ios - 从 UIPageViewController 和/或其数据源获取 TRUE 当前页面

Question

我在 Storyboard中创建了一个教程窗口，其中包含两个 View ，一个用于显示教程，另一个用作每页内容的模板。

某些元素在 ViewDidLoad 事件中以编程方式编码。

PageViewController 按要求 100% 工作，它显示三页内容并允许前后滑动而不会出现问题。

我已经以编程方式向主 ViewController 添加了一个 UIPageControl，但我无法正确更新其 CurrentPage 值。来回滑动时访问数据源 PageIndex 值会出现奇怪的结果。

有没有一种可靠的方法可以准确知道显示了哪个页面？

或者想知道页面过渡往哪个方向移动，这样我就可以手动更新了？不完全确定如何从页面 Controller 的“DidFinishAnimating”事件访问 UIPageViewControllerNavigationDirection。

我的主视图 Controller 代码如下:

using Foundation;
using System;
using UIKit;

namespace Performance
{
    partial class VCOnboardHome : UIViewController
    {
        const int pageCount = 3;

        public UIPageViewController pvcOnboarding{ get; set; }

        private OnboardingDataSource onboardDataSource;

        UIStoryboard board;

        public UIPageControl pgControlIndicator;

        public VCOnboardHome (IntPtr handle) : base (handle)
        {

        }

        /// <summary>
        /// ViewDidLoad event method
        /// </summary>
        public override void ViewDidLoad ()
        {
            base.ViewDidLoad ();

            board = UIStoryboard.FromName ("Main", null);

            // Programmatically create a PageView controller
            pvcOnboarding = new UIPageViewController (UIPageViewControllerTransitionStyle.Scroll, 
                UIPageViewControllerNavigationOrientation.Horizontal,
                UIPageViewControllerSpineLocation.None, 20f);

            // PageView Controller datasource
            var views = CreateViews ();
            onboardDataSource = new OnboardingDataSource (views);
            pvcOnboarding.DataSource = onboardDataSource;
            pvcOnboarding.SetViewControllers (new UIViewController[] { views [0] },
                UIPageViewControllerNavigationDirection.Forward,
                false, null);

            // Set PageView size
            pvcOnboarding.View.Frame = View.Bounds;

            // Add the page view control to this view controller
            Add (pvcOnboarding.View);

            // Create Page Control
            var frame = UIScreen.MainScreen.Bounds;
            pgControlIndicator = new UIPageControl ();
            pgControlIndicator.Frame = new CoreGraphics.CGRect (20f, frame.Height - 60f, frame.Width - 40f, 40f);
            pgControlIndicator.Pages = pageCount;
            pgControlIndicator.UserInteractionEnabled = false;

            Add (pgControlIndicator);

            // Update the Page Control to indicate the current page we are showing.
            // Only do this if the full page transition happened and not a partial page turn
            pvcOnboarding.DidFinishAnimating += (sender, e) => {

                foreach(UIViewController u in e.PreviousViewControllers){
                    // TODO - Not needed, remove once page control working
                    // u = the previous viewcontroller
                }

                if(e.Finished && e.Completed){
                    // Page transition completed
                    // Update Page Control here
                }else{
                    // Incomplete page transition
                }
            };


        }

        // Content for each page
        VCOnboardContentNew[] CreateViews ()
        {
            var pageData = new [] {
                new ContentOnBoardData {
                    headerLblText = @"Page 1",
                    bodyContentText = @"Page 1 body text blah blah blah blah",
                    buttonText = @"Ok, next no. 1",
                    pageImage = UIImage.FromBundle("ios_images_v2/onboarding/icon-qr-code.png"),
                    currentPage = 1,
                    totalPages = 3
                },
                new ContentOnBoardData {
                    headerLblText = @"Page 2",
                    bodyContentText = @"Page 2 body text blah blah blah blah",
                    buttonText = @"Ok, next no. 2",
                    pageImage = UIImage.FromBundle("ios_images_v2/onboarding/icon-id-check.png"),
                    currentPage = 2,
                    totalPages = 3
                },
                new ContentOnBoardData {
                    headerLblText = @"Page 3",
                    bodyContentText = @"Page 3 body text blah blah blah blah",
                    buttonText = @"Ok, got it",
                    pageImage = null,
                    currentPage = 3,
                    totalPages = 3
                }
            };

            var views = new VCOnboardContentNew[pageData.Length]; 
            for (int i = 0; i < pageCount; i++) {
                int pageIndex = i;

                views [i] = (VCOnboardContentNew)board.InstantiateViewController ("sbid_onboardcontent");
                views [i].PageIndex = pageIndex;
                views [i].HeaderText = pageData [i].headerLblText;
                views [i].ContentText = pageData [i].bodyContentText;
                views [i].PageImage = pageData [i].pageImage;
                views [i].CurrentPage = pageData [i].currentPage;
                views [i].TotalPages = pageCount;
                views [i].ButtonText = pageData [i].buttonText;

                views [i].ButtonClicked += (s, e) => {
                    DismissViewController (true, null);
                };
            }

            return views;
        }
    }

    /// <summary>
    /// Onboarding data source.
    /// </summary>
    class OnboardingDataSource : UIPageViewControllerDataSource
    {
        readonly VCOnboardContentNew[] _views;

        public OnboardingDataSource (VCOnboardContentNew[] views)
        {
            _views = views;
        }

