[Xamarin.Android.Build.Tasks] Fragments & CodeBehind

While trying to repro Issue dotnet#1296, I had a brilliant idea: let's use
the new CodeBehind support from 7c31899!

Everything then fell apart.

For starters, Issue dotnet#1296 deals with Fragments, and 7c31899 didn't
support the presence of `<fragment/>` within Layout files.

Plumb support for that, by adding:

	partial class MainActivity {
	  partial void OnLayoutFragmentNotFound<T> (int resourceId, ref T type)
	    where T : global::Android.App.Fragment;
	}

Another issue was noticed as well: all the line numbers in the `#line`
pragmas were always `1`. This was narrowed down to a bug in
`GetLineInfo()`.

Then there's an issue with where I was using the CodeBehind file:
within the `src/Mono.Android/Test` project, which is in the
`Xamarin.Android.RuntimeTests` namespace. This prompted all manner of
namespace resolution failures:

	error CS0234: The type or namespace name 'App' does not exist in the namespace 'Xamarin.Android' (are you missing an assembly reference?)
	...

Fix this by using `CodeTypeReferenceOptions.GlobalReference` as much
as is practical (which isn't enough), and by "kludging" up the
`CodeNamespaceImport` construction so that we instead emit:

	using global::System;

Finally, the generated codebehind had some weird nesting going on:

	partial class MainActivity {
	  public __first_text_view_Views first_text_view {get;}
	  public sealed partial class __first_text_view_Views {
	    public __second_text_view_Views second_text_view {get;}
	    public sealed partial class __second_text_view_Views {
	      public sealed partial class __csharp_simple_fragment_Views {
	        public sealed partial class __csharp_partial_assembly_Views {
	        }
	      }
	    }
	  }
	}

It was bizarre *and* unusable: the `second_text_view` property --
corresponding to `<TextView android:id="@+id/second_text_view" />` --
was *nested within* a generated `MainActivity.__first_text_view_Views`
type, and I'm not sure why that existed. Furthermore, it *can't* work,
as the generated
`MainActivity.__first_text_view_Views.__CreateClass___second_text_view_Views()`
method depends on a constructor which doesn't exist:

	private @__second_text_view_Views @__CreateClass___second_text_view_Views() {
	  // There *is* a __second_text_view_Views(Activity) constructor,
	  // but not __second_text_view_Views(__first_text_view_Views).
	  return new @__second_text_view_Views(this);
	}

I "solved" (?) this by updating `LoadWidgets()` so that it always used
`widgetRoot` for all recursive calls to `LoadWidgets()`, so that there
is only ever one root. This removed all the nested types.

src/Mono.Android/Test/Mono.Android-Tests.csproj

@@ -97,6 +97,8 @@
     <AndroidResource Include="Resources\drawable\android_focused.png" />
     <AndroidResource Include="Resources\drawable\android_normal.png" />
     <AndroidResource Include="Resources\drawable\android_button.xml" />
+    <AndroidResource Include="Resources\layout\FragmentFixup.axml" />
+    <AndroidResource Include="Resources\layout\Main.axml" />
     <AndroidResource Include="Resources\xml\XmlReaderResourceParser.xml" />
   </ItemGroup>
   <Import Project="$(MSBuildExtensionsPath)\Xamarin\Android\Xamarin.Android.CSharp.targets" />

src/Mono.Android/Test/Resources/layout/FragmentFixup.axml

@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:orientation="vertical"
+    android:layout_width="fill_parent"
+    android:layout_height="fill_parent"
+    >
+  <fragment
+      android:name="Xamarin.Android.RuntimeTests.MyFragment"
+      android:id="@+id/csharp_simple_fragment"
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+  />
+  <fragment
+      android:name="xamarin.android.runtimetests.MyFragment"
+      android:id="@+id/csharp_legacy_fragment"
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+  />
+  <fragment
+      android:name="Xamarin.Android.RuntimeTests.MyFragment, Mono.Android-Tests"
+      android:id="@+id/csharp_partial_assembly"
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+  />
+  <fragment
+      android:name="Xamarin.Android.RuntimeTests.MyFragment, Mono.Android-Tests, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
+      android:id="@+id/csharp_full_assembly"
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+  />
+</LinearLayout>

