As suggested in this question GWT - Where should i use code splitting while using places/activities/mappers?, I created an ActivityProxy to nest my activities.
I based my implementation on this http://code.google.com/p/google-web-toolkit/issues/detail?id=5129 (6th comment), with one modification: I added a check on the provider before calling GWT.RunAsync:
if (provider != null)
{
GWT.runAsync(new RunAsyncCallback()
{
#Override
public void onFailure(Throwable reason)
{
// ...
}
#Override
public void onSuccess()
{
ActivityProxy.this.nestedActivity = provider.create();
//...
}
});
}
But for some reason, this doesn't work in release mode: the onFailure methode is never called but my activity is never displayed the first time I use it. If I reload the place, everything display just fine.
Then I realised that doing the following solves the problem:
GWT.runAsync(new RunAsyncCallback()
{
#Override
public void onFailure(Throwable reason)
{
// ...
}
#Override
public void onSuccess()
{
if (provider != null)
{
ActivityProxy.this.nestedActivity = provider.create();
//...
}
}
});
So even if I don't understand why it works, I started using it for all my activities.
I ran into the problem again when I decided to use a generator for my ActivityProxy (to avoid writing a provider for each Activity). The synthax becomes GWT.create(ActivityProxy).wrap(MyActivity.class);
Basically, the generated code looks like this:
if (clazz.getName() == "FooClass")
{
nestedActivity = new FooClass(); //inside a RunAsync
}
if (clazz.getName() == "BarClass")
{
nestedActivity = new BarClass(); //inside a RunAsync
}
And the same problem occurs: my app fails to display my activities the first time they are used.
So simple question : "Why?"
Related
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.
This question is very useful. There're some questions about calling multiple AsyncCallback but they didn't tell how to call them in a loop.
Here is my problem. I am doing a project using Gwt-platform. I got a presenter TestPresenter.java which has these codes:
#Inject
DispatchAsync dispatchAsync;
private AsyncCallback<GetDataResult> getDataCallback = new AsyncCallback<GetDataResult>() {
#Override
public void onFailure(Throwable caught) {
// TODO Auto-generated method stub
}
#Override
public void onSuccess(GetDataResult result) {
// do Something o show the gui here
}
};
public void load_All_Gui_At_Once() {
for(int i=0; i<5; i++) {
GetData getDataAction=new GetData(i);
dispatchAsync.execute(getDataAction, getDataCallback);
}
}
The problem is that the program show the data but it showed in the wrong order. This is cos the next Async method started to run while the previous one has not finish yet.
Some suggested me to put the 2nd call inside onSuccess, but that is only for simple 2 sync calls. But in my case, I have to loop many unknown number of Async calls, then how can i do it?
This is a question similar to this one. All your calls are executed in the same instant, but the response time is unknown and it is not guaranteed the order. So the solution is almost the same, call the loop inside the callback. Your code should look like:
#Inject
DispatchAsync dispatchAsync;
private AsyncCallback<GetDataResult> getDataCallback = new AsyncCallback<GetDataResult>() {
int idx = 0;
#Override
public void onFailure(Throwable caught) {
// TODO Auto-generated method stub
}
#Override
public void onSuccess(GetDataResult result) {
if (result != null) {
// do Something or show the gui here
}
if (idx < 5) {
GetData getDataAction = new GetData(idx);
dispatchAsync.execute(getDataAction, getDataCallback);
}
idx ++;
}
};
public void load_All_Gui_At_Once(){
// Start the loop, calling onSuccess the first time
getDataCallback.onSuccess(null);
}
Just for example, let's check the code below
private void loadUserFromServer() {
dispatchAsync.execute(new FindLoggedUserAction(),
new AsyncCallback<FindLoggerUserResult>() {
#Override
public void onFailure(Throwable caught) {
//do something
}
#Override
public void onSuccess(BuscarUsuarioLogadoResult result) {
//dosomething with user
result.getUser();
}
operationTwo();
}
My problem is, I have to execute operationTwo(); after some result of dipatcher(Success or failure).
This is just an example, let's assume I can't put operationTwo() inside the onSucess or onFailure()
My real PROBLEM
My GateKeeper of presenters that user must be login.
private UserDTO user;
#Override
public boolean canReveal() {
if(getUser() == null){
ShowMsgEvent.fire(eventBus,"Must Login first", AlertType.ERROR);
return false;
}
return true;
}
}
public UserDTO getUser()
{
if(user == null)
{
//call server
loadUserFromServer();
}
return user;
}
private void loadUsuarioFromServer() {
dispatchAsync.execute(new BuscarUsuarioLogadoAction()
,new AsyncCallback<BuscarUsuarioLogadoResult>() {
#Override
public void onFailure(Throwable caught) {
//something
}
#Override
public void onSuccess(BuscarUsuarioLogadoResult result) {
if(!(result.getDto().equals(user)))
{
setUsuario(result.getDto(), false); //Set user UserDTO user
//event for update Presenter Login/Logout
// and Label with username
fireUserUpdateEvents();
}
else
{
setUsuario(result.getDto(), false);
}
}
});
As you can see, when a Presenter with that Gatekeeper is called and user is null,
getUser() is called, but when dispatch executes, the method doesn't wait until the return of Sucess or Failure
Result: getUser() returns null.
After the sucessful result of dispatch, getUser() returns a DTO. But, as you can see canReveal() already returned false.
Do not think that GateKeeper is a good approach to handle security in your case. You will not be able to reach stable work. Problem that you will have:
You are not handling network connection lost. If you code is already cached but you need to reload User it will be a big problem with double checking.