        /// <summary>
        /// Gets the previous view controller.
        /// </summary>
        /// <returns>The previous view controller.</returns>
        /// <param name="pageViewController">Page view controller.</param>
        /// <param name="referenceViewController">Reference view controller.</param>
        public override UIViewController GetPreviousViewController (UIPageViewController pageViewController, UIViewController referenceViewController)
        {
            int index = ((VCOnboardContentNew)referenceViewController).PageIndex;

            bool controlCheck = (index <= 0);
            UIViewController vcToReturn = controlCheck ? null : (_views [index - 1]);

            return vcToReturn;
        }

        /// <summary>
        /// Gets the next view controller.
        /// </summary>
        /// <returns>The next view controller.</returns>
        /// <param name="pageViewController">Page view controller.</param>
        /// <param name="referenceViewController">Reference view controller.</param>
        public override UIViewController GetNextViewController (UIPageViewController pageViewController, UIViewController referenceViewController)
        {
            int index = ((VCOnboardContentNew)referenceViewController).PageIndex;

            bool controlCheck = index + 1 >= _views.Length;
            UIViewController vcToReturn = controlCheck ? null : _views [index + 1];

            return vcToReturn;
        }
    }

    /// <summary>
    /// Content onboard data.
    /// </summary>
    struct ContentOnBoardData
    {
        public string headerLblText;
        public string bodyContentText;
        public string buttonText;
        public UIImage pageImage;
        public int currentPage;
        public int totalPages;
    }
}

我的页面内容代码 View Controller 如下:

using System;
using UIKit;

namespace Performance
{
    /// <summary>
    /// Class: VCOnboardContentNew
    /// </summary>
    partial class VCOnboardContentNew : UIViewController
    {
        public EventHandler ButtonClicked;

        public int PageIndex { get; set; }

        public string HeaderText{ get; set; }

        public UIImage PageImage{ get; set; }

        public int CurrentPage{ get; set; }

        public int TotalPages{ get; set; }

        public string ContentText{ get; set; }

        public string ButtonText{ get; set; }

        public VCOnboardContentNew (IntPtr handle) : base (handle)
        {

        }

        public override void ViewDidLoad ()
        {
            base.ViewDidLoad ();

            // Set text for the main title
            lblTest.Font = UIFont.FromName("FreightDispLight", 26f);
            lblTest.Text = HeaderText;

            // Set text for body content
            lblContentBodyText.Font = UIFont.FromName("FreightDispLight", 14f);
            lblContentBodyText.Text = ContentText;

            pgCtrlWhichPageWeOn.Hidden = true;

            if(PageImage != null){
                pageContentImage.Hidden = false;
                pageContentImage.Image = PageImage;
            }else{
                pageContentImage.Hidden = true;
            }

            btnCallToAction.SetTitle (ButtonText, UIControlState.Normal);
            btnCallToAction.TouchUpInside += (object sender, EventArgs e) => {
                if (ButtonClicked != null) {
                    ButtonClicked.Invoke (this, null);
                }
            };
        }
    }
}

Answer 1

当过渡样式设置为滚动时，页面 View Controller 似乎:

1. 一旦一个转换完成，它会立即调用下一个(或上一个)View Controller(使用 GetNextViewController)，即使用户可能没有开始下一次滑动；和
2. 它保留从中转换过来的 View Controller ，并假定它是之前的 VC，因此如果用户向后滑动，它不会调用之前的 VC(使用 GetPreviousViewController)。

这使得跟踪当前显示的 VC 实际上非常困难。如果发现(参见 this answer)我必须同时使用 WillTransition 事件和 DidFinishAnimating 事件。我不熟悉 Xamarin 和 C#，所以如果这种语法有偏差，请原谅我，但我认为是这样的:

        pvcOnboarding.WillTransition += (sender, e) => {

            nextVCIndex = ((VCOnboardContentNew)e.PendingViewControllers[0]).PageIndex
        }

        pvcOnboarding.DidFinishAnimating += (sender, e) => {

            if(e.Finished && e.Completed){
                // Page transition completed
                currentVCIndex = nextVCIndex
                // Update Page Control here

            }else{
                // Incomplete page transition
            }
        };

您需要添加 currentVCIndex 和 nextVCIndex 作为类级变量。