I have an application that has a UITableView. This UITableView is populated by an NSMutableArray being held (as a property) in the appDelegate. You can think of this as an email window. It lists messages in a subclassed UITableViewCell. When a new message appears, I have all the code done which downloads the message, adds the data to the appDelegate's NSMutableArray which holds all of the messages. This code is working fine.
Now, once the new message is downloaded and added to the array, I am trying to update my UITableView using the following code, however - the UITableView's delegate functions do not get called.
The odd thing is when I scroll my UITableView up and down, the delegate methods finally get called and my section headers DO change (they show the message count for that section). Shoudn't they update in real-time and not wait for my scrolling to trigger the refresh? Also, the new cell is never added in the section!!
Please Help!!
APPDELEGATE CODE:
[self refreshMessagesDisplay]; //This is a call placed in the msg download method
-(void)refreshMessagesDisplay{
[self performSelectorOnMainThread:#selector(performMessageDisplay) withObject:nil waitUntilDone:NO];
}
-(void)performMessageDisplay{
[myMessagesView refresh];
}
UITableViewController Code:
-(void) refresh{
iPhone_PNPAppDelegate *mainDelegate = (iPhone_PNPAppDelegate *)[[UIApplication sharedApplication] delegate];
//self.messages is copied from appDelegate to get (old and) new messages.
self.messages=mainDelegate.messages;
//Some array manipulation takes place here.
[theTable reloadData];
[theTable setNeedsLayout]; //added out of desperation
[theTable setNeedsDisplay]; //added out of desperation
}
As a sanity check, have you verified that theTable is not nil at that point?
You could try putting a delay on the reloadData call - I had a similar problem when I was trying to get my tableview to update when reordering cells, except that the app crashed if I called reloadData during it.
So something like this might be worth a try:
Refresh method:
- (void)refreshDisplay:(UITableView *)tableView {
[tableView reloadData];
}
and then call it with (say) a 0.5 second delay:
[self performSelector:(#selector(refreshDisplay:)) withObject:(tableView) afterDelay:0.5];
Hope it works...
If you call reloadData from within a dispatched method, make sure to execute it on the main queue.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND,0), ^(void) {
// hard work/updating here
// when finished ...
dispatch_async(dispatch_get_main_queue(), ^(void) {
[self.myTableView reloadData];
});
});
..same in method form:
-(void)updateDataInBackground {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND,0), ^(void) {
// hard work/updating here
// when finished ...
[self reloadTable];
});
}
-(void)reloadTable {
dispatch_async(dispatch_get_main_queue(), ^(void) {
[myTableView reloadData];
});
}
Have you tried setting a breakpoint in your refresh method just to be sure your messages array has the correct content before calling reloadData?
Related
I have two UITableViewControllers A and B, and this is what I'm trying to do when I click on a table view cell in A:
Prepare to segue from A to B by setting some of B's variables from A.
Perform segue from A to B.
B appears.
Display a "Loading" activity indicator with [MBProgressHUD][1].
In a background task, retrieve data from a URL.
If an error occurs in the URL request (either no data received or non-200 status code), (a) hide activity indicator, then (b) display UIAlertView with an error message
Else, (a) Reload B's tableView with the retrieved data, then (b) Hide activity indicator
However, this is what's happening, and I don't know how to fix it:
After clicking a cell in A, B slides in from the right with an empty plain UITableView. The MBProgressHUD DOES NOT SHOW.
After a while, the tableView reloads with the retrieved data, with the MBProgressHUD appearing very briefly.
The MBProgressHUD immediately disappears.
There doesn't seem to be an error with the way the background task is performed. My problem is, how do I display the MBProgressHUD activity indicator as soon as my B view controller appears? (And actually, how come it's not showing?) Code is below.
A's prepareForSegue
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
B *b = (B *)[segue destinationViewController];
// Set some of B's variables here...
}
Relevant methods in B
- (void)viewDidAppear:(BOOL)animated {
[self startOver];
}
- (void)startOver {
[self displayLoadingAndDisableTableViewInteractions];
[self retrieveListings];
[self.tableView reloadData];
[self hideLoadingAndEnableTableViewInteractions];
}
- (void)displayLoadingAndDisableTableViewInteractions {
MBProgressHUD *hud = [MBProgressHUD showHUDAddedTo:self.view animated:YES];
hud.labelText = #"Loading";
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
self.tableView.userInteractionEnabled = NO;
}
- (void)hideLoadingAndEnableTableViewInteractions {
[MBProgressHUD hideHUDForView:self.view animated:YES];
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
self.tableView.userInteractionEnabled = YES;
}
- (void)retrieveListings {
__block NSArray *newSearchResults;
// Perform synchronous URL request in another thread.
dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
newSearchResults = [self fetchNewSearchResults];
});
// If nil was returned, there must have been some error--display a UIAlertView.
if (newSearchResults == nil) {
[[[UIAlertView alloc] initWithTitle:#"Oops!" message:#"An unknown error occurred. Try again later?" delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil] show];
} else {
// Add the retrieved data to this UITableView's model. Then,
[self.tableView reloadData];
}
}
- (NSArray *)fetchNewSearchResults {
// Assemble NSMutableArray called newSearchResults from NSURLConnection data.
