[Xaml] allow the Previewer to provide their own Xaml files for any type (#262)

* [Xaml] allow the Previewer to provide their own Xaml files for any type

* [Xaml] use a Func instead of an interface, easier to use by reflection. Add tests

* [XamlC] move the InitializeComponent duplication to XamlC task

* [XamlC] generate branching code

* [XamlC] fix the XamlC issue

* [XamlC] make the API public

* [docs] fix docs

10 files changed, 179 insertions, 14 deletions

diff --git a/.nuspec/Xamarin.Forms.Debug.targets b/.nuspec/Xamarin.Forms.Debug.targets
index 68f61bd7..ce197713 100644
--- a/.nuspec/Xamarin.Forms.Debug.targets
+++ b/.nuspec/Xamarin.Forms.Debug.targets
@@ -14,8 +14,8 @@
 	<PropertyGroup>
 		<CompileDependsOn>
 			$(CompileDependsOn);
-			GenerateDebugCode;
 			XamlC;
+			GenerateDebugCode;
 		</CompileDependsOn>
 	</PropertyGroup>
 
diff --git a/Xamarin.Forms.Build.Tasks/DebugXamlCTask.cs b/Xamarin.Forms.Build.Tasks/DebugXamlCTask.cs
index bec6386d..e0f81972 100644
--- a/Xamarin.Forms.Build.Tasks/DebugXamlCTask.cs
+++ b/Xamarin.Forms.Build.Tasks/DebugXamlCTask.cs
@@ -67,18 +67,11 @@ namespace Xamarin.Forms.Build.Tasks
 						LogLine(2, "no InitializeComponent found... skipped.");
 						continue;
 					}
-					if (typeDef.Methods.FirstOrDefault(md => md.Name == "InitCompRuntime") != null)
-					{
-						LogLine(2, "InitCompRuntime already exists... skipped");
+					var initCompRuntime = typeDef.Methods.FirstOrDefault(md => md.Name == "__InitComponentRuntime");
+					if (initCompRuntime == null) {
+						LogLine(2, "no __InitComponentRuntime found... skipped.");
 						continue;
 					}
-					LogLine(2, "");
-
-					LogString(2, "   Duplicating {0}.InitializeComponent () into {0}.InitCompRuntime ... ", typeDef.Name);
-					var initCompRuntime = new MethodDefinition("InitCompRuntime", initComp.Attributes, initComp.ReturnType);
-					initCompRuntime.Body = initComp.Body;
-					typeDef.Methods.Add(initCompRuntime);
-					LogLine(2, "done.");
 
 					//					IL_0000:  ldarg.0 
 					//					IL_0001:  callvirt instance void class [Xamarin.Forms.Core]Xamarin.Forms.ContentPage::'.ctor'()
@@ -92,7 +85,7 @@ namespace Xamarin.Forms.Build.Tasks
 					//					IL_0013:  br IL_001e
 					//
 					//					IL_0018:  ldarg.0 
-					//					IL_0019:  callvirt instance void class Xamarin.Forms.Xaml.XamlcTests.MyPage::InitCompRuntime()
+					//					IL_0019:  callvirt instance void class Xamarin.Forms.Xaml.XamlcTests.MyPage::__InitComponentRuntime()
 					//					IL_001e:  ret 
 
 					var altCtor =
diff --git a/Xamarin.Forms.Build.Tasks/XamlCTask.cs b/Xamarin.Forms.Build.Tasks/XamlCTask.cs
index 19548b80..b6387c0f 100644
--- a/Xamarin.Forms.Build.Tasks/XamlCTask.cs
+++ b/Xamarin.Forms.Build.Tasks/XamlCTask.cs
@@ -232,6 +232,16 @@ namespace Xamarin.Forms.Build.Tasks
 					}
 					LogLine(2, "");
 
