Others, most notably the Tweetie developer, have discussed this, but I wanted to share my two cents on fast scrolling in UITableViews with (or without) dynamic cell heights.

I've been working on an app (I can let the cat out of the bag soon) that has (amongst other items) three main UITableViews. The first has static-height UITableViewCells with just three UILabels and the second has static-height UITableViewCells three UILabels and one UIImageView. For those two, the following settings are pretty important (translate Interface Builder settings to iPhone SDK calls if you are working – as I am – purely in code):



The next item of utmost importance is doing all of the calculations for the content of the cells outside of tableView:cellForRowAtIndexPath:. When I was prototyping, I had a good portion of the transformation code in that method and have since moved it to the XML parsing routines. Since I was not able to set my cells to be opaque, limiting the number of "inner" UIViews was also high on the priority list. I did not need to background load the images in the cells, so I did not have to resort to using a subclass of UITableViewCell but I *did* implement a very rudimentary caching system which helped to speed things up a bit:



For the dynamic height cells, I setup an NSMutableDictionary called "heights" (the key is the row number) which caches the row heights of each cell since one of the UILabels can drastically vary in height. You need to do something like the following in tableView:heightForRowAtIndexPath::



and then explicitly set the UILabel's frame size each time in tableView:cellForRowAtIndexPath: and also retrieve said hight and calculate the number of rows in tableView:cellForRowAtIndexPath::



If your table cells get any more complex or you need to delay or thread the loading of the images, then you will need to implement a custom table cell. When writing code to see what goes on behind the scenes, it turns out that there are many, many, many calls to those two methods for each table view, so it is very important to make them as lightweight as possible.

I needed to strip the tags from some HTML that was embedded in an XML feed so I could display a short summary from the full content in a UITableView. Rather than go through the effort of parsing HTML on the iPhone (as I already parsed the XML file) I built this simple method from some half-finished snippets I found. It has worked in all of the cases I have needed, but your mileage may vary. It is at least a working method (which cannot be said about most of the other examples). It works on the iPhone and in standard OS X coding.

- (NSString *)flattenHTML:(NSString *)html {

    NSScanner *theScanner;
    NSString *text = nil;

    theScanner = [NSScanner scannerWithString:html];

    while ([theScanner isAtEnd] == NO) {

        // find start of tag
        [theScanner scanUpToString:@"<" intoString:NULL] ; 

        // find end of tag
        [theScanner scanUpToString:@">" intoString:&text] ;

        // replace the found tag with a space
        //(you can filter multi-spaces out later if you wish)
        html = [html stringByReplacingOccurrencesOfString:
                           [ NSString stringWithFormat:@"%@>", text]
                     withString:@" "];

    } // while //
    
    return html;

}