Develop Reference

ViewModel not updating the view on postValue

I used the lifecycle callback onCreate to fetch data like below
mWeOutViewModel.getPlaceListLiveData()
.observe(this, weOutItemViewModels -> {
AppLogger.i(getCustomTag() + "adding items " + weOutItemViewModels.size());
if (weOutItemViewModels != null && weOutItemViewModels.size() > 0)
mWeOutListAdapter.addToExisting(weOutItemViewModels);
});
As you can see the AppLogger output the initial size which is 0 when the fragment is displayed, then I fetch the data and call postValue (setValue crashes the app and it expected because I fetch data from the internet using a background thread). So I call post value like below :
private void updatePlaces(List<WeOutGroupedViewModels> weOutGroupedViewModels) {
List<WeOutGroupedViewModels> oldList = placeMutableLiveData.getValue();
oldList.addAll(weOutGroupedViewModels);
AppLogger.i(TAG +" updating places "+oldList.size());
placeMutableLiveData.postValue(oldList);
}
As you can see the other AppLogger before postValue, the size of the list is displayed(not empty), but nothing happens until the app crashes and nothing is shown in the logs. I have no ways of debugging since even on debug mode nothing happens. The post value doesn't trigger the observer.
I initialize the mutableLivedata like this :
private final MutableLiveData<List<WeOutGroupedViewModels>> placeMutableLiveData = new MutableLiveData<>();
and access like this :
public LiveData<List<WeOutGroupedViewModels>> getPlaceListLiveData() {
return placeMutableLiveData;
}
Event when I make the livedata public to access directly the livedata, there is no change (just in case someone thinks that's is where the issue comes from)

Instead of placeMutableLiveData.postValue(oldList);
I recommend using
placeMutableLiveData.postValue(Collections.unmodifiableList(new ArrayList<>(newList));
That way, the next time you access this list, you won't be able to mutate it in place, which is a good thing. You're not supposed to mutate the list inside a reactive state holder (MutableLiveData).
So theoretically it should look like this:
private void updatePlaces(List<WeOutGroupedViewModels> weOutGroupedViewModels) {
List<WeOutGroupedViewModels> newList = new ArrayList<>(placeMutableLiveData.getValue());
newList.addAll(weOutGroupedViewModels);
AppLogger.i(TAG +" updating places "+newList.size());
placeMutableLiveData.postValue(Collections.unmodifiableList(newList));
}

When realmResults.asObservable is called?

I'm implementing a chat client.
Everytime user clicks Send message button - I perform a Realm insert of this message.
I have a service 'waiting' for this change to send this message via socket.
Like this:
Observable<RealmResults<RealmMessage>> observable = getUnsentMessages();
subscribeUnsendMessages = observable
...
.subscribe(message -> {
launchMessageSending(message);
});
and method for getting this observable looks like this:
public Observable<RealmResults<RealmMessage>> getUnsentMessages() {
final Realm instance = getRealmInstance();
return instance.where(RealmMessage.class)
...
.findAllAsync()
.asObservable()
.filter(o -> ... )
.doOnUnsubscribe(instance::close);
}
And here is the problem - there is a corner case, when I perform two operations roughly at the same time.
The second one looks like this:
public boolean shouldTrack(#NonNull RealmChat chat) {
getRealmInstance().executeTransactionAsync(realm ->{
RealmTrackedState trackedStates = realm.where(RealmTrackedState.class).findFirst();
trackedStates.getRealmChats().add(chat);
});
return true;
}
The above method is a tracking cache for remembering if I tracked given chat or not.
(This is a bit more complicated than this, bear with me).
This PROBABLY causes the observer to react on the second database change.
Because these two operations happen almost at the same time - the second notification is still "valid" because there is an unsent message.
So, questions:
Am I right?
If so - how should I handle this?
I don't really want to 'delay' the shouldTrack(); method because I'm afraid that the same problem will occur in a different way.
Maybe create a flag for this message being 'handled', so the second will be ignored - but this is a bit nasty I guess. The second 'send' shouldn't happen.
EDIT:
Here is my TrackedState object
public class RealmATrackedState extends RealmObject {
#PrimaryKey
private int id = 1;
private RealmList<RealmChat> realmChats;
private boolean isSomething;
}
Is updating such object (as posted above) causing RealmMessage table be notified?

