I want get data from url, but until process complete, i want show loading icon
I use this code but not work for me
DispatchQueue.global(qos: .background).async {
// show loading icon
// start get data
DispatchQueue.main.async {
// remove loading icon
}
}
From UIView
Threading Considerations
Manipulations to your application’s user interface must occur on the
main thread. Thus, you should always call the methods of the UIView
class from code running in the main thread of your application. The
only time this may not be strictly necessary is when creating the view
object itself but all other manipulations should occur on the main
thread.
Which means you should probably show/hide and manipulate therefore your View in the Main thread and not in a background thread as you are doing in "show loading view".
Related
When I present a view controller or perform a segue in swift should I call it in DispatchQueue.main.async {} or is that a problem. My problem is that should I run it in the background thread or the main thread. If I load data from the database should I also present the view in DispatchQueue.main.async {} or should I run it in the background thread.
You should call all the UI related transition, changes and updates on the main thread. But where should you use DispatchQueue.main.async {} ?
It is to be used when the call is made from a background thread. Example,if you are downloading data and parsing from an API, you usually do that in a background thread, once that is completed, maybe you want a UI transition or update, So that update will take place in the main thread, and since currently you are on background thread, you require DispatchQueue.main.async {} to make the changes on UI.
All UI work should happen on the main thread, so unless you're on a background queue there is no reason to dispatch to the main queue. In the common case the segue is triggered from user interaction (e.g. a button press) which would already be on the main thread.
If loading the data for the view that is being presented takes a long time, then you can dispatch asynchronously to a background queue to load it and dispatch back to the main queue when the data has finished loading.
Since this is asynchronous, it will mean that the view will be without data from the time where it is presented to the time where the data has finished loading. This is something that you have to handle in your UI. Depending on your application, one example could be to displayed a loading indicator while the data is loading. Another could be to fetch or pass a minimal amount of data to display and load the larger amount of data asynchronously.
I have a custom view within my ViewController that I want to update some info on. This info is being drawn asynchronously from Firebase.
I'm trying to use view.setNeedsDisplay or view.setNeedsLayout to update the view. But since each only changes the view after the next drawing cycle, how can I force the next drawing cycle to happen without forcing the user to leave the ViewController and come back?
Calling setNeedsDisplay or setNeedsLayout is sufficient to trigger “the next drawing cycle”, if you call it on the main thread. It sounds like you might not be calling it on the main thread. If you're not sure which thread you're calling it on, dispatch back to the main queue:
dispatch_async(dispatch_get_main_queue()) {
self.someView.setNeedsDisplay()
}
I am trying to add activity indicator while updating annotation on the map. But it seems not to work such a way. Application screen disables and becomes frozen once process of update is started, so that's why probably activity indicator is not visible.
My question is: Is it possible to update annotations on the map asynchronous with the app, so activity indicator would be visible.
I believe it is really annoying for the user not to see indicator if it takes more then 2 sec.
Solution:
self.activityIndicator.startAnimating()
dispatch_after(DISPATCH_TIME_NOW, dispatch_get_main_queue(), {
self.showPins(self.initialLat, locationLong: self.initialLong)
})
self.activityIndicator.stopAnimating()
You have to make sure you are doing these things:
1. Load all annotations at once
Apple recommends in the MKMapView Class Reference all annotations (pins) should be loaded at once:
When configuring your map interface, you should add all of your annotation objects right away. The map view uses the coordinate data in each annotation object to determine when the corresponding annotation view needs to appear onscreen. [...] Because annotation views are needed only when they are onscreen, the MKMapView class provides a mechanism for queueing annotation views that are not in use. Annotation views with a reuse identifier can be detached and queued internally by the map view when they move offscreen. This feature improves memory use by keeping only a small number of annotation views in memory at once and by recycling the views you do have. It also improves scrolling performance by alleviating the need to create new views while the map is scrolling.
2. Reuse your annotation views
You have to make sure you are correctly reusing existing annotation views by using dequeueReusableAnnotationViewWithIdentifier in the viewForAnnotation method.
3. Do heavy loading on background threads
If you can't fetch / load the annotations at once you could use Grand Central Dispatch to let the 'heavy' method run on a background thread so the UI doesn't block. Note: any changes to the UI from within that method (on the bg thread) will need to explicitly happen on the main UI thread.
Regarding backgrounding, take a look at this Stackoverflow answer:
let qualityOfServiceClass = QOS_CLASS_BACKGROUND
let backgroundQueue = dispatch_get_global_queue(qualityOfServiceClass, 0)
dispatch_async(backgroundQueue, {
print("This is run on the background queue")
dispatch_async(dispatch_get_main_queue(), { () -> Void in
print("This is run on the main queue, after the previous code in outer block")
})
})
Or alternatively, use this 'Async' library for some syntactic sugar.
How do I get the UIActivityIndicatorView to display first, then execute other code?
I've experimented with using sleep, and it works but it doesn't "feel" right and adds an extra second to processing a bunch of core data stuff. I've also tried dispatching it to the main thread which only works some of the time. (I'm guessing when the rest of the block is executed outside of the main thread).
Ideally as soon as a user touches the button the instance of the UIActivityIndicatorView would display (which seems to happen where I've used it in other apps by itself or with other minimal processing).
Details: I have an IBAction connected to a button that executes a bunch of core data stuff, sometimes including images, that takes between 1 - 3 seconds to finish. When it finishes it dismisses the view controller. The view controller where this is executed is presented as a modal over current context.
Here is a code snippet:
// get the background queue
let bg_queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)
dispatch_async(bg_queue, {
// long running code here...
dispatch_async(dispatch_get_main_queue(), {
self.activityIndicator.stopAnimating()
})
})
I have a table view, and when the user selects a row, i push them to a new ViewController. At first, I initialized all my view objects in the ViewDidLoad method (involving web service calls) but I saw that it made the transition from my tableview to my new viewcontroller very long.
Instead, I moved most of my UI initialization in the ViewDidAppear method, and I like that it sped up my transition from tableview to new viewcontroller.
However, I cannot press any buttons in my NavigationBar at the top of the screen (like the back button) until my ViewDidAppear method completes and the UI is loaded.
What's the solution for this? Is there another way for me to load my UI without it preventing the user from interacting with the buttons in my NavigationBar?
Thanks!!
you do too much on the main thread. off load your longer operations like IO or longer computations BUT take care to not mess with the UI in the background thread.
Only touch the UI on the main thread. (Note sometimes it might seem safe, but in the long run it always end up producing weird issues)
one easy way is to use GCD:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0),^{
//insert web service requests / computations / IO here
dispatch_async(dispatch_get_main_queue(),^{
//back to the main thread for UI Work
});
});
You could use grand central dispatch to make your web service calls asynchronously, which will keep the UI on the main thread responsive.
//create new queue
dispatch_queue_t backgroundQueue = dispatch_queue_create("com.siteName.projectName.bgqueue", NULL);
//run requests in background on new queue
dispatch_async(backgroundQueue, ^{
//insert web service requests here
});
Here's a more in-depth tutorial:
http://www.raywenderlich.com/4295/multithreading-and-grand-central-dispatch-on-ios-for-beginners-tutorial
Try to initialize your UI in the background by using the following method
[self performSelectorInBackground:#selector(initYourUI) withObject:yourObj];
You can call this in the ViewDidLoad