UIView element not updating - multithreading

I need to get data from a API I’ve used debug prinln’s and these print almost instantly including the information gotten from the API, but when I try to display this info to the user in the ViewController this takes around 30 seconds to display.
I will get the information from the API here
func httpGet(request: NSURLRequest!, callback: (NSData?, String?) -> Void) {
var session = NSURLSession.sharedSession()
var task = session.dataTaskWithRequest(request){
(data, response, error) -> Void in
if error != nil {
callback(nil, error.localizedDescription)
} else {
callback(data, nil)
}
}
task.resume()
}
I invoke the request and return a string for debugging
func loadSchedule() {
httpGet(request) {
(data, error) -> Void in
onComplete(“Milo Cesar”)
}
And here I will display the data to the user
#IBAction func settingsButtonPress(sender: AnyObject) {
println("Settings Button Pressed: Invoking Schedule")
Schedule().loadSchedule(){
(scheduleData) in
println("Found Schedule: Setting Title to \(scheduleData)")
self.settingsButton.setTitle(scheduleData, forState: UIControlState.Normal)
}
}
The whole process from the “Settings Button Pressed: Invoking Schedule” statement in my console till I get “Found Schedule: Settings Title to Milo Cesar” takes less than a second.
Since the name already gets displayed in that console log I think that the information has been loaded. Though it takes up to 35 seconds for the Button to change it’s title.
Why does it take so long for my UIButton to update it’s title after the data has been retrieved?

Are you sure you are updating its title in main thread? try to wrap it up in GCD
dispatch_async(dispatch_get_main_queue()){
self.settingsButton.setTitle(scheduleData, forState: UIControlState.Normal)
}
EDIT
it fixes it because everything UI related must be performed by main thread, its a restriction that comes directly from Apple. You can use background threads for long taking tasks(download data, perform long taking calculations or sort large arrays) but everything that needs to be displayed on your screen must be performed by main thread(tableview reload, animations, inserting text into label).
Also here is a great tutorial on GCD and its functionality: http://www.raywenderlich.com/60749/grand-central-dispatch-in-depth-part-1

Related

Acumatica return to function with PXLongOperation

I'm creating an integration for Acumatica that loads data from another application to synchronize inventory items. It uses an API call to get a list (of up to 5000 items) and then I'm using PXLongOperation to insert or update these items. I can't run it without this method as the large batches (aka inserting 5000 stock items) will timeout and crash.
The processing form is a custom table/form that retrieves this information then parses the JSON list of items and calls a custom function on the InventoryItemMaint graph. All that works perfectly, but it never returns to the calling function. I'd love to be able to write information to record to record that it was a success or failure. I've tried PXLongOperation.WaitCompletion but that doesn't seem to change anything. I'm sure I'm not using the asynchronous nature of this correctly but am wondering if there is a reasonable work around.
// This is the lsit of items from SI
List<TEKDTools.TEKdtoolModels.Product> theItems;
if (Guid.TryParse(Convert.ToString(theRow.DtoolsID), out theCatID))
{
// Get the list of items from dtools.
theItems = TEKDTools.TEKdtoolsCommon.ReadOneCatalog(theCatID);
// Start the long operation
PXLongOperation.StartOperation(this, delegate () {
// Create the graph to make a new Stock Item
InventoryItemMaint itemMaint = PXGraph.CreateInstance<InventoryItemMaint>();
var itemMaintExt = itemMaint.GetExtension<InventoryItemMaintTEKExt>();
foreach (TEKDTools.TEKdtoolModels.Product theItem in theItems)
{
itemMaint.Clear();
itemMaintExt.CreateUpdateDToolsItem(theItem, true);
PXLongOperation.WaitCompletion(itemMaint.UID);
}
}
);
}
stopWatch.Stop(); // Just using this to figure out how long things were taking.
// For fun I tried the Wait Completion here too
PXLongOperation.WaitCompletion(this.UID);
theRow = MasterView.Current;
// Tried some random static values to see if it was writing
theRow.RowsCreated = 10;
theRow.RowsUpdated = 11;
theRow.Data2 = "Elasped Milliseconds: " + stopWatch.ElapsedMilliseconds.ToString();
theRow.RunStart = startTime;
theRow.RunEnd = DateTime.Now;
// This never gets the record udpated.
Caches[typeof(TCDtoolsBatch)].Update(theRow);
One possible solution would be to use the PXLongOperation.SetCustomInfo method. Usually this is used to update the UI thread after the long operation has been finished. In this "class" you can subscribe to events which you can use to update rows. The definition of the class is as follows:
public class UpdateUICustomInfo : IPXCustomInfo
{
public void Complete(PXLongRunStatus status, PXGraph graph)
{
// Set Code Here
}
}
The wait completion method you are using, generally is used to wait for another long operation to finish by passing the key of that long operation.

