tableview cell load all at once in iphone

Question

I have implemented following code in my application.

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {    
NSString *CellIdentifier = [NSString stringWithFormat:@"%@%i",searchQueryString,indexPath.row];
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
 XML_SearchResult *t=[arrayResults objectAtIndex:indexPath.row];
    cell=((indexPath.row%2)==0) ? 
  [self getCellContentView:CellIdentifier drillTitle:t.drill_title stroke_type:t.stroke_type exercise_type:t.exercise_type level_name:t.level_name age_range:t.age_range alterNate:NO] :
  [self getCellContentView:CellIdentifier drillTitle:t.drill_title stroke_type:t.stroke_type exercise_type:t.exercise_type level_name:t.level_name age_range:t.age_range alterNate:YES] ;
 CGRect a=[cell frame];
 UIImageView *bImg=[[UIImageView alloc] initWithFrame:a];
 bImg.image=[UIImage imageNamed:@"white-rect-tab-3.png"];
 [bImg setContentMode:UIViewContentModeScaleToFill]; 
 cell.selectedBackgroundView=bImg; [bImg release];
}
return cell;
}
-(UITableViewCell*)getCellContentView:(NSString*)cellIdentifier drillTitle:(NSString*)drillTitle stroke_type:(NSString*)stroke_type exercise_type:(NSString*)exercise_type level_name:(NSString*)level_name age_range:(NSString*)age_range alterNate:(BOOL)alterNate
{
CGRect label1Frame=CGRectMake(5, 20, 260, 32),label2Frame=CGRectMake(5, 62, 120, 30),label3Frame=CGRectMake(130, 62, 170, 30);//,BgFrame=CGRectMake(0, 0, 320, 60);
UITableViewCell *cell=[[[UITableViewCell alloc] initWithFrame:CGRectMake(0, 0, 312, 95) reuseIdentifier:cellIdentifier] autorelease];
UILabel *tmp; UIImageView *imgBg;
cell.backgroundColor=[UIColor clearColor];
// drill title label
tmp=[[UILabel alloc] initWithFrame:CGRectMake(5, 1, 260, 32)]; 
tmp.textColor=[UIColor colorWithRed:(9.0/255.0) green:(68.0/255) blue:(85.0/255) alpha:1.0];
[tmp setFont:[UIFont fontWithName:@"ArialRoundedMTBold" size:18]];  tmp.text=drillTitle; [tmp setShadowColor:[UIColor lightGrayColor]];
tmp.backgroundColor=[UIColor clearColor]; [cell.contentView addSubview:tmp]; [tmp release]; 
// title label - tip
tmp=[[UILabel alloc] initWithFrame:label1Frame]; 
tmp.textColor=[UIColor colorWithRed:(9.0/255.0) green:(68.0/255) blue:(85.0/255) alpha:1.0];
[tmp setFont:[UIFont fontWithName:@"ArialRoundedMTBold" size:18]];  tmp.text=stroke_type; [tmp setShadowColor:[UIColor lightGrayColor]];
tmp.backgroundColor=[UIColor clearColor]; [cell.contentView addSubview:tmp]; [tmp release];
// sub title - exercise type label - tip
tmp=[[UILabel alloc] initWithFrame:CGRectMake(5, 40 , 260, 32)]; 
tmp.textColor=[UIColor colorWithRed:(14.0/255.0) green:(105.0/255) blue:(128.0/255) alpha:1.0];
[tmp setFont:[UIFont fontWithName:@"ArialRoundedMTBold" size:15]]; tmp.text=exercise_type; [tmp setShadowColor:[UIColor lightGrayColor]];
tmp.backgroundColor=[UIColor clearColor]; [cell.contentView addSubview:tmp]; [tmp release];
// Age - Range 
tmp=[[UILabel alloc] initWithFrame:label2Frame]; tmp.adjustsFontSizeToFitWidth=0; tmp.text=[NSString stringWithFormat:@"Age Range : %@",age_range];
tmp.textColor= [UIColor blackColor];//[UIColor colorWithRed:(14.0/255.0) green:(105.0/255) blue:(128.0/255) alpha:1.0];// : [UIColor blackColor] ;
[tmp setBackgroundColor:[UIColor clearColor]];
[tmp setFont:[UIFont fontWithName:@"ArialMT" size:14]]; [tmp setShadowOffset:CGSizeMake(1,1)]; [tmp setShadowColor:[UIColor lightGrayColor]];
[cell.contentView addSubview:tmp]; [tmp release];
// Difficulty leve - Range 
tmp=[[UILabel alloc] initWithFrame:label3Frame]; tmp.adjustsFontSizeToFitWidth=0; tmp.text=[NSString stringWithFormat:@"| Diff. Level : %@",level_name];
tmp.textColor=[UIColor blackColor];//[UIColor colorWithRed:(14.0/255.0) green:(105.0/255) blue:(128.0/255) alpha:1.0]; 
[tmp setShadowColor:[UIColor lightGrayColor]];
[tmp setBackgroundColor:[UIColor clearColor]];
[tmp setFont:[UIFont fontWithName:@"ArialMT" size:14]]; [tmp setShadowOffset:CGSizeMake(1,1)];
[cell.contentView addSubview:tmp]; [tmp release];
// arrow
imgBg=[[UIImageView alloc] initWithFrame:CGRectMake(280, 35, 13, 13)];  imgBg.contentMode=UIViewContentModeScaleToFill;
imgBg.image=[UIImage imageNamed:@"arrow-2.png"];
[cell.contentView addSubview:imgBg]; [cell.contentView sendSubviewToBack:imgBg]; [imgBg release]; 
// line
imgBg=[[UIImageView alloc] initWithFrame:CGRectMake(-4, 94, 298, 2)];  imgBg.contentMode=UIViewContentModeScaleToFill;
imgBg.image=[UIImage imageNamed:@"line.png"];
[cell.contentView addSubview:imgBg]; [cell.contentView sendSubviewToBack:imgBg]; [imgBg release]; 
[cell setSelectionStyle:UITableViewCellSelectionStyleGray];
return cell;
}

That's all about customizing cell dynamically.

But the problem is - first time only visible cells are created, then after - user tries to scroll down. other cells which are going to be visible is going to be created & then displayed. Due to this, there is some delay in scrolling tableview at first time.

What is the solution for this ?

Answer 1

It is probably the image loading which takes all the time. Creating cells should not take very long, especially if you reuse old ones. If the images are often the same, then you could cache those. Also scaling takes time and also if the images are not PNG they will take longer to load. But the solution for me has been to not load the images when I create the cell, i.e. NOT in:

tableView:cellForRowAtIndexPath:

but instead implement:

scrollViewDidEndDecelerating

This is a delegate function which is called when the table stops scrolling. Then you can get a list of the visible cells (indexPathsForVisibleRows) and set the image on each of those.

Answer 2

When developing for mobile platforms, you need to be concerned about memory footprints. I feel that if you tried to load 400 cells with images all at once, you might be asking for trouble. It's not the recommended method and you will certainly introduce a huge delay in loading this.

Instead of hacking like this, work in improving the performance of your cellForIndexPath function to make it load quicker. Or asynchronously.