I have to add a control inside a changeCompany() in an existing class.
I suppose the code below is OK, but I have a doubt : Does the "return" order imply that a return to the original company is done ?
Or is there to add a statement, unknown by me, something like revertToPreviousCompany()?
try
{
changeCompany(companyId)
{
// the method will produce a message and return false if an error
if (!this.doSomeChecks()) {
return;
}
// much more code below
Yes that is OK as in some situations you wouldn't even be able to revert it if not done by the runtime itself.
Imagine a callstack in which you have try - catch around some code your are calling and you expect there may be thrown an error but if the code which calls your code already established a transaction your handler is not called and therefore you wouldn't have a chance to undo the changeCompany
Related
[Edit]
The main question here loosely translates as 'is Flex multi-threaded'? I have since found out that it is not, so I won't have data mysteriously changing half way through an operation. The code below worked, but made things awkward and confusing. I eventually fixed the problem with an architecture change, eliminating the need to suppress events. As the first commenter suggested.
Infinite loops were eliminated by changing the way events were listened to and performing certain actions explicitly rather than via events.
Collating events was made easier using a command pattern.
Basically, do not use the code below if you come across this page!
[/Edit]
I'm building some Flex applications using a simple, lightweight MVC pattern. Models extend or encapsulate a dispatcher and fire events when updated. I'm stuck with Flex 3.5.
In some situations, I'll want to suppress these events to avoid infinite loops or help collate multiple actions into a single event.
My first stab at a solution that doesn't litter the models with unnecessary and confusing code is this:
private var _suppressEvents:Boolean = false;
public function suppressEvents(callback:Function):void
{
// In case of error, ensure the suppression is turned off, then re-throw
var err:Error = null;
_suppressEvents = true;
try
{
callback();
}
catch(e:Error)
{
err = e;
}
_suppressEvents = false;
if (err)
{
throw (err);
}
}
public function dispatch(type:String, data:*):void
{
// Suppress if called from a suppress callback.
if (!_suppressEvents)
{
_dispatcher.dispatchEvent(new DataEvent(type, data));
}
}
Obviously I call 'suppressEvents' with a function containing the model code I wish to run.
My questions:
1: Is there a chance I could accidentally lose events using this technique?
2: Do I need to think about any other error edge cases when it comes to ensuring I don't accidentally end up in a suppressed state after a call?
3: Is there a cleaner way I'm missing?
Thanks!
Have a look at this:
function doGeolocation() {
if (navigator.geolocation) {
navigator.geolocation.getCurrentPosition(positionSuccess, positionError);
if(//here i need check)
{
Save();
}
}
else
{
positionError(-1);
}
}
So in the inner 'if' i would like to check if the navigator.geolocation.getcurrentposition(); has successfully completed. Any help will highly be appreciated.
Thanks..
getCurrentPosition does its own check on success, and calls a different function depending on the result.
In your function, on success a function called positionSuccess will be called; if the geolocation fails then positionError will be called.
So you need to provide a function called positionSuccess() which can do the saving. You don't need to do your own check.
Bear in mind that getCurrentPosition will take some time. This is handed off to a separate process [this is called asynchronous processing], and your code will continue to the next line. In your current code, execution will reach the "here I need check" test well before the geolocation result has been found. This is why there are other functions to handle success and failure — there is no guarantee when the result will be returned.
I've recently started programming with PHP again, after a long stint with other languages during which i've developed a more functional style - which i'm hoping to try and maintain.
I've noticed some weird behaviour, which I managed to distill into a testcase that I'm hoping someone can explain.
$func = function($item) {
if ($item == 0)
throw new Exception("Can't do 0");
return $item;
};
try {
array_map($func, array(1, 2, 3, 0, 5));
} catch (Exception $ex) {
echo "Couldn't map array";
}
When executing the above code, i see the following output:
Warning: array_map(): An error occurred while invoking the map callback in map_closure.php on line 10
Couldn't map array
I can suppress the error with # on array_map, but this seems hacky at best.
The warning is generated because, put simply, the callback function is not returning normally (due to throwing the Exception). This is just the way that array_map() is coded, if the callback function does not complete its execution. Remember an Exception breaks out of execution immediately, as far as your PHP code is concerned.
As for how to silence the warning, that's entirely up to you. Unfortunately, the warning will be generated and it's your choice to bury it or let it get displayed.
As an aside, maybe your test case was over-simplified but, it would make much more sense to use array_filter() (or perhaps array_reduce()) there.
As preinhaimer says, array_map makes it really hard for you to see exactly what happened during its execution because it predates exceptions. It would not be practical to change its behavior anymore since that would lead to lots of (poorly-coded) applications breaking; that's life.
If you want a mechanism with which to check if the array_map completed without errors or not, I have posted a detailed answer (with code) to this question which deals with practically the same problem. It's not as easy as try/catch, but you work with what you have.
Either use # or a foreach instead of array_map
array_map() predates exceptions so it still uses warnings. There's a few annoying places in PHP where you're still forced to use error handling, this is one of them.
You're left with options like having it return null or some other un-used value when it encounters a problem, or filtering the array to ensure it only contains valid options before you run it through array_map.
When I'm in the flash debugger, and I have some callbacks saved, I can see that the functions have a property named savedThis that is very usefull to know where that callback came from.
I'm trying to access that property from code, but for some reason I can't.
callback.savedThis throws an Error because it can't find the property, probable because it's private.
So I tried to add a method to the Function class that would give me access to it:
Function.prototype.getSavedThis = function()
{
return this.savedThis
}
But it gives me the same error about not finding the property, even though I can see it in the debugger.
Is there a way to access it?
Note: I'm not planing on using this in production code, I'm making some classes to help me with debugging by automating some data gathering, and it would be incredible useful to get this information without having to add code to every callback saved informing of the this object.
You can get a reference to a calling function by using the 'arguments.callee' property.
For example:
bar( arguments.callee );
public function bar( caller:Function ) : void { trace( caller ); }
I am seeing strange behaviour with the flash.media.Sound class in Flex 3.
var sound:Sound = new Sound();
try{
sound.load(new URLRequest("directory/file.mp3"))
} catch(e:IOError){
...
}
However this isn't helping. I'm getting a stream error, and it actually sees to be in the Sound constructor.
Error #2044: Unhandled IOErrorEvent:.
text=Error #2032: Stream Error. at... ]
I saw one example in the Flex docs where they add an event listener for IOErrorEvent, SURELY I don't have to do this, and can simply use try-catch? Can I set a null event listener?
IOError = target file cannot be found (or for some other reason cannot be read). Check your file's path.
Edit: I just realized this may not be your problem, you're just trying to catch the IO error? If so, you can do this:
var sound:Sound = new Sound();
sound.addEventListener(IOErrorEvent.IO_ERROR, ioErrorHandler);
sound.load(new URLRequest("directory/file.mp3"));
function ioErrorHandler(event:IOErrorEvent):void {
trace("IO error occurred");
}
You will need to add a listener since the URLRequest is not instantaneous. It will be very fast if you're loading from disk, but you will still need the Event-listener.
There's a good example of how to set this up (Complete with IOErrorEvent handling) in the livedocs.
try...catch only applies for errors that are thrown when that function is called. Any kind of method that involves loading stuff from the network, disk, etc will be asynchronous, that is it doesn't execute right when you call it, but instead it happens sometime shortly after you call it. In that case you DO need the addEventListener in order to catch any errors or events or to know when it's finished loading.