+					if (typeDef.Methods.FirstOrDefault(md => md.Name == "__InitComponentRuntime") != null) {
+						LogLine(2, "   __InitComponentRuntime already exists... not duplicating");
+					} else {
+						LogString(2, "   Duplicating {0}.InitializeComponent () into {0}.__InitComponentRuntime ... ", typeDef.Name);
+						var initCompRuntime = new MethodDefinition("__InitComponentRuntime", initComp.Attributes, initComp.ReturnType);
+						initCompRuntime.Body = initComp.Body;
+						typeDef.Methods.Add(initCompRuntime);
+						LogLine(2, "done.");
+					}
+
 					LogString(2, "   Parsing Xaml... ");
 					var rootnode = ParseXaml(resource.GetResourceStream(), typeDef);
 					if (rootnode == null)
@@ -249,6 +259,45 @@ namespace Xamarin.Forms.Build.Tasks
 						var body = new MethodBody(initComp);
 						var il = body.GetILProcessor();
 						il.Emit(OpCodes.Nop);
+
+						// Generating branching code for the Previewer
+						//	IL_0007:  call class [mscorlib]System.Func`2<class [mscorlib]System.Type,string> class [Xamarin.Forms.Xaml.Internals]Xamarin.Forms.Xaml.XamlLoader::get_XamlFileProvider()
+						//  IL_000c:  brfalse IL_0031
+						//  IL_0011:  call class [mscorlib]System.Func`2<class [mscorlib]System.Type,string> class [Xamarin.Forms.Xaml.Internals]Xamarin.Forms.Xaml.XamlLoader::get_XamlFileProvider()
+						//  IL_0016:  ldarg.0 
+						//  IL_0017:  call instance class [mscorlib]System.Type object::GetType()
+						//  IL_001c:  callvirt instance !1 class [mscorlib]System.Func`2<class [mscorlib]System.Type, string>::Invoke(!0)
+						//  IL_0021:  brfalse IL_0031
+						//  IL_0026:  ldarg.0 
+						//  IL_0027:  call instance void class Xamarin.Forms.Xaml.UnitTests.XamlLoaderGetXamlForTypeTests::__InitComponentRuntime()
+						//  IL_002c:  ret
+						//  IL_0031:  nop
+
+						var nop = Instruction.Create(OpCodes.Nop);
+						var getXamlFileProvider = body.Method.Module.Import(body.Method.Module.Import(typeof(Xamarin.Forms.Xaml.Internals.XamlLoader))
+								.Resolve()
+								.Properties.FirstOrDefault(pd => pd.Name == "XamlFileProvider")
+						        .GetMethod);
+						il.Emit(OpCodes.Call, getXamlFileProvider);
+						il.Emit(OpCodes.Brfalse, nop);
+						il.Emit(OpCodes.Call, getXamlFileProvider);
+						il.Emit(OpCodes.Ldarg_0);
+						var getType = body.Method.Module.Import(body.Method.Module.Import(typeof(object))
+										  .Resolve()
+						                  .Methods.FirstOrDefault(md => md.Name == "GetType"));
+						il.Emit(OpCodes.Call, getType);
+						var func = body.Method.Module.Import(body.Method.Module.Import(typeof(Func<Type, string>))
+								 .Resolve()
+								 .Methods.FirstOrDefault(md => md.Name == "Invoke"));
+						func = func.ResolveGenericParameters(body.Method.Module.Import(typeof(Func<Type, string>)), body.Method.Module);
+						il.Emit(OpCodes.Callvirt, func);
+						il.Emit(OpCodes.Brfalse, nop);
+						il.Emit(OpCodes.Ldarg_0);
+						var initCompRuntime = typeDef.Methods.FirstOrDefault(md => md.Name == "__InitComponentRuntime");
+						il.Emit(OpCodes.Call, initCompRuntime);
+						il.Emit(OpCodes.Ret);
+						il.Append(nop);
+
 						var visitorContext = new ILContext(il, body);
 
 						rootnode.Accept(new XamlNodeVisitor((node, parent) => node.Parent = parent), null);
diff --git a/Xamarin.Forms.Xaml.UnitTests/Xamarin.Forms.Xaml.UnitTests.csproj b/Xamarin.Forms.Xaml.UnitTests/Xamarin.Forms.Xaml.UnitTests.csproj
index 417e800a..cd22258c 100644
--- a/Xamarin.Forms.Xaml.UnitTests/Xamarin.Forms.Xaml.UnitTests.csproj
+++ b/Xamarin.Forms.Xaml.UnitTests/Xamarin.Forms.Xaml.UnitTests.csproj
@@ -347,6 +347,9 @@
     <Compile Include="SharedResourceDictionary2.xaml.cs">
       <DependentUpon>SharedResourceDictionary2.xaml</DependentUpon>
     </Compile>
+    <Compile Include="XamlLoaderGetXamlForTypeTests.xaml.cs">
+      <DependentUpon>XamlLoaderGetXamlForTypeTests.xaml</DependentUpon>
+    </Compile>
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <Import Project="..\.nuspec\Xamarin.Forms.Debug.targets" />
@@ -617,6 +620,9 @@
     <EmbeddedResource Include="SharedResourceDictionary2.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
+    <EmbeddedResource Include="XamlLoaderGetXamlForTypeTests.xaml">
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
   </ItemGroup>
   <ItemGroup>
     <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
diff --git a/Xamarin.Forms.Xaml.UnitTests/XamlLoaderCreateTests.cs b/Xamarin.Forms.Xaml.UnitTests/XamlLoaderCreateTests.cs
index a175b57f..23c72a00 100644
--- a/Xamarin.Forms.Xaml.UnitTests/XamlLoaderCreateTests.cs
+++ b/Xamarin.Forms.Xaml.UnitTests/XamlLoaderCreateTests.cs
@@ -3,6 +3,8 @@ using NUnit.Framework;
 
