[Xamarin.Android.Build.Tasks] clean intermediates if NuGets change

Context: dotnet#1741 Fixes: dotnet#1828 PR dotnet#1741 is a good attempt at fixing this, but... - It is a little heavy handed and basically "nukes the world". - It does not reproduce an issue in a test and "fix it", it fixes an "unknown" #deletebinobj problem. I also have a few nitpicks about PR dotnet#1741: - It only comes into effect if `BuildingInsideVisualStudio` is `True`. We should also fix command-line builds. - The `$(ProjectLockFile).stamp` file isn't added to `FileWrites`. So let's improve on dotnet#1741! As it had some good ideas, we just need to narrow its focus. First, I reproduced a real issue in a test with the following scenario: - Create a Xamarin.Forms 2.3.4 app that uses the 25.4.x support libraries - Build it - Update the NuGets to Xamarin.Forms 3.0.x and the 27.x support libraries - Build again - Stuff breaks... namely the following message: bin\Debug\lib\xamarin.android\xbuild\Xamarin\Android\Xamarin.Android.Common.targets(2153,3): error MSB4018: The "GenerateJavaStubs" task failed unexpectedly. System.IO.FileNotFoundException: Could not load assembly 'System.IO, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. Perhaps it doesn't exist in the Mono for Android profile? File name: 'System.IO.dll' at Java.Interop.Tools.Cecil.DirectoryAssemblyResolver.Resolve(AssemblyNameReference reference, ReaderParameters parameters) in external\Java.Interop\src\Java.Interop.Tools.Cecil\Java.Interop.Tools.Cecil\DirectoryAssemblyResolver.cs:line 241 at Java.Interop.Tools.Cecil.DirectoryAssemblyResolver.Resolve(AssemblyNameReference reference) in external\Java.Interop\src\Java.Interop.Tools.Cecil\Java.Interop.Tools.Cecil\DirectoryAssemblyResolver.cs:line 191 at Mono.Cecil.MetadataResolver.Resolve(TypeReference type) in external\mono\external\cecil\Mono.Cecil\MetadataResolver.cs:line 101 at Mono.Cecil.ModuleDefinition.Resolve(TypeReference type) in external\mono\external\cecil\Mono.Cecil\ModuleDefinition.cs:line 774 at Mono.Cecil.TypeReference.Resolve() in external\mono\external\cecil\Mono.Cecil\TypeReference.cs:line 280 at Java.Interop.Tools.Cecil.TypeDefinitionRocks.GetBaseType(TypeDefinition type) in external\Java.Interop\src\Java.Interop.Tools.Cecil\Java.Interop.Tools.Cecil\TypeDefinitionRocks.cs:line 14 at Java.Interop.Tools.Cecil.TypeDefinitionRocks.<GetTypeAndBaseTypes>d__1.MoveNext() in external\Java.Interop\src\Java.Interop.Tools.Cecil\Java.Interop.Tools.Cecil\TypeDefinitionRocks.cs:line 21 at System.Linq.Enumerable.Any[TSource](IEnumerable`1 source, Func`2 predicate) at Java.Interop.Tools.Cecil.TypeDefinitionRocks.IsSubclassOf(TypeDefinition type, String typeName) in external\Java.Interop\src\Java.Interop.Tools.Cecil\Java.Interop.Tools.Cecil\TypeDefinitionRocks.cs:line 55 at Java.Interop.Tools.JavaCallableWrappers.JavaTypeScanner.AddJavaTypes(List`1 javaTypes, TypeDefinition type) in external\Java.Interop\src\Java.Interop.Tools.JavaCallableWrappers\Java.Interop.Tools.JavaCallableWrappers\JavaTypeScanner.cs:line 46 at Java.Interop.Tools.JavaCallableWrappers.JavaTypeScanner.GetJavaTypes(IEnumerable`1 assemblies, IAssemblyResolver resolver) in external\Java.Interop\src\Java.Interop.Tools.JavaCallableWrappers\Java.Interop.Tools.JavaCallableWrappers\JavaTypeScanner.cs:line 36 at Xamarin.Android.Tasks.GenerateJavaStubs.Run(DirectoryAssemblyResolver res) in src\Xamarin.Android.Build.Tasks\Tasks\GenerateJavaStubs.cs:line 138 at Xamarin.Android.Tasks.GenerateJavaStubs.Execute() in src\Xamarin.Android.Build.Tasks\Tasks\GenerateJavaStubs.cs:line 91 at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute() at Microsoft.Build.BackEnd.TaskBuilder.