// Return nil if an error or a non-200 response code occurred.
return newSearchResults;
}
I think you have to call [self hideLoadingAndEnableTableViewInteractions]; after newSearchResults = [self fetchNewSearchResults]; You are retrieving data in another thread which means -startOver will continue executing after calling [self retrieveListings]; and will hide the HUD right away. Also because you are updating the display you have to make sure you are doing that on the main thread. See example
dispatch_async(dispatch_get_main_queue(), ^{
//update UI here
});
When B appears, it displays a plain and empty UITableView, but does not display the MBProgressHUD even if the task does begin in the background (and yet, the MBProgressHUD is called to show before that). Hence, my solution is to show the MBProgressHUD in viewDidLoad, which precedes viewWillAppear.
- (void)viewDidLoad {
// ...
[self displayLoadingAndDisableUI];
}
I set up two additional boolean properties to B--one in .h, called shouldStartOverUponAppearing, and one in a class extension in .m, called isLoadingAndDisabledUI. In startOver, I added the following lines:
- (void)startOver {
if (!self.isLoadingAndDisabledUI) {
[self displayLoadingAndDisabledUI];
}
}
The check is done so that startOver doesn't display another MBProgressHUD when it has already been displayed from viewDidLoad. That is because I have a third view controller, called C, that may call on B's startOver, but doesn't need to call viewDidLoad just to display the MBProgressHUD.
Also, this is how I defined viewDidAppear:
- (void)viewDidAppear:(BOOL)animated {
if (self.shouldStartOverUponAppearing) {
[self startOver];
self.shouldStartOverUponAppearing = NO;
}
}
This way, startOver will only be invoked IF B appeared from A. If B appears by pressing "Back" in C, it will do nothing and only display the old data that was there.
I think that this solution is FAR from elegant, but it works. I guess I'll just ask for a better approach in a separate SO question.
I have used a common method for MBProgressHUD.
#import "MBProgressHUD.h" in AppDelegate.h also following methods.
- (MBProgressHUD *)showGlobalProgressHUDWithTitle:(NSString *)title;
- (void)dismissGlobalHUD;
In AppDelegate.m add following methods.
- (MBProgressHUD *)showGlobalProgressHUDWithTitle:(NSString *)title {
[MBProgressHUD hideAllHUDsForView:self.window animated:YES];
MBProgressHUD *hud = [MBProgressHUD showHUDAddedTo:self.window animated:YES];
hud.labelText = title;
return hud;
}
- (void)dismissGlobalHUD {
[MBProgressHUD hideHUDForView:self.window animated:YES];
}
How to use?
AppDelegate *appDel = (AppDelegate *)[[UIApplication sharedApplication]delegate];
//Show Indicator
[appDel showGlobalProgressHUDWithTitle:#"Loading..."];
//Hide Indicator
[appDel dismissGlobalHUD];
Hope this helps.
I am using the [performSelector:#selector(reloadData) withObject:nil afterDelay:0.01] inside IBAction of a UIButton, the reloadData method draw some subviews on the main view in a particular way, the issue is when I tap the button quickly and repeatedly the selector "ReloadData" executed multiple times, event though I am canceling the all previous requests to that selector, and this results in duplication for the subviews in the main view
-(IBAction) myButtonIsTapped
{
[NSObject cancelPreviousPerformRequestsWithTarget:self selector:#selector(reloadData) object:nil];
[self performSelector:#selector(reloadData) withObject:nil afterDelay:0.01];
}
and reload data method like the following:
-(void) reloadData
{
#synchronized(self){
// clear all subviews from the main view
// draw new subviews
}
}
What about this:
-(IBAction) myButtonIsTapped
{
[self.myButton setUserInteractionEnabled:NO];
[self performSelector:#selector(reloadData) withObject:nil afterDelay:0.01];
}
-(void) reloadData
{
// Long task...
// Enable the button again:
[self.myButton setUserInteractionEnabled:YES];
}
Sometimes is just easier to control what the user is doing (UI), than logically dealing with what he has done.
Do one Thing create one BOOL variable and set in viewdidload yes and check in function if it is yes then method call and also make it no in buttonmake method.
I have a view, when it starts, the array of objects is read from memory and the Table View is completed with the objects. When I go to another view and write another objects to file and get back to the first view, the objects are loaded into the array from file as it should but the doesn't reload somehow... [myTableView reloadData] doesn't work, neither does setNeedsDisplay.
-(void)viewWillAppear:(BOOL)animated
{
contactsToLayNow=[NSKeyedUnarchiver unarchiveObjectWithFile:fPath()];
NSLog(#"NOW IN VIEW WILL APPEAR");
for(Contact *cn in contactsToLayNow)
{
NSLog(#"%#", cn.fName);
}
//[self.view setNeedsDisplay];
[quickDialTableView reloadData]; //MOREOVER EXCEPTION HERE IS THROWN
[super viewWillAppear:YES];
}
you will need to retain contactsToLayNow - I guess it's being autoreleased sometime during your tableViews's drawing :)
contactsToLayNow = [[NSKeyedUnarchiver unarchiveObjectWithFile:fPath()] retain];
PS It's not required but you should put your call to super at the top of this method ;)
Move your [super viewWillAppear:animated]; to first line of viewWillAppear: method.
