在MonoTouch的自定义TabBarController的ViewDidLoad中，公共属性总是空的

我一直在一个类派生自UITabBarController。在最基本的层面上，我要做的是添加一个BackgroundColor属性，以及其他公共属性，当我在构建TabBarController时，我可以在AppDelegate中实例化它们。

我遇到的问题是，我可以有所有的公共属性结束为空当ViewDidLoad被调用，或者，我可以添加一个构造函数和一个[注册]属性，并最终有属性不为空，但ViewControllers属性(其中包含所有标签)变得莫名其妙的空(即使当你在ViewDidLoad设置它)。

显然，我需要这两件事都为真，而我遗漏了一些具体的东西。

这是总是导致null BackgroundColor的代码版本，即使我在AppDelegate中显式设置了它:

public class TabBarController : UITabBarController
{
    public UIColor BackgroundColor { get; set; }
    public override ViewDidLoad()
    {
        base.ViewDidLoad();
        if(BackgroundColor != null) // Always null, even when set explicitly
        {
            var frame = new RectangleF(0.0f, 0.0f, this.View.Bounds.Size.Width, 46);
            UIView myTabView = new UIView(frame);
            myTabView.BackgroundColor = BackgroundColor;
            myTabView.Alpha = 0.5f;
            this.TabBar.InsertSubview(myTabView, 0);
        }
        // Add tabs here, which show up correctly (on default background color)
        ViewControllers = new UIViewController[] { one, two, three, etc };
    }
}

这是编辑的代码，显示正确的背景颜色(属性不是null)，但拒绝允许ViewControllers属性为null以外的任何东西，即使它只是设置在ViewDidLoad:

[Register("TabBarController")]
public class TabBarController : UITabBarController
{
    public UIColor BackgroundColor { get; set; }
    // Added a binding constructor
    [Export("init")]
    public TabBarController() : base(NSObjectFlag.Empty)
    {
    }
    public override ViewDidLoad()
    {
        base.ViewDidLoad();
        if(BackgroundColor != null) // Hey, this works now!
        {
            var frame = new RectangleF(0.0f, 0.0f, this.View.Bounds.Size.Width, 46);
            UIView myTabView = new UIView(frame);
            myTabView.BackgroundColor = BackgroundColor;
            myTabView.Alpha = 0.5f;
            this.TabBar.InsertSubview(myTabView, 0);
        }
        // Tabs disappear, ViewControllers is always null
        ViewControllers = new UIViewController[] { one, two, three, etc };
        if(ViewControllers == null)
        {
            Console.WriteLine("Not bro");
        }
    }
}

如果我必须显式地添加所有元素而不能在运行时访问公共属性，这显然会阻碍我编写一些自定义控件的能力。有人知道我哪里出错了吗?

 public TabBarController() : base(NSObjectFlag.Empty)

public class TabBarController : UITabBarController
{
    UIViewController one = new UIViewController ();
    UIViewController two = new UIViewController ();
    UIViewController three = new UIViewController ();
    private UIView myTabView;
    public UIColor BackgroundColor { 
        get { return myTabView.BackgroundColor; }
        set { myTabView.BackgroundColor = value; }
    }       
    public TabBarController()
    {
        var frame = new RectangleF(0.0f, 0.0f, this.View.Bounds.Size.Width, 46);
        myTabView = new UIView(frame);
        myTabView.Alpha = 0.5f;
        this.TabBar.InsertSubview(myTabView, 0);
        // Add tabs here, which show up correctly (on default background color)
        ViewControllers = new UIViewController[] { one, two, three };
    }
}
    public override bool FinishedLaunching (UIApplication app, NSDictionary options)
    {
        TabBarController controller = new TabBarController ();
        // change background (to cyan) works before adding subview
        controller.BackgroundColor = UIColor.Cyan;
        window.AddSubview (controller.View);
        // change background (to blue) works after adding subview
        controller.BackgroundColor = UIColor.Blue;
...