Question

I have two arrays, each containing strings. The first array is a list of words, the second array contains alternatives to those words in different languages.

The arrays are matched such that the word at index n in the second array is a translation of the word at index n in the first array.

The words and their translations are displayed in a table view. The user can filter the table view by entering text in a search field. When this is done, I create a filtered array from the first array like this:

- (void)filterContentForSearchText:(NSString*)searchText

[self.filteredarray removeAllObjects]; 
[firstarray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop)
 {
     if ([obj compare:searchText options:NSCaseInsensitiveSearch range:NSMakeRange(0, [searchText length])] == NSOrderedSame)
     {
         idx= [firstarray indexOfObjectIdenticalTo:obj];
         NSUInteger maxindex = idx + 50;
         for (idx ; (idx < [firstarray count] && idx <= maxindex && idx!= NSNotFound); idx ++)
         {
             [self.filteredarray addObject:[firstarray objectAtIndex: idx]];
         }
         *stop = YES;
     }
 }];     

Then, when I am displaying the values in my table view, I use the following code. This is an exerpt from my cellForRowAtIndexPath method. I am trying to get the index from the original array using the object that has been added to the filtered array.

contentForThisRow = [self.filteredarray objectAtIndex:row];
NSUInteger index = [self.firstarray indexOfObjectIdenticalTo:contentForThisRow];
contentForThisRow2 = [self.secondarray objectAtIndex:index];

This works on the simulator, but on the device I will sometimes get repeats of the same entry from the second array. For example, my first array contains the word “hello” three consecutive times, at indexes x, y and z. My second array contains “hei”, “heisan” and “hoppsan”, which are all translations of “hello”, at indexes x, y and z.

On the simulator, I get three cells, each with a different translation. On the device, I get three cells, all with “hei”, the first translation. This does not happen for all repeated translations.

Why is this happening, and how can I get around it?

Answer 1

I think the problem is that iOS (on the device) may be using a slightly different optimisation to the emulator somewhere, either in NSString or NSArray. That is a guess.

indexOfObjectIdenticalTo: returns the index of the first object that has the same memory address as the object you are passing in. On the phone it appears to have re-used the identical string objects in your first array when building the filtered array (possibly even when building firstArray), so you are getting the same index value back each time.

A better solution would be to build your filtered array as an array of dictionaries, storing the values from the correct indexes of firstArray and secondArray at that point. You can then use these values directly when populating the cell instead of searching through both arrays again. This should also have some performance benefits.

You would achieve this using the following code. First, inside your loop when you are building the filtered array, instead of adding the object from firstarray, do this:

[self.filteredArray addObject:[NSDictionary dictionaryWithObjectsAndKeys:[firstarray objectAtIndex:idx],@"english",[secondarray objectAtIndex:idx],@"translated",nil];

Then, in your cellForRowAtIndexPath, to get your two content variables:

NSDictionary *rowData = [self.filteredarray objectAtIndex:row];
contentForThisRow = [rowData objectForKey:@"english"];
contentForThisRow2 = [rowData objectForKey:@"translated"];

An even better solution would be to hold your data like this in the first place, and not try to keep two separate arrays synchronised. I imagine if you want to add or alter anything in your two separate files you could quickly get them out of step. However, I feel I’ve done enough for the day…