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Xamarin.Android 7.3

Xamarin.Android 7.3: Yay, more fixes!

OSS Core

Xamarin.Android 7.0 is the first release to use the open-source repositories:

System Requirements

Xamarin.Android 7.3 requires JDK 1.8 to use the Android Nougat (API 24) APIs. Using the Android build-tools r24+ package may also require using JDK 1.8. You can continue to use earlier versions of the JDK when using earlier build-tools packages and when targeting earlier Android API levels:

Additionally, a 64-bit version of the JDK is required to use custom controls in the Android designer.

The simplest option is to install the 64-bit version of JDK 1.8 since it is backwards compatible with all of the previous API levels and supports the new Android designer features.

Vulkan Support

Android v7.0 Nougat adds support for the Vulkan API. Vulkan support will not be distributed as part of the core Xamarin.Android binding. Instead, please use the VulkanSharp NuGet package, and the XLogo sample app.

Native Library Use

Due to a change by Google, Android N will now only permit linking to NDK-provided native libraries. is not an NDK-provided native library. Consequently, existing apps using e.g. Mono.Data.Sqlite.dll will crash when running on Android N. This may include other SQLite-using assemblies, not distributed with Xamarin.Android.

Xamarin.Android 7.0 updated Mono.Data.Sqlite.dll to include a custom built version of, named

All Developers need to audit their code for P/Invoke and ensure that referenced native libraries are either included in the Android NDK, or are included within the app.apk itself. The only Xamarin.Android-provided assembly impacted by this change is Mono.Data.Sqlite.dll.

Known Issues

Xamarin.Android changed the default GC Bridge from old to tarjan.

Unfortunately, a few bugs have been reported which suggest a bug within the Tarjan GC bridge.

If this happens, create an @(AndroidEnvironment) file and add the following line:


This will cause the app to use the previous GC bridge.


Xamarin.Android is a hotfix release which fixes $(BundleAssemblies) support.

Bug Fixes

  • 56786: Command line build fails: fatal error: mono/metadata/mono-config.h: No such file or directory

Xamarin.Android 7.3.1

Xamarin.Android 7.3.1 contains bug fixes.

In particular, fixes a bug responsible for a large slowdown in Xamarin.Forms apps.

Bug Fixes

  • 56238: Could not connect to debugger after upgrading to VS 2017 15.2
  • 56275: Partial: Unable to copy appname.dll from obj to bin because it is being used by another process.
    A cause of file sharing within pdb2mdb is fixed, but there are other known issues.

Integrated Mono Features/Fixes

Xamarin.Android uses Mono 5.0.0 commit 5077205.

  • 54448: Unable to revert to thread-local storage for CurrentThread.CultureInfo
  • 55041: Stripping mscorlib in simple example changes IntPtr (5) behavior?
  • 55087: System.NotSupportedException: Stack walks are not supported on this platform - System.Reflection.MethodBase.GetCurrentMethod
  • 55681: System.Reflection.Emit.ModuleBuilder.build_metadata bug when running FAKE's test suite
  • 56240: Performance Degradation When Using Expressions
  • 56260: Possible regression: This stream does not support writing at System.IO.Compression.DeflateStream.BeginWrite

Xamarin.Android 7.3

The Xamarin.Android 7.3 release primarily includes bug fixes.

New Features

Bundled ProGuard

Previous releases would use the copy of ProGuard included with the Android SDK in order to use @(ProguardConfiguration) files and various other features which rely on ProGuard.

Unfortunately the Android SDK distributes a version of ProGuard which doesn't support Java 8-generated bytecode, resulting in pain and suffering when attempting to use later API levels (which require a Java 8 compiler).

The Xamarin.Android 7.3 release includes its own copy of ProGuard 5.3.2, supporting use of the Java 8 compiler with Xamarin.Android projects.

Experimental Features

Xamarin.Android 7.3 retains the experimental features from previous releases:

TLS 1.2 support in WebRequest

Xamarin.Android 7.1 added AndroidClientHandler, which uses the native Java APIs to provide TLS 1.2 support. However, there are two problems with AndroidClientHandler:

  1. It can only be used with HttpClient, and
  2. It requires Android 5.0 and later to operate. (Prior Android versions might not support TLS 1.2, and since AndroidClientHandler uses the native Java TLS stack...)

To solve these problems, Boring SSL can be used as the lowest-level TLS implementation. Originally announced last September, Boring SSL can be embedded within a Xamarin.Android application, allowing HttpWebRequest to communicate with TLS 1.2 endpoints. When enabled, the normal HttpClient stack also uses Boring SSL.

To enable use of BoringSSL, add the $(AndroidTlsProvider) MSBuild property to the application project, with a value of btls:


When enabled, a new shared library will be present within the .apk.

The default value of the $(AndroidTlsProvider) MSBuild property is the empty string, i.e. not set, which will use the managed TLS implementation, which does not support TLS 1.2.

The default value may change in a future release.

Concurrent GC Support

The new $(AndroidEnableSGenConcurrent) MSBuild property which controls whether or not the concurrent GC is enabled.

$(AndroidEnableSGenConcurrent) is a boolean value. When True, then Mono's GC is set to marksweep-conc; when False, then Mono's GC is set to marksweep.

The default value is False.

See Mono's ConcurrentSGen documentation for more information.

