When setting up notification, you can set different selector to react to it. But there seems no way to remove notification by selector. For example:
// e.g. React to background notification by calling method 1
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(method1:) name:notification object:nil];
// e.g. React to background notification by calling method 2
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(method2:) name:notification object:nil];
Now when the notification fires, both methods will react to it.
How do I remove notification selectively (e.g. remove notification handler method1)?
There is a way to do it, but I don't think you will like it.
Use -addObserverForName:object:queue:usingBlock: instead.
__weak typeof(self) weakSelf = self;
// e.g. React to background notification by calling method 1
self.method1Observer = [[NSNotificationCenter defaultCenter] addObserverForName:notification object:nil queue:nil usingBlock:^(NSNotification *note) {
[weakSelf method1:note];
}];
// e.g. React to background notification by calling method 2
self.method2Observer = [[NSNotificationCenter defaultCenter] addObserverForName:notification object:nil queue:nil usingBlock:^(NSNotification *note) {
[weakSelf method2:note];
}];
Then later on:
// Remove method 1 observer while keeping method 2 observer.
if (self.method1Observer != nil) {
[[NSNotificationCenter defaultCenter] removeObserver:self.method1Observer];
self.method1Observer = nil;
}
Update: I forgot to nil check self.method1Observer before passing it to -removeObserver:.
you have to remove that notification when it will not necessary in that class. So simply use below code for remove already added Notification.
[[NSNotificationCenter defaultCenter] removeObserver:self name:#"Notification" object:nil];
Related
I have these lines of code:
-(void)someMethod:(UIScrollView*)scrollView{
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:#selector(keyboardWasShown:)
name:UIKeyboardDidShowNotification object:nil];
}
-(void)keyboardWasShown:(NSNotification *)aNotification{
// I want to get scrollView over here
}
Is there a way to make this possible? I've tried to perform this staff according to
How to pass a NSDictionary with postNotificationName:object:
but aNotification.userInfo doesn't contain my data
[[NSNotificationCenter defaultCenter]
postNotificationName:UIKeyboardDidShowNotification
object:self
userInfo:#{#"scrollView":scrollView}];
You are listening to UIKeyboardDidShowNotification and then you post UIKeyboardWillHideNotification that won't work. First maybe you like create your own notification name i.e XYZKeyboardDidShowNotification and then register for that and post using that name with the additional data you want. And then you can do:
-(void)keyboardWasShown:(NSNotification *)aNotification{
UIScrollView *scrollView = aNotification.userInfo[#"scrollView"];
}
I have an app which has to work in both portrait and landscape more and the UITabBar should adjust to current orientation (it has custom background and selected items). So, for the rest of views I just override the - (void) didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation method and it works perfectly.
How would I do that for the .moreNavigationController of UITabBarController ? I've tried adding an observer (the selector is in extension of UITabBarController):
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(didRotate:)
name:UIApplicationDidChangeStatusBarOrientationNotification
object:self.moreNavigationController];
but it never get called.
Am I missing something or what would be the best way to handle this situation ?
Solution: somewhy UIDeviceOrientation is not firing correctly, so better to use statusBarOrientation, works as a charm.
the final code which work is this:
in main UITabBarController, viewDidLoad:
[[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(didRotate:)
name:UIApplicationDidChangeStatusBarOrientationNotification
object:nil];
the didRotate selector method:
- (void) didRotate:(NSNotification *)notification{
UIInterfaceOrientation orientation = [UIApplication sharedApplication].statusBarOrientation;
if(UIInterfaceOrientationIsPortrait(orientation)) {
// Portrait
} else {
// Landscape
}
}
Thanks for help.
You are registering your UITabBarController for a notification which never gets posted. Take a look at the documentation NSNotificationCenter Reference for the addObserver:selector:name:object method
- (void)addObserver:(id)notificationObserver selector:(SEL)notificationSelector name:(NSString *)notificationName object:(id)notificationSender
notificationSender:
The object whose notifications the observer wants to receive; that is, only notifications sent by this sender are delivered to the observer.
If you pass nil, the notification center doesn’t use a notification’s sender to decide whether to deliver it to the observer.
so, if you specify the . moreNavigationController as the sender, you wont get those notifications, because it never posts such ones. Instead pass nil to ignore the sender and listen to the status bar change regardless of who sent it.
By the way, in this SO Answer is a summary of how you can react to orientation change.
And at last. If it still doesn't work, you can try this:
[[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(didRotate:)
name:UIDeviceOrientationDidChangeNotification
object:nil];
Yes, you forgot to post notification, which will call you own notification:
[[NSNotificationCenter defaultCenter] postNotificationName: UIApplicationDidChangeStatusBarOrientationNotification object:self];
or if you dont wont to send anything just set object as nil:
[[NSNotificationCenter defaultCenter] postNotificationName: UIApplicationDidChangeStatusBarOrientationNotification object:nil];
The best way to implement the same is first addObserver and then remove observer to avoid the crash:-
-(void)viewDidLoad{
[[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(didRotate:)
name:#"UIDeviceOrientationDidChangeNotification" object:nil];
}
//Now Remove Observer
-(void)viewDidDisappear:(BOOL)animated
{
[[NSNotificationCenter defaultCenter] removeObserver:self #"UIDeviceOrientationDidChangeNotification" object:nil];
}
I want to know that which method will be called when the following key is pressed.
