onResize is not called after zooming.
Current GWT implementation:
public native void initWindowResizeHandler() /*-{
var oldOnResize = $wnd.onresize;
$wnd.onresize = $entry(function(evt) {
try {
#com.google.gwt.user.client.Window::onResize()();
} finally {
oldOnResize && oldOnResize(evt);
}
});
}-*/;
The only solutions I found for capturing resize events use polling.
Is polling the best (only) way? If so, how can the Scheduler be used for optimal performance?
Once the event is captured, does calling com.google.gwt.user.client.Window::onResize() seem like a good idea?
Thanks
Current solution looking for improvements
#Override
protected void onLoad() {
Scheduler.get().scheduleFixedDelay(new RepeatingCommand() {
#Override
public boolean execute() {
if (listOuter.getOffsetWidth() != knownWidth)
onResize();
return SomeListViewImpl.this.isAttached();
}
}, 200);
}
onResize is called on Window.onresize and on zooming.
#Override
public void onResize() {
knownWidth = listOuter.getOffsetWidth();
GWT.log("resize: " + knownWidth);
//some magic
}
Related
I've seen a lot of examples of how to turn finite things like arrays or Iterables into Observables, but I'm not sure I understand how to make an Observable out of something live and effectively unbounded like an event receiver. I studied the RxJava2 docs and came up with this, using an Android LocationListener as an example.
Is there a simpler and/or more correct way to do this? I'm aware of the "RxBus" concept, but it seems like a way of clinging to the old event bus paradigm.
final Observable<Location> locationObservable = Observable.create(new ObservableOnSubscribe<Location>() {
final LocationManager mLocationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
#Override
public void subscribe(final ObservableEmitter<Location> emitter) throws Exception {
final LocationListener listener = new LocationListener() {
#Override
public void onLocationChanged(final Location location) {
emitter.onNext(location);
}
#Override
public void onStatusChanged(final String s, final int i, final Bundle bundle) {
// TODO ???
}
#Override
public void onProviderEnabled(final String s) {
// TODO ???
}
#Override
public void onProviderDisabled(final String s) {
// TODO ???
}
};
mLocationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, listener);
emitter.setCancellable(new Cancellable() {
#Override
public void cancel() throws Exception {
mLocationManager.removeUpdates(listener);
}
});
emitter.setDisposable(new Disposable() {
private AtomicBoolean mDisposed;
#Override
public void dispose() {
if(mDisposed.compareAndSet(false, true)) {
mLocationManager.removeUpdates(listener);
}
}
#Override
public boolean isDisposed() {
return mDisposed.get();
}
});
}
});
using Observable.create() is indeed a correct way.
However, with RxJava2 the default way is to extend an Observable, you can see this answer for greater details.
some comments though regarding your implementation:
- there is no point setting both Cancellable and Disposable, as the later one will cancel/dispose the first one, you can see the difference between them here.
- I think it's best practice, to register cancellable/disposable before you start listening to update, in order to prevent weird edge cases races.
I am sure it's just a simple fault, but I'm not able to solve it.
My RecyclerView.Adapter loads its data with help of an AsyncTask (LoadAllPersonsFromDb) out of a SQLite DB. The response is handled by a callback interface (ILoadPersonFromDb.onFindAll).
Here is the code of the Adapter:
public class ListViewAdapter extends RecyclerView.Adapter<ListViewViewholder> implements LoadAllPersonsFromDb.ILoadPersonFromDb {
private int layout;
private List<Person> persons;
private Context context;
private AdapterDataSetListener adapterDataSetListener;
public ListViewAdapter(int layout, Context context,
AdapterDataSetListener adapterDataSetListener) {
this.layout = layout;
persons = new ArrayList<>();
this.context = context;
this.adapterDataSetListener = adapterDataSetListener;
new LoadAllPersonsFromDb(context, this).execute();
}
#Override
public ListViewViewholder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(layout, parent, false);
return new ListViewViewholder(view, context);
}
#Override
public void onBindViewHolder(ListViewViewholder holder, int position) {
holder.assignData(persons.get(position));
}
#Override
public int getItemCount() {
return persons.size();
}
#Override
public void onFindAll(List<Person> persons) {
Log.d("LISTVIEW", "Counted: " + persons.size() + " elements in db");
if (this.persons != null) {
this.persons.clear();
this.persons.addAll(persons);
} else {
this.persons = persons;
}
adapterDataSetListener.onChangeDataSet();
//notifyDataSetChanged();
}
public interface AdapterDataSetListener {
void onChangeDataSet();
}
}
As you can see, I tried more than one way to get it running. The simple notifyDataSetChanged did not do anything, so I made another interface which is used to delegate the ui information to the relating fragment. Following code documents this interface which is implemented in the relating fragment:
#Override
public void onChangeDataSet() {
Log.d("Callback", "called");
listViewAdapter.notifyDataSetChanged();
/*
getActivity().runOnUiThread(new Runnable() {
#Override
public void run() {
listViewAdapter.notifyDataSetChanged();
}
});
*/
}
Here I also tried to put it on the MainUiThread but nothing works. I'm just not able to see where my problem is. Hopefully any of you guys can give me a hint.