textView updates do not show

Ok - preface with I am new to android and new to java as well. But I did code in a previous lifetime.....
I am working on an application and now trying to pull some methods out and place into a utility class. In particular, I have a method which updates text views that I wanted to move out of an activity.
When in the activity, I had two versions of the method the only difference being that one would accept a view in the parameter list (I used this to populate some fields in a custom dialog). They all worked fine.
Once placed in the external utility package/class, the method no longer works - no errors, and it appears to have all it needs - I've done some logging and the view claims to be visible and the textview ids appear to be correct. Yet nothing changes on the screen.
I'm guessing this is something completely obvious and stupid but I can't seem to sort it out.
package xxx.xxx.Utility;
(some imports)
public class Utility {
public static void updateTextView(int id, String opt_data, View v) {
String TAG = "updateTextView: ";
if (v.getVisibility() == View.VISIBLE) Log.i(TAG," visible");
TextView tvTarget = (TextView) v.findViewById(id);
if (tvTarget == null) {
Log.i(TAG, "Error: updateTextView target is null");
}
if (opt_data != null) {
if (tvTarget != null) {
tvTarget.setText(opt_data);
}
} else {
if (tvTarget != null) {
tvTarget.setText(" ");
}
}
}
}
EDIT w/ Additional Info:
In the inital description I mentioned that this method was also being used to populate some fields of a pop-up dialog with data. In fact, I can request any number of dialogs in that manner and they all display properly and with the correct (and different) data. So it seems to fail only when trying to update the tv data of the main activity (the initial) view.

I'm guessing this is something completely obvious and stupid but I
can't seem to sort it out.
It helps to get the root(?) parent (?) view properly. IE,
currentView = this.findViewById(android.R.id.content).getRootView();
and now all is well.

TextViews not update in android UI

we have two activities one is where we make the connection via bluetooth and managing the blutooth other one is the update the UI where we want to update the GUI containing the TextViews.
We successfully send and recieve the message within two activities and vice versa.
private OnMessageReceivedListener dataReceivedListener = new OnMessageReceivedListener() {
public void OnMessageReceived(String device, String message) {
//t.setText(message);
Log.d("Message" , message);
msg = message;
UpdateGUI();
}
};
THE above function recieves the message and we did that successfully.
private void UpdateGUI() {
//i++;
//tv.setText(String.valueOf(i));
myHandler.post(myRunnable);
}
final Runnable myRunnable = new Runnable() {
public void run() {
btBoard.UpdateYoursBoard(mystring);
}
};
The above function of connection class calls the method of our GUI class and send a recieved message to it.
In our GUI class we want this
public void UpdateYoursBoard(String positions)
{
Log.d("Positions" , positions);
tv.setText(positions);
};
we successfully recieved the message in log.d but when we want to change our textview text it gives following errors.
java.lang.NullPointerException
at net.clc.bt.Board.UpdateYoursBoard(Board.java:3460)
NOTE : we are working with bluetooth and we have 3 mobile connected simultaneously and UpdateYourBoard will change the TextViews of 3 mobiles GUI's.
kindly help me to fix the problem.
Thanks in advance

First your Board class is far too big. 3 500 lines in a java file is very bad idea. Design more, decouple and split things. You are missing the divide and conqueer principle of IT.
In your case, tv is null. How and when do you get a reference to it ? If you used findViewById in your onCreate method (after super.onCreate has been called), it should work.

