UITableView not being displayed after reloading data - ios

I have a strange problem with my tableView.
I load data via JSON into my tableView. While the JSON is being requested from the web in another class, I show an activity indicator view in my current view and the tableView is hidden.
I ve got a delegate method, which is called as soon as the json is ready.
-(void)didReceivePlayers:(NSArray *)players {
[activityIndicator stopAnimating];
tableViewPlayers.hidden = false;
startButton.hidden = false;
playersData = [[NSMutableArray alloc] initWithArray:players];
[tableViewPlayers reloadData];
NSLog(#"done reloading");
}
The method is being called perfectly.
The code is pretty straight forward. I hide my activity indicator and show my tableView.
Then I call reloadData. It takes only a few milliseconds. BUT after reloadData, my activityIndicator is still shown and it takes several seconds to show my tableview, although the nslog is being called right away.
I also tried calling reload data in mainThread, but this did not change a thing.
Thanks for your help!

Be sure that the code is being executed on the main thread. You can use the main operation queue like this:
-(void)didReceivePlayers:(NSArray *)players {
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
[activityIndicator stopAnimating];
tableViewPlayers.hidden = false;
startButton.hidden = false;
playersData = [[NSMutableArray alloc] initWithArray:players];
[tableViewPlayers reloadData];
NSLog(#"done reloading");
}];
}

Related

Upload new items to table view

I have table view that load new data (depend on page) from SQL data base. Problem is, when i load it in main thread, it block UI for a while. When i try to do "hard work" in background, and reload data in main thread, odd things start to happen, for example, table view section header move in wrong place, and i load enormous amount of data.
First case, all work but block UI for while:
[self.tableView addInfiniteScrollingWithActionHandler:^{
#strongify(self)
if (!self.viewModel.isUpdating){
self.viewModel.isUpdating = YES;
[self.tableView.infiniteScrollingView startAnimating];
[self.viewModel nextPage];
[self.tableView reloadData];
self.viewModel.isUpdating = NO;
}
}];
In second case, i tried to do background work, following not work as expected:
if (!self.viewModel.isUpdating){
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//Add some method process in global queue - normal for data processing
self.viewModel.isUpdating = YES;
[self.tableView.infiniteScrollingView startAnimating];
[self.viewModel nextPage];
dispatch_async(dispatch_get_main_queue(), ^(){
//Add method, task you want perform on mainQueue
//Control UIView, IBOutlet all here
[self.tableView reloadData];
self.viewModel.isUpdating = NO;
});
//Add some method process in global queue - normal for data processing
});
}
}];
How should i modify my code to not load main thread, and without "weird" things?
have you tried something like this.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
.....
dispatch_async(dispatch_get_main_queue(), ^{
[self performSelectorOnMainThread:#selector(updateView) withObject:nil waitUntilDone:YES];
});
});
......
-(void)updateView{
[self.tableView reloadData];
self.viewModel.isUpdating = NO;
}
user PerformSelectorOnMainThread it may help you.

How to Update Label With Downloading Data

In my model, data is downloaded from website in a for loop and in a each turn data is sending to my viewController using protocol method. In model file;
for(NSString* data in DataArray){
[self.delegate passUpdatingCourse:data_name];
//other operations
}
In my viewController data name coming from model is saving to NSArray property in other thread;
ModelClass *modelObject = [[ModelClass alloc] init];
[modelObject setDelegate:self];
dispatch_queue_t otherQ = dispatch_queue_create("Q", NULL);
dispatch_async(otherQ, ^{
//other operations
[self performSelectorOnMainThread:#selector(passUpdatingCourse:) withObject:nil waitUntilDone:YES];
dispatch_async(dispatch_get_main_queue(), ^{
[self.myIndicator stopAnimating];
self.indicatorText.hidden = YES;
[self.changingCourseLabel setNeedsDisplay];
});
});
And also data coming via protocol method is setting viewController label;
-(void)passUpdatingCourse:(NSString *)data_in{
self.myLabel.text = data_in;
}
When each data came, myLabel in a viewController must be update. But it is not happens. In a protocol method when I use this;
NSLog(#"Data:%#",self.myLabel.text);
Yeah it shows data in a console but myLabel in a view is not changing.
I searched questions like that but couldn't find a solution.
Assuming your loop is on a background thread, dispatch your label updates to the main queue (async).
If you're inside a for loop on the main thread nothing is going to get updated in the UI until your method returns and dispatch won't help in that case.

