I am using RemoteObjects to call ZendAMF PHP from Flex/Flash Builder 4.6. I want to stop or abort a method call before it sends the request to the server based on an event or similar.
I have a class where I create and store all the RemoteObjects - for example:
activityLogService = new RemoteObject("zend");
activityLogService.endpoint=endpointServer;
activityLogService.addEventListener(FaultEvent.FAULT,faultHandler);
Then later I can simply call this object:
remotingService.activityLogService .getRecords();
I am trying to find a way in my remotingService object to stop the request - and not send anything to the server - for example if some variables are not set properly.
I noticed there is an invoke event:
activityLogService.addEventListener(InvokeEvent.INVOKE,invokeHandler);
However, I can not tell if that's going to stop things at the proper point, or if it's even possible to actually STOP the request - if so, how?
Thanks!
Check out this question
Flex : Is it possible to stop a remote call?
If you're using a RemoteObject you should be able to call
getOperation() method and then cancel() on the corresponding
operation.
Related
We have a case where we only want one HTTP request to go out at a time and only want to allow retry or call again if the pending call either succeeds or fails. We've been doing the classic wrap it in a boolean but were wondering if there was an operator for it. My hunch is no.
I think you would need switchMap. It will only subscribe to the last value of the external observable and it will map it to an internal observable. With switchMap, its possible to cancel previous http requests on the fly.
For more info take a look in the following link
I am using an http service object to make servlet requests inside a method in flex. The method is being invoked simultaneously in parallel by two events. I could see that both requests have reached the servlet, but only one returns to the result event. Also this behaviours is not consistent . is it possible that parallel invocation of the httpservice result in loss of some requests? I am sure that both requests have reached the servlet and data is returned from it. Its just that the result event is not triggered in certain cases.
Thanks in advance.
Including code to describe the issue better.
Please find the method below. The below method "callServlet" is being invoked by two separate events
private var httpObj:HTTPService=new HTTPService();
private function callServlet(text:String):void{
Alert.show(text);
httpObj = new HTTPService();
httpObj.url=<servlet URL>;
httpObj.method="POST";
httpObj.resultFormat="xml";
httpObj.contentType="application/xml";
var requestString:String=text;
httpObj.request=requestString;
httpObj.addEventListener(ResultEvent.RESULT,onResultMethods);
httpObj.addEventListener(FaultEvent.FAULT,onFaultMethod);
httpObj.send();
}
Each time i call the method, i pass a different "text" variable. I can see that the alert displays the two different texts send to it. And as explained earlier, both requests does reach the servlet and a response is sent from servlet.
But the result event "onResultMethod" is invoked just once.It doesnt invoke the "faultonFaultMethod" either.
Yes, I have seen this problem before, if you are making multiple requests from flex, some of them will be lost, that was back in 3.0 times. Browsers has a way of stopping the number of http calls, they can allow maximum of 2 calls at a time(depends on the browser), may be chain your requests one after the other or use a singleton which manages your calls.
Thanks all for help. I think i ve got the issue though i cannot guarantee the answer to be right.
The above method is called twice by two events. The httpOject variable is a private var global to the method callServlet. The listeners created in this method are being removed in the result and fault handler methods(this is not shown in the code above).
So i believe when multiple events call the method simultaneously there is a chance that the global variable httpObj is modified by both the events and hence both events result in servlet call using the same httpservice object. When the first call returns to the resulthandler i am removing the listener for resulthandler due to which the second result does not reach the resulthandler method.
This is my assumption and as of now i dont have any better solution. Do let me know if anyone comes up with a better explanation.
In Signalr, is there any support for having events instead of callbacks.
Let me explain before you grab your pitchforks.
In following with the first example here
Clients.All.addContosoChatMessageToPage(name, message);
Wouldn't call a hub proxy's addContosoChatMessageToPage(name, message), but would dispatch a addContosoChatMessageToPage event with some extra information. (not asking that it be the same api call exactly)
The reason I'm asking all of this is because
This works much better alongside functional reactive programming frameworks like ELM and bacon.js
I don't want to do this myself and essentially create my own sub-framework. Of course I could always do Clients.All.CreateEvent(name,params...) where I'm continually calling back my method to do this event creation
I actually think events work better in some scenarios for separation of concerns.
Am I crazy? does something like this exist?
This is already supported. If you don't want to do the dispatching yourself and you know the name of the "event" or "method" at runtime you can do this:
IClientProxy proxy = Clients.All;
proxy.Invoke(name, args);
This lets you write code where you may not know the name of the event you're trying to callback on the client at compile time.
