UITableView with performance issues

Question

I make an UITableview (with IB) in my application with 3 types of cell. All works fine except when i drag my tableview all become very slow. So if someone can help me to improve the performance of my app it'll be cool.

My Code for the tableview :

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [[myData objectForKey:@"listnews"] count];
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.row == 0) {
        return 154;
    }
    if (indexPath.row == 1) {
        return 34;
    }
    else return 70;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    [myTextField resignFirstResponder];

    ListNewsCell *cCell = (ListNewsCell *)[myTable dequeueReusableCellWithIdentifier:[NSString stringWithFormat:@"cCellIdentifier%d",indexPath.row]];

    cCell = [[ListNewsCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:[NSString stringWithFormat:@"cCellIdentifier%d",indexPath.row]];

    if (indexPath.row == 0) {
        NSString * caroline = [[[myData objectForKey:@"listnews"] objectAtIndex:indexPath.row] objectForKey:@"urlimage"];
        cCell.c1Image1.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@",caroline]]]];

        cCell.c1Image2.image = [UIImage imageNamed:@"barreNoireHub.png"];

        NSString * sophie = [[[myData objectForKey:@"listnews"] objectAtIndex:indexPath.row] objectForKey:@"titre"];
        NSString *itemTitle = sophie ? [sophie stringByConvertingHTMLToPlainText] : @"[No Title]";
        cCell.c1Label1.text = itemTitle;

        NSString * sonia = [[[myData objectForKey:@"listnews"] objectAtIndex:indexPath.row] objectForKey:@"extrait"];
        NSString *itemExtrait = sonia ? [sonia stringByConvertingHTMLToPlainText] : @"[No Title]";
        cCell.c1Label2.text = itemExtrait;
        }

    if (indexPath.row == 1) {        
        UIImageView * imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 320, 34)];
        imageView.backgroundColor = [UIColor whiteColor];
        imageView.image = [UIImage imageNamed:@"barreSearchHub.png"];
        [cCell addSubview:imageView];
        [imageView release];

        UIView * insertView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 34)];
        myTextField = [[UITextField alloc] initWithFrame:CGRectMake(15, 6, 270, 25)];
        myTextField.placeholder = @"Recherche";
        myTextField.tag = 1;
        myTextField.delegate = self;
        myTextField.returnKeyType = UIReturnKeySearch;

        [insertView addSubview:myTextField];
        cCell.accessoryView = insertView;
    }

    if (indexPath.row > 1) {
        cCell.c2Image1.image = [UIImage imageNamed:@"cellM.png"];

        NSString * caroline = [[[myData objectForKey:@"listnews"] objectAtIndex:indexPath.row] objectForKey:@"urlimage"];
        cCell.c2Image2.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@",caroline]]]];

        NSString * sophie = [[[myData objectForKey:@"listnews"] objectAtIndex:indexPath.row] objectForKey:@"titre"];
        NSString *itemTitle = sophie ? [sophie stringByConvertingHTMLToPlainText] : @"[No Title]";
        cCell.c2Label1.text = itemTitle;

        NSString * sonia = [[[myData objectForKey:@"listnews"] objectAtIndex:indexPath.row] objectForKey:@"extrait"];
        NSString *itemExtrait = sonia ? [sonia stringByConvertingHTMLToPlainText] : @"[No Title]";
        cCell.c2Label2.text = itemExtrait;
    }
    return cCell;
}

The code of the UITableViewCell:

#import "ListNewsCell.h"

@implementation ListNewsCell

@synthesize c1Image1, c1Image2, c1Label1, c1Label2;
@synthesize c2Image1, c2Image2, c2Label1, c2Label2;

- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
    self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
    if (self) {
        c1Image1 = [[UIImageView alloc] initWithFrame:CGRectMake(0,0,320,154)];
        c1Image1.backgroundColor = [UIColor clearColor];
        [self addSubview:c1Image1];
        [c1Image1 release];

        c1Image2 = [[UIImageView alloc] initWithFrame:CGRectMake(0,98,320,56)];
        c1Image2.backgroundColor = [UIColor clearColor];
        [self addSubview:c1Image2];
        [c1Image2 release];

        c1Label1 = [[UILabel alloc] initWithFrame:CGRectMake(5, 100, 310, 20)];
        c1Label1.font = [UIFont fontWithName:@"Arial-BoldMT" size:14];
        c1Label1.textColor = [UIColor whiteColor];
        c1Label1.backgroundColor = [UIColor clearColor];
        [self addSubview:c1Label1];

        c1Label2 = [[UILabel alloc] initWithFrame:CGRectMake(5, 112, 310, 45)];
        c1Label2.font = [UIFont fontWithName:@"Arial" size:12];
        c1Label2.textColor = [UIColor whiteColor];
        c1Label2.numberOfLines = 2;
        c1Label2.backgroundColor = [UIColor clearColor];
        [self addSubview:c1Label2];

        c2Image1 = [[UIImageView alloc] initWithFrame:CGRectMake(0,0,320,70)];
        c2Image1.backgroundColor = [UIColor clearColor];
        [self addSubview:c2Image1];
        [c2Image1 release];

        c2Label1 = [[UILabel alloc] initWithFrame:CGRectMake(105, 8, 180, 20)];
        c2Label1.font = [UIFont fontWithName:@"Arial-BoldMT" size:14];
        c2Label1.textColor = [UIColor blackColor];
        c2Label1.backgroundColor = [UIColor clearColor];
        [self addSubview:c2Label1];

        c2Label2 = [[UILabel alloc] initWithFrame:CGRectMake(105, 25, 180, 45)];
        c2Label2.font = [UIFont fontWithName:@"Arial" size:12];
        c2Label2.textColor = [UIColor blackColor];
        c2Label2.numberOfLines = 2;
        c2Label2.backgroundColor = [UIColor clearColor];
        [self addSubview:c2Label2];

        c2Image2 = [[UIImageView alloc] initWithFrame:CGRectMake(20,10,75,55)];
        c2Image2.backgroundColor = [UIColor clearColor];
        [self addSubview:c2Image2];
        [c2Image2 release];
    }
    return self;
}

- (void)setSelected:(BOOL)selected animated:(BOOL)animated
{
    [super setSelected:selected animated:animated];
}

- (void)dealloc
{
    [super dealloc];
}

@end

Thanks to all !

Answer 1

The following line causes the big delay:

cCell.c2Image2.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@",caroline]]]];

Everytime one of these cells will be loaded, it will make a URL Request. Try to preload a bunch of the data instead of requesting it per cell.

Load the image once, make it a class variable, then just reuse its pointer like:

cCell.c2Image2.image = preloadedImage;

Declare in your .h file:

UIImage * preloadedImage;

And in the - (void) loadView -method put:

preloadedImage = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@",caroline]]]];

Also mind that as jrturton wrote, you want to reuse your dequeued cells for the extra performance boost.

Answer 2

In cellForRowAtIndexPath method you have dequeued some cells from the table view. But you have never used that value. That caused the problem of loading every time rather than re-using.

Try the following code in which I've modified a little..

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath

{

[myTextField resignFirstResponder];

ListNewsCell *cCell = (ListNewsCell *)[myTable dequeueReusableCellWithIdentifier:[NSString stringWithFormat:@"cCellIdentifier%d",indexPath.row]];

if(cCell == nil)

{

cCell = [[ListNewsCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:[NSString stringWithFormat:@"cCellIdentifier%d",indexPath.row]];

}

if (indexPath.row == 0) {
   // Some code here
    }

if (indexPath.row == 1) {        
    //Some code here
}

if (indexPath.row > 1) {
  // some code here
}
return cCell;

}

Thanks, Arun.

Answer 3

You are never reusing your dequeued cells, so you are recreating everything from scratch every time. Since you have a unique cell for each row (is this really necessary for cells in row 2 and above?) you only need to create and populate them once.

So, you could wrap everything after dequeueReusableCellWithIdentifier onwards inside if (cCell == nil) (the return statement excepted, obviously).