Here is the problem that I want to implement a solution, I have some data that needs to be writen in a database,data comes from network and it could arrive in "parallel", also for performance reasons the code is using async connection. The problem is that I have some bugs in my implementation ,I want to rewrite this code so it also uses transactions and rolloback,handle all possible errors and the code should be clean and easy to understand.
I am unable to find example code to read to get inspired or something to use directly, looking on what others done would help a lot.
So anyone know or has such example code?
I think I need to write some code that will allow me to chain this methods :begin->execute->commit->end transaction and in case of errors rollback
Update
what I want to find or implement is something like
Update2 so where things get confusing is when you want to insert an array of stuff, you will need to use a loop and then use the execute method async, and then when it succeds insert the next element and so on, this makes it a little more complicated especialy if I want to abstract this ito have all this section of code in a single place and not all over my code.
function executeAssyncAsTransaction(statement:SqlStatement,responder:Responder):void{
//step 1 begin transaction
//step 2 execute
//step 3 commit
//step 4 end transaction
//step 5 handle errors and rollback
//use responders above no event listeners
}
I think I know how to implement this but I know that there is a chance I do it wrong (my current implementation that is in production crashes sometimes on some machines so I I know is hard to write 100% error free code)
I am, also thinking to implement a queue that will store my statements if needed(if database is busy) so I don't get an error and have to try again later
Use event listeners, error and callback functions in Adobe Air for JavaScript like this:
var conn = new air.SQLConnection();
conn.addEventListener(air.SQLEvent.OPEN, openHandler);
conn.addEventListener(air.SQLErrorEvent.ERROR, errorHandler);
// The database file is in the application storage directory
var folder = air.File.applicationStorageDirectory;
var dbFile = folder.resolvePath("DBSample.db");
conn.openAsync(dbFile);
function openHandler(event)
{
air.trace("the database was created successfully");
}
function errorHandler(event)
{
air.trace("Error message:", event.error.message);
air.trace("Details:", event.error.details);
}
For ActionScript read these ressources:
http://de.slideshare.net/peterelst/introduction-to-sqlite-in-adobe-air-1627545
Related
First, I want to mention, I understand how the Firebase onDisconnect method works in JavaScript. It tells the server what to do once the user is disconnected, in advance.
Now, I am using AS3. How should I tell the server the same thing as achieved by the 'onDisconnect' method?
When I tried debugging the code in JavaScript, it doesn't seem to send something to the server.(or maybe i am wrong).
Sample code in JavaScript:
userRef.on('value', function(snapshot) {
if (snapshot.val()) {
userRef.onDisconnect().remove(); //this line does the magic
}
});
What is being done by the onDisconnect method which tells the server what to do? What is the equivalent code if written in AS3?
EDITED:
The code in AS3, as reference by here, it works for Realtime Database.
private var myStream:URLStream;
private function loadLiveFeed():void
{
var header:URLRequestHeader = new URLRequestHeader("Accept", "text/event-stream");
var request:URLRequest = new URLRequest("https://<YOUR-PROJECT-ID>.firebaseio.com/breakingnews.json");
request.requestHeaders.push(header);
myStream:URLStream = new URLStream();
myStream.addEventListener(ProgressEvent.PROGRESS, progress);
myStream.load(request);
}
private function progress(event:ProgressEvent):void
{
var message:String = myStream.readUTFBytes(myStream.bytesAvailable);
trace(message);
}
The code you shared accesses the Firebase Database through its REST API:
new URLRequest("https://<YOUR-PROJECT-ID>.firebaseio.com/breakingnews.json");
This means that it is using a connectionless method to interact with the database. Unfortunately that also means that there is no way to register an onDisconnect() handler, since it would essentially have to fire between any two HTTP calls that you make.
No time to answer this, but you'd have to reverse engineer the communication. Under the hood, it's all just HTTP (or similar) as can be seen in the As3 code. To know what's going on exactly, get a working example code in JavaScript that contains the magic line you are curious about, then execute it in the browser. All requests can be monitored in the developer tools of the browser. You should be able to identify what's being sent.
