I'm having a problem when trying to add a UITabBar as a subview of my AppDelegate's window.
The link above shows a screenshot of the messy state of the screen.
TabBarInAMessyState.png
The results are unpredictable. In this picture only the UITabBarItem's titles were affected, but sometimes the TabBar background is not shown (consequently we can see the window's background). Sometimes the NavigationBar is also affected (not show in this picture).
When I start the Application I first have to check if there's network connection, so It is called a method (verifyNetworkAvailability:) that will run in a thread different from the main thread. This is done in order not to freeze the application.
- (void)applicationDidFinishLaunching:(UIApplication *)application {
[window makeKeyAndVisible];
// check if there's network connection in another thread
[NSThread detachNewThreadSelector: #selector(verifyNetworkAvailability:) toTarget:self withObject:self];
}
- (void) verifyNetworkAvailability:(MyAppDelegate*) appDelegate {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
// Check if there's network connection..
// If so, call the verifyNetworkAvailabilityDidEnd method
[appDelegate verifyNetworkAvailabilityDidEnd];
[pool release];
}
- (void) verifyNetworkAvailabilityDidEnd {
[window addSubview:tabBarController.view];
}
I'd like to know if it is possible to add the tabBarController.view in this way (by a method call done in thread other than the main thread).
Thanks in advance
Try this
- (void) verifyNetworkAvailability:(MyAppDelegate*) appDelegate {
// other code here ...
[appDelegate performSelectorOnMainThread:#selector(verifyNetworkAvailabilityDidEnd) withObject:nil waitUntilDone:NO];
}
UIKit has some trouble when you try to access it from any thread but the main thread. Think about dispatching a notification to have your primary app thread to add the view rather than adding the view directly in your secondary thread.
Related
I have a UINavigationController in my application where I am pushing a view controller. On that viewcontroller, there is a preloader view that shows animation while the data is being downloaded and parsed in the background. Below the animation is a button that should redirect the user to some other view controller.
Now, I can accomplish this by popping the viewcontroller since the view I need to be directed to is the view the current view was pushed from. The problem here, however, is that the downloading, parsing, timer, etc.. everything keeps happening in the background.
The functionality I need is for the viewcontroller to completely stop working as soon as I pop the VC by clicking on the button.
Thanks in advance.
What are you using to run the background operations?
You can simplify background operations by subclassing NSOperation and using NSOperationQueue to run it. You just have to release NSOperationQueue and iOS will clean up for you automatically.
https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/NSOperation_class/Reference/Reference.html
https://developer.apple.com/library/ios/#documentation/Cocoa/Reference/NSOperationQueue_class/Reference/Reference.html
Here is an example.
#interface MyBackgroundOperation : NSOperation
#end
#implementation MyBackgroundOperation
- (id)init
{
self = [super init];
if(self != nil)
{
// stuff that needs to be done at init
}
return self;
}
- (void)main
{
#try
{
// run my background operations
}
#catch (NSException *e)
{
// catch the exception
}
}
- (void)dealloc
{
// clean up
[super dealloc];
}
#end
Then you start the operation like this
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
MyBackgroundOperation *myOperation = [[MyBackgroundOperation alloc] init];
[operationQueue addOperation:myOperation];
[myOperation release];
[operationQueue release];
The OS will retain the operation until it's finished so that releasing the view controller will not effect it. However, if you want to stop the operation after it's already started you're going to have to use a bit more fancy techniques, maybe notifications or KVO.
I am trying to implement the SVProgressHUD progress activity indicator. I copied the class from the [demo].1
My app loads up but the activity indicator doesn't show up. This is my first time trying to use one of these, so any help would be appreciated.
Here is the code:
#import "SVProgressHUD.h"
#implementation QuotesAppDelegate
- (void)startLoading
{
//call this in your app delegate instead of setting window.rootViewController to your main view controller
//you can show a UIActivityIndiocatorView here or something if you like
[SVProgressHUD show];
[self performSelectorInBackground:#selector(loadInBackground) withObject:nil];
}
- (void)loadInBackground
{
//do your loading here
//this is in the background, so don't try to access any UI elements
[self populateFromDatabase];
[SVProgressHUD dismiss];
[self performSelectorOnMainThread:#selector(finishedLoading) withObject:nil waitUntilDone:NO];
}
- (void)finishedLoading
{
//back on the main thread now, it's safe to show your view controller
[window addSubview:[navigationController view]];
[window makeKeyAndVisible];
}
- (void)applicationDidFinishLaunching:(UIApplication *)application {
[self copyDatabaseIfNeeded];
[self startLoading];
}
For anyone else having a similar problem, this can also happen because you have a long loop or a piece of code that takes a long time to execute. If this happens, your progress bar wont be shown until after the loop, which kind of defeats the purpose.
