App get crashed while loading large amount of data in UITableview - objective-c

Question

I am showing more than 10 columns in uitableview cell and having more than 100 rows but when i scroll tableview or reload table it received memory warning and app get crashed.
And we are also using collapse and expand on this table view.
Following code applied in cellforrowatindexpath
for(i=0;i<[appDel.tempItemDic count];i++)
{
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(CNT+30, -30, 350,100)];
label.font = [UIFont systemFontOfSize:14.0];
label.text =[tempDic objectForKey:[appDel.arrColumnList objectAtIndex:[[appDel.tempArr objectAtIndex:i]intValue]]];
label.textAlignment = UITextAlignmentLeft;
label.textColor = [UIColor whiteColor];
label.backgroundColor=[UIColor clearColor];
label.numberOfLines=1;
[cell.contentView addSubview:label];
[label release];
backgroundView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:#"ListItems_secondLevel(3).png"]];
cell.backgroundView = backgroundView;
cell.imageView.image=[UIImage imageNamed:#"arrow.png"];
CNT+=350;
}

Answer 1

You need to create the UILabels only while creating the cell. While reusing the cell, you can get the UILabel using tag and set the value to that. Do not create again and again.
Edit:
In addition to that, as Sarah mentioned, you don't need to do that in loop. As for every cell the method will get called, and you can set the value depend on the indexPath.

Answer 2

you don't need for loop in the method. As objectatIndex works for the same. remove the for loop as you are already using objectAtIndex and try again.

Answer 3

Probably you're not reusing the cell. So if you create 100 cells and each cell has 10 labels at the you will have UILabel views all kept in memory.
You should reuse the cell in this way (code not tested, just to give you an idea, I'm not commenting the way you create the text, I'm concerned only about memory warning):
-(UITableViewCell *)tableView:(UITableView *)tv cellForRowAtIndexPath:(NSIndexPath *)indexPath {
// add your code here to get the number of columns; I assume you defined a "getNumberOfColumnsForRowAtIndexPath:" somewhere in your code to retrieve this figure
NSInteger numberOfColumns = [appDel getNumberOfColumnsForRowAtIndexPath:indexPath];
NSString *cellId=[NSString stringWithFormat:#"MyComplexCellID_%d",numberOfColumns];
UITableViewCell *cell = [tv dequeReusableCellWithIdentifier:cellId];
if(!cell) {
// here you create the cell and add the labels; DON'T GIVE TEXT TO THE LABELS HERE
// in order to get the right label give them a tag; e.g. 500 is column 0, 501 column 1,...
for(int i=0;i<numberOfColumns;i++) {
UILabel *myLabel = ...
myLabel.tag=500+i;
}
}
// here you configure the cell
for(int i=0;i<numberOfColumns;i++) {
NSString *columnText = retrieve here your column text;
UILabel *labelColumn = (UILabel *)[cell.contentView viewWithTag:500+i];
labelColumn.text = columnText;
}
return cell;
}

Answer 4

If you are loading a large amount of data in table view I will suggest you
1:-
(void)viewDidLoad {
[super viewDidLoad];
dispatch_async(dispatch_get_main_queue(), ^{
[self.tableview reloadData];
});
}
2:-
(void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
dispatch_queue_t q = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_async(q, ^{
NSLog(#"DISPATCH_QUEUE_PRIORITY_HIGH - Main Thread");
[self methodForServerResponse];
});
}
In that methodForServerResponse-
(void)methodForServerResponse{
dispatch_queue_t q = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0);
dispatch_async(q, ^{
NSLog(#"DISPATCH_QUEUE_PRIORITY_HIGH - Main Thread within Main Thread");
//implement what you stuff need from server
});