposes);
}
/*
* Inner class for handle a single proposal and display it:
*/
public class HandleSinglePropose extends Behaviour {
private ACLMessage propose;
private Vector<ACLMessage> acceptances;
private boolean finish=false;
public HandleSinglePropose (ACLMessage propose, Vector<ACLMessage> acceptances) {
this.propose=propose;
this.acceptances=acceptances;
// This is GUI in 3.1 point
GoodsChoiceBox gcb = new GoodsChoiceBox(shipperAgent, this, propose); // fill the JTable
gcb.setVisible(true);
}
#Override
public void action() {
MessageTemplate mt = MessageTemplate.and(
MessageTemplate.MatchSender(shipperAgent.getAID()),
MessageTemplate.and(
MessageTemplate.MatchReplyWith("response"+propose.getReplyWith()),
MessageTemplate.or(
MessageTemplate.MatchPerformative(ACLMessage.ACCEPT_PROPOSAL),
MessageTemplate.MatchPerformative(ACLMessage.REJECT_PROPOSAL)
) ) ) ;
// Read data from GUI. The user accept or reject:
ACLMessage decisionFromGUI = shipperAgent.receive(mt);
if (decisionFromGUI != null) {
ACLMessage reply = propose.createReply();
// bla bla...
finish=true;
HandleProposes.this.restart();
} else {
block();
}
}
public boolean done() {
return finish;
}
public void handleChoice(ACLMessage propose, boolean bool, Vector<Goods> selectedGoods) {
ACLMessage reply;
if (bool){
reply = new ACLMessage(ACLMessage.ACCEPT_PROPOSAL);
//...
} else {
reply = new ACLMessage(ACLMessage.REJECT_PROPOSAL);
//...
}
reply.addReceiver(shipperAgent.getAID());
reply.setReplyWith("response"+propose.getReplyWith());
shipperAgent.send(reply);
}
} // closes HandleSinglePropose
} // closes HandleProposes
}
SearchJobResponder.java
The responder is simple. The only thing of note: I extends SSContractNetResponder, don't extends ContractNetResponder.
public class SearchJobResponder extends SSContractNetResponder {
BuyerAgent buyerAgent;
public SearchJobResponder(BuyerAgent a, ACLMessage cfp) {
super(a, cfp);
buyerAgent = a;
}
/*
* override methods...
*/
}
GoodsChoiceBox.java
The GUI for show the proposals...
public GoodsChoiceBox(final Agent agent, final HandleSinglePropose behaviour, final ACLMessage propose){
/*
* graphics stuff
*/
// if goods selected and press Execute
behaviour.handleChoice(propose,true,selectedGoods);
//else
behaviour.handleChoice(propose,false,null);
/*
* bla bla
*/
}
I know, I have dwelt much, but I did not know how else to explain.
However, now my project work. But I'm open to any suggestions.

I often run into this problems of this sort. These are Finite State machine behaviours so you should be able to pause and resume a behavior but I'm not sure how. What I do is create two separate Interaction behaviors on the initiator side and one on the responder side.
Initiator Responder
| |
| |
| First behaviour |The responder only has 1 behaviour
|| CFP-> ||
|| <-Proposal ||
| ||
| Second behaviour ||
|| Accept prop-> ||
|| <-Response ||
| |
Two points to remember
(1)
Make sure that you save the conversationID
msgRecieved.getConversationID
from the first behaviour and use it in the second Behaviour.
msg.setConversationID().
(2)
The second behavior is another Contract net initiator but in prepareCFPs method set MESSAGE performative to accept proposal
class ContractServiceList extends ContractNetInitiator
{
protected Vector prepareCfps(ACLMessage cfp) {
ACLmessage AP= new ACLmessage(ACLmessage.ACCEPT_PROPOSAL)
.....
These things are hard to explain so I tried to attached a picture but have 2 little rep points.
I now have enough rep points to attach the picture which I am doing.