The logging works, which is the prove for the working callbacks.
Thank you in advance.
PS: If you need any more code, just tell me and I will provide it.
instead of using the interface-llistener pattern, try this
#Override
public void onFindAll(List<Person> persons) {
Log.d("LISTVIEW", "Counted: " + persons.size() + " elements in db");
if (this.persons != null) {
this.persons.clear();
this.persons.addAll(persons);
} else {
this.persons = persons;
}
refereshAdapter(persons);
}
public void refereshAdapter(List<Person> persons){
listViewAdapter.clear();
listViewAdapter.addAll(persons);
listViewAdapter.notifyDataSetChanged();
}
To tell the background, I used RecyclerView in Version 23.1.1 because the latest 23.2.0 had some weird behaviour in holding a huge space for each card.
//Update: the problem with the space between cards, was because of a failure of myself in the layout file (match_parent instead of wrap_content). -_-
The upshot was using the latest version again and everything worked just fine. I have no idea why, but at the moment I am just happy, that I can go on. This little problem wasted enough time.
Maybe somebody has a similar situation and can use this insight.
Thx anyway #yUdoDis.
Consider the following example, it creates an Observable that wraps another API that produces Widgets
public Observable<Widget> createWidgetObservable() {
return Observable.create(new Observable.OnSubscribe<Widget>() {
#Override
public void call(final Subscriber<? super Widget> subscriber) {
WidgetCreator widgetCreator = new WidgetCreator();
widgetCreator.setWidgetCreatorObserver(new WidgetCreator.WidgetCreatorObserver() {
#Override
public void onWidgetCreated(Widget widget) {
if (!subscriber.isUnsubscribed()) {
subscriber.onNext(widget);
}
}
#Override
public void onWidgetError(Throwable e) {
if (!subscriber.isUnsubscribed()) {
subscriber.onError(e);
}
}
});
}
});
}
Are the subscriber.isUnsubscribed() checks necessary prior to calling subscriber.onNext() and subscriber.onError()?
If so, are the checks always necessary or does it depend on the composition / subscriber that's using the observable?
Is it best practice to include the checks?
You can use them to narrow the window between an emission and an unsubscription but if you don't have loops, it is unnecessary most of the time. The more important thing is that if an unsubscription happen, you'd have to "unset" the WidgetCreatorObserver otherwise it will keep receiving and dropping data and keeping alive every reference it may hold.
WidgetCreator widgetCreator = new WidgetCreator();
WidgetCreator.WidgetCreatorObserver wo = new WidgetCreator.WidgetCreatorObserver() {
#Override
public void onWidgetCreated(Widget widget) {
if (!subscriber.isUnsubscribed()) {
subscriber.onNext(widget);
}
}
#Override
public void onWidgetError(Throwable e) {
if (!subscriber.isUnsubscribed()) {
subscriber.onError(e);
}
}
}
widgetCreator.setWidgetCreatorObserver(wo);
wo.add(Subscriptions.create(() -> widgetCreator.removeWidgetCreatorObserver(wo)));
I have an webapp with a large collection. So my user get a text box to filter the collection.
But every time the user put in one letter the filter action starts. This is very slow some times.
So I want only get the value change event when the user stop typing for one second.
I tried it this way:
#Override
public void onValueChange( ValueChangeEvent<String> event )
{
Timer t = new Timer()
{
#Override
public void run()
{
addChangeHandler( new ChangeHandler()
{
#Override
public void onChange( ChangeEvent event1 )
{
ValueChangeEvent.fire( TextBoxPSG.this, getValue() );
}
} );
}
};
t.schedule( 15000 );
}
But this doesn't work.
Maybe someone has an Idea or the same problem.
Thanks in advance.
Do not use ValueChangeEvent. Use KeyUpEvent.
private static Timer timer = new Timer() {
#Override
public void run() {
// do you filter work;
}
};
...
myTextBox.addKeyUpHandler(new KeyUpHandler() {
#Override
public void onKeyUp(KeyUpEvent event) {
if (timer.isRunning()) {
timer.cancel();
}
timer.schedule(1000);
}
});
I have the following problem:
I am trying to model a process using GWT, where i have a couple of views with a couple of submit buttons. And pressing button1 will create a server interaction and if everything was ok, the next view will be loaded. My problem is now that I get really nasty spaghetti code (just very highlevel to show you what i mean):
onClick {
AsyncCallback {
onSuccess {
load new view with another clickhandler and an asynccallback
}
}
}
Is there some way to create some kind of abstraction or something? Maybe a state pattern? How? Thanks a lot!