Also, it's JavaScript, which means you have to have the source code which you can simply read. It might be minified and/or obfuscated, but maybe you can find a readable one.
With the knowledge of what the bare requests look like, you can then implement an API of your own in any language that's capable of performing the necessary network communication.
I'm trying to fill some data from an xml feed we made into my Flash movie. The main action of this is in the constructor for MediaElementJS's .as file.
Anyway, the main problem is that I keep reading there is no way to load a URL synchronously in AS3 (which i still find hard to believe). This constructor calls both parse('url') and a function addEventListener(EVENT.ADDED_TO_STAGE, initializeAds);
Now the ads need info from the XML but the XML aint ready yet. I tried to call the ads at the end of the XML parser when I knew it would be prepped but it messes them up and the ad values never change from their defaults..
Oh wherefor art thou actionscript locking mechanism..
So is there anyway to preload data from a URL?
CODE:
public function LoadXML(e:Event):void
{
removeEventListener(Event.COMPLETE, LoadXML);
var xmlData:XML = new XML(e.target.data);
episodeData.pre.type = xmlData.episode.pre.ad.#type;
episodeData.pre.url = xmlData.episode.pre.ad.text();
episodeData.video = Number(xmlData.episode.video.#id); /*************** I CAN'T REMEMBER ***********/
episodeData.pageTitle = xmlData.episode.video.#pagetitle;
episodeData.title = xmlData.episode.video.#title;
episodeData.source = xmlData.episode.video.source.text();
episodeData.post.type=xmlData.episode.post.ad.#type;
episodeData.post.url=xmlData.episode.post.ad.text();
episodeData.nextEpisode=xmlData.episode.post.nextepisode.text(); //if not empty redirect to this
xmlLoading = false;
//THIS IS WHERE I TRIED TO CALL THE FUNCTION I NEED TO LOAD LATER
}
public function parse()
{
var xmlLoader:URLLoader = new URLLoader();
//var xmlData:XML = new XML();
xmlLoader.load(new URLRequest(rootURL + '/episode.aspx?associd=' + _episode));
//xmlLoader.addEventListener(Event.COMPLETE, processXML);
xmlLoader.addEventListener(Event.COMPLETE, LoadXML);
}
I've tried it with a static URL address and whatnot of course but no dice.
The code in the constructor works if I dynamically assign a static value but if I try chaining to events together to get the dynamic value and dynamic assignment it crunches.
In the constructor, definitely runs both by themselves:
parse();
// Google IMA EventListener
addEventListener(Event.ADDED_TO_STAGE, initialize);
Loading URLs is always asynchronous, so add the event listener in the response function for the URL loader.
Now your question sounds like you tried that but had some problem, so post that code and let us take a look.
Edit START
When I have multiple asynchronous calls that happen and I need something to happen after both of them are done I usually use booleans to store if each one has happened yet, then in a third function they both call I check both the booleans.
Here's how I'd do that:
protected function viewnavigatorapplication1_preinitializeHandler(event:FlexEvent):void
{
var loader1:Loader = new Loader();
var loader2:Loader = new Loader();
loader1.addEventListener(Event.COMPLETE, loader1_completeHandler);
loader1.load(new URLRequest("http://www.whitehouse.gov"));
loader2.addEventListener(Event.COMPLETE, loader2_completeHandler);
loader2.load(new URLRequest("http://www.nasa.gov"));
}
private function loader1_completeHandler():void
{
loader1Done = true;
//Maybe do some stuff here
moveOn();
}
private function loader2_completeHandler():void
{
loader2Done=true;
//Maybe do some stuff here
moveOn();
}
private function moveOn():void
{
if(!loader1Done||!loader2Done)
return;
//Do whatever needs to be done once both asynchronous events have completed
}
If this isn't your problem I think you need to provide more of the code in place of the comments that indicate other things happen, because it is a bit unclear.