src/Mono.Android/Test/Resources/layout/Main.axml

@@ -3,15 +3,37 @@
     android:orientation="vertical"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
+    xmlns:tools="http://schemas.xamarin.com/android/tools"
+    tools:class="Xamarin.Android.RuntimeTests.MainActivity"
     >
   <TextView
-    android:layout_width="wrap_content" android:layout_height="wrap_content"
+    android:id="@+id/first_text_view"
+    android:layout_width="wrap_content"
+    android:layout_height="wrap_content"
     android:editable="false"
-    android:background="@color/uicolor_lightGrayColor"
-	/>
+  />
   <TextView
-    android:layout_width="wrap_content" android:layout_height="wrap_content"
+    android:id="@+id/second_text_view"
+    android:layout_width="wrap_content"
+    android:layout_height="wrap_content"
     android:editable="false"
-    android:background="@color/WhiterShadeOfPale"
-	/>
+  />
+  <fragment
+      android:name="Xamarin.Android.RuntimeTests.MyFragment"
+      android:id="@+id/csharp_simple_fragment"
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+  />
+  <fragment
+      android:name="Xamarin.Android.RuntimeTests.MyFragment, Hello"
+      android:id="@+id/csharp_partial_assembly"
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+  />
+  <fragment
+      android:name="Xamarin.Android.RuntimeTests.MyFragment, Hello, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
+      android:id="@+id/csharp_full_assembly"
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+  />
 </LinearLayout>

src/Mono.Android/Test/Xamarin.Android.RuntimeTests/MainActivity.cs

@@ -1,16 +1,26 @@
 using System.Reflection;
 using Android.App;
 using Android.OS;
+using Android.Views;
+using Android.Widget;
 using Xamarin.Android.NUnitLite;
 
 namespace Xamarin.Android.RuntimeTests
 {
 	[Activity (Label = "runtime", MainLauncher = true,
 			Name="xamarin.android.runtimetests.MainActivity")]
-	public class MainActivity : TestSuiteActivity
+	public partial class MainActivity : TestSuiteActivity
 	{
 		protected override void OnCreate (Bundle bundle)
 		{
+			// Note; for testing <fragment/> fixup only.
+			// The actual view is set/replaced in `TestSuiteActivity.OnCreate()`
+			SetContentView (Resource.Layout.FragmentFixup);
+
+			first_text_view.Click += delegate {
+				// ignore
+			};
+
 			// tests can be inside the main assembly
 			AddTest (Assembly.GetExecutingAssembly ());
 			// or in any reference assemblies
@@ -20,5 +30,17 @@ protected override void OnCreate (Bundle bundle)
 			base.OnCreate (bundle);
 		}
 	}
+
+#if __ANDROID_11__
+	public class MyFragment : Fragment {
+
+		public override View OnCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
+		{
+			return new TextView (Activity) {
+				Text = "via fragment!",
+			};
+		}
+	}
+#endif  // ANDROID_15
 }
 

src/Xamarin.Android.Build.Tasks/Tasks/GenerateLayoutCodeBehind.cs

@@ -46,6 +46,7 @@ public bool IsLeaf {
 			public Widget Parent { get; set; }
 			public bool IsInaccessible { get; set; }
 			public bool IsRoot { get; set; }
+			public bool IsFragment { get; set; }
 
 			public void AddChild (Widget child)
 			{
@@ -121,7 +122,7 @@ public override bool Execute ()
 
