How can I make the data persistent when using plist ?

Question

I have a UITableView table1. And when I touch any cell in the table a new UIViewController appears and it have two UITextField's name and description. After entering the data in both the text fields I used the save button to save them. In save method I wrote the code for the data to be stored in plist.
-(void)save:(id)sender
indexOfDataArray = temp;
NSString *string1 = [[NSString alloc]init];
NSString *string2 = [[NSString alloc]init];
string1 = nameField.text;
string2 = descriptionField.text;
NSDictionary *myDict = [[NSDictionary alloc] initWithObjectsAndKeys:string2, string1, nil];
[myArray addObject:myDict];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:@"VideoData.plist"];
[myArray writeToFile:path atomically:YES];
UIAlertView *alertMesage = [[UIAlertView alloc] initWithTitle: @"Save Alert" message:@"The data entered is saved" delegate:nil cancelButtonTitle:@"cancel" otherButtonTitles:nil] ;
[alertMesage show];
[alertMesage release];
[myArray retain];
But the problem is every time I restart my application the data in the plist is deleted. How can I retain the data in the plist name I specified ?

Answer 1

I think yes, I am specifying only one file name to store in the path. I understood my where I am wrong.
If I added data in plist for two items(item1 and item2). And again I need to add next two items(item3 and item4) . How can I make item3 and item 4 do not replace item1 and item2 ?
Thank You.