KSPAutomaticHeightCalculationTableCellView

A useful superclass for a custom view-based NSTableView’s cell.

Sample Application

There is a simple application that demonstrates KSPAutomaticHeightCalculationTableCellView in action. The app shows a single window with an embedded split view. The left pane has a fixed-height cells (AHCUserTableCellView) that represent some fictional users. The right pane has cells (AHCMessageTableCellView) whose heights depend both on their textual content and a column width. When window is resized the table view on the right is notified to re-query the row heights from the delegate.

How To Use

Your custom cell class should inherit from KSPAutomaticHeightCalculationTableCellView

This is how it used to look in Objective-C:

#import <KSPAutomaticHeightCalculationTableCellView+Private.h>

@interface MyLovelyCell : KSPAutomaticHeightCalculationTableCellView
…
@end

Put your cell into a separate XIB and let the KSPAutomaticHeightCalculationTableCellView know how to find it at runtime

It is generally a good idea to put your cell into a separate XIB, but usage of a KSPAutomaticHeightCalculationTableCellView makes this mandatory.

By default KSPAutomaticHeightCalculationTableCellView will look for a nib file named exactly like your cell's subclass in a main bundle.

That is, if you call your cell class MyLovelyCell you have to name your XIB MyLovelyCell.xib. This xib should contain one and only one root view of MyLovelyCell class. You still can have an arbitrary number of other objects in a XIB, though.

You can customize the behaviour by overriding the following class methods:

+ (nonnull NSString*) correspondingNibName
{
  return @"SomethingDifferent";
}

+ (nonnull NSBundle*) correspondingBundle
{
  return [NSBundle bundle...];
}

Decide whether your custom table cell should have a variable height

Cell has a variable height == Cell's height depends on a represented object value OR cell's height depends on cell's width.

By default, KSPAutomaticHeightCalculationTableCellView assumes that your cell has a variable height, since this is the basic reason to use the class in your project at all.

Override +hasFixedHeight and return YES if your cell's height is really fixed.

+ (BOOL) hasFixedHeight
{
  return YES;
}

In this case KSPAutomaticHeightCalculationTableCellView will cache the height after it will be calculated for the first time. Subsequent calls to +heightWithRepresentedObject:width: will return the stored value.

Layout your cell via Auto Layout

This step is also mandatory. KSPAutomaticHeightCalculationTableCellView only functions in Auto Layout-enabled mode. There is no point of using the class if you perform manual frame computations.

Attention, this part is really important:
After you add layout constraints, the height of your cell should be unambiguous! This means, height have to be constraint either directly (via explicit height constraint, which will render KSPAutomaticHeightCalculationTableCellView usage pretty pointless, since you already know the height value) or in a derived-fashion (in which height of a cell somehow depends on a geometry of its subviews, and the geometry, in its turn, depends on content).

Remember it, cause if you leave your cell view's height ambigous you will end up with a table view rows having a zero height.

Implement a NSTableViewDelegate method -tableView:heightOfRow:

- (CGFloat) tableView: (NSTableView*) tableView heightOfRow: (NSInteger) row
{
  // Get the width of a column in which the cell should reside.
  CGFloat columnWidth = [tableView tableColumnWithIdentifier: @“MainColumn”].width;

  // Let the KSPAutomaticHeightCalculationTableCellView to calculate the preffered cell height for you.
  return [MyLovelyCell heightWithRepresentedObject: #<a model object for this row> width: columnWidth];
}

At this point KSPAutomaticHeightCalculationTableCellView will create a prototype cell instance, set its objectValue property to the passed value, constrain its width to the columnWidth and calculate the minimum required height.

Make sure you don't make unnecessary work in your table cell view prototype

When KSPAutomaticHeightCalculationTableCellView instantiates a cell for measurement purposes it sets its boolean prototype property to YES. If you happen to do some heavy-lifting in your table cell view subclass, for example, doing expensive calculations in response to an objectValue change, please refrain from doing so if the calculation result doesn't affect the layout.

if(!self.prototype)
{
  // Do some fancy visual effects pre-calculation (image caching, data detection and so on...).
}
else
{
  // This cell is a prototype that is being reused for a row height calculation (possibly hundreds times per second).
}

That's it!