Save contents of NSMutableArray to file

Question

I have an app which has several ViewControllers. Each ViewController has a question with 2-5 buttons as possible answers. The title of a button is saved to a NSMutableArray called submission. The user can go back to previous questions, change their answer, and the NSMutableArray will be updated accordingly. I need to save this array to file so new results can be saved into a UITableView each time the questionnaire is completed. I have researched and it sounds like a .plist is a good option, as all of my objects in the array are NSStrings.

A sample of my array:

2013-12-17 14:06:34.210 Questionnaire[1724:70b] (
    1234,
    "Dec 17, 2013",
    Yes,
    Games,
    "Not Applicable",
    Yes
)

"1234" is the User ID, the date is the Date of Birth, and the other submissions are the answers to each question.

My ViewControllers look like this:

MainViewController
InfoViewController <-- Array allocated + initialised, inserting ID and DoB
Q1ViewController <-- question
..
Q4ViewController <--question
ENDViewController <-- offers user options for Home or Results
ResultsViewController <-- UITableView ordered by User ID
SavedResultsViewController <-- UITableView showing complete submission

The NSMutableArray gets passed through each ViewController.

My questions: What method of saving to file would best suit my needs? (.plist, filetype, etc). Viewing the results on Excel would be nice (but not essential). Where should the save take place? I was thinking when the last object is inserted into the array on Q4 ViewController, so it would be saved to file when the ENDViewController is popped, is this logical? Do I need to create a new Objective-C file to store the data? I have saw a few tutorials explaining this, declaring each object in a separate NSObject file, although I'm not sure if that is needed as my objects are already stored in the array.

As you've probably guessed I am quite new to Objective-C and iOS programming, so any help offered is greatly appreciated. I am not sure how else to describe my problem, so apologies if the question is still unclear.

Edit: I have learnt a bit more about Objective-C since creating this post, and have decided to save my data to a .csv file. This file is strictly for the purpose of emailing, it doesn't get displayed on the UITableView (I am currently implementing Core Data for that). This solution might help someone in the future, so here it is:

// Set column titles for .csv
NSArray *columnTitleArray = @[@"User ID", @"DoB", @"Question 1", @"Question 2", @"Question 3", @"Question 4"];

NSString *columnTitle = [columnTitleArray componentsJoinedByString:@","];
NSString *columnTitleToWrite = [columnTitle stringByAppendingString:@"\n"];

// Separate submissions from array into cells
NSString *questionResults = [self.submission componentsJoinedByString:@","];
NSString *questionResultsToWrite = [questionResults stringByAppendingString:@"\n"];

// Find documents directory
NSString *docPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
// Set file name and type
NSString *survey = [docPath stringByAppendingPathComponent:@"result.csv"];
// Create new file if none exists
if (![[NSFileManager defaultManager] fileExistsAtPath:survey]){
    [[NSFileManager defaultManager] createFileAtPath:survey contents:nil attributes:nil];

    // Set column titles for new file
    NSFileHandle *fileHandle = [NSFileHandle fileHandleForUpdatingAtPath:survey];
    [fileHandle writeData:[columnTitleToWrite dataUsingEncoding:NSUTF8StringEncoding]];
}

NSFileHandle *fileHandle = [NSFileHandle fileHandleForUpdatingAtPath:survey];
[fileHandle seekToEndOfFile];
[fileHandle writeData:[questionResultsToWrite dataUsingEncoding:NSUTF8StringEncoding]];
[fileHandle closeFile]; 

Answer 1

You could save your array as a JSON file. This would allow you to view it in a text editor, but not a spreadsheet. The following code will write it out as JSON to a file:

NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
url = [url URLByAppendingPathComponent:@"yourdata.json"];
NSError *e = nil;
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:yourdata options:NSJSONWritingPrettyPrinted error:&e];

if (jsonData) {
    [jsonData writeToFile:url.path atomically:YES];
}

You could also save your data as a plist file. The following will write the data to a plist:

NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
url = [url URLByAppendingPathComponent:@"yourdata.plist"];
NSError *e = nil;
NSData *plistData = [NSPropertyListSerialization dataWithPropertyList:yourdata format:NSPropertyListXMLFormat_v1_0 options:0 error:&e];

if (plistData) {
    [plistData writeToFile:url.path atomically:YES];
}

Plists can be saved in binary or XML format, and the above will save it as XML format, which means the XML will also be readable with a text editor. Again, this won't be viewable as a spreadsheet. If you want to export your data in CSV format, you'll probably have to write your own code to output it.