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How to tell when controller has resumed from background?
How to refresh View after user enters applicationWillEnterForeground?
I want to complete recall for example HomeViewController.
I have and update function in HomeViewController and I want when user enters to call update function and reload table data.
Any class can register to UIApplicationWillEnterForegroundNotification, and react accordingly. It's not reserved to the app delegate, and helps for better separation of source code.
Create a viewDidLoad method like this for your HomeViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(yourUpdateMethodGoesHere:)
name:UIApplicationWillEnterForegroundNotification
object:nil];
}
// Don't forget to remove the observer in your dealloc method.
// Otherwise it will stay retained by the [NSNotificationCenter defaultCenter]...
- (void) dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
[super dealloc];
}
If your ViewController is a tableViewController your could also directly call the reload data function:
- (void)viewDidLoad
{
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver:[self tableView]
selector:#selector(reloadData)
name:UIApplicationWillEnterForegroundNotification
object:nil];
}
- (void) dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
[super dealloc];
}
Or you could use a block:
[[NSNotificationCenter defaultCenter] addObserverForName:UIApplicationWillEnterForegroundNotification
object:nil
queue:[NSOperationQueue mainQueue]
usingBlock:^(NSNotification *note) {
[[self tableView] reloadData];
}];
You could declare a property in your app delegate class that would point to the HomeViewController object. Then you can call your update function in applicationWillEnterForeground.
Related
This is my code.
Here create the observer to Notification called Example into ViewController
- (void)addObserverExample
{
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(example:)
name:#"Example"
object:nil];
}
- (void)example:(NSNotification *)notification{
NSLog(#"Example!!!");
}
From viewDidLoad register my observer
- (void)viewDidLoad
{
[self addObserverExample];
}
In my second ViewController. When tapped a button excute this code:
[[NSNotificationCenter defaultCenter] postNotificationName:#"Example" object:self.dictKeys userInfo:nil];
The problem I have is that the notification is never executed.
Any idea.
Have created demo for NSNotificationCenter as per your question and it's working fine for me. Here it is the link of that code: NSNotificationCenter Demo
- (void)viewDidLoad {
[super viewDidLoad];
[self addObserverExample];
}
- (void)addObserverExample
{
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(example:)
name:#"Example"
object:nil];
}
- (void)example:(NSNotification *)notification{
NSLog(#"Example!!!");
NSLog(#"%#",notification.userInfo);
}
- (IBAction)btnFireNotification:(id)sender {
[[NSNotificationCenter defaultCenter] postNotificationName:#"Example" object:nil userInfo:#{#"key" : #"value"}];
}
I believe the problem you're having may be related to the fact that in your second view controller, you're passing self.dictKeys in the object parameter.
If you want to pass data via the NSNotificationCenter, you should use the userInfo parameter instead.
Darshan's example does this the correct way.
I am facing an issue with NSNotificationCenter.
I am not able to send message and receive message using NSNotificationCenter in latest ios 8.4 (XCode 6.4)
Please check the following code:
1) I want to send data using first view controller to another view.
so i have written the following code in first viewcontroller:
When user btn clicked method as following :
- (IBAction)btnClicked:(id)sender
{
[self postNotification];
[self performSegueWithIdentifier:#"asGo" sender:self];
}
-(void)postNotification{
[[NSNotificationCenter defaultCenter] postNotificationName:#"MyNotification" object:self];
}
2) In Second view controller i have added observer in ViewWillApper as following :
-(void) viewWillAppear:(BOOL)animated
{
[super viewWillAppear:YES];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(eventListenerDidReceiveNotification:)
name:#"MyNotification"
object:nil];
}
-(void)eventListenerDidReceiveNotification:(NSNotification*)txt
{
NSLog(#"i got notfication:");
}
so eventListenerDidReceiveNotification is not called while come on view.
But i am not getting above log while i come on second vc with navigation
As others have noted, NSNotificationCenter doesn't work like a post office. It only delivers notifications if someone actually listens to them at the moment they arrived. This is the reason your eventListenerDidReceiveNotification method is not being called: you add an observer in viewWillAppear, which is called after the segue (I assume that you're using segues because of the performSegueWithIdentifier method in your code) is finished, so it's definitely called after postNotification has been called.
So, in order to pass data via NSNotificationCenter you have to add an observer before you post a notification.
The following code is completely useless and unnecessarily overcomplicated, you shouldn't do anything like that, but since you keep insisting on using a scheme like this, here you go:
//Didn't test this code. Didn't even compile it, to be honest, but it should be enough to get the idea.