<ExecuteInstantiatedTask>d__26.MoveNext() [bin\TestDebug\temp\BuildAfterUpgradingNuget\UnnamedProject.csproj] The real problem here though is that many of the intermediate files in `obj\Debug\lp` (among others) are out of sync. Namely we can see messages like this from the `ResolveLibraryProjectImports` MSBuild task in the build log: Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.animated.vector.drawable\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.Animated.Vector.Drawable.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.annotations\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.Annotations.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.compat\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.Compat.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.core.ui\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.Core.UI.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.core.utils\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.Core.Utils.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.design\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.Design.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.fragment\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.Fragment.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.media.compat\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.Media.Compat.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.transition\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.Transition.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.v4\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.v4.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.v7.appcompat\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.v7.AppCompat.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.v7.cardview\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.v7.CardView.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.v7.mediarouter\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.v7.MediaRouter.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.v7.palette\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.v7.Palette.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.v7.recyclerview\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.v7.RecyclerView.dll: extracted files are up to date Skipped resource lookup for C:\Users\myuser\.nuget\packages\xamarin.android.support.vector.drawable\27.0.2.1\lib\MonoAndroid81\Xamarin.Android.Support.Vector.Drawable.dll: extracted files are up to date These are *bad*, since the extracted files were from the 25.4.x support libraries! It is happening because the timestamps of these system-wide `%UserProfile%\.nuget` NuGet packages are quite old. So a solution for now, based on dotnet#1741: - When NuGet packages change - Clean some subset of files/directories -- not a full `Clean` I borrowed the logic for calculating `$(_NuGetAssetsFile)` from dotnet#1741, since it was working pretty well. I added a `_CleanIntermediateIfNuGetsChange` MSBuild target that runs the `_CleanMonoAndroidIntermediateDir` target as this was the smallest deletion I could figure out that fixes the problem. At first I tried deleting other subsets of files/directories, but couldn't find a combination that worked. This change does have some impact on build times, when `_CleanIntermediateIfNuGetsChange` runs and deletes files, it takes 1-2 seconds on my machine for the test case. There will also be further build time taken from other targets that run because files were deleted. However, we would likely prefer a slightly slower, correct build, than a faster incorrect one... It is certaining going to be faster than the `Build`, error message, `Rebuild` cycle -- or nuking `bin` and `obj`. Down the road, we could consider some other change to refactor how `obj\Debug\lp` is generated and make it resilient to NuGet changes.
jonathanpeppers · Jun 25, 2018 · 0c78e36 · 0c78e36
