Author Archives: lantean

Debugging Autolayout

If you need to debug the constraints that produced any view layout, just hit LLVM, and type:

po [[UIWindow keyWindow] _autolayoutTrace]

This will help you get the Autolayout Trace. Pick up the troublesome view, find its memory address, and then try:

po [0x12341234 constraintsAffectingLayoutForAxis:1]

Note that you should replace 0x12341234 with the memory address of the view you’d like to debug. AxisX = 0, while AxisY = 1.

Props to this extremely useful post.

iOS 8 Autosizing Cells

The latest iOS release (8.0 at the time this was written!) added a new cool feature: autosizing cells. Meaning that we don’t really need to implement tableView:heightForRowAtIndexPath: anymore.

How can we enable this?. Super simple, just add the following snippet:

self.tableView.estimatedRowHeight = SomeConstant;
self.tableView.rowHeight = UITableViewAutomaticDimension;

Now, here’s the deal. iOS 7 still requires tableView:heightForRowAtIndexPath: to be implemented. And if you do implement it, iOS 8 will disregard the Automatic Dimension settings.

Solution?.. import objc/runtime.h, and place this hack in your UITableView’s delegate:

- (BOOL)respondsToSelector:(SEL)aSelector {
  if (sel_isEqual(aSelector, @selector(tableView:estimatedHeightForRowAtIndexPath:)) ||
    sel_isEqual(aSelector, @selector(tableView:heightForRowAtIndexPath:))) {
      return false;
  }
  return [super respondsToSelector:aSelector];
}

YES. It’s a hack =)

Fixing: StatusBar covering your UIViewController’s view

Ever since iOS 7, if you’re not using a UINavigationController instance, you’ll need to perform a very simple step, in order to prevent iOS’s StatusBar from covering your view:

1. Press Control, click over the “Top Layout Guide”, and drag it upon the troublesome view.
2. You’ll get a small popup. Please, click on “Vertical Spacing”.
3. Edit the new constraint, and update the Constant value, as needed.

Reference here!

CoreData HeavyWeight Migration Issues

We recently hit a pretty severe bug. In one of our apps, users began experiencing token issues after an upgrade.

Bottomline?… the last upgrade had a Heavyweight migration. So far so good, but what happened?. Turns out that the URIRepresentation that can be used to map a NSManagedObjectID, is and is not reliable. Everything is okay, until you perform a heavyweight migration!.

Heavyweight migrations might swizzle your NSManagedObjectID’s. Fix?, create your own primaryKeys. NSUUID helper class is the easiest way to accomplish that.

Reference here!