What is a good concept to implement activity indicator

In our iPgone & iPad app we use push segue transitions between different ui contollers, most of them extend UICollectionViewController. In each controller we load data from our internal API. Loading is done viewWillAppear or viewDidLoad.
Now, the thing is, that this API call sometime can take a second or two, or even three... well, lot's of stuff there, let's assume we can't change it. But, we can change the user experience and at least add the "loading" circle indicator. The thing is, what I can't understand by means of correct concept, while transition from A to B, the "load" is done at B, while page A still presented.
So, question is "how do I show indicator on page A, while loading controller for page B?"
Thanks all,
Uri.
Common approach in this case is to load data in destination view controller NOT in main thread. You can show indicator while loading data in background thread and then remove it.
Here is sample of code from my project solving the same problem:
- (void) viewDidLoad {
...
// add indicator
self.spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
self.spinner.hidesWhenStopped = YES;
self.spinner.center = self.view.center;
[self.view addSubview:self.spinner];
...
// fetch news
[self.spinner startAnimating];
__weak typeof(self) weakSelf = self
[[BitrixApiClient sharedInstance] getLatestNewsWithCompletionBlock:^(NSArray *newsArray, NSUInteger maxPageCount, NSUInteger currentPageNumber, NSError *error) {
if (!error) {
weakSelf.newsArray = newsArray;
weakSelf.currentPageNumber = currentPageNumber;
[weakSelf.newsTableView reloadData];
}
// stop spinning
[weakSelf.spinner stopAnimating];
}];
}

Objective C- Trouble updating UI on main thread

I am having some trouble updating my UI using performSelectorOnMainThread. Here is my situation. In my viewDidLoad I set up an activity indicator and a label. Then I call a selector to retrieve some data from a server. Then I call a selector to update the UI after a delay. Here's the code:
- (void)viewDidLoad
{
[super viewDidLoad];
self.reloadSchools = [[UIAlertView alloc] init];
self.reloadSchools.message = #"There was an error loading the schools. Please try again.";
self.reloadSchools.title = #"We're Sorry";
self.schoolPickerLabel = [[UILabel alloc]init];
self.schoolPicker = [[UIPickerView alloc] init];
self.schoolPicker.delegate = self;
self.schoolPicker.dataSource = self;
self.server = [[Server alloc]init];
schoolList = NO;
_activityIndicator = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
[self.view addSubview:_activityIndicator];
[self.view bringSubviewToFront:_activityIndicator];
[_activityIndicator startAnimating];
[NSThread detachNewThreadSelector: #selector(getSchoolList) toTarget: self withObject: nil];
[self performSelector:#selector(updateUI) withObject:nil afterDelay:20.0];
}
The selector updateUI checks to see if the data was retrieved, and calls a selector on the main thread to update the UI accordingly. Here is the code for these parts:
-(void)updateUI
{
self.schools = [_server returnData];
if(!(self.schools == nil)) {
[self performSelectorOnMainThread:#selector(fillPickerView) withObject:nil waitUntilDone:YES];
}
else {
[self performSelectorOnMainThread:#selector(showError) withObject:nil waitUntilDone:YES];
}
}
-(void)showError {
NSLog(#"show error");
[_activityIndicator stopAnimating];
[self.reloadSchools show];
}
-(void)fillPickerView {
NSLog(#"fill picker view");
schoolList = YES;
NSString *schoolString = [[NSString alloc] initWithData:self.schools encoding:NSUTF8StringEncoding];
self.schoolPickerLabel.text = #"Please select your school:";
self.shoolArray = [[schoolString componentsSeparatedByString:#"#"] mutableCopy];
[self.schoolPicker reloadAllComponents];
[_activityIndicator stopAnimating];
}
When the selector fillPickerView is called the activity indicator keeps spinning, the label text doesn't change, and the picker view doesn't reload its content. Can someone explain to me why the method I am using isn't working to update my ui on the main thread?
dispatch_async(dispatch_get_global_queue(0, 0), ^{
//load your data here.
dispatch_async(dispatch_get_main_queue(), ^{
//update UI in main thread.
});
});
First of all you should not be using detachNewThreadSelector. You should use GCD and submit your background task to an async queue. Threads are costly to create. GCD does a much better job of managing system resources.
Ignoring that, your code doesn't make a lot of sense to me. You submit a method, getSchoolList, to run on a background thread. You don't show the code that you are running in the background.
Then use performSelector:withObject:afterDelay to run the method updateUI on the main thread after a fixed delay of 20 seconds.
updateUI checks for self.schools, which presumably was set up by your background thread, and may or may not be done. If self.schools IS nil, you call fillPickerView using performSelectorOnMainThread. That doesn't make sense because if self.schools is nil, there is no data to fill the picker.
If self.schools is not nil, you display an error, again using performSelectorOnMainThread.
It seems to me that the logic on your check of self.schools is backwards. If it is nil you should display an error and if it is NOT nil you should fill the picker.
Next problem: In both cases you're calling performSelectorOnMainThread:withObject:waitUntilDone: from the main thread. Calling that method from the main thread doesn't make sense.
Third problem: It doesn't make sense to wait an arbitrary amount of time for a background task to run to completion, and then either succeed or fail. You won't have any idea what's going on for the full 20 seconds. If the background task finishes sooner, you'll never know.
Instead, you should have your background task notify the main thread once the task is done. That would be a valid use of performSelectorOnMainThread:withObject:waitUntilDone:, while calling it from the main thread is not. (Again, though, you should refactor this code to use GCD, not using threads directly.
It seems pretty clear that you are in over your head. The code you posted needs to be rewritten completely.

