Develop Reference

Difference between DJI onProductChange and onProductConnect

Context
I'm building a Flutter Plugin above the DJK SDK. For that, I have to implement the communication with the aircraft on the native side, and I'm doing it with Java. I'm also doing it only for Android.
One of the methods of the API is boolean connectToAircraft(), which must return if the connection with the aircraft succeeded.
Expected/current behavior
After I call connectToAircraft() - which invokes the DJISDKManager.getInstance().startConnectionToProduct() method, I expected to be able to use anything related to aircraft immediately, but this doesn't happen. I have to wait a few seconds before I can retrieve data from the aircraft.
Some code
public class UavApi implements IUavApi, DJISDKManager.SDKManagerCallback {
...
private final CountDownLatch onConnectToUavFinishedSignal = new CountDownLatch(1);
...
public boolean connectToUav() throws InterruptedException {
Logger.v("connectToUav()");
DJISDKManager.getInstance().startConnectionToProduct();
synchronized (onConnectToUavFinishedSignal) {
onConnectToUavFinishedSignal.await();
}
return DJISDKManager.getInstance().getProduct() instanceof Aircraft;
}
...
#Override
public void onProductConnect(#Nullable final BaseProduct baseProduct) {
Logger.v(MessageFormat.format("onProductConnect(product: {0})", baseProduct));
if (baseProduct != null) {
handleProductConnected(baseProduct);
}
}
#Override
public void onProductChanged(#Nullable final BaseProduct baseProduct) {
Logger.v(MessageFormat.format("onProductChanged(product: {0})", baseProduct));
if (baseProduct != null) {
handleProductConnected(baseProduct);
}
}
...
private void handleProductConnected(#NonNull final BaseProduct baseProduct) {
Logger.d(MessageFormat.format("Is null? {0}", baseProduct == null ? "Yes" : "No"));
Logger.d(MessageFormat.format("Type: {0}", baseProduct.getClass().getSimpleName()));
onConnectToUavFinishedSignal.countDown();
}
...
}
Problem
The code above is what I tried to do, but it's not working and guess it's because I'm misunderstanding the use of the onProductChange() and onProductConnect() methods.
The DJISDKManager.getInstance().getProduct() is always returning null.
OBS: It's always returning null immediately after the onConnectToUavFinishedSignal.await() call finishes. After a few seconds, I get a valid instance of the aircraft.
Something I've also noticed is that sometimes the onProductChange() is called with some value that the log outputs as Unknwoun and None. What are those and how can I test for them? Like if (baseProduct == ???) doSomething()
Environment
Android 9
MSDK 4.13.1
Phantom 4 Pro

Difference
According to the SDK Docs onProductChanged is primarily used to detect when the connection status changes from only remote controller connected to a full connection between the aircraft and the SDK running on your device.
Keep in mind that when the aircraft is disconnected, this method will be called with an instance of an aircraft, but this instance will come with property isConnected as false. If you print the aircraft object to the console you will notice that if isConnected is true, it will print the aircraft name, otherwise, it will print "None".
As long for the onProductConnect, it will be called always after DJISDKManager.getInstance().registerApp() succeeded or after you manually connect to the aircraft with success using DJISDKManager.getInstance().startConnectionToProduct(). In my tests, even though the app registration succeeds, the method will return false, so you might need to check if the SDKManagerCallback::onRegister results in DJISDKError.REGISTRATION_SUCCESS.
Solution
You need to listen to component change events. Unfortunately just because the product is connected it does not mean that the individual components, such as the flight controller, camera etc are connected. You will need to implement onComponentChange and add a listener to detect when a component is connected. These don't always connect in the same order and may start to connect before or after the product is connected.
#Override
public void onComponentChange(
BaseProduct.ComponentKey componentKey,
BaseComponent oldBaseComponent,
BaseComponent newBaseComponent
) {
newBaseComponent.setComponentListener(isConnected -> {
// check if component connected and access data
if (isConnected) {
if(componentKey == ComponentKey.FLIGHT_CONTROLLER) {
// DJISDKManager.getInstance().getProduct() should no longer be null
DJISDKManager.getInstance().getProduct().getModel();
}
}
})
}

