I am loading data of NSArray into UITableView . Its going ok. I really confuse to show UIActivityindicator at time of loading uitableview.
So please, give guideline, sample code.
Thanks.
No matter how much data you have (how many elements your NSArray model contains), only the visible cells will be needed for the table view, that is small. So if you already have you model data loaded then you don't need an activity monitor.
If you are talking about acquiring the data prior to refreshing the table view (filling your array based data model), or downloading data from a remote URL then you will need to do this in a background thread so that the main thread is free to update your UI (specifically your activity indicator). Once your data is ready you reload your table view on the main thread.
NSObject has a number of convenience methods to achieve this including
- (void)performSelectorInBackground:(SEL)aSelector withObject:(id)arg
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait
Except if you have a LOT of data in your array, or if some data come from the internet, the loading of your UITableView (well, the cells that are displayed) should take less than a frame, so it is useless to try to display a UIActivityIndicator in this case.
Related
My application consists of data downloaded from an XML file. data contains short text and images.
currently I'm downloading up all data and building up the view in a view controller, in the ViewDidLoad method, which causes the application not to show up the root view until all data is downloaded. I want it to show up in a more user friendly way, at least to preload some of the data during the splash screen.
By the way I've done the lazy image loading so images can load while the main view is displayed.
As long as the number of views depend on number of rows in XML, loading XML asynchronously while building up the the view does not suite my need (or maybe I'm wrong).
I understand that describing the solution in an answer is quite a challenge, so maybe you could point to an article or even a book that has a detailed explanation of asynchronous and multithread handling.
I don't see why you can't load it asynchronously o_O
You should show some "Loading" view anyway (preferably with an activity Indicator)
A progress bar would be nice, too.
And when it's done downloading you just reload and relayout your view.
If by "number of views" you mean the number of cells in a table row you can just tell the tableview to reload all data whereas your numberOfRowsInSection function (or whatever you want to use) should return appropriate values depending on whether it's loading or not.
EDIT: you shouldn't do that while the application is still loading because that's extremely user-unfriendly and slows down the loading of the application aswell
I think you should parse all data in didFinishLaunchingWithOptions: method of appDelegate and then use following methods to do parsing.
[self performSelectorInBackground:#selector(downloadData:) withObject:nil];
method downloadData: contain parsing procedure.
I am processing several large RSS feeds and displaying results in a TableView. The processing starts after the user clicks on the relevant tab. All works well, but as it takes a couple of seconds to process, the NIB and Table don't load until the processing finishes and it looks like the iPhone has seized up. I have added an Activity indicator to the NIB, but because it doesn't load until the table is ready to display, it appears too late to be of any use.
Does anyone have any ideas how to display a message to a user while the table builds/loads? I have tried loading a UIView first and adding the Table as a subview but, again, both seem to load only after the table is ready.
Guidance appreciated.
It's kind of hard to guess what's going on from your description but it looks like your calls aren't asynchronous. Here's what you should be doing in your code:
Make all calls asynchronous. You said your phone is seizing up. Makes it sound like your requests and responses are happening on the main thread. There are many libraries you could use to handle asynchronous calls. ASIHTTPRequest for one example....
Don't wait for the data to come in before displaying the tableView. It's a design principle that you load as much of the UI as possible so that the user has something to look at while your data loads up in the background. What you should be doing is initializing an NSMutableArray to hold the data. Initially this array will contain no objects. This is the array that you use in your data source methods: Use array size for numberOfRowsInSection and use the array objects in cellForRowAtIndexPath. Once your RSS feed XML comes in and is parsed, store that in your arrays and call [tableView reloadData]. This way you don't leave your users looking at a blank screen. (Another good practice is when the array size is zero, show one cell in your tableview that says "data is loading" or something).
When you first initialize and load up your table and then fire off those RSS feed requests, that's where you show an activity indicator view on the tableView. Stop animating the indicator when the RSS data comes in and your tableView reloads.
These are the standard steps you should follow while showing non local data in a tableview. Makes for a smooth user experience.
Like I said before, it seems from your question that your calls are not asynchronous. If I'm wrong, correct me and let's take it from there...
