NSTimeInterval in seconds between dates = nan

Question

NSTimeInterval executionTime = [self.EndDownloadTime timeIntervalSinceDate:self.StartDownloadTime];
NSLog(@"Execution Time: %f", executionTime);

Result is always "nan". When i switch EndDownloadTime and StartDownloadTime, time is "0.00000"

StartDownloadTime and EndDownloadTime are types of NSDate.

How do i get the seconds between the two dates?

Thank you in advance.

Answer 1

Your code looks right. Try this and print value of variables to know if the two dates are correct.

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NSTimeInterval executionTime = [self.EndDownloadTime timeIntervalSince1970] - [self.StartDownloadTime timeIntervalSince1970];
NSLog(@"Execution Time: %f", executionTime);

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Answer 2

The simplest solution is a better method, check the docs when things seem complicated:

NSTimeInterval executionTime = [self.EndDownloadTime timeIntervalSinceDate:self.StartDownloadTime];

When you are debugging a problem and everything looks correct but the code is failing then an assumption must be wrong. There are two assumptions here (at least): the values of self.EndDownloadTime and self.StartDownloadTime. NSLog them or use the debugger examining the values as you step through.

Check everything:

NSLog(@"StartDownloadTime: %@", self.StartDownloadTime);
NSLog(@"StartloadTimeInterval: %f", [self.StartDownloadTime timeIntervalSince1970]);
NSLog(@"EndDownloadTime: %@", self.EndDownloadTime);
NSLog(@"EndDownloadTimeInterval: %f", [self.EndDownloadTime timeIntervalSince1970]);

NSTimeInterval executionTime = [self.EndDownloadTime timeIntervalSince1970] - [self.StartDownloadTime timeIntervalSince1970];
NSLog(@"Execution Time: %f", executionTime);

Note: In Cocoa* properties and variables and method names by convention begin with a lower case letter, class names with an uppercase letter. This makes it easier for others to understand your code.