I feel as though there is a really simple solution to my problem, but thus far I have had little success... I want to load my initial .xib file (exiting the default.png splash screen early), so that I may display an activity indicator while loading my html data and setting the text label fields created by my xib file.
Unfortunately, when I execute the following code below, I display my default.png image until all of the data is loaded from each website... What may I change in order to first display my mainView, then start the activity indicator, load my html data, and set the text labels in my mainView?
#implementation MainViewController
- (void)viewDidLoad {
[super viewDidLoad];
[activityIndicator startAnimating];
[self runTimer];
}
- (void)viewDidAppearBOOL)animated {
[super viewDidAppear:animated];
[self loadHTMLData1];
[self loadHTMLData2];
[self loadHTMLData3];
[self loadHTMLData4];
[activityIndicator stopAnimating];
}
...
It's all to do with how iOS updates the ui. When you call
[activityIndicator startAnimating];
it doesn't mean start animating immediately, it means you're telling the ui the next time you are updating the display, start animating.
All of this updating happens on the main thread (if you haven't made a thread, you're already on the main thread) so if you do something else that takes a long time, it will do this before updating the display.
There are a few ways to fix this and they all involve making another thread that runs in the background.
Take a look at NSOperation (and NSOperationQueue) - this will let you queue up individual tasks that iOS will run in the background for you. then when they are complete you can update your display again and turn off your activity indicator.
There's NSOperationQueue tutorials all over google :)
Hope that helps.
Related
I have a controller that uses an animated UIImageView to display a sequence of 30 512 x 512 frames. When I run the application the view quickly does the following.
- (void)viewDidLoad {
[super viewDidLoad];
[[self imageView] setAnimationImages:[[self dataModel] framesForLOOP]];
[[self imageView] setAnimationDuration:2.5];
[[self imageView] setAnimationRepeatCount:1];
[[self imageView] startAnimating];
NSLog(#"MARKER_001");
}
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
NSLog(#"MARKER_002");
}
This all works fine but what I am trying to work out is that after viewDidLoad: is called there is a 2 second delay before viewDidAppear: is called (between MARKER_001 and MARKER_002).
I was thinking there might be a delay setting up the frames NSArray or after calling setAnimationImages: or maybe after startAnimating.
Is there anyway to reduce/remove this delay, I would prefer to preload the animation at startup and take a hit there rather than having the delay when the viewController loads as it makes the button that fires the segue to instantiate the new controller feel laggy.
Just a few ideas:
reduce the pain - do you need 30x512x512?
distribute the pain - load the first image on viewWillAppear, kick off an operation to load the others and update the animation images as new images are ready (can supply code e.g. if needed)
move the pain - prepare the array of UIImages in app init.
dig deeper - let's have a look at the framesForLoop method, maybe there's some more opportunity to reduce/distribute/move the pain in there.
Note that even if you call startAnimating in viewDidLoad, the animation won't start there. You can't get an animation running in a controller which has not been not displayed yet.
You should call the startAnimating in viewDidAppear instead.
Two seconds delay between these two methods is not anything strange. The delay can be much longer or shorter, depending on what happens inside your application.
Measuring the time between two methods which are not connected doesn't make sense. What about measuring how much time the individual methods take?
If anything is laggy, you should probably paste all the code that happens between the user action and the moment when everything is displayed and the lag happens.
I have two issues with activity indicator:
1. Activity Indicator not showing up on UIViewController
I have activity indicator added in .xib file. On button click it should start animating. and when response from server is received, before going to next page it should stop animating.
I am doing it as follows:
activityIndicator.hidden = NO;
[activityIndicator performSelector:#selector(startAnimating) withObject:nil afterDelay:0.1];
[self.view bringSubviewToFront:activityIndicator];
....rest of code here....
activityIndicator.hidden = YES;
[activityIndicator stopAnimating];
Activity Indicator not showing up on UITableView
For table view I am doing it same way but on didselectrowatindexpath...
For tableview I also tried adding activity view to cell accessory, but still not showing up
In both cases activity Indicator is not showing up.
Please help
Thanks
If all this code is in one method or in response to one event, then none of the changes to the views are going be visible until you return to the event loop. You set the activityIndicator.hidden to NO and then set it again to YES before the UI has an opportunity to even refresh.
You also apparently stop the animation before you start it.
What you need to do is make the activity indicator visible here and start its animation. Then schedule the work to be done (start an asynchronous network connection, or put some work into a queue, or whatever it is you need to get done) and return from this method so that the UI can refresh, the indicator can be drawn, and the animation can actually start.
Then later at some point after the work is complete, you can hide the indicator and stop the animation. But you can't do all of that on the main thread within one single turn of the event loop. None of your changes will be visible because no drawing at all will happen here while this method is executing (assuming this is on the main thread)
I hope that makes sense?
Now I modified the code to this:
activityIndicator.hidden = NO;
[activityIndicator startAnimating];
[self performSelector:#selector(saveClicked) withObject:nil afterDelay:0.1];
[self.view bringSubviewToFront:activityIndicator];
and it worked :)
May be, in tableView, instead of self.view , it will be self.navigationController.view ??
I had the UIActivityIndicatorView working fine in simulator and other 3.0 devices in my app. But I found out that it was not spinning (or showing) in the new iphone 4. Basically I need to show the activity indicator when a button is clicked and hide it when the button click event is complete. I was using the approach below.
