Why does item in plist gets overwritten?

I am trying to add a new item to my plist. However, it gets overwritten every time i press save:

-(IBAction)save:(id)sender {

 appDelegate = (JobTestAppDelegate*)[[UIApplication sharedApplication]delegate]; 

 NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
 NSString *documentsDirectory = [paths objectAtIndex:0];
 NSString *fileName = [documentsDirectory stringByAppendingPathComponent:@"Work.plist"];

 NSMutableDictionary* newNote = [[NSMutableDictionary alloc] init];  

 NSMutableDictionary *set = [NSMutableDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"", @"", nil] forKeys:[NSArray arrayWithObjects:@"Work Name", @"Work ID", nil]];

NSArray *work = [NSArray arrayWithObjects:set, nil];

int row = 0;
newNote = [appDelegate.job objectAtIndex:row];
[newNote setValue:work forKey:@"Work"];         

[appDelegate.job writeToFile:fileName atomically:TRUE];

[newNote release];  

[self dismissModalViewControllerAnimated:YES];
 }

I don't know which part of the code is wrong. I've been trying to solve the problem for days.

EDIT: appDelegate.job - a mutable array in my main app delegate class to create the plist :

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *fileName = [documentsDirectory stringByAppendingPathComponent:@"Work.plist"];

job = [[NSMutableArray alloc] initWithContentsOfFile:fileName];


[job writeToFile:fileName atomically:YES];

EDIT2:

I need to store the user input (NSArray*work) into the work array

Root (Array)

        Item 0 (Dict)
                      Name (String)
                      Work (Array)
                                       Item 0 (Dict)
                                                    Work Name (String)
                                                    Work ID (String)
                                       Item 1 (Dict)
                                                    Work Name (String)
                                        开发者_JS百科            Work ID (String)
        Item 1 (Dict)
                      Name (String)
                      Analysis (Array)
                                       Item 0 (Dict)
                                                    Work Name (String)
                                                    Work ID (String)
                                       Item 1 (Dict)
                                                    Work Name (String)
                                                    Work ID (String)

Edit3: NSMutableDictionary* newNote = [[NSMutableDictionary alloc] init];

 NSMutableDictionary *set = [NSMutableDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"", @"", nil] forKeys:[NSArray arrayWithObjects:@"Work Name", @"Work ID", nil]];

NSArray *work = [NSArray arrayWithObjects:set, nil];

int row = item;
newNote = [appDelegate.job objectAtIndex:row];
[newNote setValue:work forKey:@"Work"];         

//i think this is the line which i am having problem with.
//without this line my data in the plist gets overwritten, 
//with this code it copies the who item and create a new item into my root array
[appDelegate.job addObject:newNote];

[appDelegate.job writeToFile:fileName atomically:TRUE];

[newNote release];  

Thanks in Advance, Leanne

You are overwriting whatever is at job index zero with your new item. You are also allocating memory here:

NSMutableDictionary* newNote = [[NSMutableDictionary alloc] init]; 

Then reassigning something else to this variable here:

newNote = [appDelegate.job objectAtIndex:row];

If you are trying to add a new item, you should be doing something like:

NSMutableDictionary* newNote = [[NSMutableDictionary alloc] init];
[newNote setValue:work forKey:@"Work"];
[appDelegate.job addObject:newNote];
[appDelegate.job writeToFile:fileName atomically:TRUE];

You are then adding a new dictionary to your job array, and writing out the whole array.

EDIT: From your comments, it looks like newNote should be a dictionary, with a name and an array in it. So, you need to add a new object to the existing array - you are currently setting a single item array to the "work" key of this dictionary.

You need something like:

NSMutableDictionary* newNote = [appDelegate.job objectAtIndex:0];
NSArray *oldWork = [newNote objectForKey:@"Work"];
NSArray *newWork = [oldWork arrayByAddingObject:set];
[newNote setObject:newWork forKey:@"Work"];