 		void GetLineInfo (IXmlLineInfo linfo, out int line, out int column)
 		{
-			if (linfo == null || linfo.HasLineInfo ()) {
+			if (linfo == null || !linfo.HasLineInfo ()) {
 				line = column = 1;
 				return;
 			}
@@ -167,7 +168,6 @@ bool GenerateLayoutMembers (CodeTypeDeclaration mainClass, string fileName)
 										LoadWidgets (fileName, subtree, lineInfo, androidNS, root, globalIdCache);
 								}
 							}
-
 						}
 					}
 				}
@@ -194,8 +194,30 @@ void LoadWidgets (string fileName, XmlReader reader, IXmlLineInfo lineinfo,  str
 				}
 			}
 			while (reader.Read ()) {
-				LoadWidgets (fileName, reader, lineinfo, androidNS, root ?? widgetRoot, globalIdCache);
+				LoadWidgets (fileName, reader, lineinfo, androidNS, widgetRoot, globalIdCache);
+			}
+		}
+
+		static readonly Dictionary<string, Func<Widget, XmlReader, Widget>> WidgetCreators = new Dictionary<string, Func<Widget, XmlReader, Widget>> {
+			["fragment"] = CreateFragmentWidget,
+		};
+
+		const string AndroidXmlNamespace  = "http://schemas.android.com/apk/res/android";
+		const string AndroidXmlName       = "name";
+
+		static Widget CreateFragmentWidget (Widget w, XmlReader e)
+		{
+			var type  = e.GetAttribute (AndroidXmlName, AndroidXmlNamespace);
+			if (type == null) {
+				return null;
 			}
+
+			w.IsFragment  = true;
+
+			var c   = type.IndexOf (',');
+			w.Type  = c < 0 ? type : type.Substring (0, c);
+			w.Type  = w.Type;
+			return w;
 		}
 
 		Widget CreateWidget (string fileName, XmlReader e, IXmlLineInfo lineInfo, string id, Widget parent)
@@ -220,6 +242,11 @@ Widget CreateWidget (string fileName, XmlReader e, IXmlLineInfo lineInfo, string
 				Column = column
 			};
 
+			Func<Widget, XmlReader, Widget> creator;
+			if (WidgetCreators.TryGetValue (e.LocalName, out creator)) {
+				return creator (ret, e);
+			}
+
 			return ret;
 		}
 
@@ -401,7 +428,7 @@ CodeMemberMethod ImplementWidgetCreator (Widget widget, CodeExpression parent, L
 
 		CodeMethodInvokeExpression CreateFindViewInvoke (Widget widget, CodeExpression parent, CodeExpression parentView)
 		{
-			var findViewRef = new CodeMethodReferenceExpression (parent, "__FindView");
+			var findViewRef = new CodeMethodReferenceExpression (parent, widget.IsFragment ? "__FindFragment" : "__FindView");
 			findViewRef.TypeArguments.Add (new CodeTypeReference (widget.Type));
 
 			return new CodeMethodInvokeExpression (findViewRef, new CodeExpression [] { parentView, new CodeSnippetExpression (widget.ID) });
@@ -416,7 +443,7 @@ CodeMemberField CreateBackingField (Widget widget, string memberType)
 
 		CodeMemberField CreateBackingFuncField (Widget widget, string memberType)
 		{
-			return new CodeMemberField ($"Func<{memberType}>", $"__{widget.Name}Func");
+			return new CodeMemberField ($"global::System.Func<{memberType}>", $"__{widget.Name}Func");
 		}
 
 		bool HasUniqueId (Widget widget, Dictionary<string, int> globalIdCache)
@@ -484,7 +511,7 @@ ITaskItem GenerateCodeBehind (ITaskItem layoutFile, CodeGeneratorOptions generat
 			var ns = new CodeNamespace (namespaceName);
 			compileUnit.Namespaces.Add (ns);
 			foreach (string import in StandardImports)
-				ns.Imports.Add (new CodeNamespaceImport (import));
+				ns.Imports.Add (new CodeNamespaceImport ($"global::{import}"));
 