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diff --git a/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BuildTest.cs b/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BuildTest.cs
@@ -2042,6 +2042,71 @@ public void BuildAfterAddingNuget ()
 			}
 		}
 
+		//This test validates the _CleanIntermediateIfNuGetsChange target
+		[Test]
+		public void BuildAfterUpgradingNuget ([Values (false, true)] bool usePackageReference)
+		{
+			var proj = new XamarinAndroidApplicationProject ();
+			proj.MainActivity = proj.DefaultMainActivity.Replace ("public class MainActivity : Activity", "public class MainActivity : Xamarin.Forms.Platform.Android.FormsAppCompatActivity");
+
+			var packages = usePackageReference ? proj.PackageReferences : proj.Packages;
+			packages.Add (KnownPackages.XamarinForms_2_3_4_231);
+			packages.Add (KnownPackages.AndroidSupportV4_25_4_0_1);
+			packages.Add (KnownPackages.SupportCompat_25_4_0_1);
+			packages.Add (KnownPackages.SupportCoreUI_25_4_0_1);
+			packages.Add (KnownPackages.SupportCoreUtils_25_4_0_1);
+			packages.Add (KnownPackages.SupportDesign_25_4_0_1);
+			packages.Add (KnownPackages.SupportFragment_25_4_0_1);
+			packages.Add (KnownPackages.SupportMediaCompat_25_4_0_1);
+			packages.Add (KnownPackages.SupportV7AppCompat_25_4_0_1);
+			packages.Add (KnownPackages.SupportV7CardView_25_4_0_1);
+			packages.Add (KnownPackages.SupportV7MediaRouter_25_4_0_1);
+
+			using (var b = CreateApkBuilder (Path.Combine ("temp", TestContext.CurrentContext.Test.Name))) {
+				if (usePackageReference) {
+					b.RequiresMSBuild = true;
+					b.Target = "Restore,Build";
+				}
+				var projectDir = Path.Combine (Root, b.ProjectDirectory);
+				if (Directory.Exists (projectDir))
+					Directory.Delete (projectDir, true);
+				Assert.IsTrue (b.Build (proj), "first build should have succeeded.");
+				Assert.IsFalse (b.Output.IsTargetSkipped ("_CleanIntermediateIfNuGetsChange"), "`_CleanIntermediateIfNuGetsChange` should have run!");
+
+				var nugetStamp = Path.Combine (Root, b.ProjectDirectory, proj.IntermediateOutputPath, proj.ProjectName + ".nuget.stamp");
+				FileAssert.Exists (nugetStamp, "`_CleanIntermediateIfNuGetsChange` did not create stamp file!");
+
+				if (!usePackageReference) {
+					foreach (var p in proj.Packages) {
+						foreach (var r in p.References) {
+							proj.References.Remove (r);
+						}
+					}
+				}
+				packages.Clear ();
+				packages.Add (KnownPackages.XamarinForms_3_0_0_561731);
+				packages.Add (KnownPackages.Android_Arch_Core_Common_26_1_0);
+				packages.Add (KnownPackages.Android_Arch_Lifecycle_Common_26_1_0);
+				packages.Add (KnownPackages.Android_Arch_Lifecycle_Runtime_26_1_0);
+				packages.Add (KnownPackages.AndroidSupportV4_27_0_2_1);
+				packages.Add (KnownPackages.SupportCompat_27_0_2_1);
+				packages.Add (KnownPackages.SupportCoreUI_27_0_2_1);
+				packages.Add (KnownPackages.SupportCoreUtils_27_0_2_1);
+				packages.Add (KnownPackages.SupportDesign_27_0_2_1);
+				packages.Add (KnownPackages.SupportFragment_27_0_2_1);
+				packages.Add (KnownPackages.SupportMediaCompat_27_0_2_1);
+				packages.Add (KnownPackages.SupportV7AppCompat_27_0_2_1);
+				packages.Add (KnownPackages.SupportV7CardView_27_0_2_1);
+				packages.Add (KnownPackages.SupportV7MediaRouter_27_0_2_1);
+				packages.Add (KnownPackages.SupportV7RecyclerView_27_0_2_1);
+				b.Save (proj, doNotCleanupOnUpdate: true);
+				Assert.IsTrue (b.Build (proj), "second build should have succeeded.");
+				Assert.IsFalse (b.Output.IsTargetSkipped ("_CleanIntermediateIfNuGetsChange"), "`_CleanIntermediateIfNuGetsChange` should have run!");
+				FileAssert.Exists (nugetStamp, "`_CleanIntermediateIfNuGetsChange` did not create stamp file!");
+				Assert.IsFalse (StringAssertEx.ContainsText (b.LastBuildOutput, "Xamarin.Android.Support.v4.dll: extracted files are up to date"), "`ResolveLibraryProjectImports` should not skip `Xamarin.Android.Support.v4.dll`!");