This is actually a very good question - and probably one without a definitive answer. It's a problem that applies to many frameworks, not just GWT, so I like your idea to look at this with some simplified code. I'll make this a little bit longer, to show what even just 4 very simple callbacks look like:
Nested callbacks
alice.call("a", new Callback() {
#Override
public void onSuccess() {
bob.call("b", new Callback() {
#Override
public void onSuccess() {
charlie.call("c", new Callback() {
#Override
public void onSuccess() {
daisy.call("d", new Callback() {
#Override
public void onSuccess() {
// finished
}
});
}
});
}
});
}
});
Named callbacks
You can use your IDE to refactor this easily into named callbacks (hint: Please read the callbacks from bottom to top!):
final Callback daisyCallback = new Callback() {
#Override
public void onSuccess() {
// finished
}
};
final Callback charlieCallback = new Callback() {
#Override
public void onSuccess() {
daisy.call("d", daisyCallback);
}
};
final Callback bobCallback = new Callback() {
#Override
public void onSuccess() {
charlie.call("c", charlieCallback);
}
};
final Callback aliceCallback = new Callback() {
#Override
public void onSuccess() {
bob.call("b", bobCallback);
}
};
alice.call("a", aliceCallback);
Problem: The control flow is not so immediately obvious anymore.
Still, an IDE can help by using "Search References" (Ctrl-G in Eclipse) or something similar.
Event Bus (or Observer/Publish-Subscribe pattern)
This is how the same calls look like with an event bus:
alice.call("a", new Callback() {
#Override
public void onSuccess() {
bus.fireEvent(BusEvent.ALICE_SUCCESSFUL_EVENT);
}
});
bus.addEventListener(BusEvent.ALICE_SUCCESSFUL_EVENT, new BusEventListener() {
#Override
public void onEvent(final BusEvent busEvent) {
bob.call("b", new Callback() {
#Override
public void onSuccess() {
bus.fireEvent(BusEvent.BOB_SUCCESSFUL_EVENT);
}
});
}
});
bus.addEventListener(BusEvent.BOB_SUCCESSFUL_EVENT, new BusEventListener() {
#Override
public void onEvent(final BusEvent busEvent) {
charlie.call("c", new Callback() {
#Override
public void onSuccess() {
bus.fireEvent(BusEvent.CHARLIE_SUCCESSFUL_EVENT);
}
});
}
});
bus.addEventListener(BusEvent.CHARLIE_SUCCESSFUL_EVENT, new BusEventListener() {
#Override
public void onEvent(final BusEvent busEvent) {
daisy.call("d", new Callback() {
#Override
public void onSuccess() {
bus.fireEvent(BusEvent.DAISY_SUCCESSFUL_EVENT);
}
});
}
});
bus.addEventListener(BusEvent.DAISY_SUCCESSFUL_EVENT, new BusEventListener() {
#Override
public void onEvent(final BusEvent busEvent) {
// finished
}
});
Under the right circumstances (when it's very clear what each event means, and
if you don't have too many), this pattern can make things very nice and clear.
But in other cases, it can make the control flow more confusing (and you easily get twice the lines of code).
It's harder to use your IDE to find out about the control flow.
The GWT History mechanism is a very positive example for where to use this technique reasonably.
Divide and Conquer
In my experience, it's often a good idea to "divide and conquer" by mixing nesting and named callbacks:
final Callback charlieCallback = new Callback() {
#Override
public void onSuccess() {
daisy.call("d", new Callback() {
#Override
public void onSuccess() {
// finished
}
});
}
};
alice.call("a", new Callback() {
#Override
public void onSuccess() {
bob.call("b", new Callback() {
#Override
public void onSuccess() {
charlie.call("c", charlieCallback);
}
});
}
});
Depending on the situation, two nested callbacks are often still readable, and they reduce jumping around between methods when reading the code by 50%.
(I created a pastebin of my examples here, if you like to play around with them: http://pastebin.com/yNc9Cqtb)
Spaghetti code is a tricky problem in GWT as it is in Javascript, where much of your code is structured around asynchronous callbacks.
Some of the techniques to deal with it that are described in the answers to this question could apply.
The suggested approach to avoid coupling between widgets is to use EventBus. Read more details here https://developers.google.com/web-toolkit/articles/mvp-architecture#events
Hope it helps.
changeview(boolean first){
if(first)
{
firstView.setVisible(true);
secondView.setVisible(false);
}else{
firstView.setVisible(false);
secondView.setVisible(true);
}
}
onClick {
AsyncCallback {
onSuccess {
changeView(false);
}
}
}
Switch between views by above.
Use MVP from very beginning. Use Activities and Places. Your code will be clean.