noobie table refresh question - ios

Question

I'm trying to learn IOS development, I've created a project from a sample RSS feed app that loads data from a XML feed file on my server. This works fine but I want it to refresh if the home button is pressed (ios multi-tasking). I've tried [table reloaddata] and put it in all the viewdidload / viewdiddisappear sections but its not working and its not stopping on the breakpoints I've put on them all.
#implementation RootViewController
- (void)viewDidLoad {
// Add the following line if you want the list to be editable
// self.navigationItem.leftBarButtonItem = self.editButtonItem;
//[newsTable reloaddata];
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [stories count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *MyIdentifier = #"MyIdentifier";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:MyIdentifier] autorelease];
}
// Set up the cell
int storyIndex = [indexPath indexAtPosition: [indexPath length] - 1];
[cell setText:[[stories objectAtIndex: storyIndex] objectForKey: #"title"]];
return cell;
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
// Navigation logic
int storyIndex = [indexPath indexAtPosition: [indexPath length] - 1];
NSString * storyLink = [[stories objectAtIndex: storyIndex] objectForKey: #"link"];
// clean up the link - get rid of spaces, returns, and tabs...
storyLink = [storyLink stringByReplacingOccurrencesOfString:#" " withString:#""];
storyLink = [storyLink stringByReplacingOccurrencesOfString:#"\n" withString:#""];
storyLink = [storyLink stringByReplacingOccurrencesOfString:#" " withString:#""];
NSLog(#"link: %#", storyLink);
// open in Safari
[[UIApplication sharedApplication] openURL:[NSURL URLWithString:storyLink]];
}
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
[newsTable reloadData];
}
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
if ([stories count] == 0) {
[newsTable reloadData];
NSString * path = #"http://www.myserver.co.uk/test.xml";
[self parseXMLFileAtURL:path];
//[NSTimer scheduledTimerWithTimeInterval:10 target:self selector:#selector(reloadData) userInfo:nil repeats:FALSE];
}
cellSize = CGSizeMake([newsTable bounds].size.width, 60);
}
-(void)viewWillDisappear:(BOOL)animated {
[newsTable reloadData];
}
- (void)viewDidDisappear:(BOOL)animated {
[newsTable reloadData];}
- (void)applicationDidBecomeActive:(UIApplication *)application {
/*
Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
*/
[newsTable reloadData];
}
- (void)applicationWillEnterForeground:(UIApplication *)application {
/*
Called as part of transition from the background to the inactive state: here you can undo many of the changes made on entering the background.
*/
[newsTable reloadData];
}
- (void)parserDidStartDocument:(NSXMLParser *)parser{
NSLog(#"found file and started parsing");
}
- (void)parseXMLFileAtURL:(NSString *)URL
{
stories = [[NSMutableArray alloc] init];
//you must then convert the path to a proper NSURL or it won't work
NSURL *xmlURL = [NSURL URLWithString:URL];
// here, for some reason you have to use NSClassFromString when trying to alloc NSXMLParser, otherwise you will get an object not found error
// this may be necessary only for the toolchain
rssParser = [[NSXMLParser alloc] initWithContentsOfURL:xmlURL];
// Set self as the delegate of the parser so that it will receive the parser delegate methods callbacks.
[rssParser setDelegate:self];
// Depending on the XML document you're parsing, you may want to enable these features of NSXMLParser.
[rssParser setShouldProcessNamespaces:NO];
[rssParser setShouldReportNamespacePrefixes:NO];
[rssParser setShouldResolveExternalEntities:NO];
[rssParser parse];
}
- (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError {
NSString * errorString = [NSString stringWithFormat:#"Unable to download story feed from web site (Error code %i )", [parseError code]];
NSLog(#"error parsing XML: %#", errorString);
UIAlertView * errorAlert = [[UIAlertView alloc] initWithTitle:#"Error loading content" message:errorString delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil];
[errorAlert show];
}
- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict{
//NSLog(#"found this element: %#", elementName);
currentElement = [elementName copy];
if ([elementName isEqualToString:#"item"]) {
// clear out our story item caches...
item = [[NSMutableDictionary alloc] init];
currentTitle = [[NSMutableString alloc] init];
currentDate = [[NSMutableString alloc] init];
currentSummary = [[NSMutableString alloc] init];
currentLink = [[NSMutableString alloc] init];
}
}
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName{
//NSLog(#"ended element: %#", elementName);
if ([elementName isEqualToString:#"item"]) {
// save values to an item, then store that item into the array...
[item setObject:currentTitle forKey:#"title"];
[item setObject:currentLink forKey:#"link"];
[item setObject:currentSummary forKey:#"summary"];
[item setObject:currentDate forKey:#"date"];
[stories addObject:[item copy]];
NSLog(#"adding story: %#", currentTitle);
}
}
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string{
//NSLog(#"found characters: %#", string);
// save the characters for the current item...
if ([currentElement isEqualToString:#"title"]) {
[currentTitle appendString:string];
} else if ([currentElement isEqualToString:#"link"]) {
[currentLink appendString:string];
} else if ([currentElement isEqualToString:#"description"]) {
[currentSummary appendString:string];
} else if ([currentElement isEqualToString:#"pubDate"]) {
[currentDate appendString:string];
}
}
- (void)parserDidEndDocument:(NSXMLParser *)parser {
[activityIndicator stopAnimating];
[activityIndicator removeFromSuperview];
NSLog(#"all done!");
NSLog(#"stories array has %d items", [stories count]);
[newsTable reloadData];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
// Return YES for supported orientations
return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning]; // Releases the view if it doesn't have a superview
// Release anything that's not essential, such as cached data
}
- (void)dealloc {
[currentElement release];
[rssParser release];
[stories release];
[item release];
[currentTitle release];
[currentDate release];
[currentSummary release];
[currentLink release];
[super dealloc];
}
#end

Answer 1

I like to use notifications to handle this situation. Add this line of code to your 'viewDidLoad' method
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(updateRSSFeed)
name:UIApplicationWillEnterForegroundNotification
object:nil];
The 'updateRSSFeed' method will do something like this
- (void) updateRSSFeed
{
NSLog( #"Feed Me!!!");
// Code to restart loading the data from the RSS feed and ultimately reloading
// the table view.
}
And don't forget to remove the observer so add this to the 'dealloc' method
[[NSNotificationCenter defaultCenter] removeObserver: self];
In a complex app with multiple view controllers a view controller can be deallocated without the app quitting and a notification may be sent to a non-existent instance and you get a crash.
Notifications are very useful so dig into the documentation and other sources to figure out how to use them.
Finally, the methods 'applicationDidBecomeActive:' and 'applicationWillEnterForeground:' will never be called in the root view controller since they are part of the application delegate protocol which your appDelegate adheres to.

Answer 2

Hey, if you want to react to the app going into background, you should implement
- (void)applicationDidEnterBackground:(UIApplication *)application
on your appDelegate, and trigger the data reload from there. viewWillAppear doesn't get called when the app is going to background (i.e. when you "minimize" it, press home button, or switch to other app.
Cheers

Answer 3

I'm not really clear where you are calling [tableView reloadData] from. Based on your description, you must be calling it during the applicationWiilResignActive:, but this will most likely not run unless you have indicated to the OS that you want to download in the background.
However I believe that you have to have already started that download before this method is called, which will explain why you see neither the table reload or the breakpoints called.
It's possible I misunderstood how you are doing the call, but I think you have a fundamental design problem since you can't start that reload at the moment of deactivation.