Using Silverlight 3 with RIA: What's the difference between the LoadOperation.Completed event and using a callback through the DomainContext.Load method? Both fire asynchronously and both provide access to the LoadOperation. When/why would I use one over the other?
Thanks :-)
There's no difference; the 2 options are offered for flexibility. Many times, the callback will suffice, but if you return the LoadOperation from a method, the caller could then choose to subscribe.
Note that even if the Load completes before you subscribe to the Completed event, your handler will still get called. We guarantee every subscriber to the event will be called.
Agreed that there is not difference in functionality. It's about coding style. If the work I have to do following completion of the query is simple, like binding data to a grid, I like the use the following syntax to inline the completed code, rather than defining a separate method.
context.Load<EntityType>(query).Completed += (lo, args) =>
{
myGrid.ItemsSource = ((LoadOperation) lo).Entities;
}
This has the cleanliness of synchronous code, but the code inside the braces will in fact be executed asynchronously.
Good luck!
Related
I am using Cmocka for unit test and that cannot be changed.
I am testing part of my software which invokes callback functions, if a value changes, indicating which data item changed and what the new value is.
The callback functions have this signature:
typedef void (* Value_changed_call_back) (int item_Id, int new_value);
For unit test, I want to register some callback functions and ensure that they are actually invoked, and that they receive the correct parameters.
I can use expect_int() in my mocks, to validate that they are invoked with the correct parameters.
But, I don't see how I can use will_return() since my call back functions are of type void (and that can't be changed).
How would I declare a mock callback function and verify that it is called with the correct parameters? Note that if the function is not called, then the test should fail.
I saw this post and thought about this in CMocka API.
You can use expect_function_call(func) to indicates which function should be called and function_called() in the callback to mark the function as called.
I'm not sure since how long this feature is available (but present in 1.1.5 version).
I answered to this question in case someone comes across this topic even if it's a 2016 ask.
I think the best way to do what you want is to create a stub for the callback and register that. Then inside the callback you set some global variable to a value. Then you would be able to assert that value that gets set in your stub function. This works so long as the assert and the callback are executed on the same thread to make sure that the assert is not a race condition.
I'm looking for a way to use a handler function to respond to changes to an observable collection in Dart. I want to pipe my change directly to a function.
List things = toObservable([]);
//...
things.onChange.listen((e) => onThingsChanged(e) ); //blows up
//...
function onThingsChanged(e){
//...
}
There obviously isn't such thing as onChange, so what am I looking for here? All the examples I find are just watching the changes with a <template> tag in the HTML.
There is a good (official) article about Observables and Data Binding with Web UI. I think it is still under construction and thus there are no links on the dartlang.org website yet.
The part that answers your question is: Expression Observers
You can do something like this:
List things = toObservable([]);
observe(() => things, onThingsChanged);
onThingsChanged(ChangeNotification e) {
// ...
}
Few additions to Marco's answer which might not be obvious.
Besides observe which takes an expression, you can also use observeChanges which takes an instance of Observable, so you can write observeChanges(things, (c) => ...).
More important is the fact that if you use ObservableList outside of Web UI context (e.g. in a standalone script), the changes will not be triggered immediately. Instead, changes are queued and you need to call deliverChangesSync to trigger the notifications. The listener will then get notified with list of changes.
If I write the following Dart code, how do I know which click handler happens first?
main() {
var button = new ButtonElement();
var stream = button.onClick.asBroadcastStream();
stream.listen(clickHandler1);
stream.listen(clickHandler2);
}
Let's say I'm in other code that doesn't know anything about the first two click handlers, but I register another one.
Can I know that the stream has two listeners?
Can I pause or cancel all other subscribers?
If I write button.onClick.asBroadcastStream() again elsewhere, does it point to the same stream as was used in main?
Can I say in one of the handlers to not pass event on to the other broadcast listener? Is that a consumer?
Let's say I'm in other code that doesn't know anything about the first
two click handlers, but I register another one.
Can I know that the stream has two listeners?
No, you can't. You could extend the stream class or wrap it and provide this functionality yourself, but it does not feel like a good design choice, because I don't think a listener should know about other listeners. What are you trying to do exactly? Perhaps there's a better way than letting listeners know about each other.
Can I pause or cancel all other subscribers?
You can cancel/pause/resume only the subscriber you are dealing with. Again, you probably shouldn't touch other listeners, but I guess you could wrap/extend the Stream class to have this behavior.
If I write button.onClick.asBroadcastStream() again elsewhere, does it point to the same stream as was used in main?
No, at least not at the current version of SDK. So, unfortunately, you need to store a reference to this broadcast stream somewhere, and refer to it, because calling asBroadcastStream() multiple times will not yield in the result you might expect. (Note: at least based on quick testing: http://d.pr/i/Ip0K although the documentation seems to indicate different, I have yet to test a bit more when I find the time).
Can I say in one of the handlers to not pass event on to the other broadcast listener?
Well, there's stopPropagation() in the HTML land which means that the event won't propagate to other elements, but it's probably not what you were looking for.
For being able to stop an event firing in other listeners, there needs to be an order of which the listeners are getting called. I believe the order is the order of registration of those listeners. From the design perspective, I don't think it would be a good idea to allow a listener to cancel/pause others.
Event propagation in HTML makes sense since it's about hierarchy, but here we don't have that (and even in case of events in HTML there can be multiple listeners for the single element).
There's no way to assign weight to listeners or define the order of importance, therefore it's not surprising that there isn't a way to stop the event.
Instead of letting listeners know about each other and manipulate each other, maybe you should try to think of another way to approach your problem (whatever that is).
Is that a consumer?
The StreamConsumer is just a class that you can implement if you want to allow other streams to be piped into your class.
Can I know that the stream has two listeners?