 namespace Xamarin.Forms.Xaml.UnitTests
 {
+#pragma warning disable 0618 //retaining legacy call to obsolete code
+
 	[TestFixture]
 	public class XamlLoaderCreateTests
 	{
@@ -35,4 +37,5 @@ namespace Xamarin.Forms.Xaml.UnitTests
 			Assert.NotNull (button);
 		}
 	}
+#pragma warning restore 0618
 }
\ No newline at end of file
diff --git a/Xamarin.Forms.Xaml.UnitTests/XamlLoaderGetXamlForTypeTests.xaml b/Xamarin.Forms.Xaml.UnitTests/XamlLoaderGetXamlForTypeTests.xaml
new file mode 100644
index 00000000..ec551771
--- /dev/null
+++ b/Xamarin.Forms.Xaml.UnitTests/XamlLoaderGetXamlForTypeTests.xaml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
+		xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+		x:Class="Xamarin.Forms.Xaml.UnitTests.XamlLoaderGetXamlForTypeTests">
+	<Button x:Name="Button"/>
+</ContentPage>
diff --git a/Xamarin.Forms.Xaml.UnitTests/XamlLoaderGetXamlForTypeTests.xaml.cs b/Xamarin.Forms.Xaml.UnitTests/XamlLoaderGetXamlForTypeTests.xaml.cs
new file mode 100644
index 00000000..10c3f2e2
--- /dev/null
+++ b/Xamarin.Forms.Xaml.UnitTests/XamlLoaderGetXamlForTypeTests.xaml.cs
@@ -0,0 +1,55 @@
+using System;
+using System.Collections.Generic;
+
+using NUnit.Framework;
+
+using Xamarin.Forms;
+
+namespace Xamarin.Forms.Xaml.UnitTests
+{
+	public partial class XamlLoaderGetXamlForTypeTests : ContentPage
+	{
+		public XamlLoaderGetXamlForTypeTests()
+		{
+			InitializeComponent();
+		}
+
+		public XamlLoaderGetXamlForTypeTests(bool useCompiledXaml)
+		{
+			//this stub will be replaced at compile time
+		}
+
+		[TestFixture]
+		public class Tests
+		{
+			[SetUp]
+			public void SetUp()
+			{
+				Xamarin.Forms.Xaml.Internals.XamlLoader.XamlFileProvider = null;
+			}
+
+			[TestCase(false)]
+			[TestCase(true)]
+			public void XamlContentIsReplaced(bool useCompiledXaml)
+			{
+				var layout = new XamlLoaderGetXamlForTypeTests(useCompiledXaml);
+				Assert.That(layout.Content, Is.TypeOf<Button>());
+
+				Xamarin.Forms.Xaml.Internals.XamlLoader.XamlFileProvider = (t) => {
+					if (t == typeof(XamlLoaderGetXamlForTypeTests))
+						return @"
+	<ContentPage xmlns=""http://xamarin.com/schemas/2014/forms""
+		xmlns:x=""http://schemas.microsoft.com/winfx/2009/xaml""
+		x:Class=""Xamarin.Forms.Xaml.UnitTests.XamlLoaderGetXamlForTypeTests"">
+		<Label x:Name=""Label""/>
+	</ContentPage>";
+					return null;
+				};
+
+				layout = new XamlLoaderGetXamlForTypeTests(useCompiledXaml);
+				Assert.That(layout.Content, Is.TypeOf<Label>());
+			}
+		}
+	}
+}
+
diff --git a/Xamarin.Forms.Xaml/XamlLoader.cs b/Xamarin.Forms.Xaml/XamlLoader.cs
index 37bea4e4..40414092 100644
--- a/Xamarin.Forms.Xaml/XamlLoader.cs
+++ b/Xamarin.Forms.Xaml/XamlLoader.cs
@@ -33,6 +33,15 @@ using System.Reflection;
 using System.Text.RegularExpressions;
 using System.Xml;
 
