iOS tip：让你的footTableView的UILabel居中

如果你需要编写一个软件，同时支持portrait&landscape，你会遇到一个问题：当屏幕旋转后，如果才能确保一些可视化的things依然居中呢。下面是一个简单的例子，无论设备是否旋转，UITableView的footer中的UILabel保持居中的方法。

    //create the uiview container
    UIView *tfooterView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, _tableView.frame.size.width, 45)];
    tfooterView.autoresizingMask = UIViewAutoresizingFlexibleWidth;
    //create the uilabel for the text
    UILabel *label3 = [[UILabel alloc] initWithFrame:CGRectMake(_tableView.frame.size.width/2-120, 0, 240, 35)];
    label3.backgroundColor = [UIColor clearColor];
    label3.font = [UIFont systemFontOfSize:12];
    label3.numberOfLines = 2;
    label3.lineBreakMode = UILineBreakModeWordWrap;
    label3.textAlignment = UITextAlignmentCenter;
    label3.text = @"Some text you want centered in your tableFooterView.";
    label3.autoresizingMask = UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleLeftMargin;
    //add the label to the view
    [tfooterView addSubview:label3];
    //add the view to the uitableview footer
    _tableView.tableFooterView = tfooterView;