I have a big paginated UIScrollView with severals image and views in it. The thing I'm trying to achieve is to pause any background operation while the user is swiping through pages. I need this because the app is downloading and computing stuff and the swipe animations isn't smooth.
Any ideas?
Thanks
You should think in reverse manner.
Once the image was downloaded in background then update it in UI by using Main thread.
The Main Thread is handling the UI updates.
Based on your description,
"the swipe animations isn't smooth"
You are downloading images on Main thread.
You can use NSOperationQueue and catch the scroll event in the UIScrollView's delegate to pause/continue the operations.
- (void)viewDidLoad{
[super viewDidLoad];
queue=[[NSOperationQueue alloc]init];
NSBlockOperation *intenseOperation=[NSBlockOperation blockOperationWithBlock:^{
//do intense stuff
}];
[queue addOperation:intenseOperation];
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{
[queue setSuspended:NO];
}
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
[queue setSuspended:YES];
}
Related
I would like to ask that is there a way to show network indicator automatically when there is network activity going on and hide the network indicator when there is no network activity
You have to control it by using your start and completion of your network calls.
Lets say:
- (void)viewDidAppear:(BOOL)animated{
[super viewDidAppear:animated];
[self showNetworkActivitySpinner];
[self fetchDataFromServer];
}
- (void)fetchDataFromServer{
[SomeApiCallClass callWebServiceWithPostData:(NSDictionary *)someDataToPost andCompletionHandler:(^void) {
[self hideNetworkActivitySpinner];
}];
}
When the keyboardWillHide, I scroll the tableView to a specified point. The code is below. This works well.
Now, I implement NSFetchedResultsControllerDelegate. I set it "on" by setting fetchedResultsController.delegate = self; The scroll animation is interrupted. The NSFetchedResultsControllerDelegate is calling [tableView beginUpdates], which I think is causing the interruption on the tableView animation.
How can I prevent the scroll animation from being interrupted and still implement NSFetchedResultsControllerDelegate?
- (void)keyboardWillHide:(NSNotification *)notification {
[screen setHidden:YES];
[suggestView setHidden:YES];
[_tableView setContentOffset:origin animated:YES];
}
I found out that you can't do animations in keyboardWillHide. You shouldn't do any animation in any "WILL" event.
I have 3 screens on my app.First is login. Second is search and third is process the task.
On login i retrieve data from a web service. It returns data in XML format. So the data is considerably large. So i am doing that task on a background thread like this to stop Mainthread freezing up on me:
-(BOOL)loginEmp
{
.....some computation
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
(unsigned long)NULL), ^(void) {
[self getAllCustomerValues];
});
}
-(void)getAllCustomerValues
{
....more computation.Bring the data,parse it and save it to CoreData DB.
//notification - EDIT
NSNotification *notification =[NSNotification notificationWithName:#"reloadRequest"
object:self];
[[NSNotificationCenter defaultCenter] postNotification : notification];
}
//EDIT
//SearchScreenVC.m
- (void)viewDidLoad
{
....some computation
[self.customerActIndicator startAnimating];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(stopActivityIndicator)
name:#"reloadRequest"
object:nil];
}
- (void)stopActivityIndicator
{
[self.customerActIndicator stopAnimating];
self.customerActIndicator.hidesWhenStopped = YES;
self.customerActIndicator.hidden =YES;
NSLog(#"HIt this at 127");
}
So on condition that login was successful, i move to screen 2. But the background thread is still in process( i know because i have logs logging values) . I want an activity indicator showing up here (2nd screen)telling user to wait before he starts searching. So how do i do it?How can i make my activity indicator listen/wait for background thread. Please let me know if you need more info.Thanks
EDIT: so I edited accordingly but the notification never gets called. I put a notification at the end of getAllCustomerValues and in viewDidLoad of SearchScreen i used it. That notification on 2nd screen to stop animating never gets called. What is the mistake i am doing.?Thanks
EDIT 2: So it finally hits the method. I dont know what made it to hit that method. I put a break point. I wrote to stop animating but it wouldn't. I wrote hidesWhenStoppped and hidden both to YES. But it still keeps animating.How do i get it to stop?
Ok, if it is not the main thread, put the following in and that should fix it.
- (void)stopActivityIndicator
{
if(![NSThread isMainThread]){
[self performSelectorOnMainThread:#selector(stopActivityIndicator) withObject:nil waitUntilDone:NO];
return;
}
[self.customerActIndicator stopAnimating];
self.customerActIndicator.hidesWhenStopped = YES;
self.customerActIndicator.hidden =YES;
NSLog(#"HIt this at 127");
}
Could you put your background operation into a separate class and then set a delegate on it so you can alert the delegate once the operation has completed?