For example I'm not sure what you mean by "The code in the constructor works if I dynamically assign a static value but if I try chaining to events together to get the dynamic value and dynamic assignment it crunches." Also since there's no example of the data or what the rootURL is there's no way to debug from here to understand what's going wrong.
Since there's no error we would need to be able to re-compile some portion of your code locally to give any better feedback.
Edit END
Blocking or synchronous calls are a horrible idea with regard to network communications due to the lack of reliability of networks and/or servers. If a front end application locked up to wait for a response before doing any other processing it would result in a horrible user experience, this is why there is no synchronous remote calls.
What happens with a synchronous call when the server bombs out, the client remains locked even though no response will result, the user can't interact with anything else in the front-end because it's waiting for said response which will never come? It's much better that remote calls of any sort are done in an asynchronous fashion, the same is true with local disk access in Java (or otherwise) where using asynchronous non-blocking calls is generally a better way to go to allow the other processes within an application to continue regardless of the state or use on the disk.
What you're doing should work just fine, you make a call to a remote service, it responds with some result and hits your "listener" or "callback" function then you want to do something with the results you can call another function, and the data is there.
It sounds to me like the only thing that's not happening is updates after the fact aren't being reflected in the UI, this is probably due to a lack of Bindable metadata/event dispatching for the properties. Have you inspected the result in the event that returns, have you put breakpoints in the method that is meant to be called after the data has returned? What you're doing is completely possible and it even looks like you have most of it right, but there's definitely something your doing wrong that's resulting in you not being able to make this work. If you can explain the behavior a bit clearer that will help, also what do you do here:
//THIS IS WHERE I TRIED TO CALL THE FUNCTION I NEED TO LOAD LATER
Here's my situation: I'm working on an AS3-based game and I'd like to have a "Report a problem!" function within the game so that users can submit feedback to me.
When my user reports a problem, I'd like to get as much information as I can about the state of their game; basically what objects are in memory, what the values are of all those variables inside all those objects; essentially the same information I can get when I hit a breakpoint in the debugger.
Is there a simple way of doing this? I'm afraid that I'll spend several days trying to write a bunch of functions that gets all this information for me, only to have somebody tell me afterwards, "Oh, why didn't you just call ASUtils.getSnapshot()"?
There is no generic way in AS3 to dump the state of your variables, but there are several things we do that you might find useful:
Capture a log of recent click activity. Use stage event listener to log clicks and trace the object "path" up the parent chain to the stage. The object path is just all the DisplayObject names, like: screenMain.dialogBuyItem.buttonBuy
Capture a screenshot, reduce it to a small thumbnail, JPEG encode it, and upload it to your server along with their feedback. We also do this when there is an exception (see #4). as3corelib has JPEG encoding functions in com/adobe/images
Write a command-line pearl or PHP script you can run on your AS3 code before you publish it that will inject call tracing at the top of each function call. This allows call history to be logged. While it's not as good as a full stack, it will give you some indication of what your code has been doing recently.
Trap asserts and unhandled exceptions and log them to your server with click activity and call history trace. Unhandled exception listeners are new in flash 10.1, but most users have this feature. You can check for that support and add a listener like this:
// Check for the presence of the Flash 10.1 global Error event (exception) handler class.