[NSThread detachNewThreadSelector: #selector(spinBegin) toTarget:self withObject:nil];
from this link. As mentioned, it correctly spins the activity indicator on all except 4.*.. not sure why. To get around this, I also followed another approach something like (from developer.apple.com)
`
(IBAction)syncOnThreadAction:(id)sender
{
[self willStartJob];
[self performSelectorInBackground:
#selector(inThreadStartDoJob:)
withObject:theJobToDo
];
}
(void)inThreadStartDoJob:(id)theJobToDo
{
NSAutoreleasePool * pool;
NSString * status;
pool = [[NSAutoreleasePool alloc] init];
assert(pool != nil);
status = [... do long running job specified by theJobToDo ...]
[self performSelectorOnMainThread:
#selector(didStopJobWithStatus:)
withObject:status
waitUntilDone:NO
];
[pool drain];
}
`
The problem with this was that, it is showing the acitivityVIewIndicator spinning correctly (at least on the simulator) but after it stops, the built in activity indicator in the top bar (where it shows the battery% etc) is still spinning.
I'm new to objective C. I have finished my app completely but for this silly thing. I realize there is no way to display UIActivityView without starting another thread. and finally, just to rant, I don't understand why they have to make it so complicated. I mean they knew it was going to have this problem, why not provide a sample code everyone can use rather than deriving their own solutions.
Finally, can anyone please provide me with a direction or some sample code. I would really appreciate it. I have been searching for a few hours now and have not found anything really that works!
Why are you starting/stopping the indicator on a separate thread? Any methods you send to your UIActivityIndicatorView must be sent on the main (UI) thread.
Any events sent by a button pressed will automatically be run on the main thread. If you're using background threads to complete the process, you could do something like:
- (IBAction)buttonPressed:(id)sender {
// This runs on the main thread
[activityIndicator startAnimating];
[self performSelectorInBackground:#selector(inThreadStartDoJob:) withObject:theJobToDo];
}
- (void)inThreadStartDoJob:(id)theJobToDo {
// Set up autorelease pool
...
// Run your long-running action
...
// Stop the spinner. Since we're in a background thread,
// we need to push this to the UI Thread
[activityIndicator performSelectorOnMainThread:#selector(stopAnimating) withObject:nil waitUntilDone:YES];
}
Edit: As for the activity indicator in the top bar (where the battery is), doesn't this automatically start/stop based on network activity?
I have a problem regarding UIActivityIndicator. I applied [spinner startAnimating] at the IBAction on a button and then doing some process. After the process activityindicator should be stopped and then navigate to another view. But the activity indicator does not appear. When I remove the line "[spinner stopAnimating]" then the indicator appears but not at the instant button is pressed. It appears just before the other view loads, and apparently does not appear, I mean it does not appear but if we see very carefully then only it appears for an instant.
Thanx in advance for any answer.
Ole is pretty much correct, but there is a trick of you don't mind synchronous processing (often that it why you want to display the activity indicator in the first place).
First move your code that you want to process while the spinner is up to its own method. Then do
[spinner startAnimating];
[self performSelector:#selector(methodname) withObject:nil afterDelay:0];
The afterDelay:0 means on the next time through the run loop. That way the spinner gets started.
The animation will not start until your code returns control to the run loop. If your processing task blocks the main thread, the no UI updates will take place until it is finished. You should do your processing asynchronously (e.g. by starting an NSOperation).
you should run in perform selector .
for ex:
[self performSelector:#selector(animation) withObject:nil afterDelay:0]
-(void)animation
{
NSAutoreleasepool *pool = [[NSAutorepleasepool alloc]init];
[indicatorView startAnimating];
[pool release];
}
This is an old question. I leaving my answer here, so that might help someone to solve their problem.
I have implemented a subview which is supposed to load immediately when I click a button in the parent view. After loading the subview(which is basically holding an activityindicator), the program is supposed to process a method(which gets data from a server, so takes time) in it.
However, I am unable to do it.
What happens now is, when I click the button on the parent view, it processes the method first and only after that does the subview load on screen.
Why is this so? Is there any specific functions I could use to make my method load only after the view has loaded?
I have faced the same problem and i have used NSAutoreleasePool and solved this problem. I hope it will help you.
- (void)viewDidLoad {
[self performSelectorInBackground:#selector(loadXml) withObject:nil];
}
-(void) loadXml{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
NSString * path =#"http:www.YOUR_RSS_FEED.com";
[self parseXMLFileAtURL:path]; //(Instead of ViewDidAppear)
[self.tableView performSelectorOnMainThread:#selector(reloadData) withObject:nil waitUntilDone:NO];
[pool drain];
}
Thanks.
A few different approaches:
If the subview has functionality as loading an image and doing more complicated stuff than just being a view, a good approach is to make it into a ViewController instead.
In the top ViewController use:
- (void) loadView {
[super loadView];
}
to set up things that need to be ready upon displaying the view.
The use:
-(void) viewDidLoad {
}
to do additional setup.
In your case it sounds as if you need to add the indicator in the loadView method, then start the retrieval of data in the viewDidLoad method.
If you are accessing web services etc. always do this on a different thread. (look into NSOperation for a good, simple way of achieving this).