NSMutableArray显示（null）/ nil？

Question

Hi i have a function like this

- (void)save{
        NSLog(@" %@ %@ %@ %@",AppAddressLine,AppCustomerName,AppPhoneNumber,AppPriceTier);

        paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        documentsDirectory = [paths objectAtIndex:0];
        path = [documentsDirectory stringByAppendingPathComponent:@"NewInAppCustomer.plist"];
        NSMutableArray *MainRoot=[[NSMutableArray alloc]initWithContentsOfFile:path];
        NSMutableDictionary *ContentDictionary=[[NSMutableDictionary alloc]init];
        [ContentDictionary setValue:AppCustomerName  forKey:@"CustomerName"];
        [ContentDictionary setValue:AppAddressLine forKey:@"CustomerAddress"];
        [ContentDictionary setValue:AppPhoneNumber forKey:@"CustomerPhoneNumber"];
        [ContentDictionary setValue:AppPriceTier forKey:@"CustomerPriceTier"];
        [MainRoot addObject:ContentDictionary];
        [MainRoot writeToFile:path atomically:YES];
        NSLog(@"%@",MainRoot);

}

when I print with

NSLog(@" %@ %@ %@ %@",AppAddressLine,AppCustomerName,AppPhoneNumber,AppPriceTier);

it is showing a correct value,

but this line

NSLog(@"%@",MainRoot);

displays nil as its value.

Can anyone please explain it to me?

Answer 1

This line:

NSMutableArray *MainRoot=[[NSMutableArray alloc]initWithContentsOfFile:path];

will return nil if:

the file can't be opened or the contents of the file can't be parsed into an array

so you have a non-existent or an invalid file.

So, you should ensure that the file is created before this code runs, or, better, check the result and create a new empty array if you need to.

if (MainRoot == nil) MainRoot = [NSMutableArray array];

Answer 2

Try this, create the file if it not exist and then write to it

- (void)save{
        NSLog(@" %@ %@ %@ %@",AppAddressLine,AppCustomerName,AppPhoneNumber,AppPriceTier);

        paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        documentsDirectory = [paths objectAtIndex:0];
        path = [documentsDirectory stringByAppendingPathComponent:@"NewInAppCustomer.plist"];
        NSMutableArray *mainRoot;
        NSFileManager *fileManager = [NSFileManager defaultManager];
        if (![fileManager fileExistsAtPath:path]) {

             [fileManager createDirectoryAtPath:path withIntermediateDirectories:NO attributes:nil error:&error];
             mainRoot = [[NSMutableArray alloc] init];
        } else {
             mainRoot = [[NSMutableArray alloc] initWithContentsOfFile:path];
        }
        ....
}