What I want is an IBAction command in Xcode that is automatically triggered every second. It would perform similar to a button, triggering a set of commands.
Thanks for your time,
jjj
Use NSTimer, which is the Foundation framework class that does exactly what you've asked for.
Related
Background:
I currently have a NSTimer running in my AppDel class (I also have a method to calculate the amount of time my app spends in the background and adds it to the total, in case anyone brings this up).
The timer is checked at different intervals to see if it has reached 12 hours, at 12 hours the app needs to refresh its data from the server.
When this occurs, I need to display a UIAlert which when its button is pressed:
• Pops off view controllers to the first view controller.
This “refresh” should only be able to occur on 3 (specific)view controllers out of 7 within my app.
The Question(s):
Is NSNotifcationCenter sufficient for my requirements?
Where I would add an observer only to the view controllers I want this to occur on?
Is there a better approach I should be taking?
ya you can implement the NSNotifcationCenter approach but best alternative is to use custom delegate approach .By this way your app will work according to apple guidelines and memory utilisation of app is also less.
Using NSNotificationCenter is a good approach when you need to send information about some event (for example need of refreshing app) and you want to make as few changes as possible, without redesign all app architecture. I recommend you https://github.com/AllinMobile/AIMObservers because is created to facilitate the work with NSNotificationCenter and NSNotification.
How would you go about implementing a "dayDidChange" method?
I have a dateLabel, that needs updating, when the day changes.
I already had 2 solutions implemented. But gave up on them.
1st, on viewWillAppear, I would set my label. Chances for date changing when the user is viewing the VC are VERY small ... and it wouldn't really introduce any "errors" to execution But still, it's not perfect.
2nd, I also implemented an NSTimer with intervals of 1 second. Works great. But I'm not too found of the idea of having a method being called if there is a chance that I don't need to do it.
Are there any other options? I need to update that label, when the day changes. Also, is it possible to use NSNotificationCenter with this?
In your appliciation delegate, implement the following method: -(void)applicationSignificantTimeChange:(UIApplication *)application
This method is called when the day changes, or if the device's time has been changed in the background for whatever reason (such as changes to time zone).
hope it helps. happy coding :)
You can calculate the time left on the day and set a timer to it. You can also listen to UIApplicationSignificantTimeChangeNotification. Note that this notification will be fired not only when the date changes, but for timezone adjustments and other changes. Keep in mind also that the firing of the notification will be triggered only if your app is not in an inactive state.
There are many ways to do so, and I can elaborate more on them if needed.
But here is a nice quick trick
use this code in your app delegate
it will listen to time changes (when the date or time changes dramatically) and when that happens - run a test and update the label if needed.
read me about this here: https://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIApplication_Class/Reference/Reference.html
It's just a quick simple way of doing it without timers.
- (void)applicationSignificantTimeChange:(UIApplication *)application {
NSLog(#"Time has changed, do a test and update the label if needed");
// [yourViewController runTimeTestAndUpdateFunction];
}
I am implementing search autocommplete. I am doing it without UISearchDisplayController/UISearchBar
A recurring problem is if I start doing something right after the guy press button then the program isn't "snappy".
A way around that is to use timer.
Then I've heard that UISearchController has a delegate to call.
Will that delegate solve my problem? What exactly does the delegate do? Wait a while after pressing button?
My experience is that searchDisplayController:shouldReloadTableForSearchString: is called immediately when the text in the search field changes. So that would not help with your problem.
I'm having some fun with objective c. As a simple program I wanted to write a clock application.
Basically, a UITextField needs to show the current time and update every second.
My initial thought was to use delegation and let UITextField call back a class when the 'Value Changed' event occurs. By 'bootstrapping' an initial value change (e.g. by setting the time at application startup) I thought I could trigger the 'Value Changed' event continuously afterwards (the UITextField would continuously change itself, hence triggering the delegate method). I tried many things, but this never worked. I even tried creating a button that would set UITextField to an arbitrary text value (as opposed to setting UITextField at startup) in the hope that the delegated method would be called, but this did not either. To prove that my code was correct, the time was updated when I'd use other actions like 'Touch Down' for example: I would get the time on every click in the UITextField.
I eventually found out that i could use a callback every second by using [self performSelector ...] and that worked.
Is there a fundamental reason my delegation using the 'Value Changed' action never worked ?
The value changed event only fires in response to a user event-- that is, you setting your textField.text = "something" doesn't fire it, by design.
And it's a good job it doesn't, because by the sounds of it you were trying to get your application into an infinite loop. If the 'value changed' event did actually fire when you set the text in the box, the program would ask the delegate again, which would set the text again, which would ask the delegate again..... you get the picture. This is called an infinite loop, and it has the effect of causing the program to hang, and then crash, since there's no way for the program execution to exit this loop.
Anyway, in order to do what you're saying, you've got two options
you can set up an NSTimer object to call your time update method every second. It's quite easy, check out the documentation.
performSelector:withObject:afterDelay:. It sounds like you might have already got the hang of this one. It's not as neat as using an NSTimer, but it will do the job.
I'm writing a plugin for an application. I cannot derive from NSApplication
as it is a third party application. I can get the callback in my plugin when any key is pressed. But I will not know what key is pressed. So is there any call in Cocoa to find the last key pressed when I get the callback? I only have NSView object.
Any ideas will help me a lot.
Thanks,
Dheeraj.
A couple of thoughts:
Use [NSApp currentEvent]. I know you don't think you have an NSApplication instance, but you should try this. It might work.
Do some event monitoring in your plugin (CGEventTap, NSEvent local monitor, etc) and record whenever you see a keypress event.