Preload UICollectionViewCells - objective-c

Question

I've got a Uicollectionview with about 800 cells in it which is very slow when scrollign or zooming in or out.
The Method updateVisibleCellsNow takes about 9000 ms and slows down the App.
I still set
cell.layer.shouldRasterize = YES;
cell.layer.rasterizationScale = [UIScreen mainScreen].scale;
But it didn't work at all.
So i've tried to cache all the cells at viewDidLoad, cache them in an NSCache and access them from the cahce, but it seams like I am forced to user a reuseIdentifiert and can't access created Cells from the cache.
Is there any solution for this problem?
greetings,
Alex

Answer 1

MY Custom CollectionViewCell:
My .h File
#interface AECalendarCell : UICollectionViewCell
{
AEProjectDayItem *item;
NSIndexPath *thePath;
UILabel *lbl;
}
#property(nonatomic, strong) UILabel *lbl;
#property(nonatomic, strong) NSIndexPath *thePath;
#property(nonatomic, strong) AEProjectDayItem *item;
#property (nonatomic) CGFloat scale;
#property bool isAM;
-(void)redrawCellWithString:(NSString*)String;
#end
My .m File
#implementation AECalendarCell
#synthesize lbl, item, thePath;
-(id)initWithFrame:(CGRect)frame
{
if (self == [super initWithFrame:frame]) {
lbl = [[UILabel alloc]init];
}
return self;
}
-(void)redrawCellWithString:(NSString*)String
{
[lbl removeFromSuperview];
lbl.frame = self.contentView.bounds;
lbl.lineBreakMode = NSLineBreakByWordWrapping;
lbl.numberOfLines = 0;
if(self.scale >= 0.9)
lbl.font = [UIFont fontWithName:#"Arial" size:14];
else if(self.scale >= 0.8)
lbl.font = [UIFont fontWithName:#"Arial" size:12];
else if(self.scale >= 0.7)
lbl.font = [UIFont fontWithName:#"Arial" size:10];
else if(self.scale >= 0.6)
lbl.font = [UIFont fontWithName:#"Arial" size:8];
else if(self.scale >= 0.5)
lbl.font = [UIFont fontWithName:#"Arial" size:6];
lbl.backgroundColor = [UIColor clearColor];
lbl.textAlignment = NSTextAlignmentCenter;
if ([String isEqualToString:#""])
lbl.text = #" ";
else
lbl.text = String;
lbl.textColor = [UIColor blackColor];
if(thePath.section == 1 && thePath.item == 0)
{
CALayer *edgeBorder = [CALayer layer];
[edgeBorder setBackgroundColor:[[UIColor blackColor] CGColor]];
[edgeBorder setFrame:CGRectMake(self.bounds.size.width-2, self.bounds.size.height-2, 2, 2)];
[lbl.layer addSublayer:edgeBorder];
}
if(thePath.section == 1 && thePath.item>0)
{
CALayer *bottomBorder = [CALayer layer];
[bottomBorder setBackgroundColor:[[UIColor blackColor] CGColor]];
[bottomBorder setFrame:CGRectMake(0, self.bounds.size.height-2, self.bounds.size.width, 2)];
[lbl.layer addSublayer:bottomBorder];
}
if(thePath.section > 1 && thePath.item == 0)
{
CALayer *rightBorder = [CALayer layer];
[rightBorder setBackgroundColor:[[UIColor blackColor] CGColor]];
[rightBorder setFrame:CGRectMake(self.contentView.bounds.size.width-2, 0, 2, self.contentView.bounds.size.width)];
[lbl.layer addSublayer:rightBorder];
}
if(thePath.section > 1 && thePath.row > 1 && thePath.row %2 == 0)
{
CALayer *endofDayLayer = [CALayer layer];
[endofDayLayer setFrame:CGRectMake(self.frame.size.width-2, 0, 2, self.frame.size.width)];
if(thePath.section % 2 == 0)
[endofDayLayer setBackgroundColor:[[UIColor blackColor] CGColor]];
else
[endofDayLayer setBackgroundColor:[[UIColor blackColor] CGColor]];
[self.lbl.layer addSublayer:endofDayLayer];
}
[self.contentView addSubview:lbl];
}
-(void)prepareForReuse
{
[super prepareForReuse];
lbl.layer.sublayers = NULL;
[lbl removeFromSuperview];
}
Adding the Cell:
-(UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
AECalendarCell *cell = [CV_plantabel dequeueReusableCellWithReuseIdentifier:#"identifier" forIndexPath:indexPath];
if(cell == nil)
{
cell = [[AECalendarCell alloc]init];
}
cell.thePath = indexPath;
cell.scale = scale;
cell.layer.shouldRasterize = YES;
cell.layer.rasterizationScale = [UIScreen mainScreen].scale;
NSDateFormatter *DateFormatter=[[NSDateFormatter alloc] init];
[DateFormatter setDateFormat:#"dd.MM.yyyy"];
