I know this question has been posted on this forum before:
How do you get the time interval for UIDatePicker in UIDatePickerModeCountDownTimer mode?
However, the answer mentioned there isnt working for me and i am not able to comment on the earlier post hence this new question.
I have a simple application where i have a UIDatePicker in CountDownTimer mode. I want to retrieve whatever value the user sets it to and store it or print it to log.
- (IBAction) datePickerValueDidChange:(id)sender {
NSLog(#"datePicker.countDownDuration: %f", timerPicker.countDownDuration);
}
the value being printed is 0 always. Dnt know where i am going wrong so any help will be appreciated.
You haven't posted much code, but my guess would be that your picker has a different name than timerPicker.
Alternately you've got a local instance variable conflict with your picker property and that referring to it as self.timerPicker.countDownDuration will do the trick.
A third option is that you've either not connected and/or declared your viewController as being the picker's delegate, or if you have then you haven't included the delegate declaration in your interface (though the latter is less likely because you should get a noticeable build-time error).
Otherwise you'll need to post some more code, including where you declare it and where you set its values.
Check this out, there is full tutorial about count down timer with date picker --- http://aarlangdi.blogspot.com.au hope this is helpful to you guys
Related
I asked a question and someone answered with the following showing very strange/unexpected Swift behavior.
https://stackoverflow.com/a/33201738/2079103
In that answer, the author shows code that compares a property of UITextView to nil and the test says reports it is nil. The code prints the value of the property, and it outputs "nil". But when he assigns the property to a variable, using ! and prints the the variable, it shows a functional font object.
How is that possible?
I assume UITextView has some kind of property observer, but what in Swift accounts for that behavior?
After updating to XCode 6.3, compiler started giving this warning.
Comparison of address of 'myObject' not equal to null pointer is always true.
Here is my piece of code,
Scratching my head with it, but didn't find any solution or workaround to get rid of this warning.
My question is linked with question over here. But, it can't be solved using answer discussed.
Any help will be welcomed :)
Correct way of checking the pointer is
if (anotherInView != nil) {
}
You are comparing address of a variable with the NULL. Every variable has an address you can't have a variable whose address is NULL, you can have a variable whose value is NULL
Also anotherRect != NULL is again not valid. anotherRect will always have a value as it's a struct
There are four mistakes here. The first two are that you aren't setting any initial values for the CGRect and UIView variables, so there's no way to detect a failure. Try setting the CGRect to a zero-width, zero-height rect initially if you think that is useful, and set the UIView to nil.
The third and fourth mistakes are that the address of a local variable is never NULL. (Note that this is not true for global variables in libraries, as I mentioned in another comment—the address of an NSString pointer constant might be NULL if the symbol didn't exist on the version of the OS you're running—but for local variables, you're guaranteed an address up to the point where your stack overflows and your app crashes.)
I'm also puzzled by why you're calling a delegate method yourself. Normally, the OS itself calls those methods, so calling them yourself is somewhat atypical usage. To be fair, I've done it on occasion when a delegate method performs a computation that I need somewhere else in the code, and I've also done it when implementing delegates that call other delegates, but in the context of this question, it seemed like a potential mistake.
For the first instruction, a changed to :
if (!CGRectIsNull(anotherRect)) {
}
How do you use UILexicon in Objective-C? I find the documentation Apple provides is extremely unhelpful.
What does it do? Does it return a dictionary or proper spellings of words? Or do I provide a word like "hellllo" and it matches it with the proper spelling "Hello" and returns that as a string?
Any help would be appreciated.
requestSupplementaryLexiconWithCompletion:
Here's my error report, but obviously I'll have errors because I'm completely guessing how to use the function, no clue what goes inside the block statement (because the docs (at the time) don't say! (Beta 4 docs)) Hahahah!
I've never used this feature, but a quick web search for "UILexicon" landed me in Apple's documentation; reading and following links from there filled in the picture pretty quick.
App Extension Programming Guide has a quick explanation of what lexicons are for:
Every custom keyboard (independent of the value of its RequestsOpenAccess key) has access to a basic autocorrection lexicon through the UILexicon class. Make use of this class, along with a lexicon of your own design, to provide suggestions and autocorrections as users are entering text.
Clicking the UILexicon link on that page took me to the reference doc for that class, which explains that it's a read-only list of Apple-provided term pairs. Each of its entries is a UILexiconEntry object -- the docs for that class say it provides a userInput (what the user typed, e.g. "ipad") and a documentText (what to substitute for it, e.g. "iPad"). Since those classes are read-only, it follows that they're probably not a way for you to provide your own autocorrection pairs -- as stated in the docs, they're for supplementing whatever autocorrection system you implement.
At this point, I don't even have to look at the doc for requestSupplementaryLexiconWithCompletion: to get a good idea how to use it: just the declaration tells me:
It's a method on UIInputViewController, the class I'd have to subclass to create a custom keyboard. Somewhere in that subclass I should probably call it on self.