I just realized that there is another solution to this problem. The second solution involves using ChildBehaviours and data stores. A child behaviour can be initiated pausing the parent behaviour. The parent behaviour must then be resumed one the child is complete.
I'm attaching a pic to better explain this interaction.
So at point A in your CNI (ContractNetInitiator) parent behaviour you want to initiate the Child behaviour. You would do this by using the CNI.registerHandlePropose(new Childbehaviour).
This is what the setup() method should look like:
protected void setup()
{
ContractNetInitiator parentBehave= new ContractNetInitiator (null, null, GlobDataStore);
ContractNetInitiator.registerHandlePropose(new ChildBehavoiur (GlobDataStore));
addBehaviour(CNI);
}
In you Child behaviour you will have to check the data from the parent (GlobDataStore) and return a message to be passed back. Code to follow:
class ChildBehaviour extends OneShotBehaviour{
#Override
public void action() {
//evaluate globalestore here;
ACLMessage CNIresponse=new ACLMessage();
if(true)
{
storeNotification(ACLMessage.ACCEPT_PROPOSAL, CNIresponse);
}
else
{
storeNotification(ACLMessage.REJECT_PROPOSAL, CNIresponse);
}
}
public void storeNotification(int performative, ACLMessage original)
{
// Retrieve the incoming request from the DataStore
String incomingCFPkey = (String) ((ContractNetResponder) parent).CFP_KEY;
incomingCFPkey = (String) ((ContractNetResponder) parent).CFP_KEY;
ACLMessage incomingCFP = (ACLMessage) getDataStore().get(incomingCFPkey);
// Prepare the notification to the request originator and store it in the DataStore
ACLMessage notification = incomingCFP.createReply();
notification.setPerformative(performative);
notification.setContent(original.getContent());
String notificationkey = (String) ((ContractNetResponder) parent).PROPOSE_KEY;
getDataStore().put(notificationkey, notification);
}
}

Yes/No dialog in Java ME

I'm looking for a simple solution for a yes/no dialog to use in a Java ME midlet. I'd like to use it like this but other ways are okey.
if (YesNoDialog.ask("Are you sure?") == true) {
// yes was chosen
} else {
// no was chosen
}

You need an Alert:
An alert is a screen that shows data to the user and waits for a certain period of time before proceeding to the next Displayable. An alert can contain a text string and an image. The intended use of Alert is to inform the user about errors and other exceptional conditions.
With 2 commands ("Yes"/"No" in your case):
If there are two or more Commands present on the Alert, it is automatically turned into a modal Alert, and the timeout value is always FOREVER. The Alert remains on the display until a Command is invoked.
These are built-in classes supported in MIDP 1.0 and higher. Also your code snippet will never work. Such an API would need to block the calling thread awaiting for the user to select and answer. This goes exactly in the opposite direction of the UI interaction model of MIDP, which is based in callbacks and delegation. You need to provide your own class, implementing CommandListener, and prepare your code for asynchronous execution.
Here is an (untested!) example class based on Alert:
public class MyPrompter implements CommandListener {
private Alert yesNoAlert;
private Command softKey1;
private Command softKey2;
private boolean status;
public MyPrompter() {
yesNoAlert = new Alert("Attention");
yesNoAlert.setString("Are you sure?");
softKey1 = new Command("No", Command.BACK, 1);
softKey2 = new Command("Yes", Command.OK, 1);
yesNoAlert.addCommand(softKey1);
yesNoAlert.addCommand(softKey2);
yesNoAlert.setCommandListener(this);
status = false;
}
public Displayable getDisplayable() {
return yesNoAlert;
}
public boolean getStatus() {
return status;
}
public void commandAction(Command c, Displayable d) {
status = c.getCommandType() == Command.OK;
// maybe do other stuff here. remember this is asynchronous
}
};
To use it (again, untested and on top of my head):
MyPrompter prompt = new MyPrompter();
Display.getDisplay(YOUR_MIDLET_INSTANCE).setCurrent(prompt.getDisplayable());
This code will make the prompt the current displayed form in your app, but it won't block your thread like in the example you posted. You need to continue running and wait for a commandAction invocation.

I dont have programed in Java ME, but i found in it's reference for optional packages the
Advanced Graphics and User Interface API, and it's used like the Java SE API to create these dialogs with the JOptionPane Class
int JOptionPane.showConfirmDialog(java.awt.Component parentComponent, java.lang.Object >message, java.lang.String title, int optionType)
Return could be
JOptionPane.YES_OPTION, JOptionPane.NO_OPTION, JOptionPane.CANCEL_OPTION...