code: function (inst) {
      if (inst.state === 'pinning') {
        inst.state = 'pinned';
        componentEvent('pinned', 'headroom', inst, inst.$headroom);
      }
  
      if (inst.state === 'unpinning') {
        inst.state = 'unpinned';
        componentEvent('unpinned', 'headroom', inst, inst.$headroom);
      }
    }
docs: 动画结束回调
  @param inst