ipad适应屏幕功能

#pragma mark 即将旋转屏幕的时候自动调用
- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration
{
[UIView animateWithDuration:duration animations:^{
// 根据即将要显示的方向来调整dock内部的布局
[_dock rotateToOrientation:toInterfaceOrientation];

// 调整当前选中控制器view的frame
CGFloat width = 768 - kDockMenuItemHeight;
_currentChild.view.frame = CGRectMake(_dock.frame.size.width, 0, width, _dock.frame.size.height);
}];
}