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POIXamlType interface implementation - weird behavior
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copied!<p>The <strong>IXamlType</strong> interface is defined as follows:</p> <pre><code>[Guid(0x7920eab1, 0xa2e5, 0x479a, 0xbd, 80, 0x6c, 0xef, 60, 11, 0x49, 0x70), Version(0x6020000), WebHostHidden] public interface IXamlType { // Methods object ActivateInstance(); void AddToMap([In] object instance, [In] object key, [In] object value); void AddToVector([In] object instance, [In] object value); object CreateFromString([In] string value); IXamlMember GetMember([In] string name); void RunInitializer(); // Properties IXamlType BaseType { get; } IXamlMember ContentProperty { get; } string FullName { get; } bool IsArray { get; } bool IsBindable { get; } bool IsCollection { get; } bool IsConstructible { get; } bool IsDictionary { get; } bool IsMarkupExtension { get; } IXamlType ItemType { get; } IXamlType KeyType { get; } TypeName UnderlyingType { get; } } </code></pre> <p>When a Metro Application is compiled a <strong>XamlTypeInfo.g.cs</strong> is generated which contains an implementation of this interface as follows:</p> <pre><code>[System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Windows.UI.Xaml.Build.Tasks", "4.0.0.0")] [System.Diagnostics.DebuggerNonUserCodeAttribute()] internal class XamlSystemBaseType : IXamlType { string _fullName; Type _underlyingType; public XamlSystemBaseType(string fullName, Type underlyingType) { _fullName = fullName; _underlyingType = underlyingType; } public string FullName { get { return _fullName; } } public Type UnderlyingType { get { return _underlyingType; } } virtual public IXamlType BaseType { get { throw new NotImplementedException(); } } virtual public IXamlMember ContentProperty { get { throw new NotImplementedException(); } } virtual public IXamlMember GetMember(string name) { throw new NotImplementedException(); } virtual public bool IsArray { get { throw new NotImplementedException(); } } virtual public bool IsCollection { get { throw new NotImplementedException(); } } virtual public bool IsConstructible { get { throw new NotImplementedException(); } } virtual public bool IsDictionary { get { throw new NotImplementedException(); } } virtual public bool IsMarkupExtension { get { throw new NotImplementedException(); } } virtual public bool IsBindable { get { throw new NotImplementedException(); } } virtual public IXamlType ItemType { get { throw new NotImplementedException(); } } virtual public IXamlType KeyType { get { throw new NotImplementedException(); } } virtual public object ActivateInstance() { throw new NotImplementedException(); } virtual public void AddToMap(object instance, object key, object item) { throw new NotImplementedException(); } virtual public void AddToVector(object instance, object item) { throw new NotImplementedException(); } virtual public void RunInitializer() { throw new NotImplementedException(); } virtual public object CreateFromString(String input) { throw new NotImplementedException(); } } </code></pre> <hr> <p>The weird thing is that some of the interface implementations are not consistent. If you try to compile this implementation in a stand-alone VS project, it gives the following error as expected:</p> <p><strong>error CS0738: 'ConsoleApplication28.XamlSystemBaseType' does not implement interface member 'ConsoleApplication28.IXamlType.UnderlyingType'. 'ConsoleApplication28.XamlSystemBaseType.UnderlyingType' cannot implement 'ConsoleApplication28.IXamlType.UnderlyingType' because it does not have the matching return type of 'ConsoleApplication28.TypeName'.</strong></p> <hr> <p>My question is how does the .g.cs compile - I confirmed by opening the compiled assembly in Reflector - it also showed the same implementation which has mis-matching signature types for some properties/methods.</p> <p><strong>Update:</strong></p> <p>To confirm what I saw, I used Reflector and saw following:</p> <p>The IXamlType.UnderlyingType (from assembly Windows, Version=255.255.255.255) is defined as:</p> <pre><code>TypeName UnderlyingType { get; } </code></pre> <p>The XamlSystemBaseType found in any Metro app defines UnderlyingType as:</p> <pre><code> public Type UnderlyingType { get; } </code></pre> <p>Given the above, I don't understand how it works!</p> <p><strong>Update #2</strong></p> <p>OK - When you open the Windows.winmd file in Reflector, you see:</p> <pre><code>TypeName UnderlyingType { get; } </code></pre> <p>However, if in Visual Studio you do:</p> <p>Place cursor on <strong>IXamlType</strong> of following line:</p> <p>internal class XamlSystemBaseType : IXamlType</p> <p>Then <strong>Press F12,</strong> the auto-generated definition file that opens has:</p> <pre><code> public Type UnderlyingType { get; } </code></pre> <p>So something is definitely happening under the scenes which I am not aware of! </p> <p>Documentation of what (if??) some types are auto-mapped to other types and rules/attributes corresponding to this would be of much help!</p>

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