Swift Weather App reload data

Hi Kyle: Maybe you can help me with what I am trying to do. I am creating a timer app, where you set a timer, starts counting down until 0. Easy app. The only problem I am having is that when the app goes into the background, the timer stops until I reopen the app. Meaning that it will resume where it left off. So what I want to do, which I think the approach is something what you showed here. So I want to retrieve the value from my counter which is a variable, save it somewhere in the delegate along with the “time” that the app went to the background, and when the app comes back to the foreground, retrieve that information, calculate the time the app has been in the background, subtract it from the counter, and resume.

Is that even possible ?

Jhoan,

Your question is a good one.

There are several good approaches that you could take with this. I'm not sure how you're approaching it now, so I'll just give general suggestions:

While I'm not sure the details of your implementation, I'd probably recommend storing the start time as an NSDate(), then instead of incrementing/decrementing from an Integer/Float/Double, you can just calculate the time since the initial date, then remove that amount of time from your totalTime. That way when the app reopens, the time calculation is always correct. The calculation for determining how long ago an NSDate() is so light that it'll be nearly instantaneous.

import UIKit

class Timer {
    private var startTime: NSDate? // Recorded when the user starts the timer.
    private var totalTime: Double = 0.0 // If you're counting down, this is the total time designated by the user (e.g. 20 mins)
    private var currentTime: Double = 0.0 // Displayed time visible to user.

    private func startTimer() {
        startTime = NSDate()
    }

    private func updateTimer() {
        let timeDifference = startTime!.timeIntervalSinceNow // See http://stackoverflow.com/questions/4084341/how-to-calculate-time-in-hours-between-two-dates-in-ios

        if timeDifference >= totalTime {
            currentTime = 0.0
        }
        else {
            currentTime = totalTime - timeDifference
        }
    }
}

What you're trying to do is definitely possible. If you're interested in storing information between sessions, then using a database system like http://realm.io would work well.

Please let me know if you need clarification or additional help.

Good luck, Kyle

I see your approach, I like it. Thanks but there are some questions I do have, please bare with me since I’m a newbie at this. This will be my very first app. Perhaps I can give you my e-mail and can explain what I am doing, and maybe you can guide me better ?

jhoannarango@msn.com

Jhoan,

I'm happy to help, I often feel this way about new projects. Researching best practices and methodologies can be intimidating.

While emailing would work just fine, I'd like to recommend you open another question here on the forum. After that, come back here and paste the link to the question by adding a comment (it emails me when you do that, so I'll be notified). That way everyone will benefit from seeing our thought process. What do you think?

Kyle

Great Idea Kyle, will do that... Thanks

Here is the question I had posted earlier.

https://teamtreehouse.com/forum/how-to-continue-a-timer-after-the-app-comes-back-from-the-background

Hey Kyle, thanks for responding. I was trying to use that applicationWillEnterForeground function but I can't call getCurrentWeatherData() inside that without getting errors. I'd like to know how to do it that way instead of the refresh for future apps. Maybe someone else knows...

Keith

Sorry, admittedly I skimmed over that part of your post. Obviously that's an important part, my bad.

Could you post the particular error you're getting? Also, after overriding the method, try printing something to the console to see if the method is doing what it should. That'd be a good place to start.

I'll think on it and see if I can come up with a good example for you in the next day or two.

Either way, best of luck!

I've been playing around with my version of the app, and that's exactly the same problem I'm having. If you're familiar with the debugger in Xcode, and look at the labels, all mine are nil upon reopening the app. This will be the problem that you and I are having. If the label is nil, for whatever reason, its properties won't be available to be updated.

It's a wierd situation to me though, because they're obviously showing back up on the screen as if they were there and already have values. Perhaps the question we really should be asking is why are UI elements (e.g. labels) nil upon re-opening the app.

I have to head to bed now, but I'm going to be looking that up tomorrow. That's something I honestly don't know yet, but really should.

If you find anything on that, please let me know, and I'll do the same.

Take care, -- Kyle

Thanks Jonathon!

The reason we use View Controller in Step 1 is because the name of the file related to the view we're storing in the variable is actually called ViewController.swift. If your app's view (like the view on the Storyboard) is connected to the file called ThisControlsMyView.swift then you can replace the line in Step 1 with:

var myViewController: ThisControlsMyView?

...instead.

The principle at work here is based on the view controller, which only means the file that is connected to the view in your storyboard. When you set up an application using a Single View app, Xcode defaults to a Storyboard with a single view that is connected to a file named ViewController.swift.

Hopefully this all makes sense. Feel free to ask additional questions for clarification.

Good luck -- Kyle

Yep, you could definitely do that! Here's a great Stack Overflow page highlighting the differences, scroll down to the first answer, by "Dano":

http://stackoverflow.com/questions/3712979/applicationwillenterforeground-vs-applicationdidbecomeactive-applicationwillre

Let me know if you have any further questions.

Good luck -- Kyle