CustomTabRenderer for Xamarin.ios

Question

我已经用了几个月了，现在还会遇到一些麻烦。我正在使用一个自定义渲染器来改变我的标签的外观和感觉。当切换到不同的选项卡时，它工作得非常好。但是，当我使用以下方法导航到我的tabbedPage时：

Children.Add(new UnitMapPage { Title = "Map", Icon = "map.png" });
CurrentPage = mapPage;

页面在正确的选项卡上打开，但是TabbarItem的文本看起来与未选择的项完全相同。一旦你点击任何选项卡，它就会改变到正确的样式。这是我的定制渲染器。

class CustomTabRenderer : TabbedRenderer
{
    private UnitViewModel _unitViewModel;
    private TabbedPage _unitPage;

    protected override void OnElementChanged(VisualElementChangedEventArgs e)
    {
        base.OnElementChanged(e);

        if (e.NewElement != null) {
            var unitPage = (TabbedPage)e.NewElement;
            _unitPage = unitPage;
            _unitViewModel = (UnitViewModel)_unitPage.BindingContext;
            _unitViewModel.PropertyChanged += OnElementPropertyChanged;
        }

        // Set Text Font for unselected tab states
        UITextAttributes normalTextAttributes = new UITextAttributes();
        normalTextAttributes.Font = UIFont.SystemFontOfSize(10.0F, UIFontWeight.Regular); // unselected
        normalTextAttributes.TextColor = UIColor.White;

        UITabBarItem.Appearance.SetTitleTextAttributes(normalTextAttributes, UIControlState.Normal);
    }

    void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
    {
        if (e.PropertyName == "AlertCount")
        {
            if (TabBar.Items != null)
            {
                foreach (var item in TabBar.Items)
                {
                    item.Image = item.Image.ImageWithRenderingMode(UIImageRenderingMode.AlwaysOriginal);
                    if (item.Title == "History" && _unitViewModel != null)
                    {
                        if (_unitViewModel.AlertCount > 0)
                            item.BadgeValue = _unitViewModel.AlertCount.ToString();
                        else
                            item.BadgeValue = null;
                    }
                }
            }
        }
    }

    public override void ViewWillAppear(bool animated)
    {
        if (TabBar.Items != null)
        {
            foreach (var item in TabBar.Items)
            {
                item.Image = item.Image.ImageWithRenderingMode(UIImageRenderingMode.AlwaysOriginal);
                if (item.Title == "History" && _unitViewModel != null)
                {
                    if (_unitViewModel.AlertCount > 0)
                        item.BadgeValue = _unitViewModel.AlertCount.ToString();
                    else
                        item.BadgeValue = null;
                }
            }
        }
        base.ViewWillAppear(animated);
    }

    public override UIViewController SelectedViewController
    {
        get
        {
            UITextAttributes selectedTextAttributes = new UITextAttributes();
            selectedTextAttributes.Font = UIFont.SystemFontOfSize(12.0F, UIFontWeight.Heavy); // SELECTED
            if (base.SelectedViewController != null)
            {
                base.SelectedViewController.TabBarItem.SetTitleTextAttributes(selectedTextAttributes, UIControlState.Normal);
            }
            return base.SelectedViewController;
        }
        set
        {
            base.SelectedViewController = value;

            foreach (UIViewController viewController in base.ViewControllers)
            {
                UITextAttributes normalTextAttributes = new UITextAttributes();
                normalTextAttributes.Font = UIFont.SystemFontOfSize(10.0F, UIFontWeight.Regular); // unselected
                normalTextAttributes.TextColor = UIColor.White;

                viewController.TabBarItem.SetTitleTextAttributes(normalTextAttributes, UIControlState.Normal);
            }
        }
    }
}

Answer 1

当我将正在测试的设备从ios9升级到ios10时，这个问题似乎悄然出现(不能确认这一点，因为我找不到可以测试这个的ios9设备)。

阅读这篇文章的答案：How do I override the Xamarin Forms TabbedPage item fonts for iOS?，让我在我自己的How do I override the Xamarin Forms TabbedPage item fonts for iOS?中尝试各种东西。

通过更改我的代码以在我的ViewWillAppear.中设置selectedTextAttributes解决了这个问题不知道这是否是最好的方法，但它做到了！

 public override void ViewWillAppear(bool animated)
    {
        if (TabBar.Items != null)
        {
            foreach (var item in TabBar.Items)
            {
                item.Image = item.Image.ImageWithRenderingMode(UIImageRenderingMode.AlwaysOriginal);
                if (item.Title == "History" && _unitViewModel != null)
                {
                    if (_unitViewModel.AlertCount > 0)
                        item.BadgeValue = _unitViewModel.AlertCount.ToString();
                    else
                        item.BadgeValue = null;
                }

                if (item.Title.Equals(_unitPage.CurrentPage.Title))
                {
                    UITextAttributes selectedTextAttributes = new UITextAttributes();
                    selectedTextAttributes.Font = UIFont.SystemFontOfSize(12.0F, UIFontWeight.Heavy); // SELECTED
                    if (base.SelectedViewController != null)
                    {
                        base.SelectedViewController.TabBarItem.SetTitleTextAttributes(selectedTextAttributes, UIControlState.Normal);
                    }
                }
            }
        }
        base.ViewWillAppear(animated);
    }

Answer 2

我相信你只需要交换一下：

CurrentPage = yourPage;

使用

SelectedItem = yourPage;