Sync calls are always problematic, specially with bad network connection. You will have tons of not responding messages.
To handle presenter access it will be better to use revealInParent method. Most of your presenter already overrides it and it looks like:
#Override
protected void revealInParent() {
RevealContentEvent.fire(...);
}
So you can just not fire Reveal event before you actually download user data. In your case the code will looks like:
#Override
protected void revealInParent() {
if(getUser() == null){
RevealContentEvent.fire(...);
return;
}
dispatchAsync.execute(new BuscarUsuarioLogadoAction()
,new AsyncCallback<BuscarUsuarioLogadoResult>() {
#Override
public void onFailure(Throwable caught) {
//something
}
#Override
public void onSuccess(BuscarUsuarioLogadoResult result) {
if(!(result.getDto().equals(user)))
{
setUsuario(result.getDto(), false); //Set user UserDTO user
//event for update Presenter Login/Logout
// and Label with username
fireUserUpdateEvents();
}
else
{
setUsuario(result.getDto(), false);
}
RevealContentEvent.fire(...);
}
});
We have also encountered similar problems. Its better to use Async call chaining. Since you can't do that there are two options for your problem
Setup a timer which will check from time to time whether the user is null or not and return only after when user is populated.
Use JSNI (Native code) and make the synchronous call. But beware this is bad practice
Yes, as Abhijith mentioned in previous answer there are 2 options -
1) Synchronous calls - which GWT doesn't support. So it is ruled out.
2) Setting timer - unless user logs in control will not come out of the timer loop. So failed status will never return from the timer. This approach serves only half of your requierment(serving only success state).
To solve your problem you try the following code snippet -
private UserDTO user;
private CanRevealCallBack revealCallBack;
public interface CanRevealCallBack {
returnStatus(boolean status);
}
#Override
public void canReveal(CanRevealCallBack callBack) {
revealCallBack = callBack;
if(user == null){
loadUserFromServer();
}
else{
revealCallBack.returnStatus( true );
}
}
private void loadUsuarioFromServer() {
dispatchAsync.execute(new BuscarUsuarioLogadoAction()
,new AsyncCallback<BuscarUsuarioLogadoResult>() {
#Override
public void onFailure(Throwable caught) {
//something
}
#Override
public void onSuccess(BuscarUsuarioLogadoResult result) {
if(!(result.getDto().equals(user)))
{
setUsuario(result.getDto(), false); //Set user UserDTO user
//event for update Presenter Login/Logout
// and Label with username
fireUserUpdateEvents();
}
else
{
setUsuario(result.getDto(), false);
}
if(result.getDto() == null){
revealCallBack.returnStatus( true );
}
else{
revealCallBack.returnStatus( false );
}
}
});
So, you have to pass a revealCallback to the canReveal method. CallBack gets executed and returns u the status on success of the async call. In returnStatus method of the callback you can program the logic with the correct user log-in status.
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.
This should not be causing me so much pain but it is. It is a very weird problem. In a GWT application, I have two .java files, login.java and application.java.
In login.java, I'm creating a user login page where if the username and password is verified the user is logged into the application and application.java takes from here.
Now in application. java's onModuleLoad() this is how i'm starting with a login page.
public void onModuleLoad() {
Login login = new Login();
login.textBoxUsername.setFocus(true);
RootLayoutPanel.get().add(login);}
This works great, except for the tiny problem of not being able to set focus on the username TextBox when the page loads. I have tried evrything I can think of. But the focus just doesn't get set on the TextBox. If anyone can suggest a solution, please do. Your help is greatly appreciated.
Solution: (In case it helps anyone facing the same issue)
final Login login = new Login();
Scheduler.get().scheduleDeferred(new ScheduledCommand() {
public void execute () {
login.textBoxUsername.setFocus(true);
}
});
RootLayoutPanel.get().add(login);
Try using Scheduler.scheduleDeferred():
public void onModuleLoad() {
Login login = new Login();
Scheduler.get().scheduleDeferred(new Scheduler.ScheduledCommand () {
public void execute () {
login.textBoxUsername.setFocus(true);
}
});
RootLayoutPanel.get().add(login);
}
Update: answer updated to use Scheduler.get().scheduleDeferred() instead of DeferredCommand, which is deprecated.
Why using DefferedCommand, I think it's better to use someWidget.getElement().focus() which is a native Javascript. I'm using it everywhere, I've not seen any problem.
If your Widget extends Composite, you can:
#Override
protected void onAttach() {
super.onAttach();
textBoxUsername.setFocus(true);
}
It would be so easy for GWT to store a 'wantsFocus' in the internal state, and call focus after the widget is attached. We are still waiting after many years for that feature however...
Still, even after the attach handler is called, setFocus does not always work.
So in the meantime, our GwtUtil library has used the following code. It is a combination of several other solutions, and has been wrapped in a utility function:
static public void setFocus(final FocusWidget focusWidget) {
if (focusWidget.isAttached()) {
Scheduler.get().scheduleDeferred(new Scheduler.ScheduledCommand() {
#Override
public void execute() {
focusWidget.setFocus(true);
}
});
} else {
focusWidget.addAttachHandler(new AttachEvent.Handler() {
#Override
public void onAttachOrDetach(AttachEvent event) {
if (event.isAttached()) {
Scheduler.get().scheduleDeferred(new Scheduler.ScheduledCommand() {
#Override
public void execute() {
focusWidget.setFocus(true);
}
});
}
}
});
}
}
And call it like this:
setFocus(myTextBox);
It makes sense to use a utility function; If and when GWT finally makes setFocus work, you won't have to change your source code in multiple places.