Xamarin.ios的CustomTabRenderer

Question

我几个月来一直在使用Xamarin，并且偶尔会遇到一些麻烦。我正在使用自定义渲染器来更改我的选项卡的外观。在不同标签之间切换时，它工作得很好。然而，当我浏览到我的tabbedPage使用：

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

页打开正确的选项卡上，但TabbarItem的文字看起来酷似非选择项目。只要你点击任何标签，它就会变成正确的样式。这是我的自定义渲染器。

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

问题似乎当我升级我从ios9检测到ios10设备已经悄悄（无法确认这一点，因为我无法找到可以测试的ios9设备）。

通过对这篇文章的回答：How do I override the Xamarin Forms TabbedPage item fonts for iOS?，让我尝试了各种各样的东西在我自己的ViewWillAppear。

该问题已通过更改我的代码以在我的ViewWillAppear中设置selectedTextAttributes来解决。不知道这是否是最好的办法，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，你只需要更换：

CurrentPage = yourPage; 

与

SelectedItem = yourPage;