How to persist data using archiving function on the iphone? - iphone

Question

I am having trouble with persisting data.
Desired Behavior:
I have a text field defined in the view that captures user input. When the submit button is clicked (touch up inside), I expect to write that data to a mutable array. As of right now, I am going to archive that mutable array upon submit, but have also played with archiving once the view disappears/unloads. When a user navigates away from the view or exits the application and re-enters, I want to display the first element of that mutable array in the textfield.
Actual Behavior:
Textfield captures data and updates myMutableArray upon submitting. I have a few labels on the view plus NSLog to verify the count grows as I hit submit. I then archive this the first time, and I see that my file now exists in myDocuments plus when I revisit the view and check the count of dataArray, which is created if that file exists, the count of dataArray matches the number of elements I created in myMutableArray. If I start to enter in data again, it resets myMutableArray and dataArray all over again. That is one of a couple problems I think I have.
Questions:
If the file exists, then dataArray is created. Now I try to set the textfield to display the first element and the program bombs out! If dataArray exists, and I can see count is some positive value, I don't understand why I can't access that first element.
I feel like when I visit the view and go through this exercise, when I revisit the view I see I have dataArray present and with positive values, but when I start adding text again through the submit button, I reset everything! So I am persisting once maybe, but then wiping it clean. So much for real persistence. What am I doing wrong?
Eventually, I will be storing a record with a few elements. I will create multiple records over time for the user to review. Is archiving the best possible way? Should I start using NSCoding instead?
- (void)viewDidLoad {
[super viewDidLoad];
// Initialize mutable array and set equal to myMutableArray property
NSMutableArray *aMutableArray = [[NSMutableArray alloc] init];
myMutableArray = aMutableArray;
// Debug Logging
// NSLog(#"Mutable Array Count is: %i", [myMutableArray count]);
NSFileManager *filemgr;
NSString *docsDir;
NSArray *dirPaths;
filemgr = [NSFileManager defaultManager];
// Get the documents directory
dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
docsDir = [dirPaths objectAtIndex:0];
// Build the path to the data file
dataFilePath = [[NSString alloc] initWithString: [docsDir stringByAppendingPathComponent: #"data.archive"]];
// Check if the file already exists
if ([filemgr fileExistsAtPath: dataFilePath])
{
NSMutableArray *dataArray;
dataArray = [NSKeyedUnarchiver unarchiveObjectWithFile: dataFilePath];
myTextField.text = #"%#", [dataArray objectAtIndex:0]; // THIS BOMBS OUT MY PROGRAM FOR SURE IF INCLUDED!!!
//myUpdatedMutableArray = dataArray;
// Debug Logging
NSLog(#"Mutable Array (dataArray) Count is: %i", [dataArray count]);
//NSLog(#"The first value in the array is: %i", [dataArray objectAtIndex:0]);
}
[filemgr release];
// Uncomment the following line to display an Edit button in the navigation bar for this view controller.
// self.navigationItem.rightBarButtonItem = self.editButtonItem;
}
- (IBAction) mySubmitButtonPressed:(id)sender {
// Debug Logging
NSLog(#"Submit Button was Pressed!");
NSLog(#"Mutable Array (myMutableArray) Count is: %i", [myMutableArray count]);
// Create string from textfield and addobject to myMutableArray; check to see that myMutableArray grows in count
NSString *myString = [[NSString alloc] initWithFormat:#"%#",myTextField.text];
[myMutableArray addObject:myString];
NSLog(#"Mutable Array (myMutableArray) Count is: %i", [myMutableArray count]);
// More Debug Logging just using on-screen labels
NSString *mySecondString = [[NSString alloc] initWithFormat:#"%i", [myMutableArray count]];
myFirstLabel.text = myString;
mySecondLabel.text = mySecondString;
// Archive myMutableArray
[NSKeyedArchiver archiveRootObject: myMutableArray toFile:dataFilePath];
//[contactArray release];
}

Answer 1

There are many issues with this code.
To begin, you leak memory all over the place. Specifically here:
NSMutableArray *aMutableArray = [[NSMutableArray alloc] init];
myMutableArray = aMutableArray;
Which should really be:
self.myMutableArray = [NSMutableArray array];
After you unarchive the data, if you want to keep it in myMutableArray, simply do this:
[myMutableArray appendArray: dataArray];
Or just:
self.myMutableArray = dataArray;
You should never release singleton instances like the NSFileManager, so completely get rid of this one:
[fileMgr release];
Your code crashes because this is not valid code:
myTextField.text = #"%#", [dataArray objectAtIndex:0];
(It actually is valid code, but it will do something very different than you think)
This is not Python, so you will have to do this:
myTextField.text = [NSString stringWithFormat: #"%#",
[dataArry objectAtIndex: 0]];
But that is really the same as:
myTextField.text = [dataArray objectAtIndex: 0];
Adding a string to your array in mySubmitButtonPressed can be done much simpler than you think. Just do this:
[myMutableArray addObject: myTextField.text];
You should really learn about autoreleased objects, memory management and what retaining properties actually do.