No, you have a ´Stream´ that wraps the DOM event handling. There is no such functionality.
Can I pause or cancel all other subscribers?
Look at Event.stopPropagation() and Event.stopImmediatePropagation(), and possibly Event.preventDefault().
If I write button.onClick.asBroadcastStream() again elsewhere, does it point to the same stream as was used in main?
[Updated] No, the current implementation doesn't gives you the same Stream back since the onClick getter returns a new stream every time it is invoked. However, the returned stream is already a broadcast stream so you shouldn't invoke asBroadcastStream() on it. If you do you will hower just get a reference to the same object back.
Stream<T> asBroadcastStream() => this;
Can I say in one of the handlers to not pass event on to the other broadcast listener? Is that a consumer?
Again, take a look at Event.stopPropagation() and Event.stopImmediatePropagation(), and possibly Event.preventDefault().
Despite my best efforts, I am unable to produce the kind of synchronization effects I would like to in ActionScript. The issue is that I need to make several external calls to get various pieces of outside information in response to a user request, and the way items will be laid out on the page is dependent on what each of these external calls returns. So, I don't care that all of these calls return asynchronously. However, is there any way to force some amount of synchronization on ActionScript, so that at least calling the method for doing the final layout and placement of items on the page is dependent on all of my calls finishing?
If I understand the question right, event listeners are probably your best bet. Most loader classes throw an Event.COMPLETE message when they finish doing everything behind the scenes. If you wrote those external calls, it would be easy to dispatch a complete event at the end.
So when you make all these external calls, have a function that listens to when those calls complete. This function would keep track of how many calls have been made, and when there's none left to run, continue building your layout.
Rough Sketch to explain below:
var numProcesses:int = 0;
slowthing.addEventListener(Event.COMPLETE,waitForSlowest);
numProcesses++;
slowthing.load();
quickThing.addEventListener(Event.COMPLETE,waitForSlowest);
numProcesses++;
quickthing.load();
function waitForSlowest(e:Event)
{
numProcesses--;
if(numProcesses == 0)
finalizeLayout();
}
I am creating an action script library.I am calling some APIs which parses some xml and gets me the result. It dispatches an Event.COMPLETE when the parsing is done. I want to monitor whether this event is dispatched in some while loop like "while(eventnotdispatched)"
is it possible? I know the other way would be to addeventlistener. But please let me know if the other thing is possible.
Thanks
NO, it is not possible. Actionscript is single threaded. Thus while you are waiting in your while loop, that is the only thread running, and the process you are waiting for can never complete. This is why everything is done with events, so that's what you should use. If you need to update your display periodically while you are waiting for something to complete...again, use events. Create a Timer object which generates a TIMER event every so often, and use that to make your updates.
EDIT: Davr is right, you would not be able to use the while loop like this. You would need a timer.
Yes, it is possible to poll for it. BUT you will still need to create an event listener. It will work something like this:
private var loadCompleted = false;
private var timer:Timer= new Timer(1);
private function onInitCompleted(event:Event):void
{
timer.addEventListener(TimerEvent.TIMER, timerHandler);
timer.start();
}
private function loadCompleteEventHandler(event:Event):void
{
loadCompleted = true;
...
}
private function timerHandler()
{
if(!loadCompleted)
{
... // stop the timer or something.
timer.stop();
}
}
Please note, this is VERY BAD code. I would NEVER use it in production because Actionscript is a event driven language. There should be absolutely NO REASON for you to need to do this. Whatever you are trying to do could be accomplished using another method much simpler. Tell me what you are trying to accomplish with this and I will present a better solution.
Sorry for yelling, it's late and I am sleepy.
Doing that means forcing a synchronous model of execution on the underlying asynchronous model (that works with callbacks).
What are you trying to achieve exactly, and why not use a callback?
I agree with the statements about it probably being a bad idea and a while loop will certainly not work this way in ActionScript. However, there may be legitimate reasons for doing what you are attempting to do. Only you can prevent bad code. Instead of judging, I'll just get to an answer for your question.
First I'm going to make an assumption, that what you really want to do is monitor a property and for some reason the API for this object does not dispatch an event when this property changes. I'm making this assumption because if you have the event available, I assume you would just use the event.
So... you have an object weirdXmlObj with a property loaded that defaults to false but goes to true when the XML is loaded.
In this case with slight modifications the code posted by CookieOfFortune would in fact work. You wouldn't need the loadCompleteEventHandler function (which was never attached anyway) and in the timer handler you would simply check if( weirdXmlObj.loaded ) and then branch however you wanted to.
Ah but there may be a simpler way, depending on what you are doing.
If you have a display object handy. (i.e. something that makes sense, not just some random object.) You can attach your code to the stage's EnterFrame event instead of using a timer.
myDisplayObject.stage.addEventListner(Event.ENTER_FRAME,frameEnterHandler);
A couple of things to be aware of:
You don't really even need to go to the stage level, all display objects support the EnterFrame event, but it's a nice place to attach the event listener.
You really should keep whatever the function calls to a minimum. In particular the actual frameEnterHandler function should do nothing more than do the if( weirdXmlObj.loaded ) check.
You are attempting to circumvent event-driven programming, which is not a good idea. This is often the case when someone approaches from an older model and does not yet have a good frame of reference to appreciate the elegance of event-driven programming.
Events are your friends. They work very well. Your loadCompleteHandler is all that is required. Want to do something else in response? Add the call in that handler:
private function loadCompletedHandler(event:Event):void
{
waitingObject.fileWasLoadedSoGoDoThatThing();
}
There is no need to make it any more complicated than that. No need for a semaphore or a loop to check the semaphore. Unnecessary environmental semaphores can break the encapsulation that could shield you from unwanted side effects.