Run Service in background Thread

Can I run Service in background thread?
I want to load data from database and during loading data i want progress bar to be indicating progress. First I have created task, run it in background thread and then update progress bar according to this task. However, I found out that this Task is not reusable, so next time i hit the button, it didn't work. Later on, I fount out that Service can run Tasks multiple times, So i have encapsulated those tasks inside of Service.
Now it works great - every time i hit button, table is reloaded - except progress bar is not moving.
How can I reach desired result?
Okay... Here is completed code: https://mega.nz/#!yUsjgJyZ!DHfuBqsujAHurS-pQ_W5y8BAflOtvxsm48goRPkDsxA
First, i want to tell you what is my goal:
When I run program, i want the progress bar to be in indeterminate state. After pressing the button, i want progress bar to reflect progress of Service. After finishing the Service, i want the progress bar to be completed (100%).
Here is what i have found. It looks like service automatically runs it's task on background thread. I have built a "sand box" program where i was playing with services and progress bar. The program comprised of progress bar, two text fields with two buttons above them. First button can start service_countTo100 and second button can run service_getActualCount.
Now in fxml file i set progress bar to indeterminate default state. After pressing the button1, a counting has started (displayed in text_field1) and progress bar has changed according to actual progress. After pressing button2, actual value of count is displayed in text_field2. And here comes some issues. To demonstrate the issues, i will show you source code of Service:
// Create the service
public static Service<Integer> serviceTo100 = new Service<Integer>() {
#Override
protected Task<Integer> createTask() {
Task<Integer> taskTo100 = new Task<Integer>() {
#Override protected Integer call() throws Exception {
int iterations;
updateProgress(-1, 100);
for (iterations = 0; iterations < 100; iterations++) {
if (isCancelled()) {
updateMessage("Cancelled");
break;
}
updateMessage("Iteration " + iterations);
updateProgress(iterations, 100);
// Now block the thread for a short time, but be sure
// to check the interrupted exception for cancellation!
try {
Thread.sleep(100);
} catch (InterruptedException interrupted) {
if (isCancelled()) {
updateMessage("Cancelled");
break;
}
}
}
//udpateProgress(100, 100);
return iterations;
}
};
return taskTo100;
}
};
As you can see, there is a simple loop which counts from 0 to 100 and there is also a updateProgress(iterations, 100); statement which updates progress. This service is located in Services class. In FXMLDocumentController.java is method called runService(Service service) defined as this:
public void runService(Service service){
service.start();
progressBar.progressProperty().bind(service.progressProperty());
service.setOnSucceeded((event) -> {
service.reset();
progressBar.progressProperty().unbind();
progressBar.setProgress(1);
});
}
The initialize looks like this:
#Override
public void initialize(URL url, ResourceBundle rb) {
btn_start1.setOnAction((event) -> {
Service service = Services.serviceTo100;
runService(service);
txt_field1.textProperty().bind(service.messageProperty());
System.out.printf("something\n");
});
.
.
.
}//end of initialize
Now the most interesting thing (at least for me, novice) comes into play.
In service definition, you can notice commented line //updateProgress(100,100). That was my try to set progress bar to completed state when counting has stopped. But java ignored that line. I tried to put System.out.print("Something"); and it worked, but updateProgress(100, 100) didn't. When counting has finished, progress bar was set to it's default state defined in fxml file, which was indeterminate.
Conclusion: Service class creates task defined inside of it and after task is completed, the task doesn't exists anymore, thus, there is no progress to be bound with progress bar.
Even though task does not exists anymore, you cannot set progress of the bounded progress bar with setProgress(double double) method. You first need to unbound it.
Now I got what i needed:
You run the program, progress bar is in indeterminate state, waiting for hit. You hit the button, service starts counting up to 100 and progress bar is progressing according to progressProperty of service. When counting is done, Progress bar is set to indeterminate state again, waiting for another start.

CaKeyframeAnimation persisting in background after dismissing view controller

Hi I have simple CAShapeLayer animation
let ballFrameAnimation = CAKeyframeAnimation()
aBall.removeFromSuperlayer()
self.view.layer.addSublayer(aBall)
ballFrameAnimation.keyPath = "position"
ballFrameAnimation.duration = 3.0
ballFrameAnimation.calculationMode = kCAAnimationDiscrete
ballFrameAnimation.fillMode = kCAFillModeForwards
ballFrameAnimation.isRemovedOnCompletion = true
ballFrameAnimation.delegate = self
with a callback to keeps it repeating
func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
let name = anim.value(forKey: "name") as? String
if name == "form" {
attachAnimation()
forwardDirection = !forwardDirection
}
However this persists and loops in the background ( at high speed) even when I pop the viewcontroller off the stack. It also shows a memory leak as well on instruments.
#IBAction func unwindDismiss(_ sender: Any) {
aBall.removeAnimation(forKey: "ballAnimation")
aBall.removeFromSuperlayer()
navigationController?.popToRootViewController(animated:true)
dismiss(animated: true, completion: nil)
}
It was simple.
The endless loop animation would not be released by simply dismissing the viewcontroller so it persisted in the background.
By adding a
if navigationController?.topViewController == self {
loop check within the animation did stop cycling.
this fixed not only the accelerating background loops but also the memory leaks. also a warning to fellow NOOBs : when using the instruments repeatedly: close and restart them frequently and also clean builds otherwise you are likely to get bogus leaks.