Codename one new gui builder-back command from EVERY form navigation

I am navigating between forms in the NEW GUI builder. The old one had a back button on every form by default.
How do I enable the back button on new gui builder in every form, every time i navigate in a new form? Tried through constants in theme.res. It is still not enabled by default.
Furthermore, is the method "new form1.show" the best way to navigate between forms ? (see code)
Assuming name files:
Main.java, myapplication.java, Form1 ,Form2 ,Form3
Code for navigation, assuming names button1 and Form3:
public void onbutton1ActionEvent(com.codename1.ui.events.ActionEvent ev) {
new Form3().show();
}
Back command from old gui builder, not working here:
public Form showForm(String resourceName, Command sourceCommand) {
try {
Form f = (Form)formNameToClassHashMap.get(resourceName).newInstance();
Form current = Display.getInstance().getCurrent();
if(current != null && isBackCommandEnabled() && allowBackTo(resourceName)) {
f.putClientProperty("previousForm", current);
setBackCommand(f, new Command(getBackCommandText(current.getTitle())) {
public void actionPerformed(ActionEvent evt) {
back(null);
}
});
}
if(sourceCommand != null && current != null && current.getBackCommand() == sourceCommand) {
f.showBack();
} else {
f.show();
}
return f;
} catch(Exception err) {
err.printStackTrace();
throw new RuntimeException("Form not found: " + resourceName);
}
}
I've tried:
form.setBackCommand(cmd);
public Command setBackCommand(String title, ActionListener<ActionEvent> listener)
public void setBackCommand(Command cmd)
public Command setBackCommand(String title, BackCommandPolicy policy, ActionListener<ActionEvent> listener)
public void setBackCommand(Command cmd, BackCommandPolicy policy)
boolean onBack() {
return true;
}
https://www.codenameone.com/blog/toolbar-back-easier-material-icons.html
on main.java and myapplication.java did not accept the commands.
Form3.getToolbar().setBackCommand("", e -> Form3.showBack());
althouth is should not work only for form3, but every form.
Did not work either. Putting "back command" on every sidemenu would not be the ideal solution, because we might be navigating to each form from different forms.
EXTRA:
Is there a way to enable global toolbar and global commands for all forms, so i do not copy paste the toolbar code for each new form? If not answered here, i might make a new thread.
Thanks.

The old GUI builder handled navigation as it was designed at a time when Nokia was the worlds leader in the mobile phone industry and a 4in device was considered large. Back then we assumed the UI was simpler for each form and the navigation was the hard part.
This changed. But the bigger problem for most developers was the concept of stateless navigation which triggered a lot of issues both in design and functionality.
The new GUI builder doesn't include any navigation code or any global code. Each form stands on its own.
Having said that you can implement your own state machine by just keeping form instances and showing the form you want to navigate to e.g.:
public static class Controller {
private static Form1 f1;
private static Form2 f2;
public static void showF1() {
if(f1 == null) f1 = new Form1();
f1.show();
}
// etc...
}
I used static context for simplicity but you can implement your own strategy. Notice that you can also insert global logic here e.g. add the toolbar as a function like:
private static void initForm(Form f) {
// add global commands to the toolbar
}
Alternatively you can derive all the forms from a common base class as the new GUI builder doesn't restrict your inheritance.

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.