+			}
+		}
+
 		[Test]
 		public void CheckTargetFrameworkVersion ()
 		{

diff --git a/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Android/KnownPackages.cs b/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.ProjectTools/Android/KnownPackages.cs
@@ -49,6 +49,15 @@ public static class KnownPackages
 					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.v4.25.4.0.1\\lib\\MonoAndroid70\\Xamarin.Android.Support.v4.dll" }
 			}
 		};
+		public static Package AndroidSupportV4_27_0_2_1 = new Package () {
+			Id = "Xamarin.Android.Support.v4",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.v4") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.v4.27.0.2.1\\lib\\MonoAndroid70\\Xamarin.Android.Support.v4.dll" }
+			}
+		};
 		public static Package AndroidSupportV4Beta = new Package () {
 			Id = "Xamarin.Android.Support.v4",
 			Version = "21.0.0.0-beta1",
@@ -103,6 +112,16 @@ public static class KnownPackages
 					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.v7.RecyclerView.21.0.0.0-beta1\\lib\\MonoAndroid\\Xamarin.Android.Support.v7.RecyclerView.dll" }
 				}
 		};
+		public static Package SupportV7RecyclerView_27_0_2_1 = new Package {
+			Id = "Xamarin.Android.Support.v7.RecyclerView",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.V7.RecyclerView") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.v7.RecyclerView.27.0.2.1\\lib\\MonoAndroid81\\Xamarin.Android.Support.v7.RecyclerView.dll"
+				}
+			}
+		};
 		public static Package SupportV7CardView = new Package {
 			Id = "Xamarin.Android.Support.v7.Cardview",
 			Version = "21.0.3.0",
@@ -130,6 +149,15 @@ public static class KnownPackages
 					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.v7.CardView.25.4.0.1\\lib\\MonoAndroid70\\Xamarin.Android.Support.v7.CardView.dll" }
 			}
 		};
+		public static Package SupportV7CardView_27_0_2_1 = new Package {
+			Id = "Xamarin.Android.Support.v7.Cardview",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.v7.CardView") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.v7.CardView.27.0.2.1\\lib\\MonoAndroid81\\Xamarin.Android.Support.v7.CardView.dll" }
+			}
+		};
 		public static Package SupportV7AppCompat_21_0_3_0 = new Package {
 			Id = "Xamarin.Android.Support.v7.AppCompat",
 			Version = "21.0.3.0",
@@ -211,6 +239,60 @@ public static class KnownPackages
 					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.Media.Compat.25.4.0.1\\lib\\MonoAndroid70\\Xamarin.Android.Support.Media.Compat.dll" }
 			}
 		};
+		public static Package SupportV7AppCompat_27_0_2_1 = new Package {
+			Id = "Xamarin.Android.Support.v7.AppCompat",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.v7.AppCompat") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.v7.AppCompat.27.0.2.1\\lib\\MonoAndroid81\\Xamarin.Android.Support.v7.AppCompat.dll" }
+			}
+		};
+		public static Package SupportCompat_27_0_2_1 = new Package {
+			Id = "Xamarin.Android.Support.Compat",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.Compat") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.Compat.27.0.2.1\\lib\\MonoAndroid81\\Xamarin.Android.Support.Compat.dll" }
+			}
+		};
+		public static Package SupportCoreUI_27_0_2_1 = new Package {
+			Id = "Xamarin.Android.Support.Core.UI",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.Core.UI") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.Core.UI.27.0.2.1\\lib\\MonoAndroid81\\Xamarin.Android.Support.Core.UI.dll" }
+			}
+		};
+		public static Package SupportCoreUtils_27_0_2_1 = new Package {
+			Id = "Xamarin.Android.Support.Core.Utils",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.Core.Utils") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.Core.Utils.27.0.2.1\\lib\\MonoAndroid81\\Xamarin.Android.Support.Core.Utils.dll" }
+			}
+		};
