the tableview update it self randomly

@interface NavigationController : UITableViewController 

My tableview is created programaticly so no xib file.At the bottom part i update the table when the user click the tab bar. This is why i put it in viewDidAppear. But the table isn't update itself every time, just randomly update.You can see the show value that is written in the table.The nslog writes correct value but the table didn't show the correct value all the time any idea why??

- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
NSString *country=[[NSUserDefaults standardUserDefaults]objectForKey:@"namecountry"];
//url's
NSURL *url = [NSURL URLWithString:@"someurl"];
ASIFormDataRequest *request = [ASIFormDataRequest requestWithURL:url];
[request setPostValue:country forKey:@"c_name"];
[request setRequestMethod:@"POST"];
[request setValidatesSecureCertificate:NO];
[request setDelegate:self];
[request startSynchronous];

NSString *response = [request responseString];
NSLog(@"%@",response);
res=[[response c开发者_开发知识库omponentsSeparatedByString:@","] retain];
NSLog(@"%@",[res objectAtIndex:18]);
show=[[NSString stringWithFormat:@"%@",[res objectAtIndex:18]] retain];
float f=[show floatValue];
show=[NSString stringWithFormat:@"%.2f %%",f];
}

edit::

 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
UITableViewCell *cell = nil;
if (indexPath.row % 2 == 0) {
    // EVEN
    cell = [tableView dequeueReusableCellWithIdentifier:@"EvenCell"];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:@"EvenCell"] autorelease];
        UIView *bg = [[UIView alloc] initWithFrame:cell.frame];
        UIColor *colour = [[UIColor alloc] initWithRed: (208.0/255.f) green: (231.0/255.f) 
                                                  blue: (241.0/255.f) alpha: 1.0];
        bg.backgroundColor = colour; 
        cell.backgroundView = bg;
        cell.textLabel.backgroundColor = bg.backgroundColor;
        [bg release];
        cell.detailTextLabel.backgroundColor=[UIColor clearColor];
        show=[[NSString stringWithFormat:@"%@",[res objectAtIndex:18]] retain];
        float f=[show floatValue];
        show=[NSString stringWithFormat:@"%.2f %%",f];
        cell.detailTextLabel.text=show;
    }
    cell.textLabel.text = [array objectAtIndex:indexPath.row];
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;

} else {
    // ODD
    cell = [tableView dequeueReusableCellWithIdentifier:@"OddCell"];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:@"OddCell"] autorelease];
        UIView *bg = [[UIView alloc] initWithFrame:cell.frame];

        UIColor *colour = [[UIColor alloc] initWithRed: (143.0/255.f) green: (169.0/255.f) 
                                                  blue: (180.0/255.f) alpha: 1.0];
        bg.backgroundColor = colour;
        cell.backgroundView = bg;
        cell.textLabel.backgroundColor = bg.backgroundColor;
        [bg release];
    }
    cell.textLabel.text = [array objectAtIndex:indexPath.row];
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;


} 
return cell;
}   

In order to show new data in your tableview, you need to call

[self.tableView reloadData];

This instructs the tableview to call all the datasource methods and grab the new data. Without making this call, it will continue using cached data.