MaterialButton: XPE when loading styles with triggers

Tái hiện lỗi bằng cách thêm kiểu MaterialButton được hiển thị vào App.xaml và khởi chạy ứng dụng trên iOS hoặc Android. Sau đó kiểm tra Material.cs quanh GetResource và Color.Secondary, cũng như UI/MaterialButton.cs quanh trình khởi tạo tĩnh của nó; được xem là hoàn tất khi App.InitializeComponent() hoàn thành mà không có XamlParseException được báo cáo.

🔙 Regression

In our Application we use MaterialButtons to emulate toggle buttons. The default ButtonType is Text.
For Buttons that are toggleable Buttons the ButtonType is set via a Binding and a custom BoolToButtonTypeConverter.
(false->Text, true->Flat)

To invert the TextColor when the Button is toggled on, we use the following style, defined in App.xaml.

<Style TargetType="ui:MaterialButton" ApplyToDerivedTypes="False">
    <Style.Triggers>
        <Trigger TargetType="ui:MaterialButton" Property="ButtonType" Value="Flat">
            <Trigger.Setters>
                <Setter Property="TextColor" Value="White"/>
            </Trigger.Setters>
        </Trigger>
    </Style.Triggers>
</Style>

Old (and correct) behavior

The app is initialized without any errors, Buttons behave as expected. (Xamarin.Forms 4.7.0.1142; XF.Material 1.5.8)

Current behavior

The app fails to start with a XamlParseException, as soon as the App-Constructor calls InitializeComponent(). (Xamarin.Forms 5.0.0.1874; XF.Material 1.7.7)
Callstack:

Xamarin.Forms.Xaml.XamlParseException: Position 62:53. Type converter failed: The type initializer for 'XF.Material.Forms.UI.MaterialButton' threw an exception. ---> System.TypeInitializationException: The type initializer for 'XF.Material.Forms.UI.MaterialButton' threw an exception. ---> System.NullReferenceException: Object reference not set to an instance of an object
  at XF.Material.Forms.Material.GetResource[T] (System.String key) [0x00000] in C:\Users\mhvdi\Documents\OpenSource\XF-Material-Library\XF.Material\Material.cs:57 
  at XF.Material.Forms.Material+Color.GetSecondaryColor () [0x00000] in C:\Users\mhvdi\Documents\OpenSource\XF-Material-Library\XF.Material\Material.cs:203 
  at XF.Material.Forms.Material+Color.get_Secondary () [0x00000] in C:\Users\mhvdi\Documents\OpenSource\XF-Material-Library\XF.Material\Material.cs:198 
  at XF.Material.Forms.UI.MaterialButton..cctor () [0x0003e] in C:\Users\mhvdi\Documents\OpenSource\XF-Material-Library\XF.Material\UI\MaterialButton.cs:20 
   --- End of inner exception stack trace ---
  at (wrapper managed-to-native) System.Reflection.RuntimeFieldInfo.GetValueInternal(System.Reflection.RuntimeFieldInfo,object)
  at System.Reflection.RuntimeFieldInfo.GetValue (System.Object obj) [0x0005e] in /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/src/Xamarin.iOS/mcs/class/corlib/System.Reflection/RuntimeFieldInfo.cs:251 
  at Xamarin.Forms.BindablePropertyConverter.ConvertFrom (System.Type type, System.String propertyName, System.Xml.IXmlLineInfo lineinfo) [0x00055] in D:\a\1\s\Xamarin.Forms.Core\BindablePropertyConverter.cs:99 
  at Xamarin.Forms.BindablePropertyConverter.Xamarin.Forms.IExtendedTypeConverter.ConvertFromInvariantString (System.String value, System.IServiceProvider serviceProvider) [0x00169] in D:\a\1\s\Xamarin.Forms.Core\BindablePropertyConverter.cs:60 
  at Xamarin.Forms.Xaml.TypeConversionExtensions.ConvertTo (System.Object value, System.Type toType, System.Func`1[TResult] getConverter, System.IServiceProvider serviceProvider, System.Exception& exception) [0x00041] in D:\a\1\s\Xamarin.Forms.Core\Xaml\TypeConversionExtensions.cs:134 
   --- End of inner exception stack trace ---
  at Xamarin.Forms.Xaml.ApplyPropertiesVisitor.SetPropertyValue (System.Object xamlelement, Xamarin.Forms.Xaml.XmlName propertyName, System.Object value, System.Object rootElement, Xamarin.Forms.Xaml.INode node, Xamarin.Forms.Xaml.HydrationContext context, System.Xml.IXmlLineInfo lineInfo) [0x0007d] in D:\a\1\s\Xamarin.Forms.Xaml\ApplyPropertiesVisitor.cs:366 
  at Xamarin.Forms.Xaml.ApplyPropertiesVisitor.Visit (Xamarin.Forms.Xaml.ValueNode node, Xamarin.Forms.Xaml.INode parentNode) [0x0007b] in D:\a\1\s\Xamarin.Forms.Xaml\ApplyPropertiesVisitor.cs:60 
  at Xamarin.Forms.Xaml.ValueNode.Accept (Xamarin.Forms.Xaml.IXamlNodeVisitor visitor, Xamarin.Forms.Xaml.INode parentNode) [0x00000] in D:\a\1\s\Xamarin.Forms.Xaml\XamlNode.cs:91 
  at Xamarin.Forms.Xaml.ElementNode.Accept (Xamarin.Forms.Xaml.IXamlNodeVisitor visitor, Xamarin.Forms.Xaml.INode parentNode) [0x00044] in D:\a\1\s\Xamarin.Forms.Xaml\XamlNode.cs:152 
  at Xamarin.Forms.Xaml.ElementNode.Accept (Xamarin.Forms.Xaml.IXamlNodeVisitor visitor, Xamarin.Forms.Xaml.INode parentNode) [0x00044] in D:\a\1\s\Xamarin.Forms.Xaml\XamlNode.cs:152 
  at Xamarin.Forms.Xaml.FillResourceDictionariesVisitor.Visit (Xamarin.Forms.Xaml.ElementNode node, Xamarin.Forms.Xaml.INode parentNode) [0x000ec] in D:\a\1\s\Xamarin.Forms.Xaml\FillResourceDictionariesVisitor.cs:57 
  at Xamarin.Forms.Xaml.ElementNode.Accept (Xamarin.Forms.Xaml.IXamlNodeVisitor visitor, Xamarin.Forms.Xaml.INode parentNode) [0x00012] in D:\a\1\s\Xamarin.Forms.Xaml\XamlNode.cs:147 
  at Xamarin.Forms.Xaml.RootNode.Accept (Xamarin.Forms.Xaml.IXamlNodeVisitor visitor, Xamarin.Forms.Xaml.INode parentNode) [0x00079] in D:\a\1\s\Xamarin.Forms.Xaml\XamlNode.cs:211 
  at Xamarin.Forms.Xaml.XamlLoader.Visit (Xamarin.Forms.Xaml.RootNode rootnode, Xamarin.Forms.Xaml.HydrationContext visitorContext, System.Boolean useDesignProperties) [0x0007e] in D:\a\1\s\Xamarin.Forms.Xaml\XamlLoader.cs:235 
  at Xamarin.Forms.Xaml.XamlLoader.Load (System.Object view, System.String xaml, System.Reflection.Assembly rootAssembly, System.Boolean useDesignProperties) [0x000a2] in D:\a\1\s\Xamarin.Forms.Xaml\XamlLoader.cs:104 
  at Xamarin.Forms.Xaml.XamlLoader.Load (System.Object view, System.String xaml, System.Reflection.Assembly rootAssembly) [0x00000] in D:\a\1\s\Xamarin.Forms.Xaml\XamlLoader.cs:78 
  at Xamarin.Forms.Xaml.Extensions.LoadFromXaml[TXaml] (TXaml view, System.String xaml, System.Reflection.Assembly rootAssembly) [0x00000] in D:\a\1\s\Xamarin.Forms.Xaml\ViewExtensions.cs:49 
  at Xamarin.Forms.Xaml.ResourcesLoader.CreateFromResource[T] (System.String resourcePath, System.Reflection.Assembly assembly, System.Xml.IXmlLineInfo lineInfo) [0x000b1] in D:\a\1\s\Xamarin.Forms.Xaml\ResourcesLoader.cs:39 
  at Xamarin.Forms.ResourceDictionary.SetAndLoadSource (System.Uri value, System.String resourcePath, System.Reflection.Assembly assembly, System.Xml.IXmlLineInfo lineInfo) [0x00063] in D:\a\1\s\Xamarin.Forms.Core\ResourceDictionary.cs:76 
  at Vendor.MobileApp.App.InitializeComponent ()

Reproduction steps

Add the style above into App.xaml and try to launch the App in an Emulator.

Configuration

Version: 1.7.7

Platform:

• 📱 iOS
• 🤖 Android
• 🏁 WPF
• 🌎 UWP
• 🍎 MacOS
• 📺 tvOS
• 🐒 Xamarin.Forms