+		public static Package SupportFragment_27_0_2_1 = new Package {
+			Id = "Xamarin.Android.Support.Fragment",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.Fragment") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.Fragment.27.0.2.1\\lib\\MonoAndroid81\\Xamarin.Android.Support.Fragment.dll" }
+			}
+		};
+		public static Package SupportMediaCompat_27_0_2_1 = new Package {
+			Id = "Xamarin.Android.Support.Media.Compat",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.Media.Compat") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.Media.Compat.27.0.2.1\\lib\\MonoAndroid81\\Xamarin.Android.Support.Media.Compat.dll" }
+			}
+		};
 		public static Package SupportV7MediaRouter_21_0_3_0 = new Package {
 			Id = "Xamarin.Android.Support.v7.MediaRouter",
 			Version = "21.0.3.0",
@@ -220,6 +302,24 @@ public static class KnownPackages
 					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.v7.MediaRouter.21.0.3.0\\lib\\MonoAndroid403\\Xamarin.Android.Support.v7.MediaRouter.dll" }
 			}
 		};
+		public static Package SupportV7MediaRouter_25_4_0_1 = new Package {
+			Id = "Xamarin.Android.Support.v7.MediaRouter",
+			Version = "25.4.0.1",
+			TargetFramework = "MonoAndroid70",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.v7.MediaRouter") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.v7.MediaRouter.25.4.0.1\\lib\\MonoAndroid70\\Xamarin.Android.Support.v7.MediaRouter.dll" }
+			}
+		};
+		public static Package SupportV7MediaRouter_27_0_2_1 = new Package {
+			Id = "Xamarin.Android.Support.v7.MediaRouter",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.v7.MediaRouter") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.v7.MediaRouter.27.0.2.1\\lib\\MonoAndroid81\\Xamarin.Android.Support.v7.MediaRouter.dll" }
+			}
+		};
 		public static Package SupportV7Palette_22_1_1_1 = new Package {
 			Id = "Xamarin.Android.Support.v7.Palette",
 			Version = "22.1.1.1",
@@ -238,6 +338,15 @@ public static class KnownPackages
 					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.Design.25.4.0.1\\lib\\MonoAndroid70\\Xamarin.Android.Support.Design.dll" }
 				}
 		};
+		public static Package SupportDesign_27_0_2_1 = new Package {
+			Id = "Xamarin.Android.Support.Design",
+			Version = "27.0.2.1",
+			TargetFramework = "MonoAndroid81",
+			References = {
+				new BuildItem.Reference ("Xamarin.Android.Support.Design") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Support.Design.27.0.2.1\\lib\\MonoAndroid81\\Xamarin.Android.Support.Design.dll" }
+				}
+		};
 		public static Package GooglePlayServices_22_0_0_2 = new Package {
 			Id = "Xamarin.GooglePlayServices",
 			Version = "22.0.0.2",
@@ -318,6 +427,28 @@ public static class KnownPackages
 				},
 			}
 		};
+		public static Package XamarinForms_3_0_0_561731 = new Package {
+			Id = "Xamarin.Forms",
+			Version = "3.0.0.561731",
+			TargetFramework = "MonoAndroid10",
+			References =  {
+				new BuildItem.Reference ("Xamarin.Forms.Platform.Android") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Forms.3.0.0.561731\\lib\\MonoAndroid10\\Xamarin.Forms.Platform.Android.dll"
+				},
+				new BuildItem.Reference ("FormsViewGroup") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Forms.3.0.0.561731\\lib\\MonoAndroid10\\FormsViewGroup.dll"
+				},
+				new BuildItem.Reference ("Xamarin.Forms.Core") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Forms.3.0.0.561731\\lib\\MonoAndroid10\\Xamarin.Forms.Core.dll"
+				},
+				new BuildItem.Reference ("Xamarin.Forms.Xaml") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Forms.3.0.0.561731\\lib\\MonoAndroid10\\Xamarin.Forms.Xaml.dll"
+				},
+				new BuildItem.Reference ("Xamarin.Forms.Platform") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Forms.3.0.0.561731\\lib\\MonoAndroid10\\Xamarin.Forms.Platform.dll"
+				},
+			}
+		};
