I've read about cancelling fetch requests by using AbortController.abort(). Is there a way to start a request again without aborting it after calling this command?
For example, in this demo from MDN, once Cancel download has been clicked, clicking Download video will trigger the fetch again, but immediately abort it.
Is there a way to allow this request again without aborting it? So, in this case, how could you click Download video to begin the download, click Cancel download to cancel the download, and then click Download video again to start the download again? For example, if the user clicked Cancel download on accident...
You can't.
An AbortController or its signal can not be reused nor reseted. If you need to "reset" it, you have to create a new AbortController instance and use that instead.
I think this is by design. Otherwise it could get messy e.g. if you hand over the controller or signal to some external library and suddenly they could remotely un-abort your internal state.
For example, in this demo from MDN, once Cancel download has been clicked, clicking Download video will trigger the fetch again, but immediately abort it.
They fixed the example. After you click Cancel download you will be able to start a new download and cancel it again, over and over. In order to achieve that the Download button instantiate a new AbortController every time, so you get a fresh signal to abort every time:
downloadBtn.addEventListener('click', fetchVideo);
function fetchVideo() {
controller = new AbortController();
signal = controller.signal;
// ...
So it's ok to instantiate new AbortControllers for each request that you may wish to cancel.
I know this might be kind of late, but I'm leaving this answer anyways in case someone needs it.
I don't know if this is the most optimal approach, but in order to keep doing fetch requests (with 'the same' signal) I had to create a new AbortController instance for each request.
In my case (all code being contained inside a class declaration), I deleted and created a new instance every time, like so:
class Foo Extends Bar {
abort_controller_instance = false;
constructor(params){
super(params);
this.resetOrStartAbortController();
}
resetOrStartAbortController(){
if(this.abort_controller_instance){
delete this.abort_controller_instance;
}
this.abort_controller_instance = new AbortController();
}
abortFetchRequest(){
if(this.abort_controller_instance){
this.abort_controller_instance.abort();
this.resetOrStartAbortController();
}
}
...
}
Probably it's not the most elegant solution, but it works.
Regards!
Related
I need to load a large file to parse and draw with OpenGL. The whole process is very time-consuming. So I want to realize a prompt dialog box before parse. But the code as following is not work.
void parseFile()
{
QMessageBox* msgbox = new QMessageBox();
msgbox->setModal(false);
msgbox->setWindowTitle(tr("message box"));
msgbox->setText("Please wait patiently......")
msgbox->show();
/* parse file and draw */
......
}
But it shows like also be frozen:
How to realize it?
show() does not actually show the content of the dialog. It only tells the event loop to show the dialog ASAP. But since you call more code after immediately after show(), the evnt loop does not have a chance to do its work.
The easiest way to solve this is to call QCoreApplication::processEvents() after msgbox->show(). This will force the event loop to do the work immediately.
If this does not work then try this parameter QCoreApplication::processEvents(QEventLoop::WaitForMoreEvents)
Another option would be to move the heavy calculation to a function and than show the dialog and then schedule the calculation using a timer.
...
msgbox->show();
QTimer::singleShot(0, &doHeavyWork);
This would first handle all events related to showing the dialog and only after that it will start the heavy work (i.e. parsing the file).
Say my application has a list of items of some kind, and users can insert new items in the list.
What Meteor normally does is: when a user inserts an item in the list, it appears in their browser immediately, without waiting for server confirmation.
What I want is: when an item is in this state (submitted but not yet acknowledged by the server), it appears at its correct position in the list, but greyed out.
Is there a way to make Meteor do this?
Sure. Make a method that does the insertion. When the method runs, have it check to see if it is running in simulation, and if so, set a 'temporary' or 'unconfirmed' flag on the inserted item. Use that to decide whether to render the item as greyed out.
Assuming you're using MongoDB:
// Put this in a file that will be loaded on both the client and server
Meteor.methods({
add_item: function (name) {
Items.insert({name: name,
confirmed: !this.isSimulation});
}
});
Calling the method:
Meteor.call("add_item", "my item name");
That's all you need to do. The reason this works is that once the server has finished saving the item, the local (simulated) changes on the client will be backed out and replaced with whatever actually happened on the server (which won't include the 'unconfirmed' flag.)
The above is the simplest way to do it, but it will result in all of the
records in your database having a 'confirmed' attrbiute of true. To avoid this, only set the confirmed attribute if it's false.
Refer to this part of documentation for more information about isSimulation and Meteor.methods
This is what I did added an observer on the server side,
I created a variable called notify false from the client side itself
once the server receives the udpate it will make notify true and the client will be updated on the same.
Collection.find({"notify":false}).observe({
"added" : function(first){
collection.update({"_id":first._id},{$set : {"notify":true}});
}
});
I'm writing a wizard UI based on the QWizard Qt object. There's one particular situation where I want the user to log in to a service using host, username, and password. The rest of the wizard then manipulates this service to do various setup tasks. The login may take a while, especially in error cases where the DNS name takes a long time to resolve -- or perhaps it may not even resolve at all.