Its return type is void, so I can't get a lexicon by assigning the result of a requestSupplementaryLexiconWithCompletion call to to a variable.
It calls the block I provide, passing me a UILexicon object as a parameter to that block.
It's got words like "request" and "completionHander" in it, so it'll probably do something asynchronous that takes awhile, and call that block when it's done.
So, I'm guessing that if I were writing a custom keyboard, I'd call this method early on (in viewDidLoad, perhaps) and stash the UILexicon it provides so I can refer to it later when the user is typing. Something like this:
#property UILexicon *lexicon;
- (void)viewDidLoad {
[super viewDidLoad];
[self requestSupplementaryLexiconWithCompletion:^(UILexicon *lexicon){
self.lexicon = lexicon;
}];
}
Because it's unclear how long requestSupplementaryLexiconWithCompletion will take to complete, any place where I'm using self.lexicon I should check to see if it's nil.
Back in the App Extension Programming Guide, it lists "Autocorrection and suggestion" under "Keyboard Features That iOS Users Expect", right before saying:
You can decide whether or not to implement such features; there is no dedicated API for any of the features just listed
So it sounds like autocorrection is something you have to do yourself, with your own UI that's part of the view presented by your UIInputViewController subclass. The API Quick Start for Custom Keyboards section in the programming guide seems to hint at how you'd do that: use documentContextBeforeInput to see what the user has recently typed, deleteBackward to get rid of it, and insertText: to insert a correction.
with MBaas services getting really affordable, and easy to use, I was wondering if anyone could give me an advice on the following design choice ?
Context: Send the content of an NSDictionary for remote storage. So the idea is to build a key/value relation, on the fly.
How:
using the piece of code here, it is possible to retrieve the name of an instance variable. so, the key/value relation results from [{ivar_name ="the value I'm interested in from this ivar"}, etc.... ]
I understand the limitations of the proposed code, but I think they are outweighed by the benefits.
In my case, the dictionary will not live beyond the class life-cycle, so I should not keep strong references on ivars, when the View is removed from the stack. Furthermore, it's going to be NSString taken from TextFields.
However, there is one question I can't really answer: if the ivars I'm looking at are part of reusable UITableViewCells (ex: IBOutlet textField in a UItableviewCell), should I make a copy of the textField.text or can I keep a reference on the string pointed at by textField.text? or it doesn't matter?
Thanks !
In line with Apple's own recommendations, when setting KVC/KVO compliant accessors manually, one should include BOTH KVO methods willChange and didChange. This is what I have done in all my manual accessor methods.
However, observeValueForKeyPath:ofObject:change:context gets called for each half of the KVC methods (will and did) with exactly the same dictionary contents.
When registering an observer using the option: NSKeyValueObservingOptionPrior the observer still gets called twice - once for each half - and, again, with identically the same dictionary contents, save only the difference that the key 'notificationIsPrior' is included in the dictionary.
Now, when KVO is used to alter 'CPU-expensive' attributes - like changing a colour or redrawing a large and elaborate design, it makes sense only to act on the 'didChange' and ignore (or at least separate out) the 'willChange'. In the past, I have achieved this by converting the key string into an enum list element that returns a left-shifted '1' and used this digit to set a flag in a 32 or 64 bit integer on receipt of the first call and when the flag is reset on the second, I execute the CPU-intensive operation(s).
However, it strikes me that this is a non-trivial overhead to implement for every case. Does anyone have any other 'preferred' way of differentiating between the callback for 'willChange' and that for 'didChange' without allowing the same processing to be done twice?
I have scoured Apple's own documentation and this help group copiously for alteranatives but Apple's own doc doesn't actually go in to much detail on the subject and several people in this group have also wrestled with a similiar concern. In neither instance has a definitive solution been offered. If anyone knows of a better way - other than dodging the 'willChange' using alternating flags - I'd be very grateful. (Why couldn't Apple just include a 'phase' key in the change dictionary???)
I think this is what you were getting at in the comments, but for the benefit of future visitors:
If you want to tell whether a callback is "before" or "after" you can look for the NSKeyValueChangeNotificationIsPriorKey key in the change dictionary. If it's a prior notification, this key will be equal to [NSNumber numberWithBool: YES] (incidentally the dictionary will also not contain a value for the NSKeyValueChangeNewKey) The presence/value of NSKeyValueChangeNotificationIsPriorKey is authoritative, so if you're seeing it when you're not expecting to, you might be getting double callbacks.
If you're getting double callbacks it may be, as it sounds like it was in VectorVictors case, that the runtime is firing them AND you're firing them. If you plan to call will/didChangeValueForKey: to manage your KVO notifications manually, (and you don't want double notifications,) you should implement the following class method:
+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)theKey {
BOOL automatic = NO;
if ([theKey isEqualToString:#"propertyYourePlanningToManageYourself"]) {
automatic = NO;
} else {
automatic=[super automaticallyNotifiesObserversForKey:theKey];
}
return automatic;
}
This is described in detail in Apple's Key-Value Observing Programming Guide.