Xamarin Forms Dark/Light Mode 主题不适用于 Android 上的 shell 导航选项卡

Question

我有一个使用 shell 进行导航的标准 xamarin 表单项目（iOS 和 Android）。我已经使用合并字典实现了主题。这是我用来应用主题的方法：

public class MyShellRenderer : ShellRenderer
    {

protected override IShellBottomNavViewAppearanceTracker CreateBottomNavViewAppearanceTracker(Xamarin.Forms.ShellItem shellItem)
        {
            return new MyShellBottomNavViewAppearanceTracker(this);
        }
    }

internal class MyShellBottomNavViewAppearanceTracker : IShellBottomNavViewAppearanceTracker
    {
        private MyShellRenderer myShellRenderer;

        public MyShellBottomNavViewAppearanceTracker(MyShellRenderer myShellRenderer)
        {
            this.myShellRenderer = myShellRenderer;
        }


Task SetAppTheme(PreferredTheme preferredTheme)
        {
            if (Application.Current is null)
                return Task.CompletedTask;

            BaseTheme defaultTheme;
            if (Application.Current.RequestedTheme == OSAppTheme.Dark)
                defaultTheme = new DarkTheme();
            else
                defaultTheme = new LightTheme();

            return _mainThread.InvokeOnMainThreadAsync(() =>
            {
                BaseTheme theme = preferredTheme switch
                {
                    PreferredTheme.Dark => new DarkTheme(),
                    PreferredTheme.Light => new LightTheme(),
                    PreferredTheme.Default => defaultTheme
                };

                CurrentTheme = theme;

                ICollection<ResourceDictionary> mergedDictionaries = Application.Current.Resources.MergedDictionaries;
                if (mergedDictionaries != null)
                {
                    mergedDictionaries.Clear();
                    mergedDictionaries.Add(theme);
                }

                
                OnPreferenceChanged(preferredTheme);
            });
        }

这适用于 iOS，但在 Android 上，ItemText 颜色不会改变。当暗模式主题的背景颜色与取消选择的选项卡的颜色相同（或接近）时，这是一个问题。图标按预期呈现。

我尝试过像这样在 android 上实现自定义渲染：

public void ResetAppearance(BottomNavigationView bottomView)
        {

            //Get and set background color from theme
            Xamarin.Forms.Color xfcolor = (Xamarin.Forms.Color)App.Current.Resources["PageBackgroundColor"];
            Android.Graphics.Color acolor = xfcolor.ToAndroid();
            bottomView.SetBackgroundColor(acolor);

            //Get and set state colors for menu items text
            Xamarin.Forms.Color xfSelectedColor = (Xamarin.Forms.Color)App.Current.Resources["ColorBlue"];
            Android.Graphics.Color aSelectedColor = xfSelectedColor.ToAndroid();

            Xamarin.Forms.Color xfDeselectedColor = (Xamarin.Forms.Color)App.Current.Resources["ColorGray"];
            Android.Graphics.Color aDeselectedColor = xfDeselectedColor.ToAndroid();

            int[][] states = new int[][]
            {
                new int[] {-Android.Resource.Attribute.Checked }, // unchecked
                new int[] { Android.Resource.Attribute.Checked }  // pressed
            };

            int[] colors = new int[]
            {
                aSelectedColor,
                aDeselectedColor
            };
            ColorStateList colorStateList = new ColorStateList(states, colors);

            bottomView.ItemTextColor = colorStateList;
...

这部分工作是因为整个文本都在应用 aSelectedColor。

这是 SDK 中的错误还是我只是做错了什么？

Answer 1

找到了解决方案（感谢 James Montemagno ！！！）

找到灵感here

因此，由于某些奇怪的原因，使用 mergeDictionaries 不适用于 Android。

相反，我根据 Hanselman.Forms 示例进行了以下重写：

 Task SetAppTheme(PreferredTheme preferredTheme)
    {
        if (Application.Current is null)
            return Task.CompletedTask;

        BaseTheme defaultTheme;
        if (Application.Current.RequestedTheme == OSAppTheme.Dark)
            defaultTheme = new DarkTheme();
        else
            defaultTheme = new LightTheme();

        return _mainThread.InvokeOnMainThreadAsync(() =>
        {
            BaseTheme theme = preferredTheme switch
            {
                PreferredTheme.Dark => new DarkTheme(),
                PreferredTheme.Light => new LightTheme(),
                PreferredTheme.Default => defaultTheme
            };

            CurrentTheme = theme;

            //Previous code
            /*ICollection<ResourceDictionary> mergedDictionaries = Application.Current.Resources.MergedDictionaries;
            if (mergedDictionaries != null)
            {
                mergedDictionaries.Clear();
                mergedDictionaries.Add(theme);
            }*/

            //New code
            var applicationResourceDictionary = Application.Current.Resources;
            ManuallyCopyThemes(theme, applicationResourceDictionary);

            
            OnPreferenceChanged(preferredTheme);
        });
    }


    void ManuallyCopyThemes(ResourceDictionary fromResource, ResourceDictionary toResource)
    {
        foreach (var item in fromResource.Keys)
        {
            if (toResource.ContainsKey(item))
                toResource[item] = fromResource[item];
            else
                toResource.Add(item, fromResource[item]);
        }
    }