如何从一个标签切换到另一个标签Xamarin IOS

我创建了UITabBarController类，有5个ViewControllers

        controller1 = new Controller1();
        controller2 = new Controller2();
        controller3 = new Controller3();
        controller4 = new Controller4();
        controller5 = new Controller5();
        controller1.TabBarItem = new UITabBarItem ("first", UIImage.FromFile("/Images/first.png"), 0);
        controller5.TabBarItem = new UITabBarItem ("second", UIImage.FromFile("/Images/four.png"), 1);
        controller5.TabBarItem = new UITabBarItem ("third", UIImage.FromFile("/Images/four.png"), 2);
        controller5.TabBarItem = new UITabBarItem ("four", UIImage.FromFile("/Images/four.png"), 3);
        controller5.TabBarItem = new UITabBarItem ("five", UIImage.FromFile("/Images/four.png"), 4);
    var tabs = new UIViewController[] {
            controller1, controller2, controller3, controller4, controller5 
        };
        ViewControllers = tabs;

在第三个控制器中有一个提交按钮。

在提交按钮动作中，我想将选项卡从controller3切换到controller5。

我该怎么做呢?

this.TabBarController.SelectedIndex = 4;