I am sending a notification from one view to another view. My problem is that the notification in the view that I am calling in my cellForRowAtIndexPath method is only getting sent when the tableview is scrolling. How can I stop this and make it send the notification once the images have downloaded? Here is my code: https://gist.github.com/756302
Thanks
MKDev
as far as I understand your code, the message will trigger the reload of the whole table. That should lead to a refresh of the cells.
Thus, you'll need to check in line 76, if the cell is being drawn because a reload was triggered from the finish-message (and the image is now ready to display) or if you need to start the asynchronous download of the image.
The first thing which comes into my mind to check this is to set a property in reloadTableView:
- (void)reloadTableView
{
[[NSUserDefaults standardUserDefaults] setBool:YES forKey:#"aaa"];
[[NSNotificationCenter defaultCenter] removeObserver:self name:#"name" object:nil];
NSLog(#"removeobserver");
loadImageFinished = YES;
// if your table has several sections you'll need to adopt the section number
NSIndexSet *indices = [[NSIndexSet alloc] initWithIndex:0];
[self.tableView reloadSections:indices withRowAnimation:UITableViewRowAnimationFade];
[indices release];
}
and then to add in
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
...
if (loadImageFinished) {
...
} else {
[asyncImage loadImageFromURL:[NSURL URLWithString:pathImage]];
}
...
}
Note that there could be other reasons why the table is being reloaded - the view could have been disappeared or unloaded and you might not wish to trigger your asynnchronous loading several times.
Your code should work right, when the connectionDidFinishLoading, you call the NSNotificationCenter to send the notification, there is no post method in cellForRowAtIndexPath
I have a tableView that loads an XML feed as follows:
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
if ([stories count] == 0) {
NSString *path = #"http://myurl.com/file.xml";
[self parseXMLFileAtURL:path];
}
}
I'd like to have the spinner to show on the top bar at the app launch and dissapear once the data is displayed on my tableView.
I thought that putting the beginning at viewDidAppear and the end at -(void)parserDidEndDocument:(NSXMLParser *)parser but it didn't work.
I'd appreciate a good explained solution on how to implement this solution.
Here's the problem: NSXMLParser is a synchronous API. That means that as soon as you call parse on your NSXMLParser, that thread is going to be totally stuck parsing xml, which means no UI updates.
Here's how I usually solve this:
- (void) startThingsUp {
//put the spinner onto the screen
//start the spinner animating
NSString *path = #"http://myurl.com/file.xml";
[self performSelectorInBackground:#selector(parseXMLFileAtURL:) withObject:path];
}
- (void) parseXMLFileAtURL:(NSString *)path {
//do stuff
[xmlParser parse];
[self performSelectorOnMainThread:#selector(doneParsing) withObject:nil waitUntilDone:NO];
}
- (void) doneParsing {
//stop the spinner
//remove it from the screen
}
I've used this method many times, and it works beautifully.
Starting a new thread can be overkilling and a source of complexity if you want to do things that are supposed to start on the main thread.
In my own code, I need to start a MailComposer by pushing a button but it can take some time to appear and I want to make sure the UIActivityIndicator is spinning meanwhile.
This is what I do :
-(void)submit_Clicked:(id)event
{
[self.spinner startAnimating];
[self performSelector:#selector(displayComposerSheet) withObject:nil afterDelay:0];
}
It will queue displayComposerSheet instead of executing it straight away. Enough for the spinner to start animating !
I typically implement an NSTimer that will call my spinner method, which I fire off right before I go into doing the heavy work (the work that will typically block the main thread).
The NSTimer fires and my spinner method is called. When the main work is finished, I disable the spinner.
Code for that is like:
IBOutlet UIActiviyIndicatorView *loginIndicator;
{
...
[loginIndicator startAnimating];
[NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:#selector(executeAuthenticationRequest)
userInfo:nil repeats:NO];
...
}
- (void) executeAuthenticationRequest
{
/* Simulate doing a network call. */
sleep(3);
[loginIndicator stopAnimating];
...
}
You can also do:
IBOutlet NSProgressIndicator *pIndicator;
Start:
[pIndicator startAnimation:self];
[pIndicator setHidden:NO];
And Stop:
[pIndicator stopAnimation:self];
[pIndicator setHidden:YES];
In Cocoa (and most other app frameworks) the user interface is updated by the main thread. When you manipulate views, they are typically not redrawn until control returns to the run loop and the screen is updated.
Because you are parsing the XML in the main thread, you are not allowing the screen to update, and that is why your activity indicator is not appearing.
You should be able to fix it by doing the following:
In viewDidAppear, show/animate the spinner and then call
[self performSelector:#selector(myXMLParsingMethod) withObject:nil afterDelay:0];
In myXMLParsingMethod, parse your XML, then hide/stop the spinner.
This way, control will return to the run loop before parsing begins, to allow the spinner to begin animating.