UITableViewCell not hiding progress bar - ios

Question

I have a UITableView that is supposed to show progress bars at various times, and then hide them when finished. However, the progress bars aren’t disappearing when they’re supposed to.
Background
The app I’m working on is designed to allow users to create multimedia-heavy projects. One of the views shows a list of all the audio files that are currently available, and also gives users the option to import additional files from a number sources, including their music library.
Details
To handle the import from the music library, I’m using a variation of the code posted by Chris Adamson in his blog here. The user can queue up as many imports as necessary, and code will automatically import them in sequence. The read/write part is performed in the background, with notifications sent out to let the rest of the app know the status of the process.
All of the audio files available to the user are shown in a UITableView. The table view uses custom cells containing a label (to display the file’s name) and a progress bar (which is always hidden unless the song is in mid-import).
Here is the code for the cell:
#interface AudioTableCell()
#property (nonatomic, strong) NSString *importingFileName;
#end
#implementation AudioTableCell
// ---------------------------------------------------------------------------------------------------------------------
- (void) prepareForReuse
{
// remove notification listeners to avoid creating duplicates
[[NSNotificationCenter defaultCenter] removeObserver:self name:kNotifMusicLibMgrUpdateProgress object:nil];
[[NSNotificationCenter defaultCenter] removeObserver:self name:kNotifMusicLibMgrFinishedImportingSong object:nil];
// reset cell properties to default values
self.isClickable = YES;
self.downloadProgress.hidden = YES;
}
// ---------------------------------------------------------------------------------------------------------------------
// called by view controller prior to deleting a cell
- (void) prepareCellForDeletion
{
[[NSNotificationCenter defaultCenter] removeObserver:self name:kNotifMusicLibMgrUpdateProgress object:nil];
[[NSNotificationCenter defaultCenter] removeObserver:self name:kNotifMusicLibMgrFinishedImportingSong object:nil];
}
// ---------------------------------------------------------------------------------------------------------------------
// called by the view controller's cellForRowAtIndexPath method
- (void) configureCell
{
// by default, cell should be clickable and the progress bar should be hidden
self.isClickable = YES;
self.downloadProgress.hidden = YES;
// listen to the import manager for updates on the import's progress
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(importWasUpdated:)
name:kNotifMusicLibMgrUpdateProgress
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(importWasFinished:)
name:kNotifMusicLibMgrFinishedImportingSong
object:nil];
// when the cell is scrolled out of view, the progress bar is hidden
// need to remember if depicted song was in process of being downloaded
if (self.importingFileName.length > 0) {
if ([self.trackLabel.text isEqualToString:[self.importingFileName stringByAppendingPathExtension:#"m4a"]]) {
self.downloadProgress.hidden = NO;
self.isClickable = NO;
}
}
}
// ---------------------------------------------------------------------------------------------------------------------
// triggered when receiving a notification that a song has been imported successfully
- (void) importWasFinished:(NSNotification *)notification
{
// the notification will pass the name of the song that was imported
NSString *fileName = [notification.userInfo objectForKey:#"audioFileName"];
// if the song that was imported matches the song being displayed by the cell, hide the progress bar
// and make the cell clickable
if ([self.trackLabel.text isEqualToString:[fileName stringByAppendingPathExtension:#"m4a"]]) {
self.downloadProgress.hidden = YES;
self.isClickable = YES;
}
// if the song that was imported matches the song that was "saved" by the cell, clear the saved song
if ([self.importingFileName isEqualToString:fileName]) {
self.importingFileName = #"";
}
}
// ---------------------------------------------------------------------------------------------------------------------
// triggered when receiving a an update notification (currently 1/second)
- (void) importWasUpdated:(NSNotification *)notification
{
// the notification will pass the name of the song being imported, its progress, and the number of songs queued
NSString *fileName = [notification.userInfo objectForKey:#"audioFileName"];
double completion = [[notification.userInfo objectForKey:#"progress"] doubleValue];
// if the cell is displaying the song being imported, disable the cell and show a progress bar
// also, store the name of the song - this way, if the cell is reused for a different song, it will still remember
// the song being downloaded and can immediately display the progress bar when brought back into view
if ([self.trackLabel.text isEqualToString:[fileName stringByAppendingPathExtension:#"m4a"]])
{
self.isClickable = NO;
self.downloadProgress.hidden = NO;
[self.downloadProgress setProgress:completion];
self.importingFileName = fileName;
} else {
self.downloadProgress.hidden = YES;
self.isClickable = YES;
}
}
#end
As you can see, the cell listens for notifications from the importer to determine when to hide/show the progress bar. If I only try to import a single song, there are no major issues (although there does seem to be slight delay between the time the song finishes and the time the progress bar hides). However, if I queue up multiple songs, the progress bar doesn’t go away at all until all of them are finished. Even worse, scrolling the cell out of view will cause the progress bar to appear for a different song when the cell gets reused.
I’ve tested the notification system using both NSLog statements and the debugger, and it’s working correctly (the “self.downloadProgressBar.hidden = YES;” section is getting called at the right time), but the progress bar remains visible. At this point I am completely out of ideas. Any and all help would be greatly appreciated.
Thanks in advance.

Answer 1

Please check that your code is executed on main thread. NSNotification can be posted on background thread so your code will be executed on background thread which won't update the UI.