Iphone - when to calculate heightForRowAtIndexPath for a tableview when each cell height is dynamic?

Question

I have seen this question asked many times but astoundingly, I have not seen a consistent answer, so I will give it a try myself:

If you have a tableview containing

Answer 1

I went with the idea I originally proposed, which appears to work fine, whereby I load all the custom cells ahead of time in viewDidLoad, store them in a NSMutableDictionary with their index as the key. I am posting the relevant code and would love any critiques or opinions anyone has about this approach. Specifically, I am not sure whether there is any memory leak issue with the way I am creating the UITableViewCells from the nib in viewDidLoad - since I don't release them.

@interface RecentController : UIViewController  {

NSArray *listData;
NSMutableDictionary *cellBank;

}

@property (nonatomic, retain) NSArray *listData;
@property (nonatomic, retain) NSMutableDictionary *cellBank;
@end



@implementation RecentController

@synthesize listData;
@synthesize cellBank;

---

- (void)viewDidLoad {

---

self.cellBank = [[NSMutableDictionary alloc] init];

---

//create question objects…

--- 

NSArray *array = [[NSArray alloc] initWithObjects:question1,question2,question3, nil];

self.listData = array;

//Pre load all table row cells
int count = 0;
for (id question in self.listData) {

    NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"QuestionHeaderCell" 
                                                 owner:self 
                                               options:nil];
    QuestionHeaderCell *cell;

    for (id oneObject in nib) {
        if([oneObject isKindOfClass:[QuestionHeaderCell class]])
            cell = (QuestionHeaderCell *) oneObject;

            NSNumber *key = [NSNumber numberWithInt:count];
            [cellBank setObject:[QuestionHeaderCell makeCell:cell 
                                                  fromObject:question] 
                         forKey:key];
            count++;

    }
}

[array release];
[super viewDidLoad];
}



#pragma mark -
#pragma mark Table View Data Source Methods

-(NSInteger) tableView: (UITableView *) tableView
numberOfRowsInSection: (NSInteger) section{

return [self.listData count];

}

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

NSNumber *key = [NSNumber numberWithInt:indexPath.row];
return [cellBank objectForKey:key];


}

-(CGFloat) tableView: (UITableView *) tableView
heightForRowAtIndexPath: (NSIndexPath *) indexPath{

NSNumber *key = [NSNumber numberWithInt:indexPath.row];
return [[cellBank objectForKey:key] totalCellHeight];

}

@end



@interface QuestionHeaderCell : UITableViewCell {

UITextView *title;
UILabel *createdBy;
UILabel *category;
UILabel *questionText;
UILabel *givenBy;
UILabel *date;
int totalCellHeight;

}

@property (nonatomic, retain) IBOutlet UITextView *title;
@property (nonatomic, retain) IBOutlet UILabel *category;
@property (nonatomic, retain) IBOutlet UILabel *questionText;
@property (nonatomic, retain) IBOutlet UILabel *createdBy;
@property (nonatomic, retain) IBOutlet UILabel *givenBy;
@property (nonatomic, retain) IBOutlet UILabel *date;
@property int totalCellHeight;

+(UITableViewCell *) makeCell:(QuestionHeaderCell *) cell 
               fromObject:(Question *) question;

@end



@implementation QuestionHeaderCell
@synthesize title;
@synthesize createdBy;
@synthesize givenBy;
@synthesize questionText;
@synthesize date;
@synthesize category;
@synthesize totalCellHeight;







- (void)dealloc {
[title release];
[createdBy release];
[givenBy release];
[category release];
[date release];
[questionText release];
[super dealloc];
}

+(UITableViewCell *) makeCell:(QuestionHeaderCell *) cell 
                 fromObject:(Question *) question{


NSUInteger currentYpos = 0;

cell.title.text = question.title;

CGRect frame = cell.title.frame;
frame.size.height = cell.title.contentSize.height;
cell.title.frame = frame;
currentYpos += cell.title.frame.size.height + 2;


NSMutableString *tempString = [[NSMutableString alloc] initWithString:question.categoryName];
[tempString appendString:@"/"];
[tempString appendString:question.subCategoryName];

cell.category.text = tempString;
frame = cell.category.frame;
frame.origin.y = currentYpos;
cell.category.frame = frame;
currentYpos += cell.category.frame.size.height;

[tempString setString:@"Asked by "];
[tempString appendString:question.username];
cell.createdBy.text = tempString;

frame = cell.createdBy.frame;
frame.origin.y = currentYpos;
cell.createdBy.frame = frame;
currentYpos += cell.createdBy.frame.size.height;


cell.questionText.text = question.text;
frame = cell.questionText.frame;
frame.origin.y = currentYpos;
cell.questionText.frame = frame;
currentYpos += cell.questionText.frame.size.height;


[tempString setString:@"Advice by "];
[tempString appendString:question.lastNexusUsername];
cell.givenBy.text = tempString;
frame = cell.givenBy.frame;
frame.origin.y = currentYpos;
cell.givenBy.frame = frame;
currentYpos += cell.givenBy.frame.size.height;


cell.date.text = [[[MortalDataStore sharedInstance] dateFormat] stringFromDate: question.lastOnDeck];
frame = cell.date.frame;
frame.origin.y = currentYpos-6;
cell.date.frame = frame;
currentYpos += cell.date.frame.size.height;

//Set the total height of cell to be used in heightForRowAtIndexPath
cell.totalCellHeight = currentYpos;

[tempString release];
return cell;

}

@end