Main thread doesn't wait background thread to finish in Swift

Here's my problem : I'm doing a background work, where I parse some JSON and write some Objects into my Realm, and in the main thread I try to update the UI (reloading the TableView, it's linked to an array of Object). But when I reload the UI, my tableView doesn't update, like my Realm wasn't updated. I have the reload my View to see the updates. Here's my code :
if (Realm().objects(Objects).filter("...").count > 0)
{
var results = Realm().objects(Objects) // I get the existing objects but it's empty
tableView.reloadData()
}
request(.GET, url).responseJSON() {
(request, response, data, error) in
let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
dispatch_async(dispatch_get_global_queue(priority, 0)) {
// Parsing my JSON
Realm().write {
Realm().add(object)
}
dispatch_sync(dispatch_get_main_queue()) {
// Updating the UI
if (Realm().objects(Objects).filter("...").count > 0)
{
results = Realm().objects(Objects) // I get the existing objects but it's empty
tableView.reloadData()
}
}
}
}
I have to do something bad with my threads, but I couldn't find what. Can someone know what's wrong?
Thank you for your answer!
such workflow makes more sense to me for your case:
let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
dispatch_async(dispatch_get_global_queue(priority, 0)) {
// Parsing my JSON
Realm().write {
Realm().add(object)
dispatch_sync(dispatch_get_main_queue()) {
// Updating the UI
if (Realm().objects(Objects).filter("...").count > 0)
{
results = Realm().objects(Objects) // I get the existing objects but it's empty
tableView.reloadData()
}
}
}
}
NOTE: you have a problem with timing in your original workflow: the UI might be updated before the write's block executed, that is why your UI looks abandoned; this idea above would be a more synchronised way between tasks, according their performance's schedule.
You are getting some new objects and storing them into "results".
How is tableView.reloadData () supposed to access that variable? You must change something that your tableView delegate will access.
PS. Every dispatch_sync () is a potential deadlock. You are using one that is absolutely pointless. Avoid dispatch_sync unless you have a very, very good reason to use it.

Implementing a blocking modal view/dialog like in Windows Forms - is it possible?

In short:
I want to show a view or action sheet and only continue code execution after the user has dismissed the view / sheet. So: line one shows the view, line two reads some result variable.
In detail why I would need this:
I'm porting a Windows Forms application over to the iPad. The original implementation has a communication class which uses a web service to communicate with the server. It offers a couple of methods to get data. Conveniently it checks prior to each call if the user still has a valid connection or if he has to re-enter his password for security reasons.
If the password is required, the .NET class shows a modal dialog which blocks any further code executio and if the password was entered, retries the last call it has made before showing the dialog.
Now using CocoaTouch I'm facing a problem. I replaced the code that shows the dialog with a UIActionSheet. Works great but code execution continues immediately, whereas in Windows Forms it is blocked (the next line in Windows Forms after showing the dialogs is to read the entered password from the dialog) until the dialog has been closed.
I tried a Thread.Sleep() until the user dismisses the UIActionSheet but the Thread.Sleep() also blocks the main loop and my view won't even be drawn.
The alternative I currently see is to change all methods in the already working class and give them a return value: if password required, handle it, then retry.
But this means that all over my code I will have to add these checks because at any given moment the password might be needed. That's why it is nested in communication class in Windows Forms.
Any other ideas?
René
Yes, it is possible.
To do this, what you can do is to run the mainloop manually. I have not managed to stop the mainloop directly, so I instead run the mainloop for 0.5 seconds and wait until the user responds.
The following function shows how you could implement a modal query with the above approach:
int WaitForClick ()
{
int clicked = -1;
var x = new UIAlertView ("Title", "Message", null, "Cancel", "OK", "Perhaps");
x.Show ();
bool done = false;
x.Clicked += (sender, buttonArgs) => {
Console.WriteLine ("User clicked on {0}", buttonArgs.ButtonIndex);
clicked = buttonArgs.ButtonIndex;
};
while (clicked == -1){
NSRunLoop.Current.RunUntil (NSDate.FromTimeIntervalSinceNow (0.5));
Console.WriteLine ("Waiting for another 0.5 seconds");
}
Console.WriteLine ("The user clicked {0}", clicked);
return clicked;
}
I think this approach using async/await is much better, and doesn't suffer from freezing the app when rotating the device, or when the autoscrolling interferes and leaves you stuck in the RunUntil loop forever without the ability to click a button (at least these problems are easy to reproduce on iOS7).
Modal UIAlertView
Task<int> ShowModalAletViewAsync (string title, string message, params string[] buttons)
{
var alertView = new UIAlertView (title, message, null, null, buttons);
alertView.Show ();
var tsc = new TaskCompletionSource<int> ();
alertView.Clicked += (sender, buttonArgs) => {
Console.WriteLine ("User clicked on {0}", buttonArgs.ButtonIndex);
tsc.TrySetResult(buttonArgs.ButtonIndex);
};
return tsc.Task;
}

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