Question

I have recently started programming for the iOS Platform but now I need some help figuring out how to do ‘something’:

• For my application I fetch some JSON data and put this data as objects into an Array
• This Array is written to my own PLIST file (in the docs directory)

Now when the users starts a sync action I:

• Fetch the data from the PLIST
• Get the timestamp for a certain object in the Array that came from the PLIST
• Use timestamp in new JSON request (for the new data)

So far so good.

Now for my (current) problem -> After receiving the new data (JSON req) I wish to update the timestamp of this ‘certain’ object in the array (and write this to the Plist).

Using an NSPredicate I am able to find the right set of data within the main Array (stampArr).

NSString *documentsDir = [NSHomeDirectory()stringByAppendingPathComponent:@"Documents"];
NSString *plistPath = [documentsDir stringByAppendingPathComponent:@"stamps.plist"];

NSMutableArray *stampArr = [[NSMutableArray alloc] initWithContentsOfFile:plistPath];

NSPredicate *filter = [NSPredicate predicateWithFormat:@"eventid = 1"];
NSMutableArray *filteredStampArr = [stampArr filteredArrayUsingPredicate:filter];

But now, after I update the filteredStampArr, I want to update the main Array with the data from the filtered Array.

In other words, I need to update the object from the Array with the new ‘timestamp’ (field of object).

I could off course use something like [stampArr addObject: [filteredStampArr copy]] after changing the filterd array but that would just create a duplicate of the information. I wish to overwrite the original object.

Somehow (I think) I need a ‘pointer’ that tells me the location of the data in the original array so that I can change the data directly in the main array?

(I hope my questions is clear – If not please say so)

Answer 1

Get the item, find it’s index in stampArr and replace it with the newItem.

NSArray *filteredStampArr = [stampArr filteredArrayUsingPredicate:filter];
id item = [filteredStampArr objectAtIndex:0]; // id because the type of the item is not known

NSUInteger itemIndex = [stampArr indexOfObject:item];

[stampArr replaceObjectAtIndex:itemIndex withObject:newItem];