How to enable / disable action in Netbeans Platform

I have spent almost three days trying to do a simple enable / disable of Actions in the netbeans plaform, something that I though was going to be simple, and should be a common feature is more complex than I thought.
At the begging I tried to see if there was an setEnable() method on the default actions generated and to my surprise there is not. Then I started looking into that and I found that most common method to do it was setting a conditionally enabled action (which depends on a Cookie class), So I figured out how to add a fake class to the Lookup so it gets enabled and disabled, I did it the following way. To test it out I added the following code to another action which should enable or disable the second one.
private final PlottingStarted plottingStarted = new PlottingStarted();
#Override
public void actionPerformed(ActionEvent e) {
// TODO implement action body
if (Lookup.getDefault().lookup(PlottingStarted.class) == null) {
ic.add(plottingStarted);
}else{
ic.remove(plottingStarted);
}
So PlottingStarted is a fake object I created which only purpose is being in the lookup to disable or enable the action.
For some reason it did not do anything at all an the Action was always disabled. I tried many things and finally I gave up.
Then I tried a different approach and was using AbstractActions which do have the setEnabled() ability.
To retrieve the action I based myself on one the Geertjan blogs and I created the following method
public Action findAction(String actionName) {
FileObject myActionsFolder = FileUtil.getConfigFile("Actions/RealTimeViewer");
if (myActionsFolder != null){
FileObject[] myActionsFolderKids = myActionsFolder.getChildren();
for (FileObject fileObject : myActionsFolderKids) {
//Probably want to make this more robust,
//but the point is that here we find a particular Action:
if (fileObject.getName().contains(actionName)) {
try {
DataObject dob = DataObject.find(fileObject);
InstanceCookie ic = dob.getLookup().lookup(InstanceCookie.class);
if (ic != null) {
Object instance = ic.instanceCreate();
if (instance instanceof Action) {
Action a = (Action) instance;
return a;
}
}
} catch (Exception e) {
ErrorManager.getDefault().notify(ErrorManager.WARNING, e);
return null;
}
}
}
}
return null;
}
This method worked perfectly and I was able to retrieve the action and call its setEnabled() method. Unfortunately no matter why I did the Action was always enabled.
Reading some literature I found that I should add the following to the registration of the action "lazy = false" and finally I was able to enable and disable the Action... But off course the default registration is lost and I have no Icons and Names.
Now I decided to post again because I cannot believe that it need to be that complex, there must be a way to do it easier. The only thing I need is to have a PLAY / STOP functionality, when PLAY is enabled STOP is disabled and vice-versa.

I have not done this myself but it seems to be covered in Chapter 5.1.2.1 "Complex Enablement" of the book "Netbeans Platform for Beginners". https://leanpub.com/nbp4beginners
The book is not free but the corresponding code sample is available on
github. https://github.com/walternyland/nbp4beginners/tree/master/chapters/ch05/5.1.2.1 He extends AbstractAction overrides the resultChanged method and uses super.setEnabled().
#ActionID(id = "org.carsales.evaluator.EvaluateCarAction1", category = "Car")
#ActionRegistration(displayName = "not-used", lazy = false)
public class EvaluateCarAction extends AbstractAction
implements ContextAwareAction, LookupListener {
// ...
#Override
public void resultChanged(LookupEvent le) {
//Optionally, check if the property is set to the value you're interested in
//prior to enabling the Action.
super.setEnabled(result.allInstances().size() > 0);
}

Thanks to everybody for your responses. I finally got it to work by extending AbstractAction, it seems that even if you register "lazy = false" some of the registration is still being done by the platform and you just need some minor tweaking in the Action constructor. The final result was
#ActionID(
category = "RealTimeViewer",
id = "main.java.com.graph.actions.StopPlotting"
)
#ActionRegistration(
//iconBase = "main/java/com/graph/images/stop-plotting-24x24.png",
displayName = "#CTL_StopPlotting",
lazy = false
)
#ActionReference(path = "Toolbars/RealTimeViewer", position = 600)
#Messages("CTL_StopPlotting=Stop Plotting")
public final class StopPlotting extends AbstractAction{
private static final String ICON = "main/java/com/dacsys/cna/core/graph/images/stop-plotting-24x24.png";
public StopPlotting() {
putValue(SMALL_ICON, ImageUtilities.loadImageIcon(ICON, false));
putValue(NAME, Bundle.CTL_StopPlotting());
this.setEnabled(false);
}
#Override
public void actionPerformed(ActionEvent e) {
// TODO implement action body
Action a = new ActionsHelper().findAction("StartPlotting");
if (a != null){
if (a != null){
if (a.isEnabled()){
a.setEnabled(false);
this.setEnabled(true);
}else{
a.setEnabled(true);
this.setEnabled(false);
}
}
}
}
}

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...