UICollectionView doesn't update immediately when calling reloadData, but randomly after 30-60 seconds

As the title implies, my UICollectionView doesn't update and display the cells immediately after calling reloadData. Instead, it seems to eventually update my collection view after 30-60 seconds. My setup is as follows:
UICollectionView added to view controller in Storyboard with both delegate and dataSource setup for the view controller and standard outlet setup
numberOfSectionsInRow & cellForItemAtIndexPath are both implemented and reference the prototyped cell and the imageView inside of it
Here is the code that goes to Twitter, get's a timeline, assigns it to a variable, reloads a table view with the tweets and then goes through the tweets to find photos and reloads the collection view with those items.
Even if I comment out the code to display the image, it still doesn't change anything.
SLRequest *timelineRequest = [SLRequest requestForServiceType:SLServiceTypeTwitter requestMethod:SLRequestMethodGET URL:timelineURL parameters:timelineParams];
[timelineRequest performRequestWithHandler:^(NSData *responseData, NSHTTPURLResponse *urlResponse, NSError *error) {
if(responseData) {
JSONDecoder *decoder = [[JSONDecoder alloc] init];
NSArray *timeline = [decoder objectWithData:responseData];
[self setTwitterTableData:timeline];
for(NSDictionary *tweet in [self twitterTableData]) {
if(![tweet valueForKeyPath:#"entities.media"]) { continue; }
for(NSDictionary *photo in [[tweet objectForKey:#"entities"] objectForKey:#"media"]) {
[[self photoStreamArray] addObject:[NSDictionary dictionaryWithObjectsAndKeys:
[photo objectForKey:#"media_url"], #"url",
[NSValue valueWithCGSize:CGSizeMake([[photo valueForKeyPath:#"sizes.large.w"] floatValue], [[photo valueForKeyPath:#"sizes.large.h"] floatValue])], #"size"
, nil]];
}
}
[[self photoStreamCollectionView] reloadData];
}
}];
This is a classic symptom of calling UIKit methods from a background thread. If you view the -[SLRequest performRequestWithHandler:] documentation, it says the handler makes no guarantee of which thread it will be run on.
Wrap your call to reloadData in a block and pass this to dispatch_async(); also pass dispatch_get_main_queue() as the queue argument.
You need to dispatch the update to the main thread:
dispatch_async(dispatch_get_main_queue(), ^{
[self.photoStreamCollectionView reloadData];
});
or in Swift:
dispatch_async(dispatch_get_main_queue(), {
self.photoStreamCollectionView.reloadData()
})
Apple say:You should not call this method in the middle of animation blocks where items are being inserted or deleted. Insertions and deletions automatically cause the table’s data to be updated appropriately.
In face: You should not call this method in the middle of any animation (include UICollectionView in the scrolling).
so, you can:
[self.collectionView setContentOffset:CGPointZero animated:NO];
[self.collectionView performSelectorOnMainThread:#selector(reloadData) withObject:nil waitUntilDone:NO];
or mark sure not any animation, and then call reloadData;
or
[self.collectionView performBatchUpdates:^{
//insert, delete, reload, or move operations
} completion:nil];

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