I want to start action on above key press.
How do I know this is pressed ?
Observe the UIKeyboardDidHideNotification notification.
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(keyboardDidHide:) name:UIKeyboardDidHideNotification object:nil];
And...
- (void)keyboardDidHide:(NSNotification *)aNotification {
}
You can also change it to UIKeyboardWillHideNotification if you need to be notified BEFORE the keyboard starts to disappear.
That's not a return key. Return key is the one above it. That's simply a button that dismisses the keyboard and you can't recognize it via standard text input methods. You need to register for UIKeyboardWillHideNotification notification.
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
and implement that method:
- (void)keyboardWillHide:(NSNotification *)notification
{
// do whatever you want to do when keyboard dismiss button is tapped
}
Not sure if it's exactly what you are looking for, but you can try using notifications. Don't have Mac nearby atm, so just copy-pasting the code from github. I have that code in viewDidLoad:
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];
and then 2 methods:
- (void)keyboardWillShow:(NSNotification *)notification {
}
- (void)keyboardWillHide:(NSNotification *)notification {
}
Hope it helps
Use keyboard hide UIKeyboardWillHideNotification notification.
Example.
So i have an app with an In App purchase. The In App purchase is managed in FirstViewController. When the user has purchased the product, i want to send out a Notification to my MainTableViewController to reload the tables data and show the new objects that were purchased in the In App purchase. So basically i want to send a notification from class A to class B and class B reloads the data of the tableview then. I have tried using NSNotificationCenter, but with no success, but i know that its possible with NSNotificationCenter i just don't know how.
In class A : post the notification
[[NSNotificationCenter defaultCenter] postNotificationName:#"DataUpdated"
object:self];
In class B : register first for the notification, and write a method to handle it.
You give the corresponding selector to the method.
// view did load
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(handleUpdatedData:)
name:#"DataUpdated"
object:nil];
-(void)handleUpdatedData:(NSNotification *)notification {
NSLog(#"recieved");
[self.tableView reloadData];
}
Ok I'm adding a little bit more information to vince's answer
In class A : post the notification
[[NSNotificationCenter defaultCenter] postNotificationName:#"DataUpdated"
object:arrayOfPurchasedObjects];
In class B : register first for the notification, and write a method to handle it.
You give the corresponding selector to the method. Make sure your class B is allocated before you post the notification otherwie notification will not work.
- (void) viewDidLoad {
// view did load
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(handleUpdatedData:)
name:#"DataUpdated"
object:nil];
}
-(void)handleUpdatedData:(NSNotification *)notification {
NSLog(#"recieved");
NSArray *purchased = [notification object];
[classBTableDataSourceArray addObjectsFromArray:purchased];
[self.tableView reloadData];
}
- (void) dealloc {
// view did load
[[NSNotificationCenter defaultCenter] removeObserver:self
name:#"DataUpdated"
object:nil];
[super dealloc];
}
Maybe you trying to send notification from another thread? NSNotification won't be delivered to the observer from another thread.
Can someone please show me an example of a Cocoa Obj-C object, with a custom notification, how to fire it, subscribe to it, and handle it?
#implementation MyObject
// Posts a MyNotification message whenever called
- (void)notify {
[[NSNotificationCenter defaultCenter] postNotificationName:#"MyNotification" object:self];
}
// Prints a message whenever a MyNotification is received
- (void)handleNotification:(NSNotification*)note {
NSLog(#"Got notified: %#", note);
}
#end
// somewhere else
MyObject *object = [[MyObject alloc] init];
// receive MyNotification events from any object
[[NSNotificationCenter defaultCenter] addObserver:object selector:#selector(handleNotification:) name:#"MyNotification" object:nil];
// create a notification
[object notify];
For more information, see the documentation for NSNotificationCenter.
Step 1:
//register to listen for event
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:#selector(eventHandler:)
name:#"eventType"
object:nil ];
//event handler when event occurs
-(void)eventHandler: (NSNotification *) notification
{
NSLog(#"event triggered");
}
Step 2:
//trigger event
[[NSNotificationCenter defaultCenter]
postNotificationName:#"eventType"
object:nil ];
Make sure to unregister notification (observer) when your object is deallocated. Apple documentation states: "Before an object that is observing notifications is deallocated, it must tell the notification center to stop sending it notifications".
For Local Notifications the next code is applicable:
[[NSNotificationCenter defaultCenter] removeObserver:self];
And for observers of distributed notifications:
[[NSDistributedNotificationCenter defaultCenter] removeObserver:self];