title: Is it possible to use AutoLayout with UITableView's tableHeaderView?
body: <p>Since I discovered <code>AutoLayout</code> I use it everywhere, now I'm trying to use it with a <code>tableHeaderView</code>.</p>
  
  <p>I made a <code>subclass</code> of <code>UIView</code> added everything (labels etc...) I wanted with their constraints, then I added this <code>CustomView</code> to the <code>UITableView</code>'<code>tableHeaderView</code>.</p>
  
  <p>Everything works just fine except the <code>UITableView</code> always displays <strong>above</strong> the <code>CustomView</code>, by <strong>above</strong> I mean the <code>CustomView</code> is <strong>under</strong> the <code>UITableView</code> so it can't be seen !</p>
  
  <p>It seems that no matter what I do, the <code>height</code> of the <code>UITableView</code>'<code>tableHeaderView</code> is <strong>always</strong> 0 (so is the width, x and y).</p>
  
  <p>My question : is it possible at all to accomplish this <strong><em>without setting the frame manually</em></strong> ?</p>
  
  <p><strong>EDIT :</strong>
  The <code>CustomView</code>'<code>subview</code> that I'm using has these constraints :</p>
  
  <pre><code>_title = [[UILabel alloc]init];
  _title.text = @"Title";
  [self addSubview:_title];
  [_title keep:[KeepTopInset rules:@[[KeepEqual must:5]]]]; // title has to stay at least 5 away from the supperview Top
  [_title keep:[KeepRightInset rules:@[[KeepMin must:5]]]];
  [_title keep:[KeepLeftInset rules:@[[KeepMin must:5]]]];
  [_title keep:[KeepBottomInset rules:@[[KeepMin must:5]]]];
  </code></pre>
  
  <p>I'm using a handy library 'KeepLayout' because writing constraints manually takes forever and way too many line for one single constraint but the methods are self-explaining.</p>
  
  <p>And the <code>UITableView</code> has these constraints :</p>
  
  <pre><code>_tableView = [[UITableView alloc]init];
  _tableView.translatesAutoresizingMaskIntoConstraints = NO;
  _tableView.delegate = self;
  _tableView.dataSource = self;
  _tableView.backgroundColor = [UIColor clearColor];
  [self.view addSubview:_tableView];
  [_tableView keep:[KeepTopInset rules:@[[KeepEqual must:0]]]];// These 4 constraints make the UITableView stays 0 away from the superview top left right and bottom.
  [_tableView keep:[KeepLeftInset rules:@[[KeepEqual must:0]]]];
  [_tableView keep:[KeepRightInset rules:@[[KeepEqual must:0]]]];
  [_tableView keep:[KeepBottomInset rules:@[[KeepEqual must:0]]]];
  
  _detailsView = [[CustomView alloc]init];
  _tableView.tableHeaderView = _detailsView;
  </code></pre>
  
  <p>I don't know if I have to set some constraints directly on the <code>CustomView</code>, I think the height of the CustomView is determined by the constraints on the <code>UILabel</code> "title" in it.</p>
  
  <p><strong>EDIT 2:</strong> After another investigation it seems the height and width of the CustomView are correctly calculated, but the top of the CustomView is still at the same level than the top of the UITableView and they move together when I scroll.</p>