 			CodeTypeDeclaration mainClass = AddMainClass (layoutFile, ns, className);
 			if (!GenerateLayoutMembers (mainClass, Path.GetFullPath (layoutFile.ItemSpec)))
@@ -578,7 +605,9 @@ void AddCommonMembers (CodeTypeDeclaration klass, ITaskItem layoutFile)
 			klass.Members.Add (ImplementFindView (activityTypeRef));
 			klass.Members.Add (ImplementFindView (new CodeTypeReference ("Android.App.Fragment", CodeTypeReferenceOptions.GlobalReference), activityTypeRef, (CodeVariableReferenceExpression parentView) => new CodePropertyReferenceExpression (parentView, "Activity")));
 			klass.Members.Add (ImplementEnsureView ());
+			klass.Members.Add (ImplementFindFragment (activityTypeRef));
 			klass.Members.Add (new CodeSnippetTypeMember ("\tpartial void OnLayoutViewNotFound<T> (int resourceId, ref T type) where T : global::Android.Views.View;"));
+			klass.Members.Add (new CodeSnippetTypeMember ("\tpartial void OnLayoutFragmentNotFound<T> (int resourceId, ref T type) where T : global::Android.App.Fragment;"));
 		}
 
 		CodeMemberMethod ImplementInitializeContentView (ITaskItem layoutFile)
@@ -609,7 +638,7 @@ CodeMemberMethod ImplementEnsureView ()
 			method.TypeParameters.Add (typeParam);
 
 			var tRef = new CodeTypeReference (typeParam);
-			var funcRef = new CodeTypeReference (typeof (Func<>));
+			var funcRef = new CodeTypeReference (typeof (Func<>), CodeTypeReferenceOptions.GlobalReference);
 			funcRef.TypeArguments.Add (tRef);
 			method.Parameters.Add (new CodeParameterDeclarationExpression (funcRef, "creator"));
 
@@ -635,7 +664,7 @@ CodeMemberMethod ImplementEnsureView ()
 			var creatorVarRef = new CodeVariableReferenceExpression ("creator");
 			var argNullEx = new CodeThrowExceptionStatement (
 				new CodeObjectCreateExpression (
-					new CodeTypeReference (typeof (ArgumentNullException)),
+					new CodeTypeReference (typeof (ArgumentNullException), CodeTypeReferenceOptions.GlobalReference),
 					new [] { new CodeSnippetExpression ("nameof (creator)") }
 				)
 			);
@@ -653,6 +682,75 @@ CodeMemberMethod ImplementEnsureView ()
 			return method;
 		}
 