I havent tried this, its just an idea :)
You could use a delegate pointing to your view controller & a method in your view controller like:
- (void) updateProgress:(NSNumber*)percentageComplete {
}
And then in the background thread:
float percentComplete = 0.5; // for example
NSNumber *percentComplete = [NSNumber numberWithFloat:percentComplete];
[delegate performSelectorOnMainThread:#selector(updateProgress:) withObject:percentageComplete waitUntilDone:NO];
i've an app that when start control updates and other things. If the app find some updates they will ask user if this updates have to be done. If user select YES i want that a spinner appear on main screen until update finish. But when i tap YES my alert view doesn't disappear and remain on screen until update is finished.
Is it possible to create a thread that run on the main thread and stop when update in finished?
Thanks
-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
if (buttonIndex==1) {
[self showActivityViewer];
[self downloadControlAndUpdatePoi];
[self downloadControlAndUpdateItinerari];
[self downloadControlAndUpdateArtisti];
[self downloadControlAndUpdateEventi];
[self hideActivityViewer];
NSLog(#"AGGIORNA");
} else {
NSLog(#"NON AGGIORNARE");
return;
}
}
If the methods
[self downloadControlAndUpdatePoi];
[self downloadControlAndUpdateItinerari];
[self downloadControlAndUpdateArtisti];
[self downloadControlAndUpdateEventi];
are executed synchronously (that means that they return only after having processed completely), so:
[self hideActivityViewer];
is executed only at the very end.
A simple approach to this is scheduling the execution of your methods on the main thread:
[self performSelector:#selector(downloadControlAndUpdatePoi) withObject:nil afterDelay:0];
....
[self hideActivityViewer];
so that those methods are executed only after control has returned to the main loop and the UI has been updated.
Otherwise, you could use:
+ detachNewThreadSelector:toTarget:withObject:
from NSThread, to do more or less the same. In this case I would suggest creating a wrapper method for all of your dowloadAndUpdate... methods, but keep in mind that you can't update the UI from a secondary thread.
In both cases, you should take some care about synchronizing the download... operations with the rest of your workflow after removing the alert view.
I'm using GCD for background downloading in my Tab Bar app.
First step is to do some background downloading in -viewWillAppear: (to setup some basic data before the view is loaded).
Second step is to the rest of the background downloading in -viewDidAppear:
For some reason, the dispatch block in -viewDidAppear: gets called before the dispatch block in -viewWillAppear:.
This only happens once after loading the application for the first time switching to the tab with the GCD background methods. Switching to another tab and then switching back to the tab with the GCD background methods. The third (and all the rest subsequent times) time I'm switching back it's works as expected (-viewWillAppear: firing first and then -viewDidAppear:).
Here are excerpts of my code (-viewWillAppear: and -viewDidAppear:):
-viewWillAppear:
- (void)viewWillAppear:(BOOL)animated {
DLog(#"viewWillAppear method running");
[super viewWillAppear:animated];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
[self setDiskCareerIds:[CareersParser idsFrom:#"disk"]];
[self setDownloadedCareerIds:[CareersParser idsFrom:#"web"]];
DLog(#"diskCareerIds after being set in viewWillAppear: %#", [self diskCareerIds])
DLog(#"downloadedCareerIds after being set in viewWillAppear: %#", [self downloadedCareerIds])
if ([[self downloadedCareerIds] isEqualToArray:[self diskCareerIds]]) {
DLog(#"viewWillAppear: ids equal, loading careers from disk.");
self.careers = [CareersParser loadCareersFromDisk];
dispatch_async(dispatch_get_main_queue(), ^{
[self.table reloadData];
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
});
}
});
//[self downloadData];
}
-viewDidAppear:
- (void)viewDidAppear:(BOOL)animated {
DLog(#"viewDidAppear method running");
[super viewDidAppear:animated];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
if (![[self downloadedCareerIds] isEqualToArray:[self diskCareerIds]]) {
DLog(#"ids not equal, saving careers to disk.");
dispatch_async(dispatch_get_main_queue(), ^{
[self showLoadingView];
});
[CareersParser saveCareersToDisk];
self.careers = [CareersParser loadCareersFromDisk];
}
dispatch_async(dispatch_get_main_queue(), ^{
[self.table reloadData];
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
[self removeLoadingView];
});
});
//[self download3];
//[self downloadData];
}
Check the debug log at Pastie.
Well, you're printing that log message in that first block (the one scheduled in viewWillAppear:) after it has done a bunch of parsing, not when it actually starts executing.
The thing is that global queue is a concurrent queue. So even though you are scheduling that first block first, it's not surprising that it sometimes falls behind the other block which is executing concurrently with it.
One simple answer would be to create a serial queue, and then you'll be sure the first block completes before the second one is executed. That seems to be what you want, right?