Comparing NSDate to [NSDate date] Fastest Way? - iphone

I have a core data table view and I am comparing dates. The method which I currently use is: if ([todayDate compare: [NSDate date]]==NSOrderedAscending) . This works perfectly but slow. I do not need to know the difference in time though. Any help is much appreciated!

I really think, that NSDates method isEqualToDate: is what you are searching for. Seems to me to be the Apple-way to answer your question:
NSDate *date1 = ...;
NSDate *date2 = ...;
BOOL datesAreEqual = [date1 isEqualToDate:date2];
For more information visit https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/nsdate_Class/Reference/Reference.html

One option could be to not actually create a new NSDate object but use the time interval for comparison. Don't know about the performance, but it might be worth a try.
if ([todayDate timeIntervalSinceReferenceDate] > [NSDate timeIntervalSinceReferenceDate]) {
...
}

You should remember the current date or current timestamp in a local variable:
NSTimeInterval current = [NSDate timeIntervalSinceReferenceDate];
And use this value later for all your comparisons:
myTimestamp = [myDate timeIntervalSinceReferenceDate]
if (myTimestamp == current) {
return NSOrderedSame;
} else if (myTimestamp > current) {
return NSOrderedDescending;
} else {
return NSOrderedAscending;
}
Or a faster way, using C functions:
// Get the current calendar time as a time_t object.
time_t time ( time_t * timer );
// Return difference between two times
double difftime ( time_t time2, time_t time1 );

I've not measured it, but you may want to try:
NSTimeInterval i = [todayDate timeIntervalSinceNow];
where the result (i) may be positive or negative.
You might also try CFDateCompare.
Or you might want to consider another way to represent a point in time in your database -- such as a CFTimeInterval (a double representing the number of seconds from a common reference time).

Related

How can validate NSDATE

How to find one text field value is within past 60 day excluding current date.
For example if I enter value in text field is 20-July-2012 using Date Picker.Then I click submit,it'll check that specific is date is within 60 days or not. If the values are entered which is before 60 days an alert message is displayed. The values are retrieved from api.
NSDate *today = [NSDate date];
NSTimeInterval dateTime;
if ([pickerDate isEqualToDate:today]) //pickerDate is a NSDate
{
NSLog (#"Dates are equal");
}
dateTime = ([pickerDate timeIntervalSinceDate:today] / 86400);
if(dateTime < 0) //Check if visit date is a past date, dateTime returns - val
{
NSLog (#"Past Date");
}
else
{
NSLog (#"Future Date");
}
Change the value of 86400 to suit your query.In this case, it is the number of seconds we want to compare.
First, convert the text into an NSDate. Then use
timeIntervalSinceDate:[NSDate dateWithTimeIntervalSinceNow:0]
There are a couple of ways to convert text into an NSDate. You can format the text correctly and then use dateWithString or you can convert everything into numbers, multiply them out, and one of the dateWithTimeInterval methods.
If you want the user to be able to enter "July" (plain text month) then you might want to write a method that converts months into their numerical equivalents with string matching.
NSDate *lastDate; //your date I hope you have created it
NSDate *todaysDate = [NSDate date];
NSTimeInterval lastDiff = [lastDate timeIntervalSinceNow];
NSTimeInterval todaysDiff = [todaysDate timeIntervalSinceNow];
NSTimeInterval dateDiff = lastDiff - todaysDiff; // number of seconds
int days = dateDiff/(60*60*24); // 5.8 would become 5 as I'm taking int
How do you define 60 days?
You may want to use NSCalendar -dateByAddingComponents:toDate:options: to ensure your 60 days really are 60 days.
NSCalendar also provides -components:fromDate: and -dateFromComponents: which are very nice when dealing with date components.
If 60 days do not need to be true calendar days (daylight saving time switches, astronomical time corrections, stuff like that), you can just have fun with NSDate and the time interval methods alone.

