How to stop overwriting data

问题

I am trying to save in my iOS app some data. I use the following code :

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

//inserting data
NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
[dict setValue:categoryField.text forKey:@"Category"];
[dict setValue:nameField.text forKey:@"Name"];
[dict setValue:eventField.text forKey:@"Event"];

NSMutableArray *arr = [[NSMutableArray alloc] init];
[arr addObject:dict];
[arr writeToFile: path atomically:YES];


//retrieving data
NSMutableArray *savedStock = [[NSMutableArray alloc] initWithContentsOfFile: path];
for (NSDictionary *dict in savedStock) {
     NSLog(@"my Note : %@",dict);
}

However the NSLog shows me only the last data... I suppose that i am overwriting here..I cant see why though!

How can i continue to save dictionaries in the array without overwriting? Any ideas?

回答1:

Since you are making a model object it would be better if you include save, remove, findAll, findByUniqueId kind of logic built into it. Will make working with the model object very simple.

@interface Note : NSObject

@property (nonatomic, copy) NSString *category;
@property (nonatomic, copy) NSString *name;
@property (nonatomic, copy) NSString *event;

- (id)initWithDictionary:(NSDictionary *)dictionary;

/*Find all saved notes*/
+ (NSArray *)savedNotes;

/*Saved current note*/
- (void)save;

/*Removes note from plist*/
- (void)remove;

Save a note

Note *note = [Note new];
note.category = ...
note.name = ...
note.event = ...

[note save];

Delete from saved list

//Find the reference to the note you want to delete
Note *note = self.savedNotes[index];
[note remove];

Find all saved notes

NSArray *savedNotes = [Note savedNotes];

Source Code

回答2:

Replace:

NSMutableArray *arr = [[NSMutableArray alloc] init];
[arr addObject:dict];
[arr writeToFile: path atomically:YES];

With:

NSMutableArray *arr = [[NSMutableArray alloc] initWithContentsOfFile: path];
[arr addObject:dict];
[arr writeToFile: path atomically:YES];

回答3:

You need to first read in the data, then APPEND the new dictionary to the old one. So read the file first, then append the new dictionary, then save.

FULL CODE:

NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
[dict setValue:categoryField.text forKey:@"Category"];
[dict setValue:nameField.text forKey:@"Name"];
[dict setValue:eventField.text forKey:@"Event"];

[self writeDictionary:dict];

- (void)writeDictionary:(NSDictionary *)dict
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *documentsDirectory = [paths objectAtIndex:0]; 
    NSString *path = [documentsDirectory stringByAppendingPathComponent:@"yourPlist.plist"];

    NSMutableArray *savedStock = [[NSMutableArray alloc] initWithContentsOfFile: path];
    if(!savedStock) {
        savedStock = [[[NSMutableArray alloc] initiWithCapacity:1];
    }
    [savedStock addObject:dict];

    // see what';s there now
    for (NSDictionary *dict in savedStock) {
         NSLog(@"my Note : %@",dict);
    }
    // now save out
    [savedStock writeToFile:path atomically:YES];
}

来源：https://stackoverflow.com/questions/16485157/how-to-stop-overwriting-data