+		CodeMemberMethod ImplementFindFragment (CodeTypeReference typeForParent, CodeTypeReference typeForOverloadCall = null, Func<CodeVariableReferenceExpression, CodeExpression> constructParentViewCall = null)
+		{
+			CodeMemberMethod method = CreateMethod ("__FindFragment", MethodAccessibility.Private, MethodScope.Final);
+
+			var typeParam = new CodeTypeParameter ("T") {
+				Constraints = {
+					new CodeTypeReference ("Android.App.Fragment", CodeTypeReferenceOptions.GlobalReference),
+				},
+			};
+			method.TypeParameters.Add (typeParam);
+			method.Parameters.Add (new CodeParameterDeclarationExpression (typeForParent, "activity"));
+			method.Parameters.Add (new CodeParameterDeclarationExpression (typeof (int), "id"));
+
+			var tReference = new CodeTypeReference (typeParam);
+			method.ReturnType = tReference;
+
+			// T fragment = FragmentManager.FindFragmentById<T> (id);
+			var id = new CodeVariableReferenceExpression ("id");
+
+			var findByIdRef = new CodeMethodReferenceExpression (
+				new CodePropertyReferenceExpression (new CodeVariableReferenceExpression ("activity"), "FragmentManager"),
+				"FindFragmentById",
+				new [] { tReference }
+			);
+
+			var findByIdInvoke = new CodeMethodInvokeExpression (findByIdRef, new [] { id });
+			var viewVar = new CodeVariableDeclarationStatement (tReference, "fragment", findByIdInvoke);
+			method.Statements.Add (viewVar);
+
+			// if (view == null) {
+			//     OnLayoutFragmentNotFound (resourceId, ref view);
+			// }
+			// if (view != null)
+			//     return view;
+			// throw new System.InvalidOperationException($"Fragment not found (ID: {id})");
+
+			var viewVarRef = new CodeVariableReferenceExpression ("fragment");
+			var ifViewNotNull = new CodeConditionStatement (
+				new CodeBinaryOperatorExpression (viewVarRef, CodeBinaryOperatorType.IdentityInequality, new CodePrimitiveExpression (null)),
+				new CodeStatement [] { new CodeMethodReturnStatement (viewVarRef) }
+			);
+
+			var viewRefParam = new CodeDirectionExpression (FieldDirection.Ref, viewVarRef);
+			var viewNotFoundInvoke = new CodeMethodInvokeExpression (
+				new CodeThisReferenceExpression (),
+				"OnLayoutFragmentNotFound",
+				new CodeExpression [] { id, viewRefParam }
+			);
+
+			var ifViewNull = new CodeConditionStatement (
+				new CodeBinaryOperatorExpression (viewVarRef, CodeBinaryOperatorType.IdentityEquality, new CodePrimitiveExpression (null)),
+				new CodeStatement [] { new CodeExpressionStatement (viewNotFoundInvoke) }
+			);
+
+			method.Statements.Add (ifViewNull);
+			method.Statements.Add (ifViewNotNull);
+
+			var throwInvOp = new CodeThrowExceptionStatement (
+				new CodeObjectCreateExpression (
+					new CodeTypeReference (typeof (InvalidOperationException), CodeTypeReferenceOptions.GlobalReference),
+					new [] { new CodeSnippetExpression ("$\"Fragment not found (ID: {id})\"") }
+				)
+			);
+
+			method.Statements.Add (throwInvOp);
+
+			return method;
+		}
+
 		CodeMemberMethod ImplementFindView (CodeTypeReference typeForParent, CodeTypeReference typeForOverloadCall = null, Func<CodeVariableReferenceExpression, CodeExpression> constructParentViewCall = null)
 		{
 			CodeMemberMethod method = CreateMethod ("__FindView", MethodAccessibility.Private, MethodScope.Final);
@@ -729,7 +827,7 @@ CodeMemberMethod ImplementFindView (CodeTypeReference typeForParent, CodeTypeRef
 
 			var throwInvOp = new CodeThrowExceptionStatement (
 				new CodeObjectCreateExpression (
-					new CodeTypeReference (typeof (InvalidOperationException)),
+					new CodeTypeReference (typeof (InvalidOperationException), CodeTypeReferenceOptions.GlobalReference),
 					new [] { new CodeSnippetExpression ("$\"View not found (ID: {resourceId})\"") }
 				)
 			);
@@ -746,7 +844,7 @@ CodeMemberMethod CreateMethod (string methodName, MethodAccessibility access, Me
 
 		CodeMemberMethod CreateMethod (string methodName, MethodAccessibility access, MethodScope scope, Type returnType)
 		{
-			return CreateMethod (methodName, access, scope, new CodeTypeReference (returnType));
+			return CreateMethod (methodName, access, scope, new CodeTypeReference (returnType, CodeTypeReferenceOptions.GlobalReference));
 		}
 
 		CodeMemberMethod CreateMethod (string methodName, MethodAccessibility access, MethodScope scope, string returnType)
@@ -813,7 +911,7 @@ void MarkAsCompilerGenerated (CodeTypeMember member)
 
 		void AddCustomAttribute (CodeAttributeDeclarationCollection attributes, Type type)
 		{
-			attributes.Add (new CodeAttributeDeclaration (new CodeTypeReference (type)));
+			attributes.Add (new CodeAttributeDeclaration (new CodeTypeReference (type, CodeTypeReferenceOptions.GlobalReference)));
 		}
 	}
 }