Imagine I have a spinner that I have to enable while something relatively heavy is being done and then deactivate the spinner after the task is done.
If I do:
[mySpinner startAnimating];
[self doSomethingHeavy];
[mySpinner stopAnimating];
I will never see the spinner running, because doSomethingHeavy will lock the thread and never let the spinner show.
I have tried to fire a new queue on the main thread using Grand Central Dispatch for the spinner and in another try for the task, but the results are the same. No spinner running.
The only way to make it work is to fire the method with a delay, using
[self performSelector:#selector(doSomethingHeavy) withObject:nil afterDelay:0.02];
but this sounds more like a hack and if I put [mySpinner stopAnimating] after that line, it will probably stop the spinner before the task is done.
This is not just valid for the spinner but for any task that that needs screen update.
...
[mySpinner startAnimating];
[self performSelectorInBackground:#selector(doSomethingHeavy) withObject:nil];
...
}
- (void)doSomethingHeavy {
...
[mySpinner performSelectorOnMainThread:#selector(stopAnimating) withObject:nil waitUntilDone:NO];
}
Or instead of stopping the spinner in doSomethingHeavy it would more likley finish with a call to:
[self performSelectorOnMainThread:#selector(finishedSomethingHeavy) withObject:nil waitUntilDone:NO];
which would stop the spinner and update the UI with the heavy results.
Hopefully I'm understanding the question properly, but normally I'd use the method
[self performSelectorInBackground:#selector(doSomethingHeavy) withObject:nil];
in this situation as this leaves the main thread free to update the UI while still performing the task in the background.
I have tried these solutions but unfortunately none worked, because my doSomethingHeavy method must be run on the main thread too.
Using the hack of firing the method with a delay works but not for methods that should run with more than one parameter, as performSelector: afterDelay: cannot be used to pass more than one parameter.
I found a solution firing a queue on the main thread using Grand Central Dispatch and then sleeping it for 0.02 seconds. Using the queue, I can put anything I want.
Related
I am not sure why, but for some reason my UIActivityIndicator spinner stays visible for awhile after I ask it to stop spinning. In my app, I check for updates with a block method callback when the check is complete after which point the activity indicator is to be hidden. The NSLog is processed immediately when the block is called, but it takes maybe 5-10 seconds for the indicator to disappear. Nothing is going on in the main as far as I can tell, the app is just sitting there. I am very confused...
[self showActivityIndicator];
[[self schedulePack] checkForUpdates:^(void)
{
NSLog(#"Done updating.");
[self hideActivityIndicator];
}];
The problem is probably that you access a UI element from a separate thread. Try replacing
[self hideActivityIndicator];
with
[self performSelectorOnMainThread:#selector(hideActivityIndicator) withObject:nil waitUntilDone:NO];
I've been researching this for a few days, but nothing I've found works.
Here's the desired process: User presses the enter button on a pop-up window -> ActivityIdicator appears -> saving process occurs -> ActivityIndicator disappears.
However, for some reason the ActivityIndicator does not show up until after the process is complete, rendering it completely useless.
I attempted to follow the process described here: UIActivityIndicator not working properly?
Here is the code for the pop-up window
-(void)alertView:(UIAlertView *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
// the user clicked one of the Enter/Cancel buttons
[self performSelector:#selector(DisplaySpinner) withObject:nil afterDelay:0];
if (buttonIndex == 1)
{
[self performSelector:#selector(EnterButtonClicked) withObject:nil afterDelay:0];
}
else
{
NSLog(#"Name Cancel Clicked");
}
[NameField resignFirstResponder];
}
Here is the code for the DisplaySpinner method:
-(void)DisplaySpinner{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init];
[self.view addSubview:loadingIndicator];
[loadingIndicator startAnimating];
[pool release];
}
The EnterButtonClicked Method contains the saving process. Despite running in seperate processes, The ActivityIndicator doesn't show up until after the process is complete.
Any suggestions?
The app doesn't update the screen to show the UIActivityIndicatorView until the main run loop regains control. 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.
When a rotation event happens, the willRotate... and willAnimateRotation... methods are called in one pass through the main run loop. So you block on the method before displaying the activity indicator.
To make this work, you need to push the method task over to another thread. That method would call back to this view controller when the work is completed so the view can be updated. I would put show the activity indicator in the willAnimateRotation... method.
What you need to do is forcing the UIActivityIndicatorView to start displaying even though the run loop won't be ended. One way is -
[self performSelector:#selector(animation) withObject:nil afterDelay:0]
-(void)startSpinner
{
NSAutoreleasepool *pool = [[NSAutorepleasepool alloc]init];
[indicatorView startAnimating];
[pool release];
}
So essentially, performSelector sets up a timer to perform the animation message on the current thread’s run loop. The timer is configured to run in the default mode (NSDefaultRunLoopMode). When the timer fires, the thread attempts to dequeue the message from the run loop and perform the selector. It succeeds if the run loop is running and in the default mode; otherwise, the timer waits until the run loop is in the default mode.
Please note that specifying a delay of 0 does not necessarily cause the selector to be performed immediately. The selector is still queued on the thread’s run loop and performed as soon as possible.
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 a question that we might answer together i have a tickertape in my iphone app (Like those stick tickers) and i use a NSThread to keep the memory away from the main thread so it will not slow down the app. Now the thing is it does its job well but when i scroll on a UITableView that i have on the same view i notice that my ticker tape animation stops to work.
ViewController.m (Main view of this object has the ticker tape on it)
-(void)startTicker {
[NSThread detachNewThreadSelector:#selector(start) toTarget:ticker withObject:nil];
}
TickerView.c (This handles the tickertape animation)
// Called from the viewcontroller
-(void) start {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
[self performSelectorOnMainThread:#selector(loop) withObject:nil waitUntilDone:YES];
[pool release];
}
-(void)loop {
timerHandle = [NSTimer scheduledTimerWithTimeInterval:.01f target:self selector:#selector(render) userInfo:nil repeats:YES];
}
-(void) render {
// Does a *** load of calculations here and moves the items in the tickertape..
}
My Question: How can i prevent the UITableview or any other view / touch event to block this thread from updating the tickertape animation ?.
Your NSTimer is not running on a background thread, but on the main thread. It will block anytime something else runs on the main thread. -performSelectorOnMainThread: means that anything done within the method called will run on the main thread.
To make your loop truly independent of the main thread, you could set up a while loop within your start method that sleeps for a given interval on every pass, then calls your render method. You'd need to make sure that all user interface updates within your render method get performed on the main thread, but make waitUntilDone NO for those method calls. I've also done this using NSOperations, where as one operation finishes I add another to the queue.
Also, running this render operation 100 times per second is excessive. I'd back that down a bit, or even better, look at using Core Animation for your ticker to make your drawing more efficient.