Creating an Array for cellForRowAtIndexPath with Other Methods - ios

Question

I have an indexed tableView that displays a list of songs from the user's iPod library. This is how I currently get the song titles, which causes scrolling to be very slow:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
cell.textLabel.text= [self titleForRow:indexPath]; //getting cell content
}
...which calls these methods:
-(NSString *)titleForRow:(NSIndexPath *)indexpath{
NSMutableArray* rowArray=[[NSMutableArray alloc]initWithCapacity:0];
rowArray=[self getArrayOfRowsForSection:indexpath.section];
NSString *titleToBeDisplayed=[rowArray objectAtIndex:indexpath.row];
return titleToBeDisplayed;
}
-(NSMutableArray *)getArrayOfRowsForSection:(NSInteger)section
{
NSString *rowTitle;
NSString *sectionTitle;
NSMutableArray *rowContainer=[[NSMutableArray alloc]initWithCapacity:0];
for (int i=0; i<self.alphabetArray.count; i++)
{
if (section==i) // check for right section
{
sectionTitle= [self.alphabetArray objectAtIndex:i]; //getting section title
for (MPMediaItem *song in songs)
{
NSString *title = [song valueForProperty:MPMediaItemPropertyTitle];
rowTitle= [title substringToIndex:1]; //modifying the statement to its first alphabet
if ([rowTitle isEqualToString:sectionTitle]) //checking if modified statement is same as section title
{
[rowContainer addObject:title]; //adding the row contents of a particular section in array
}
}
}
}
return rowContainer;
}
The problem is: for each cellForRowAtIndexPath, I am calling these methods and creating these arrays for each cell. So I need to create a separate array and simply call the objectAtIndex from that array.
This is what I have tried so far: created an NSMutableArray *newArray, and the following method:
-(NSMutableArray *)getNewArray:(NSInteger)section
{
NSString *rowTitle;
NSString *sectionTitle;
for (int i=0; i<self.alphabetArray.count; i++)
{
if (section==i) // check for right section
{
sectionTitle= [self.alphabetArray objectAtIndex:i]; //getting section title
for (MPMediaItem *song in songs)
{
NSString *title = [song valueForProperty:MPMediaItemPropertyTitle];
rowTitle= [title substringToIndex:1]; //modifying the statement to its first alphabet
if ([rowTitle isEqualToString:sectionTitle]) //checking if modified statement is same as section title
{
[newArray addObject:title]; //adding the row contents of a particular section in array
}
}
}
}
return newArray;
}
But this seems very wrong and I'm really confused on how to solve this. I have no clue how to create a separate array with these methods, populating newArray with the song titles, and I've searched Google for quite some time now and I can't find anything that would help me.
Could somebody point me in the right direction, or please show me how I'd creat newArray? I've attached my tableView data source here. Thanks. Any help would be much appreciated.

Answer 1

Table View cells are enqueued and dequeued in a serial manner. Leveraging this ability you should expect that only sections change in less frequency. You can use static variables to exempt the fetching of a section. Look at my code
-(NSString *)titleForRow:(NSIndexPath *)indexpath{
static NSIndexPath *funIndexPath;
static NSMutableArray *funSectionArray;
if (!funIndexPath || funIdexpath.section != indexpath.section) {
funIndexPath = indexpath;
funSectionArray = [self getArrayOfRowsForSection:indexpath.section];
}
rowArray = funSectionArray;
NSString *titleToBeDisplayed = [rowArray objectAtIndex:indexpath.row];
return titleToBeDisplayed;
}
This is the first optimisation possible.
When I look at your fetching results array, some things are not clear. Why are you iterating to check section == i. You can just substitute section for i in your code.
-(NSMutableArray *)getNewArray:(NSInteger)section {
NSString *rowTitle;
NSString *sectionTitle;
sectionTitle = [self.alphabetArray objectAtIndex:section]; //getting section title
for (MPMediaItem *song in songs) {
NSString *title = [song valueForProperty:MPMediaItemPropertyTitle];
rowTitle= [title substringToIndex:1]; //modifying the statement to its first alphabet
if ([rowTitle isEqualToString:sectionTitle]) //checking if modified statement is same as section title
{
[newArray addObject:title]; //adding the row contents of a particular section in array
}
}
return newArray;
}
Its still not clear what you are trying to achieve here.
Going against my own answer, I suggest you that you do not compute you data for display during view rendering time. You need to create the cells as fast as possible. Why not create a property or an iVar (like #bauerMusic is Suggesting) and compute the date in viewDidLoad or declare a custom function which will reload your property (possible an Array or Dictionary) and while rendering the UI, just set the values (in you viewForIndexPath)?
You can use an array of two level depth to store for maintaining sections and rows. i.e. Level 1 - Sections and Array of rows, Level 2 - row.

Answer 2

The center of it all is:
cell.textLabel.text = [self titleForRow:indexPath];
Now, what you're actually using are NSString. Simple. Instead, you're creating a new array for each cell each call??
Why not have one array, say an NSMutableArray. Have it as a #property or local iVar.
#property (strong, nonatomic) NSMutableArray *rowArray;
// Instantiate in -viewDidLoad
rowArray = [NSMutableArray array]; // Much more elegant IMHO
Now call a method that do all the content loading, but do it ONCE. You can always call it again to refresh.
Something like:
// In -viewDidLoad
rowArray = [NSMutableArray array];
[self loadArrayContent];
Then, your cellForRowAtIndexPath should only be using your preloaded rowArray and simply pulling NSString titles from it.

Answer 3

My general way to handle a table view is to create (during table view setup) an NSMutableArray for the rows (anchored in the data source object). Each entry in the array is an NSMutableDictionary that is "primed" with the basic stuff for the row, and if more info needs to be developed to display the row, that is cached in the dictionary. (Where there are multiple sections I use an array of sections containing arrays of rows.)
What I might do for a play list is initialize the array with empty dictionaries, then, as one scrolls, access each play list element and cache it in the dictionary.
In fact, if one really wanted, updating the dictionary could be done via a background task (with appropriate locking) so that scroll speed wouldn't be hampered by the lookup operations.