To solve this issue you need to you this:
- (void)performSelectorInBackground:(SEL)aSelector withObject:(id)arg
Basically your code would look something like this:
- (IBAction)submitPost:(id)sender {
//now we show the loading bar and submit the comment
[SVProgressHUD showWithStatus:#"Submitting post" maskType:SVProgressHUDMaskTypeGradient];
SEL aSelector = #selector(submitDataOfPost);
[self performSelectorInBackground:aSelector withObject:sender];
}
This will basically load the progress bar, and in a background thread, the method you want to execute will be called. This makes sure that the UI is updated (shows the progress hud) at the same time that your code is executed.
First of all you were not adding your SVProgressHUD to the view.
If your class inherited from UIViewController then [self.view addSubview:]; or if your class is simple UIView then [self addSubView:];
I do not understand your requirement but as far as i can understand through your code that you are showing [SVProgressHUD show]; in your startLoading method and then you are calling loadInBackground method in that method where you are hiding your hud using [SVProgressHUD dismiss];
I will suggest you to trace it by using breakpoint and figure it out.
I had the same problem. When I changed a version of SVProgressHUD to the later one the problem disappeared. My current version supports ARC.
=>
(IBAction)fetchData:(id)sender
{
[SVProgressHUD showWithStatus:#"Loading..." maskType:SVProgressHUDMaskTypeGradient];
[self performSelectorOnMainThread:#selector(getDataFromSomeWhere) withObject:nil waitUntilDone:NO];
}
=>
(void)getDataFromSomeWhere
{
//Do your data populating here. and dismiss the ProgressHud.
[SVProgressHUD dismiss];
}
So when I click on a callout accessory in my mapView, nothing happens for several seconds because it is making a url request and parsing it, so I wanted to show the activity indicator so the user doesn't think it's frozen. Here's the code:
- (void)mapView:(MKMapView *)mv annotationView:(MKAnnotationView *)pin calloutAccessoryControlTapped:(UIControl *)control {
// start activity indicator
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
NSLog(#"tapped");
ArtPiece *artPiece = (ArtPiece *)pin.annotation;
//when annotation is tapped switches page to the art description page
artDescription *artD = [[artDescription alloc] initWithNibName:#"artDescription" bundle:nil];
artD.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
artD.startingLocation = mapView.userLocation.location.coordinate;
artD.selectedArtPiece = artPiece;
NSLog(#"0");
[self presentModalViewController:artD animated:YES];
NSLog(#"1");
[artD loadArt:artPiece];
NSLog(#"2");
// stop activity indicator
//[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
[artD release];
}
Strangely (to me anyway, maybe I'm missing something obvious as I'm pretty inexperienced), the activity indicator does not show until after the method is done, and the modal view starts animating into view. I put the NSLogs in to see what was taking time. I had about a 2 second pause between "0" and "1" and another couple seconds between "1" and "2". Then the indicator finally showed, so I am sure it is waiting until the end of the method for some reason. Any ideas why?
The change to the UI, displaying the activity indicator, does not take effect until control has returned to the application's main run loop. This does not occur until after your method has ended and the stack has unwound. You need to show the activity indicator, then dump the activity you are waiting for onto a background thread:
[self performSelectorInBackground:#selector(doThingINeedToWaitFor:)
withObject:anObject];
(Note that Apple recommends that you move away from using threads explicitly; performSelectorInBackground:withObject: is the simplest method to get some code run off the main thread. More complex options are available for other situations. See the Concurrency Programming Guide.)
The important gotcha is that UI updates still need to be handled on the main thread, so in that method, when the work is done, you need to call back to stop the activity indicator:
- (void) doThingINeedToWaitFor: (id)anObject {
// Creating an autorelease pool should be the first thing
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
// Do your work...
// ...
// Update the UI back on the main thread
[self performSelectorOnMainThread:#selector(allDoneWaiting:)
withObject:nil
waitUntilDone:YES];
// Clear out the pool as the final action on the thread
[pool drain];
}
In your callback method, you hide the activity indicator again and do any other post-processing that's necessary.
You cannot start and stop the activity indicator in the same function.
See the answer I provided for this question: How show activity-indicator when press button for upload next view or webview?
Edit for clarity:
- (void) someFunction
{
[activityIndicator startAnimation];
// do computations ....