 		public static Package CocosSharp_PCL_Shared_1_5_0_0 = new Package {
 			Id = "CocosSharp.PCL.Shared", 
 			Version = "1.5.0.0",
@@ -405,6 +536,36 @@ public static class KnownPackages
 				}
 			}
 		};
+		public static Package Android_Arch_Core_Common_26_1_0 = new Package {
+			Id = "Xamarin.Android.Arch.Core.Common",
+			Version = "26.1.0",
+			TargetFramework = "MonoAndroid80",
+			References = {
+				new BuildItem.Reference("Xamarin.Android.Arch.Core.Common") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Arch.Core.Common.26.1.0\\lib\\MonoAndroid80\\Xamarin.Android.Arch.Core.Common.dll"
+				}
+			}
+		};
+		public static Package Android_Arch_Lifecycle_Common_26_1_0 = new Package {
+			Id = "Xamarin.Android.Arch.Lifecycle.Common",
+			Version = "26.1.0",
+			TargetFramework = "MonoAndroid80",
+			References = {
+				new BuildItem.Reference("Xamarin.Android.Arch.Lifecycle.Common") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Arch.Lifecycle.Common.26.1.0\\lib\\MonoAndroid80\\Xamarin.Android.Arch.Lifecycle.Common.dll"
+				}
+			}
+		};
+		public static Package Android_Arch_Lifecycle_Runtime_26_1_0 = new Package {
+			Id = "Xamarin.Android.Arch.Lifecycle.Runtime",
+			Version = "26.1.0",
+			TargetFramework = "MonoAndroid80",
+			References = {
+				new BuildItem.Reference("Xamarin.Android.Arch.Lifecycle.Runtime") {
+					MetadataValues = "HintPath=..\\packages\\Xamarin.Android.Arch.Lifecycle.Runtime.26.1.0\\lib\\MonoAndroid80\\Xamarin.Android.Arch.Lifecycle.Runtime.dll"
+				}
+			}
+		};
 	}
 }
 
diff --git a/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets b/src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets
@@ -271,6 +271,7 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
 	<_AndroidLibrayProjectAssemblyMapFile>$(_AndroidLibrayProjectIntermediatePath)map.cache</_AndroidLibrayProjectAssemblyMapFile>
 	<_AndroidProguardInputJarFilter>(!META-INF/MANIFEST.MF)</_AndroidProguardInputJarFilter>
 	<_AndroidAapt2VersionFile>$(IntermediateOutputPath)aapt2.version</_AndroidAapt2VersionFile>
+	<_AndroidNuGetStampFile>$(IntermediateOutputPath)$(MSBuildProjectName).nuget.stamp</_AndroidNuGetStampFile>
 
 	<!-- $(EnableProguard) is an obsolete property that should be removed at some stage. -->
 	<AndroidEnableProguard Condition="'$(AndroidEnableProguard)'==''">$(EnableProguard)</AndroidEnableProguard>
@@ -524,6 +525,7 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
     _CheckTargetFramework;
     _RemoveLegacyDesigner;
     _ValidateAndroidPackageProperties;
+    _CleanIntermediateIfNuGetsChange;
     $(BuildDependsOn);
     _CompileDex;
     $(_PostBuildTargets)
@@ -542,6 +544,7 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
     _CheckTargetFramework;
     _RemoveLegacyDesigner;
     _ValidateAndroidPackageProperties;
+    _CleanIntermediateIfNuGetsChange;
     $(BuildDependsOn);
   </BuildDependsOn>
 </PropertyGroup>
@@ -643,6 +646,23 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
 	</CreateProperty>
 </Target>
 
+<Target Name="_BeforeCleanIntermediateIfNuGetsChange">
+  <PropertyGroup>
+    <_NuGetAssetsFile Condition="Exists('$(ProjectLockFile)')">$(ProjectLockFile)</_NuGetAssetsFile>
+    <_NuGetAssetsFile Condition="'$(_NuGetAssetsFile)' == '' and Exists('packages.config')">packages.config</_NuGetAssetsFile>
+  </PropertyGroup>
+</Target>
+
+<Target Name="_CleanIntermediateIfNuGetsChange" DependsOnTargets="_BeforeCleanIntermediateIfNuGetsChange"
+    Inputs="$(_NuGetAssetsFile)"
+    Outputs="$(_AndroidNuGetStampFile)">
+  <CallTarget Targets="_CleanMonoAndroidIntermediateDir" />
+  <Touch Files="$(_AndroidNuGetStampFile)" AlwaysCreate="true" />
+  <ItemGroup>
+    <FileWrites Include="$(_AndroidNuGetStampFile)" />
+  </ItemGroup>
+</Target>
+
 <Target Name="_ResolveMonoAndroidFramework" DependsOnTargets="GetReferenceAssemblyPaths" >
 </Target>