i am able to fetch images asynchronously on to uitableview.i am fetching these images are from a url.on scrolling up uitableview these images disappear and  they take time to load again and sometimes they dont load at all.i dont want to use any 3rd party libraries.i dont want to go with synchronous approach.please suggest any correct approach to improve performance.thanks for help in advance.my code is below:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
static NSString *identifier=@"cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
if (cell == nil) {
    cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:@"identifier"];
}
UIImageView *imgVw=[[UIImageView alloc]initWithFrame:CGRectMake(250, 10, 40, 30)];
[cell.contentView addSubview:imgVw];
Attributes *att = [listOfObjects objectAtIndex:indexPath.row];
strImgUrl=@"http:image url";
strImgName=att.classifiedImg;
if (strImgName == nil) {
    UIImage *myImg=[UIImage imageNamed:@"user_circle.png"];
    imgVw.image=myImg;
}
else{
    strImg=[strImgUrl stringByAppendingString:strImgName];
}
dispatch_async(dispatch_get_global_queue(0,0), ^{
    NSData *data = [[NSData alloc] initWithContentsOfURL: [NSURL URLWithString:strImg]];
    if ( data == nil )
        return;
    dispatch_async(dispatch_get_main_queue(), ^{

        UIImage *img=[UIImage imageWithData: data];
        imgVw.image=img;
    });

});



return cell;
}



Question: Create Valid XML from XSD Loaded at Runtime (without xsd.exe)
Answer: For others that wound up here: the best solution given the constraints, create XML at runtime and using .NET, is probably the first link: 
Is there a class to generate a sample XML document from XSD schema in .NET
At least, that's what I am going to try :).