iOS Using the UINavigation Bar Erases Data Entered into Text Fields - ios

Question

When I go from my home segue into another I enter data into text fields. I have a navigation bar at the top and if I hit the back button to go to the home segue I lose all the data I entered. What is an efficient way of keeping the data in those fields?
Thank you.
Edit:
Maybe this helps, but when I load the screen it calls the method-
- (void)viewDidLoad {
NSLog(#"Testing viewDidLoad");
[super viewDidLoad];
// Do any additional setup after loading the view.
_YourName.delegate = self;
_Notes.delegate = self;
// Set up the scroll view.
_scroller.delegate = self;
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(keyboardWillHide:) name:UIKeyboardWillHideNotification object:nil];}
but when I go back to the previous viewcontroller or hit the home button on the ipad it does not call:
- (void)viewDidUnload{
NSLog(#"Testing viewDidUnload");
[self setYourName:nil];
[self setPartnersName:nil];
[self setStartTime:nil];
[self setEndTime:nil];
[self setCurrentTemp:nil];
[self setCurrentWeather:nil];
[self setProjectName:nil];
[self setInstructorName:nil];
[self setClassNum:nil];
[self setWaypoints:nil];
[self setNotes:nil];
[super viewDidUnload];}
Also the data remains in the UITextFields and UITextViews if I hit the home button and then reopen the app. It just goes away if I segue back to the previous UIViewController.
- (IBAction)saveCurrent:(id)sender {
if([self checkFields]){
[self getEndingTime]; //gets the time when saved
// save all data to string using csv formatting
NSString *resultLine = [self getCSVformat];
NSArray *paths = NSSearchPathForDirectoriesInDomains
(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
// get today's date for file name ****DO DATE FORMATTER ONLY ONCE
NSDate *today = [NSDate date];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"yyyy-MM-dd"];
NSString *todayDate = [dateFormatter stringFromDate:today];
//make a file name to write the data to using the documents directory:
NSString *fileName = [NSString stringWithFormat:#"%#/%#_%#_%#.csv",documentsDirectory,
todayDate,[[self ProjectName] text],[[self YourName] text]];
//save content to the documents directory
[resultLine writeToFile:fileName
atomically:NO
encoding:NSUTF8StringEncoding
error:nil];
}}
- (IBAction)retractKeyboard:(id)sender {
[self resignFirstResponder];}

Answer 1

When you push your second view controller, a new instance of the second view controller is created and this is what is shown. When you press the back button this instance is destroyed and the original view controller pops back. When you access the second view controller again, it is another new instance so all of the fields are empty.
If you press the home button your app is suspended, but the second view controller instance is still in memory, so if you return immediately to your app, the values are still there. If you ran some other apps then eventually iOS would terminate your app to releae the memory and you would see your app start from the beginning if you open it.
There are a couple of different approaches you can take to persist the data, depending on the type of data and what you need to do with it in your app. The simplest way is to store data in NSUserDefaults - This works for small amounts of data such as simple strings. For example
[[NSUserDefaults standardUserDefaults] setObject:self.projectName forKey:#"projectKey"];
will save a string. and
self.projectName = [[NSUserDefaults standardUserDefaults] stringForKey:#"projectKey"];
would read it back again. You could use the first line in an action handler for a "save" button and the second in viewDidLoad
If you need to store more complex data then you should look at Core-Data which provides database-style storage mapped to data classes or even online solutions like Parse.com
The other location where you can handle data save/load is in prepareForSegue:sender: - you can examine the segue name and access properties of the source and destination view controller

Answer 2

You will never lose your entered data unless you remove it or the container is removed from the superview.