// If it exists, we'll listen for it and it will allow us to report errors to our server.
if ( loaderInfo.hasOwnProperty( 'uncaughtErrorEvents' ) )
loaderInfo.uncaughtErrorEvents.addEventListener( "uncaughtError", onUncaughtError ); // UncaughtErrorEvent.UNCAUGHT_ERROR
If you have global state variables that you want to log with feedback, you can write a function to dump them to a string for uploading with the user feedback. While you can enumerate class and object properties using for each, this only works for public members. Google around and you'll find some functions people have written to dump objects and array data recursively using this enumeration trick.
i'd like to add it as a comment, but don't want to lose code formatting
this is what i'm using to trace complex objects:
private function parseObject(o:Object, prefix:String = '>'):String {
var retStr:String = '';
for (var s:String in o) {
retStr += prefix + s + ' = ' + o[s] + '\n';
if (typeof(o[s]) == 'object') {
retStr += parseObject(o[s], prefix + '>');
}
}
return retStr;
}
hope it'd be helpful
I'm trying to make a server program for a game, I need to run 3 extra threads in a windows form app. all the threads needs to be able to access the same variables, (thread1: is going to be pulling user commands from my database and executing them, thread2: is going to be updating all the users data and thread3: is going to be sending all the new variables back to the database.) I've looked into background threads and I'm not sure if thats going to do what i want them todo (they look like they could run my code but it looks like they would have a hard time working with the same variables for the all the threads.)
So i guess my question is, is this possible and what is best way to accomplish this, would background workers and invoke do the trick? what problems would i be looking at doing that, anyone have any better idea.
On a side note i had another question thats related ive tried a bunch of times to accomplish this using just simple threads. Now from what i understand doing all of my work on another thread should not lock up my ui, however it does. maybe im doing thread the wrong way, my code looks something like
dim newthread as new system.threading.thread(addressof runmycode)
newthread.start()`
this code isn't exact but why would using threading like this lock up the UI? Shouldn't it be running separately?
You need to create a 'new' instance of the object class to be 'threaded' and expose the function you want to call, e.g.
Public Class MyNewCode
Public Function runmycode()
' My code goes here '
End Function
End Class
Public Class frmMain ' or under an onClick event or whatever.... '
Dim s As New MyNewCode ' This is the class above '
t = New System.Threading.Thread(AddressOf s.runmycode) ' This is the function above '
t.start()
End Class
Here's a tutorial I wrote a little while back that walks you through creating a basic multi-threading program in VB2008. With VB2010 you can remove the delegates if you want but the idea is pretty much the same.
Creating a simple multi-threaded VB.Net application
Let's say that I have a bunch of objects (thumbnails in a matrix for example) and I need to load some data files for all of those over the network (HTTP). So each thumbnail has the thumbnail image itself and an xml file for instance.
There's a number of things that can go wrong from IO errors to bad URLs to badly formatted XML and so on. The question is what is the best / most elegant / most robust way of organizing all of this. What I usually end up doing is having a load manager that tells the
child objects to start loading and then monitors the loading. The child objects have listeners for IO errors and HTTP status events. When all children have loaded everything (with some possible failures) something is done (the thumbnails are shown or whatever).
I was thinking that there has to be a better way of doing this, something that would allow me to maybe use throw clauses when errors occur. Throwing something from the listener isn't going to do much good of course. So what to do. Have a local flag(s) in the child objects and abort if something fails or what?
I am using AS3 but the question should be pretty much the same for other languages, at least for object oriented ones.
Just to be clear I'm not looking for any program code, just general ideas on a design pattern. I also realise that because of the asynchronous load I'm tied in to event handling at least in the child objects.
i use a "queue" package which is able to deal with all sorts of asyncronous operations. the nice thing is you can nest these operations (composite pattern) and create quite complex stuff easily. if events occur you can catch them either at the root as they "bubble up the queue tree) or directly where they originate, depending on the listeners you add.
interface Qable extends IEventDispatcher {
function start()
function stop()
}
interface Q extends Qable {
function add(item:Qable):Q
function remove(item:Qable):Q
...
}
var q1: Q = new Q
q1.add(new Qable(...))
q1.add(new Qable(...))
var q : Q = new Q
q.addEventListener(Event.COMPLETE, onComplete)
q.addEventListener(Event.ERROR, onError)
q.add(new Qable(...))
q.add(new Qable(...)).addEventListener(Event.Error, onItemXError)
q.add(m1)
q.start()