[activityIndicator stopAnimation];
}
The above code will not work because you do not give the UI time to update when you include the activityIndicator in your currently running function. So what I and many others do is break it up into a separate thread like so:
- (void) yourMainFunction {
activityIndicator = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
[NSThread detachNewThreadSelector:#selector(threadStartAnimating) toTarget:self withObject:nil];
//Your computations
[activityIndicator stopAnimating];
}
- (void) threadStartAnimating {
[activityIndicator startAnimating];
}
Something is slowing down your spinner. I would recommend doing your heavy lifting in background, using a thread. Try this:
-(void)myMethod{
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
[NSThread detachNewThreadSelector:#selector(startWorkingThread) toTarget:self withObject:nil];
}
-(void)startWorkingThread{
//Heavy lifting
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}
I assume that you have commented the:
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
For testing purposes...
I've this bit of code:
- (IBAction)registerAction:(id)sender {
[NSThread detachNewThreadSelector:#selector(registerThread) toTarget:self withObject:nil];
}
- (void)registerThread {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
MyDelegate *delegate = (MyDelegate *)[[UIApplication sharedApplication] delegate];
NSInteger locationID = [delegate.api checkCoordinate:[NSString stringWithFormat:#"%f,%f",
location.coordinate.latitude, location.coordinate.longitude]];
NSNumber *status = [api registerWithUsername:usernameField.text
password:passwordField.text email:emailField.text andLocation:locationID];
[self performSelectorOnMainThread:#selector(registrationDoneWithStatus:) withObject:[NSNumber numberWithInt:1] waitUntilDone:NO];
[pool release];
}
it works nicely, but sometimes I get this error:
void _WebThreadLockFromAnyThread(bool), 0x6157e30: Obtaining the web lock from a thread other than the main thread or the web thread. UIKit should not be called from a secondary thread.
And it seems that only using the delegate I get this error, and I don't know how to resolve.
Thanks in advance :)
I've run into the same problem recently.
There may be some active views (eg. UITextField,UITextView). Try resignFirstResponder those views before accessing delegate
You fix the problem by very carefully thinking through your application's concurrency architecture and ensuring that you aren't exercising anything from a thread that should only be done on the main thread.
In this case, you are causing the UIKit to execute code from a secondary thread. If you were to set a breakpoint on _WebThreadLockFromAnyThread, you would know exactly where.
It is exceedingly atypical to use the app's delegate from a secondary thread in anything but the most extremely controlled circumstances.
tl;dr You can't make an app threaded by detaching a new thread against a random selector.
I have a strange problem with a UIView :
I want to show an Activity Indicator View that I created with Interface Builder to indicate long running activity.
In the viewDidLoad function of my principal viewController I init the ActivityIndicator View like this :
- (void)viewDidLoad {
[super viewDidLoad];
appDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
load = [[ActivityIndicatorViewController alloc] init];
...
When I push a button it call this IBAction :
- (IBAction)LaunchButtonPressed{
// Show the Activity indicator view.
[self.view addSubview:load.view];
// eavy work
[self StartWorking];
// Hide the loading view.
[load.view removeFromSuperview];
}
In the StartWorking function, I ask a request to an internet serveur and parse the XML file that it return me.
The problem is that if I Call my StartWorking function, the application do not start by showing the Activity Indicator view but with the StartWorking function.
Whereas if I remove the call to StartWorking function, the view is shown.
Is someone able to explain me why? :s
Have you tried to call the StartWorking method on a different thread?
Maybe its heavy process prevents other instructions to take place.
Look at the NSThread class, especially the detachNewThreadSelector:toTarget:withObject: method.
EDIT: About the pool problem, you need to create a pool in your StartWorking method, if it's called on a different thread:
- ( void )StartWorking
{
NSAutoreleasePool * pool = [ [ NSAutoreleasePool alloc ] init ];
/* Code here... */
[ pool release ];
}
Replace :
[self.view addSubview:load.view];
With :
[self performSelector:#selector(addLoadingSubview) afterDelay:0.1f];
And create the method :
-(void)addLoadingSubview{[self.view addSubview:load.view];}
Ok, I found a solution based on santoni answer :
- (IBAction)LaunchButtonPressed{
// Show the Activity indicator view.
[self performSelector:#selector(ShowActivityIndicatorView) withObject:nil afterDelay:0];
// eavy work
[self performSelector:#selector(StartWorking) withObject:nil afterDelay:2];
// Hide the loading view.
[load.view removeFromSuperview];
}
The Activity Indicator view is dislayed before the call to the eavy function.
Thank's for answering.