NSString * const SOUselessNotificationName = #"MyUselessNotification";
#pragma mark - FIRST VC
#interface SOFirstVC : UIViewController
#end
#implementation SOFirstVC
NSString * const SOasGoSegueIdentifer = #"asGo";
- (IBAction)btnClicked:(id)sender {
[self performSegueWithIdentifier:SOasGoSegueIdentifer sender:self];
}
-(void)postNotification {
[[NSNotificationCenter defaultCenter] postNotificationName:SOUselessNotificationName object:self];
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifer isEqualToString:SOasGoSegueIdentifer]) {
SOSecondVC *destinationVC = (SOSecondVC *)segue.destinationViewController;
[destinationVC registerToReceiveNotificationsFromObject:self];
[self postNotification];
}
}
#end
#pragma mark - SECOND VC
#interface SOSecondVC : UIViewController
-(void)registerToReceiveNotificationsFromObject:(id)object;
#end
#implementation SOSecondVC
-(void)registerToReceiveNotificationsFromObject:(id)object {
[[NSNotificationCenter defaultCenter] addObserver:self selector:(eventListenerDidReceiveUselessNotification:) name:SOUselessNotificationName object:object];
}
-(void)eventListenerDidReceiveUselessNotification:(NSNotification*)uselessNotification {
NSLog(#"I got a useless notfication! Yay!");
}
-(void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
#end
NSNotificationCenter basically has 3 steps
Adding Observer like [[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(open:) name:#"OpenDetail" object:nil];
Posting Notification [[NSNotificationCenter defaultCenter] postNotificationName:#"OpenDetail" object:self];
Removing Observer [[NSNotificationCenter defaultCenter] removeObserver:self name:#"OpenDetail" object:nil];
I think you are posting your notification and then later adding observer while it's vie versa. You have to add observer first then post notification.
HTH
First you have to setup the data you want to send
NSDictionary *userInfo = [NSDictionary dictionaryWithObject:myObject forKey:#"aKey"];
Then you post it with the data like so:
[[NSNotificationCenter defaultCenter] postNotificationName: #"MyNotification" object:nil userInfo:userInfo];
And finally you read the data off the notification:
-(void)eventListenerDidReceiveNotification:(NSNotification*)notification
{
NSLog(#"i got notification:");
NSDictionary *userInfo = notification.userInfo;
NSString *myObject = [userInfo objectForKey:#"aKey"];
}
My code:
-(void)viewWillAppear:(BOOL)animated {
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(handleKeyboard:) name:UIKeyboardWillChangeFrameNotification object:nil];
}
-(void)viewWillDisappear:(BOOL)animated {
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
-(void)handleKeyboard:(NSNotification*)notification {
NSLog(#"triggered");
}
See:
The disappearing handler is triggered once as normal, but 3 times when appears. Is this a iOS bug?
Possibly not helpful for your problem but you need to be calling [super viewWill… for your overrides.
-(void)viewWillAppear:(BOOL)animated
-(void)viewWillDisappear:(BOOL)animated
From the docs.
If you override this method, you must call super at some point in
your implementation.
Hi I am using NSNotificationCenter defaultCenter to implement the 'like' and 'comment' functions in my app.
//In Answer Table View
#implementation AnswerTableView
- (id)initWithParentController:(UIViewController *)pController andResourcePath:(NSString *)thisResourcePath {
....
// Notification to reload table when a comment is submitted
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(reloadTable)
name:#"Comment Submitted"
object:nil];
// Notification to reload table when an answer is liked
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(reloadTable)
name:#"Answer Liked"
object:nil];
}
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
[super dealloc];
}
//In custom button implementation - THIS BUTTON IS CREATED IN EVERY CELL OF THE TABLEVIEW
#implementation UICustomButton
-(id)initWithButtonType:(NSString *)type {
self = [super init];
if (self) {
//Initialization done here
}
return self;
}
- (void)buttonPressed {
if ([btnType isEqualToString:#"like"]) {
[[NSNotificationCenter defaultCenter] postNotificationName:#"Answer Liked" object:nil];
}
else if ([btnType isEqualToString:#"comment"]) {
[[NSNotificationCenter defaultCenter] postNotificationName:#"Comment Submitted" object:nil];
}
}
However, I realize that after using these functions for a while, the response speed of the table reload gets slower and slower (to a point where it crashes).
Did I miss out anything in the implementation i.e. deallocating etc
You are repeatedly adding observers and the slowdown occurs because the notification code has to cycle over more and more observers to send notifications. You are probably crashing because you are leaking so many of these views.
Put a log statement in your dealloc to see if these instances are ever cleaned up. Also there can be timing issues with removeObserver in a dealloc method. try to remove the observer before dealloc if you can.
Sometimes its good to queue the event with Grand Central Dispatch to make sure its running on the main thread.
dispatch_async(dispatch_get_main_queue()
I have the following code that adds an observer in the loading of the view.
- (void)viewDidLoad
{
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserverForName:#"com.app.livedata.jsonupdated"
object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification *notif) {
NSLog(#"JSONUPDATED");
}];
}
And this fires fine. However when the view is unloaded and I confirm the dealloc is called the Notification is still firing.
There doesn't seem to be a method for deactivating this observer?
Seems the solution is to track the object in the View and then you can reference it in the dealloc methods.
id observer = [[NSNotificationCenter defaultCenter] addObserverForName: /* ... */ ];
And then remove as following:
[[NSNotificationCenter defaultCenter] removeObserver:observer];
observer = nil;