I have a need to validate a field against our database to verify unique-ness. The problem I seem to be having is that the validators doValidation() exits before we've heard back from database.
How can I have the validator wait to return its payload until after we've heard from the DB?
Or perhaps a better question might be (since I think the first question is impossible), how can I set this up differently, so that I don't need to wait, or so that the wait doesn't cause the validation to automaticallly return valid?
If you're using a remote object, you can specify the method call inside your remote declaration and assign a function to the result call. The result call only runs once the remote server returns something, so it won't be run before your validation.
Do your validation call in said result function call (which you will have to create) and you should be good. Your code should go something like this:
<s:RemoteObject id="employeeService"
destination="ColdFusion"
source="f4iaw100.remoteData.employeeData"
endpoint="http://adobetes.com/flex2gateway/"
result="employeeService_resultHandler(event)"/>
**<s:method name="dataCheckCall" result="dataCheckResult(event)"/>**
<s:RemoteObject />
And in your script:
function protected dataCheckResult(event:ResultEvent):void {
**doValidate();**
}
Edit: As soon as you call "dataCheckCall" the method will start running. If, for whatever reason, you want to call this WITHIN your validator, you can do so, and then dataCheckResult will run whenever it returns with it's payload (pretend doValidate is called elsewhere). I've left a message below as well.
You are trying to fit an asynchronous process (fetching data from a DB) into a synchronous process (checking all the validators in turn).
This won't work...
You'll need to either roll your own validator framework, or use a different method of determining the legality of your controls.
P.S. The MX validators are rubbish anyway!
What I've managed to do, seems to work, mostly. I don't like it, but it at least performs the validation against the remote source.
What I've done, then, is to use an 'keyUp' event handler to spin off the database lookup portion. In the meanwhile, I set up a string variable to act as some kind of a Flag, which'll be marked as 'processing'. When the response event fires, I'll examine its contents, and either clear the flag, or set it to some kind of other error.
Then, I have created a new 'EmptyStringValidator' will check the contents of this flag, and do its job accordingly.
Its indirect, but, so far, seems to work.
I have a function that loads a user object from a web service asynchronously.
I wrap this function call in another function and make it synchronous.
For example:
private function getUser():User{
var newUser:User;
var f:UserFactory = new UserFactory();
f.GetCurrent(function(u:User):void{
newUser = u;
});
return newUser;
}
UserFactory.GetCurrent looks like this:
public function GetCurrent(callback:Function):void{ }
But my understanding is there is no guarantee that when this function gets called, newUser will actually be the new user??
How do you accomplish this type of return function in Flex?
This way madness lies.
Seriously, you're better off not trying to force an asynchronous call into some kind of synchronous architecture. Learn how the event handling system works in your favour and add a handler for the result event. In fact, here's the advice straight from the flexcoders FAQ :
Q: How do I make synchronous data calls?
A: You CANNOT do synchronous calls. You MUST use the result event. No,
you can't use a loop, or setInterval or even callLater. This paradigm is
quite aggravating at first. Take a deep breath, surrender to the
inevitable, resistance is futile.
There is a generic way to handle the asynchronous nature of data service
calls called ACT (Asynchronous Call Token). Search for this in
Developing Flex Apps doc for a full description.
See my answer here:
DDD and Asynchronous Repositories
Flex and Flash Remoting is inherently asynchronous so fighting against that paradigm is going to give you a ton of trouble. Our service delegates return AsyncToken from every method and we've never had a problem with it.
If you want to ensure that the application doesn't render a new view or perform some other logic until the result/fault comes back, you could do the following:
Attach an event listener for a custom event that will invoke your "post result/fault code"
Make the async call
Handle the result/fault
Dispatch the custom event to trigger your listener from #1
Bear in mind this going to lead to a lot of annoying boilterplate code every time you make an async call. I would consider very carefully whether you really need a synchronous execution path.
You can't convert async call into sync one without something like "sleep()" function and as far as I know it is missing in AS3. And yes, it is not guaranteed that newUser would contain user name before return statement.
The AS3 port of the PureMVC framework has mechanisms for implementing synchronous operations in a Model-View-Controller context. It doesn't try to synchronize asynchronous calls, but it lets you add a synchronous application pattern for controlling them.
Here's an example implementation: PureMVC AS3 Sequential Demo.
In this example, five subcommands are run sequentially, together composing a whole command. In your example, you would implement getUser() as a command, which would call commandComplete() in the getURL() (or whatever) callback. This means the next command would be certain that the getUser() operation is finished.