tableView Scrolling Really Slow - I'm Calling Too Many Methods? - ios

Question

I have a tableView that shows a list of songs from a user's iPod library. Each cell calls too many methods which is probably why scrolling is so sluggish (I think 'calling methods' is the right terminology, I'm fairly new to programming), like so:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
// Configure the cell...
cell.textLabel.text= [self titleForRow:indexPath]; //getting song title
cell.detailTextLabel.text = [self subtitleForRow:indexPath]; //get song artist
cell.imageView.image = [self artworkForRow:indexPath]; //get song image
return cell;
}
These are the methods:
- GET SONG TITLE
-(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;
}
- GET ARTIST
-(NSString *)subtitleForRow:(NSIndexPath *)indexpath{
NSMutableArray* subtitleRowArray=[[NSMutableArray alloc]initWithCapacity:0];
subtitleRowArray=[self getSubtitle:indexpath.section];
NSString *subtitleToBeDisplayed=[subtitleRowArray objectAtIndex:indexpath.row];
return subtitleToBeDisplayed;
}
-(NSMutableArray *)getSubtitle:(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];
NSString *subtitle = [song valueForProperty:MPMediaItemPropertyArtist];
rowTitle= [title substringToIndex:1]; //modifying the statement to its first alphabet
if ([rowTitle isEqualToString:sectionTitle]) //checking if modified statement is same as section title
{
if (subtitle){
[rowContainer addObject:subtitle]; //adding the row contents of a particular section in array
}
else {
[rowContainer addObject:#"Unknown Artist"];
}
}
}
}
}
return rowContainer;
}
- GET IMAGE
-(UIImage *)artworkForRow:(NSIndexPath *)indexpath{
NSMutableArray* artworkRowArray=[[NSMutableArray alloc]initWithCapacity:0];
artworkRowArray=[self getArtwork:indexpath.section];
UIImage *artworkToBeDisplayed=[artworkRowArray objectAtIndex:indexpath.row];
return artworkToBeDisplayed;
}
-(NSMutableArray *)getArtwork:(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];
MPMediaItemArtwork *artwork = [song valueForProperty:MPMediaItemPropertyArtwork];
UIImage *artworkImage = [artwork imageWithSize: CGSizeMake (50, 50)];
rowTitle= [title substringToIndex:1]; //modifying the statement to its first alphabet
if ([rowTitle isEqualToString:sectionTitle]) //checking if modified statement is same as section title
{
if (artworkImage){
[rowContainer addObject:artworkImage]; //adding the row contents of a particular section in array
}
else {
[rowContainer addObject:[UIImage imageNamed:#"noArtworkSongsCell"]];
}
}
}
}
}
return rowContainer;
}
Is there any way to smoothen scrolling here? Each of those methods are important.
Any help would be much appreciated, thanks!

Answer 1

The methods you're using shouldn't be called in cellForRowAtIndexPath -- you shouldn't be creating those arrays every time you need to populate a label in your cell. The arrays should be created once, outside of cellForRowAtIndexPath, and then queried inside that method to get the correct item out of the arrays.

Answer 2

Always prepare your data BEFORE drawing the table itself. In methods such as cellForRow, heightForCellAtIndexPath etc. you should just access your data, not modify it and/or manipulate it. In your example you not only iterate over array for every cell, you even call extremely slow methods such as string comparisons. You could put a breakpoint in cellForRowAtIndex path and see how many times it's called during scrolling, and then just imagine how much work you want to be done.