So my idea is to make all three fields mandatory using the registerField mechanism, and when the user hits Next, we show a little throbber on the wizard page saying "Connecting to server, please wait..." while we try to connect in the background. If the connection succeeds, we advance to the next page. If not, we highlight the offending field and ask the user to try again.
However, I'm at a loss for how to accomplish this. The options I've thought of:
1) Override validatePage and have it start a thread in the background. Enter a wait inside validatePage() that pumps the Qt event loop until the thread finishes. You'd think this was the ugliest solution, but...
2) Hide the real Next button and add a custom Next button that, when clicked, dispatches my long running function in a thread and waits for a 'validation complete' signal to be raised by something. When that happens, we manually call QWizard::next() (and we completely bypass the real validation logic from validatePage and friends.) This is even uglier, but moves the ugliness to a different level that may make development easier.
Surely there's a better way?
It's not as visually appealing, but you could add a connecting page, and move to that page. If the connection succeeds, call next() on the wizard, and if the connection fails, call previous() and highlight the appropriate fields. It has the advantage of being relatively straightforward to code.
My final choice was #2 (override the Next button, simulate its behavior, but capture its click events manually and do the things I want to with it.) Writing the glue to define the Next button's behavior was minimal, and I was able to subclass QWizardPage with a number of hooks that let me run my task ON the same page, instead of having to switch to an interstitial page and worry about whether to go forwards or backwards. Thanks Caleb for your answer though.
I know this has already been answered (a long time ago!) but in case anyone else is having the same challenge. Another method for this is to create a QLineEdit, initiate it as empty and set it as a mandatory registered field. This will mean that "Next" is not enabled until it is filled with some text.
Run your connection task as normal and when it completes use setText to update the QLineEdit to "True" or "Logged in" or anything other than empty. This will then mean the built in isComplete function will be passed as this previously missing mandatory field is now complete. If you never add it to the layout then it won't be seen and the user won't be able to interact with it.
As an example ...
self.validated_field = QLineEdit("")
self.registerField('validated*', self.validated_field)
and then when your login process completes successfully
self.validated_field.setText("True")
This should do it and is very lightweight. Be sure though that you consider the scenario where a user then goes back to that page and whether you need to reset the field to blank. If that's the case then just add in the initialisePage() function to set it back to blank
self.validated_field.setText("")
Thinking about it you could also add the line edit to the display and disable it so that a user cannot update it and then give it a meaningful completion message to act as a status update...
self.validated_field = QLineEdit("")
self.validated_field.setDisabled(True)
self.validated_field.setStyleSheet("border:0;background-color:none")
self.main_layout.addWidget(self.validated_field)
self.registerField('validated*', self.validated_field)
and then when you update it..
self.validated_field.setText("Logged in")
I need to call FileReference.save() after a web service call has completed, but this method has a restriction: "In Flash Player, you can only call this method successfully in response to a user event (for example, in an event handler for a mouse click or keypress event). Otherwise, calling this method results in Flash Player throwing an Error exception." (from the documentation here)
This restriction is a bit vague. Does it mean that I can only call the FileReference.save() method from within an event handler function that is registered as a listener for certain types of user events? If so then exactly which user events are valid? (Perhaps there's an event that will never be dispatched by user interaction with my application and I could register an event handler function for that event type and make the save() call from within that function?)
My difficulty is that I can't safely call the FileReference.save() method until my web service returns with the data that will be used as the argument of the FileReference.save() method call, so the event that triggers the FileReference.save() call is actually a ResultEvent rather than a user event, and I'm leery of dispatching a new (faux) user event type in order to be able to trigger the FileReference.save() call unless it's definitely a user event that would never be dispatched as a result of actual user interaction with my application.
In a nutshell what I'm doing now is this: I have a function that is registered as a handler for a button click. In this function I make my web service call to fetch data from the server. I also have a result handler function which gets invoked when the web service call completes, and it's in here that I want to call the FileReference.save() method since it's at this point that I know that the data is ready to be saved to a file. But the aforementioned restriction is blocking me from doing this -- I get an error:
Error #2176: Certain actions, such as those that display a pop-up window,
may only be invoked upon user interaction, for example by a mouse click
or button press.
I've tried many things to get around this such as creating a second mouse click event handler function with the FileReference.save() call within and calling it after a timeout interval (to give the web service time to complete), but I keep running into the same error -- maybe that approach doesn't work since the second function isn't registered as an event listener for the event type used as its argument.
I'm new to Flex development so perhaps I'm just not thinking about this in the right way. If anyone can suggest another approach I'd really appreciate it. Thanks in advance for your comments or suggestions.
--James
Adobe does this as a sort of security measure to ensure users are the ones messing with files rather than potentially harmful code. My understanding is that they enforce this by only allowing handlers of (click?) events that originate from UI components to execute the FileReference methods, so generating your own events programmatically will not work, although I have not tried to verify this. Unfortunately the best resolution I've found is to re-work the UI a bit to conform to this constraint. In your particular situation, you could make this a two click process with a button that says something like "Prepare Download", which changes to "Download File" after the web service is complete. This is less than ideal from a user perspective, but I don't think there's much else that can be done unless you can somehow complete your web service call prior to displaying the button that triggers the FileReference.save() call.
