How can I speed up a UITableView?

Question

I have a UITableView with about 400 cells in 200 sections and it\'s a little sluggish in responding to user interaction (scrolling, selecting cells.) I\'ve made sure the met

Answer 1

Two suggestions: One is to use -initWithStyle:reuseIdentifier: for your table view cells instead of -initWithFrame:. The other is to comment out setting the cell.backgroundView to an image with a gradient and see if that's the culprit. Every time I've had poor performance in a table view it's been because of an image.

Answer 2

1. use a shared image instance for the background (you alloc/init/release one for every time a new cell is created). When your table view is big , this means that the background X cells in memory takes much more memory than it should.

   instead of
   cell.backgroundView= [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"cell gradient2.png"]];
   just use :
   cell.backgroundView= [SomeHelperClass sharedBackgroundUIImageResource];

2. If that doesn't help , use CG instead of labels and other subviews (a screenshot will help here.. to know what we're talking about).

Answer 3

This is a little off-topic here (because you have only one background image for all cells):

My app displays different images in each cell. After adding about 5 cells to UITableView - table is slowed down drastically. It takes about 1-2 seconds to process all images each time i open view controller.

if let image = UIImage(contentsOfFile: photoFile){
    // just set it and let system fit it
    //cell.imageView!.image = image

    // 1 - Calculate sized
    let DEFAULT_THUMBNAIL_WIDTH: CGFloat  = (cellHeight / 4) * 5;
    let DEFAULT_THUMBNAIL_HEIGHT: CGFloat = cellHeight;

    let aspectRatio: CGFloat = image.size.width / image.size.height
    var willBeHeight = DEFAULT_THUMBNAIL_HEIGHT
    var willBeWidth  = DEFAULT_THUMBNAIL_HEIGHT * aspectRatio

    if(willBeWidth > DEFAULT_THUMBNAIL_WIDTH){
        willBeWidth = DEFAULT_THUMBNAIL_WIDTH
        willBeHeight = willBeWidth / aspectRatio
    }

    let eps:CGFloat = 0.000001
    assert((willBeHeight - eps) <= DEFAULT_THUMBNAIL_HEIGHT);
    assert((willBeWidth - eps) <= DEFAULT_THUMBNAIL_WIDTH);

    // 2 - Create context
    var size:CGSize = CGSize(
        width: DEFAULT_THUMBNAIL_WIDTH,
        height: DEFAULT_THUMBNAIL_HEIGHT)
    UIGraphicsBeginImageContext(size)

    // one-to-one rect
    //var imageRect: CGRect = CGRectMake(0.0, 0.0, size.width, size.height)
    var imageRect: CGRect = CGRectMake(0.0, 0.0, willBeWidth, willBeHeight)

    // 3 - Draw image
    image.drawInRect(imageRect)
    var imageResult: UIImage = UIGraphicsGetImageFromCurrentImageContext()
    cell.imageView!.image = imageResult

    UIGraphicsEndImageContext()
}else{
    DDLogError("Can not draw photo: \(photoFile)")
}

So i've ended up with generating small THUMBNAILS for all my images.