The reference to your TextView 'tv' is null. Initialize it somewhere using findViewById() or some other appropriate method.
Check your scopes etc so that the reference is maintained properly at the point where you call the setText() method.

programming style with modal dialog

in my android application at some event in an activity I want to ask the user for a name (string). I know how to do this: call showDialog, create the dialog in the Activity.onCreateDialog method (I need to supply a string for the label) and handle the result in the onClick of the dialog. This works fine and to my satisfaction.
BUT this way I have three different places, where this simple task spreads throughout the code of my activity. I would much more prefer to keep this code together, to write some code like this:
string result;
if (showSimpleEditDialog(idForLabelString, result)==DIALOG_OK)
{
// do something with the result
}
or maybe with a class instance
SimpleEditDialog dlg = new SimpleEditDialog(idForLabelString);
if (dlg.showModal()==DIALOG_OK)
{
string result = dgl.getResult();
// do something with the result
}
(The "idForLabelString" would be some resource id for the label to use, DIALOG_OK would be some constant returned when the user clicks OK)
I know, I would have to write this methodes or this class. But for better readibility of my code I would do it. Any suggestions?
Thank you,
Gerhard

"BUT this way I have three different places, where this simple task spreads throughout the code"
So why don't you create a Method for this task? What you are talking about sounds like some sort of 'ActionListener' to me. This can be done in Java/Swing, but not in Android.
But, if you have three Dialogs, which all need to do the same when "YES" e.g. "NO" is pressed, you could define the 'DialogInterface.OnClickListener()' as a global inner-Class (or in a second class which extends the 'onClickListener') and then use it for all the Dialogs.

Now actually the problem with modal dialogs is mostly a problem with programm flow. You want to keep things together that belong together. You want to display a dialog that returns "ok" or "cancel" and additionaly e.g. a string that the user entered into one of the dialog widgets.
I do not want to write half of the code up to the line where I need the result of the dialog on one place and the rest of the code on another place namely the onClickListener of the dialog.
In some scenarios the first dialog might invoke a second dialog e.g. to specify a color which is not in the list of the first dialog's ListView.
Your code will be scattered all over the place (in each dialog's button onClickListener) and will be hard to read or to maintain.
Now after having written some unclear code like that I came up with the following solution which certainly respects the android design guides.
Instead of directly showing a dialog I create a Handler derived class which handles messages.
I send it a first message which creates and shows a dialog. It also forwards the handler to the dialog and the diaolg in it's onStop method sends another message to the handler, indicating the end of the dialog. There you can examine the dialogs properties, the contents of the edit fields or whether it was stopped with OK or CANCEL.
Now in the message handler all the logic of the task sits in different cases of the messages arg1 value.
Some cases might be skipped (e.g. the user selected a standard color and did not need a special color dialog).
The dialogs are independant of the scenario from which they are called and in their code only reflect their simple task (selecting from a list, some checkboxes etc.). They may be reused from other scenarios.
Following a kind of a template how to use this approach:
public class DoSomethingWithDialogs extends Handler
{
Context context; // from which it was called
final static int stepBegin = 0;
final static int stepNext = 1;
final static int stepSomethingElse = 2;
final static int stepLast = 3;
protected DoSomethingWithDialogs(Context context)
{
this.context = context;
}
public static void start(Context context)
{ // this is the main (only) entry point from outside
DoSomethingWithDialogs st = new DoSomethingWithDialogs(context);
st.sendMessage(st.obtainMessage(0, stepBegin, 0));
}
#Override
public void handleMessage(Message msg)
{
// step by step handling the task
switch (msg.arg1)
{
case stepBegin:
{
SomeDlg somedlg = new SomeDlg(context, this, stepNext);
// when the dialog closes, it sends a message to this with stepNext as arg1
somedlg.show();
}
break;
case stepNext:
{ // this message was send by the dialog when it finished
SomeDlg somedlg = (SomeDlg) msg.obj;
if (msg.arg2 == Dialog.BUTTON_NEGATIVE)
{
// has been canceled, nothing to do
} else
{
if (somedlg.someProperty)
{
} else
{
sendMessage(obtainMessage(0, stepSomethingElse, 0));
}
}
}
break;
case stepSomethingElse:
break;
}
}
}