After struggling for that for well, a couple hours I found a workaround: you can use both mouseDown AND mouseUp events instead of just click.
For instance:
s:Button
mouseDown="prepare_PDF()"
mouseUp="save_PDF()"
Works fine for me!
Happy coding!
--Thomas
As a workaround I used the ExternalInterface class. I created a javascript function with this code
function downloadFile (url) {
window.open(url);
}
An in AS3 I call
var url = 'www.example.com/downloadfile.php?file_id=xxx';
ExternalInterface.call('downloadAttachmentFile', url);
So with that I transfer the file handling to JS/HTML.
This is a comment on Thomas' answer (I don't have enough XP to comment yet): The mousedown and mouseup workaround works nicely. Just a note that if you make any changes in prepare_PDF() that need 'undoing' in save_PDF(), then its a good idea to call that code on the mouseout event as well, since there might be a case that the user mousedown's on the button, but then moves the mouse away from the button.
This was particularly relevant for my case, in which we increase the size of a watermark on an image when the user clicks the download button (that triggers the .save() call). I reduce the size of the watermark down to normal on the mousedown and mouseout events.
I had this same issue, I chose to use flash.net methods. Call flash.net.navigateToURL(url); from an actionscript or navigateToURL(url); from mxml.
What i do to solve this is to show an alert message with an anonymous function so i don't have to create a button.
Alert.show("Do you wish to download the file?", "Confirm", Alert.OK | Alert.CANCEL, this, function (eventObj:CloseEvent):void {
if (eventObj.detail == Alert.OK) {
fileReference.save(zipOut.byteArray, dateFormater_titulo.format(new Date ()) + ".zip");
}//if
}/*function*/, null, Alert.OK);
So I'm trying to build a tool that will allow me and other users to all open the same .swf, and then I as the Admin user am able to interact with mine while they all see my mouse movements and button clicks etc on theirs.
I'm using BlazeDS to manage this and I'm getting data sent back and forth etc - no difficulties there. The issue I'm running into is this:
In an "Admin" instance, I click a button. I capture that X and Y, then tell Blaze to tell my clients to dispatch a Click event at that X and Y. On my client side, I get that data and dispatch a Click event at that X and Y - but the click is actually caught at the stage level. The click on my client side takes place UNDER all of my buttons and other content - so the whole thing fails.
Does this make sense? Is there a way to tell it to start the click event at the top?
If you are unable to architect the loaded swf's to use a better architecture you could try something a little more hackish to get buttons working.
Have a look at the methods getObjectsUnderPoint and areInaccessibleObjectsUnderPoint of the DisplayObjectContainer. Combined with hasEventListener you should be able to emulate what you want.
Here is some untested pseudo-code:
function detectClick(pt:Point):void
{
var objsUnderPoint:Array = containerStage.getObjectsUnderPoint(pt);
var clickable:Array = [];
for each(dispObj:DisplayObject in objsUnderPoint)
{
if(dispObj.hasEventListener(MouseEvent.CLICK))
{
clickable.push(dispObj);
}
}
if(clickable.length)
{
// sort on depth here
// that might be tricky since you'll be looking at grandchildren
// and not just children but it is doable.
var topMostClickable:DisplayObject = ???
topMostClickable.dispatchEvent(new MouseEvent(MouseEvent.CLICK, true, false));
}
}
areInaccessibleObjectsUnderPoint is important if you think their might be security restrictions (e.g. cross-domain issues) so you can debug if things go wrong.
Also note that you may want to (or need to) fill in more details of the MouseEvent (like the proper target, localX, localyY etc.)
Sounds like you need to set focus to the top most component of the x and y positions before dispatching the click event.
That said, I wonder what the use case is for something like this; as opposed to using a screen sharing tool such as Connect.
This seems like a poor way to implement what you are trying to do. If you "click" in the admin tool you are probably actually triggering some event. Why not trigger that event instead of sending the mouse click?
I'd just keep a map of actions and then when something happens in the Admin interface send the key to the action.
e.g.
In the admin:
myButton.addEventListener(MouseEvent.CLICK, handleClickButton);
function handleClickButton(event:MouseEvent):void
{
doSomeAction();
sendTriggerToClient(MyActions.SOME_TRIGGER);
}
In the client:
var actionMap:Object = {};
actionMap[MyActions.SOME_TRIGGER] = doSomeAction;
function receiveTriggerFromAdmin(trigger:String):void
{
var responseFunc:Function = actionMap[trigger];
responseFunc();
}
I hope that pseudo-code makes sense. Just abstract what happens as a result of a click into a separate function (doSomeAction) and then have the admin send a message before calling that function. In the client wait for any trigger that comes through and map it to the same function.