How to compare current and manual NSDate

there is a function where option NSDate is specified putting up manually.
How can I prevent execution of the function with the parameter of time, less than the current time?
I have tried this
if ([currentDate timeIntervalSinceDate: myTime] < 0)
but unfortunately sometimes it doesn't work
Thanks in advance.
Another option is to convert both the date to timeIntervals using timeIntervalSince1970
int interval1 = [date1 timeIntervalSince1970];
int interval2 = [date2 timeIntervalSince1970];
if(interval1 > interval2) //etc...
It sounds like you want to compare the current date with your custom date. More specifically, if the current date takes place after myTime, then the condition should be true.
if ([[NSDate date] compare: myTime] == NSOrderedDescending) {
NSLog(#"Current date is later than myTime");
}
To the opposite, you would check the comparison against NSOrderedAscending.

finding NSDate's in an NSArray that have a time of day after a given time (e.g. 8pm)?

Is there a quick way in Objective-C of identifying NSDate's in an NSArray that have a time of day after a given time (e.g. 8pm)?
I can't quite see anyway other than manually walking through each NSDate in the array and then using NSDateComponents to break out the hour/minute/second...Not even sure if there is a simple way to get the time from an NSDate in a fashion that represents a fraction of 24hours, as this might help a little. (e.g. 6pm would be 18/24 = 0.75 in this case)
There is no need to break in NSDateComponents.
NSTimeInterval interval = [date1 timeIntervalSinceDate:date2];
if (interval > 0) {
// date2 is earlier
} else {
// date1 is earlier
}
Now you can represent your target time(8 P.M., for example) with date2 and compare all dates of array with that.
Haven't tried this myself, but I guess
- (NSArray *)filteredArrayUsingPredicate:(NSPredicate *)predicate
is what you're looking for.

Check if NSTimeInterval equals 0

//Gets the time right now
NSDate *now = [NSDate date];
//Stores the difference in seconds between when the test was started and now.
NSTimeInterval interval = [self.expires timeIntervalSinceDate:now];
if (interval == 0) {
...
}
Any reason why the condition wont be true?
Thanks.
Since NSTimeInterval is only a double, you might have floating point rounding error. Try using something like
if (abs(interval) < EPS) {
where EPS is a small enough constant.
Or, if you want to know seconds and not milliseconds, you can truncate that double to int.
But judging from your code, I think you might want to check if timeline has already expired, not that it expires at this exact moment. Probability of the later is very small. This should do the trick.
if (interval < 0) {

Best way to store a 'time' value

My class needs two properties: startTime and endTime. What is the best class to use? I know there is NSDate, but I only need to store a specific time (something in between 00:00-23:59), I don't need a date. What is the most elegant solution here?
NSTimeInterval is probably good enough for this.
It stores a time value in seconds as a double.
Eg. 5 mins = 300.0
I believe the most elegant solution, and what you want, is NSTimeInterval, that is the primitive type that NSDate is built on top.
NSTimeInterval is a typedef for double, and is a measurement of time in seconds. This primitive time type do not have any concept of a reference date. What NSDate do is to add this concept of reference date and anchor the 0.0 time at 1 January 2001 GMT. There is nothing that stops you from inventing your own reference date or anchor, like for example "midnight of whatever day there is".
What you can do is to add two properties of the NSTimeInterval either as startTime and endTime and let them both use midnight as the reference. Or you could skip endTime and go for a startTime and duration combo.
There's NSDateComponents, which "can also be used to specify a duration of time, for example, 5 hours and 16 minutes."
The NSDate class is similar to the DateTime class in C#: both hold a date and time, but they can be independent of each other. In Cocoa, you would compare two NSDate classes:
//Create NSDate objects in the time format
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"HH:mm:ss"];
NSString *startTimeString = #"00:00:00"; //0 seconds
NSString *endTimeString = #"00:00:52"; //52 seconds
NSDate *startTime = [dateFormatter dateFromString:startTimeString];
NSDate *endTime = [dateFormatter dateFromString:endTimeString];
//Compare the time
BOOL date1before2 = [startTime compare:endTime] == NSOrderedAscending;