In my UIView I've got a UITableView (UITV) which is controlled by an NSFetchedResultsController (NSFRC). The UIView is inside a UINavigationController.
When the view is about to be loaded/displayed I start some background activities which fetch data from a remote server (JSON) and parse into Core Data.
The NSFRC is being called when the parsing is done and the threaded NSManagedObjectContext have been merged into the main context.
The problem is that sometimes many rows are being inserted to Core Data at once, a lot of table cells are being added and there is quite a delay from that the actual fetching and parsing is done, until the rows are being displayed.
Now I wonder if anyone knows of any solution to, for example:
hook up a spinner to some "fetched results controller inserted all its rows for this time" (or something) notification/delegate call to at least tell the user that "something is going to show up soon"?
Or might the best solution simply be to not initialize the NSFRC until the background fetching and processing is completed?
Thanks!
If I understand your question correctly, you may want to look into the NSFetchedResultsControllerDelegate methods, with documentation available here: http://developer.apple.com/library/ios/#documentation/CoreData/Reference/NSFetchedResultsControllerDelegate_Protocol/Reference/Reference.html
There are delegate methods available for pre changes with controllerWillChangeContent:, post changes with controllerDidChangeContent and during changes with didChangeSection: and didChangeObject.
I hope it helps!
Rog
I have a subview where there is an uitableview that gets data from an online server (title, subtitle and image). When I click the button that shows the subview it takes a little time to get there using WiFi connection, but under 3G network it takes longer, so that you really feel the gap between loading the view and having pressed the button
what I'd like to do, is to display an uiactivityindicatorview when you press the button and after loading the view, and when it has loaded stop the activity indicator
how can I check that the uitableview has finished loading ?
do you have other suggestions ?
Thanks in advance
Use asynchronious requests or threading (take a look at NSOperation)
Look into doing network operations asynchronously, rather than blocking the main UI's thread. ASIHTTPRequest is a really good library for this: http://allseeing-i.com/ASIHTTPRequest/
As the others said, if you are not using an asynchronous approach to this, I strongly suggest you to do so, because otherwise you will block your application for as long as the data is being downloaded.
With that said, you could show the activity indicator while the data is being loaded, and that is until the delegate method
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
is called. Then, your table should be populated with the data and the indicator would dissapear.
I hope this helped you a bit
I have a UITableView subclass and a UITableViewCell subclass that I'm using for cells. I'm bulding all my cells in advance and store them in an array from where I use them in cellForRowAtIndexPath. Aside from this I have a thread that loads some images in each cell, in the background. The problem is that the cells don't get refreshed as fast as the images are loaded. For example, if I don't scroll my table view, the first cells only get refreshed when all cells have been modified and the thread has exited.
Any ideas on how I can effectively refresh my tableview/cell?
Have you tried calling [cell setNeedsDisplay] but on the main thread?
setNeedsDisplay when called on a background thread does pretty much nothing,
try this:
[cell performSelectorOnMainThread:#selector(setNeedsDisplay) withObject:nil waitUntilDone:NO];
Are you using a callback to notify the controller of your tableview that the images have been loaded? If not, that would be an ideal method.
When the image loads, fire off a callback to the table view controller that sets the image on the cell, and then calls reloadData on the tableView.
This way whenever a new image loads, the table will update to display it.
Not sure exactly what you are trying to achieve with the images - but can I guess they are coming from a server and that is why you want to download them in another thread?
I would not try to load up the cells before you display the table - you should use lazy loading as much as possible to make sure you are making the most of the memory on a device.
My suggestion would be to look at using a subclass of NSOperation to manage the loading of images. Firstly NSOperation will handle all the complexity of threading for you and allow you to queue up the operations. You will then be able to prioritise the operations that you want completed for the cells at the top.
As each operation completes you can make a call back to the cell or tableViewController (perhaps create a delegate protocol to make this really easy).
If you have an operation per image/cell combination then you should be able to refresh each cell as the operation completes. Doing this along with prioritising the operations will give you an optimal solution.
If the NSOperations sound complex or you are put off by this - please do try it - it is a lot simpler than I might have made it sound.
Have you tried calling [cell setNeedsDisplay]?