+namespace Xamarin.Forms.Xaml.Internals
+{
+	public static class XamlLoader
+	{
+		public static Func<Type, string> XamlFileProvider { get; internal set; }
+		internal static bool DoNotThrowOnExceptions { get; set; }
+	}
+}
+
 namespace Xamarin.Forms.Xaml
 {
 	internal static class XamlLoader
@@ -64,12 +73,16 @@ namespace Xamarin.Forms.Xaml
 
 					var rootnode = new RuntimeRootNode (new XmlType (reader.NamespaceURI, reader.Name, null), view, (IXmlNamespaceResolver)reader);
 					XamlParser.ParseXaml (rootnode, reader);
-					Visit (rootnode, new HydratationContext { RootElement = view });
+					Visit (rootnode, new HydratationContext {
+						RootElement = view,
+						DoNotThrowOnExceptions = Xamarin.Forms.Xaml.Internals.XamlLoader.DoNotThrowOnExceptions
+					});
 					break;
 				}
 			}
 		}
 
+		[Obsolete ("Use the XamlFileProvider to provide xaml files. We will remove this when Cycle 8 hits Stable.")]
 		public static object Create (string xaml, bool doNotThrow = false)
 		{
 			object inflatedView = null;
@@ -113,6 +126,12 @@ namespace Xamarin.Forms.Xaml
 
 		static string GetXamlForType(Type type)
 		{
+			string xaml = null;
+
+			//the Previewer might want to provide it's own xaml for this... let them do that
+			if (Xamarin.Forms.Xaml.Internals.XamlLoader.XamlFileProvider != null && (xaml = Xamarin.Forms.Xaml.Internals.XamlLoader.XamlFileProvider(type)) != null)
+				return xaml;
+
 			var assembly = type.GetTypeInfo().Assembly;
 
 			string resourceId;
@@ -129,7 +148,6 @@ namespace Xamarin.Forms.Xaml
 
 			// first pass, pray to find it because the user named it correctly
 
-			string xaml = null;
 			foreach (var resource in resourceNames)
 			{
 				if (ResourceMatchesFilename(assembly, resource, likelyResourceName))
diff --git a/docs/Xamarin.Forms.Xaml/Xamarin.Forms.Xaml.Internals/XamlLoader.xml b/docs/Xamarin.Forms.Xaml/Xamarin.Forms.Xaml.Internals/XamlLoader.xml
new file mode 100644
index 00000000..ae6d96b9
--- /dev/null
+++ b/docs/Xamarin.Forms.Xaml/Xamarin.Forms.Xaml.Internals/XamlLoader.xml
@@ -0,0 +1,34 @@
+<Type Name="XamlLoader" FullName="Xamarin.Forms.Xaml.Internals.XamlLoader">
+  <TypeSignature Language="C#" Value="public static class XamlLoader" />
+  <TypeSignature Language="ILAsm" Value=".class public auto ansi abstract sealed beforefieldinit XamlLoader extends System.Object" />
+  <AssemblyInfo>
+    <AssemblyName>Xamarin.Forms.Xaml</AssemblyName>
+    <AssemblyVersion>2.0.0.0</AssemblyVersion>
+  </AssemblyInfo>
+  <Base>
+    <BaseTypeName>System.Object</BaseTypeName>
+  </Base>
+  <Interfaces />
+  <Docs>
+    <summary>To be added.</summary>
+    <remarks>To be added.</remarks>
+  </Docs>
+  <Members>
+    <Member MemberName="XamlFileProvider">
+      <MemberSignature Language="C#" Value="public static Func&lt;Type,string&gt; XamlFileProvider { get; }" />
+      <MemberSignature Language="ILAsm" Value=".property class System.Func`2&lt;class System.Type, string&gt; XamlFileProvider" />
+      <MemberType>Property</MemberType>
+      <AssemblyInfo>
+        <AssemblyVersion>2.0.0.0</AssemblyVersion>
+      </AssemblyInfo>
+      <ReturnValue>
+        <ReturnType>System.Func&lt;System.Type,System.String&gt;</ReturnType>
+      </ReturnValue>
+      <Docs>
+        <summary>To be added.</summary>
+        <value>To be added.</value>
+        <remarks>To be added.</remarks>
+      </Docs>
+    </Member>
+  </Members>
+</Type>
diff --git a/docs/Xamarin.Forms.Xaml/index.xml b/docs/Xamarin.Forms.Xaml/index.xml
index 1c4a761e..4627dd66 100644
--- a/docs/Xamarin.Forms.Xaml/index.xml
+++ b/docs/Xamarin.Forms.Xaml/index.xml
@@ -75,6 +75,7 @@
     <Namespace Name="Xamarin.Forms.Xaml.Internals">
       <Type Name="NameScopeProvider" Kind="Class" />
       <Type Name="SimpleValueTargetProvider" Kind="Class" />
+      <Type Name="XamlLoader" Kind="Class" />
       <Type Name="XamlServiceProvider" Kind="Class" />
       <Type Name="XamlTypeResolver" Kind="Class" />
       <Type Name="XmlLineInfoProvider" Kind="Class" />