NSDateFormatter *headerDateFormatter=[[NSDateFormatter alloc] init];
[headerDateFormatter setDateFormat:#"dd.MM"];
NSDate *today = [DateFormatter dateFromString:[DateFormatter stringFromDate:startDate]];
NSDate *headerDay;
if(indexPath.section == 0)
headerDay = [today dateByAddingTimeInterval:60*60*24*(indexPath.row-1)];
else
headerDay = [today dateByAddingTimeInterval:60*60*12*(indexPath.row-1)];
if(indexPath.section==0)
{
cell.backgroundColor = [UIColor grayColor];
if(indexPath.row>0)
[cell redrawCellWithString:[headerDateFormatter stringFromDate:headerDay]];
}
else if(indexPath.section == 1)
{
cell.backgroundColor = [UIColor grayColor];
if(indexPath.row == 0)
[cell redrawCellWithString:#"Name"];
else
{
if(indexPath.row % 2 == 1)
{
[cell redrawCellWithString:#"AM"];
}
else
{
[cell redrawCellWithString:#"PM"];
}
}
}
else
{
[cell redrawCellWithString:#""];
if(indexPath.row % 2 == 1)
{
cell.item = [[AEProjectDayItem alloc]initWithDate:headerDay andUser:[[[users objectAtIndex:indexPath.section-2]valueForKey:#"userID"]intValue] andisAM:YES];
}
else
{
cell.item = [[AEProjectDayItem alloc]initWithDate:headerDay andUser:[[[users objectAtIndex:indexPath.section-2]valueForKey:#"userID"]intValue] andisAM:NO];
}
//set Colors
if(indexPath.section % 2 == 0)
{
[cell setBackgroundColor:[UIColor grayColor]];
}
else
{
[cell setBackgroundColor:[UIColor darkGrayColor]];
}
//set Data
if(indexPath.item == 0)
{
if(self.currentScale >= 0.6)
[cell redrawCellWithString:[[users objectAtIndex:indexPath.section-2]valueForKey:#"name"]];
else
[cell redrawCellWithString:[[users objectAtIndex:indexPath.section-2]valueForKey:#"nachname"]];
}
//adjust row height
for(NSArray *item in projectDayItems)
{
if(indexPath.item>0)
{
if([[item valueForKey:#"datum"]isEqualToString:[DateFormatter stringFromDate:headerDay]] &&
[[item valueForKey:#"AM"]boolValue] == cell.item.isAM &&
[[item valueForKey:#"userID"]integerValue] == cell.item.theUserID &&
cell.item != NULL)
{
cell.item.projectDayId = [[item valueForKey:#"projectDayID"]integerValue];
cell.item.bereich = [item valueForKey:#"bereich"];
cell.item.project = [[AEProject alloc]initwithID:[[item valueForKey:#"projectID"]integerValue] andName:[item valueForKey:#"projectname"]];
cell.item.theClass = [item valueForKey:#"class"];
cell.item.sequenceID = [[item valueForKey:#"sequence"]integerValue];
[cell redrawCellWithString:cell.item.project.projectName];
}
else
{
[cell redrawCellWithString:cell.item.project.projectName];
}
}
}
}
//set the Accessibility Label
if(cell.item != NULL && indexPath.section > 1 && indexPath.item>0)
{
NSDateFormatter *DateFormatter=[[NSDateFormatter alloc] init];
[DateFormatter setDateFormat:#"EEEE, d. MMMM"];
NSString *accString;
if(cell.item.project != nil)
{
if(cell.item.isAM)
accString = [NSString stringWithFormat:#"%# Vormittag, %# für %#", [DateFormatter stringFromDate:cell.item.theDate], cell.item.project.projectName, [[users objectAtIndex:indexPath.section-2]valueForKey:#"name"]];
else
accString = [NSString stringWithFormat:#"%# Nachmittag, %# für %#", [DateFormatter stringFromDate:cell.item.theDate], cell.item.project.projectName, [[users objectAtIndex:indexPath.section-2]valueForKey:#"name"]];
cell.lbl.accessibilityLabel = accString;
}
else
{
if(cell.item.isAM)
accString = [NSString stringWithFormat:#"%# Vormittag für %#", [DateFormatter stringFromDate:cell.item.theDate], [[users objectAtIndex:indexPath.section-2]valueForKey:#"name"]];
else
accString = [NSString stringWithFormat:#"%# Nachmittag für %#", [DateFormatter stringFromDate:cell.item.theDate], [[users objectAtIndex:indexPath.section-2]valueForKey:#"name"]];
cell.lbl.accessibilityLabel = accString;
}
}
//set Layout
if(indexPath.row > 0 && indexPath.section > 1)
[self setLayoutforCell:cell];
[self setCell:cell forIndexPath:indexPath];
return cell;
}

Answer 2

You create your cells without identifier, you should add this line when your view is being loaded.
[self.collectionView registerClass:[AECalendarCell class] forCellWithReuseIdentifier:#"identifier"];