Improved Fast Deployment

Fast Deployment is a way to avoid rebuilding and redeploying Android Packages (.apk files) when assemblies have changed in a way that doesn’t require changing the generated Android Callable Wrappers or altered any included Android Assets and Resources.

Xamarin.Android 7.0 will optionally allow Android Assets, Resources, and compiled Java libraries to particpate in fast deployment as well, further reducing the number of situations in which a possibly slow .apk rebuild and redeploy will be required.

This new behavior is disabled by default. It will be enabled by default in the Xamarin.Android 7.1 series.

To enable this new functionality, set the $(AndroidFastDeploymentType) MSBuild property to Assemblies:Dexes:


Adding Resources to the Default Project

For example, assume a new (default) Application project which has already been deployed to a target device.

  1. Copy Resources\layout\Main.axml to Resources\layout\Another.axml, and add Resources\layout\Another.axml to the project.
  2. Run the project.

(2) will require that the .apk be rebuilt and re-deployed to the target. In previous versions, (2) could take 16 seconds.

With the new system


Add some small benchmarks about what happens during dev when code changes, or a resource changes, numbers before/after

File name and line number information in release builds

File name and line number information in Release builds is supported through the build-time generation of .pdb files (and .msym files for AOT builds). The generation of the sequence points is controlled by the new $(MonoSymbolArchive) MSBuild property, which must be set to True to enable generation:


You also need to set $(DebugSymbols) to True and $(Optimize) to True for your release build. This will ensure that your assemblies do not contain debug information but that the required data is stored in the .pdb/.mSYM files.

When enabled, a new $(OutputPath)\@PACKAGE_NAME@.mSYM directory will be created which contains all information required to correlate IL offset information (found in stack traces) back to file name and line number information through the use of the mono-symbolicate tool.

Next, grab a crash log which an unhandled exception

adb logcat -d > errors.txt

Finally, use mono-symbolicate to convert the errors to contain file and line numbers:

mono-symbolicate path-to-dll-in-.mSYM-directory path-to-errors.txt

mono-symbolicate can be found at:

  • macOS: /Library/Frameworks/Xamarin.Android.framework/Commands/mono-symbolicate
  • Windows: %ProgramFiles(x86)%\MSBuild\Xamarin\Android\mono-symbolicate.exe

For example, given an errors.txt with the contents:

I/MonoDroid( 1545): System.Exception: wow it broke
I/MonoDroid( 1545):   at CrashApp.MainActivity+<OnCreate>c__AnonStorey0.<>m__0 (System.Object , System.EventArgs ) [0x00030] in <filename unknown>:0
I/MonoDroid( 1545):   at Android.Views.View+IOnClickListenerImplementor.OnClick (Android.Views.View v) [0x00014] in <filename unknown>:0
I/MonoDroid( 1545):   at Android.Views.View+IOnClickListenerInvoker.n_OnClick_Landroid_view_View_ (IntPtr jnienv, IntPtr native__this, IntPtr native_v) [0x00011] in <filename unknown>:0
I/MonoDroid( 1545):   at (wrapper dynamic-method) System.Object:5616285d-461b-4005-a31b-d4637a8cdddc (intptr,intptr,intptr)

mono-symbolicate will translate the above into:

I/MonoDroid( 1545): System.Exception: wow it broke
I/MonoDroid( 1545):   at CrashApp.MainActivity+<OnCreate>c__AnonStorey0.<>m__0 (System.Object , System.EventArgs ) [0x00030] in /Users/dean/Projects/CrashApp/CrashApp/MainActivity.cs:30
I/MonoDroid( 1545):   at Android.Views.View+IOnClickListenerImplementor.OnClick (Android.Views.View v) [0x00014] in /Users/dean/Documents/Sandbox/Xamarin/dellismonodroid/src/Mono.Android/platforms/android-19/src/generated/Android.Webkit.WebBackForwardList.cs:68
I/MonoDroid( 1545):   at Android.Views.View+IOnClickListenerInvoker.n_OnClick_Landroid_view_View_ (IntPtr jnienv, IntPtr native__this, IntPtr native_v) [0x00011] in /Users/dean/Documents/Sandbox/Xamarin/dellismonodroid/src/Mono.Android/platforms/android-19/src/generated/Android.Webkit.WebBackForwardList.cs:23
I/MonoDroid( 1545):   at (wrapper dynamic-method) System.Object:5616285d-461b-4005-a31b-d4637a8cdddc (intptr,intptr,intptr)

Notice that the <filename unknown>:0 messages were translated into appropriate filename and line number information.

Known Issues

Bug Fixes

  • 129: Fix class-parse to use InvariantCulture to format floating-point values.
  • 12935: sensorPortrait should be sensorPortait
  • 36079: $(AndroidExplicitCrunch) does not parallelize calls to aapt
  • 50587: AndroidClientHandler.AllowAutoRedirect = false makes HTTPS requests fail as no body returned
  • 51804: AndroidClientHandler has unobserved aggregate exception and Java.IO Exceptions in place of WebException
  • 52521: AndroidClientHandler does not support 304 redirect
  • 53054: AAPT packaging error ignored
  • 53787: Application crashes onto the Simulator and Physical device when running on Debug mode

Integrated Mono Features/Fixes

Xamarin.Android uses Mono 5.0 commit e464ddae.

Among the many highlights in Mono 5.0 is support for Portable .pdb files.

  • 7467: DefaultNonPersistentConnectionLimit is to low
  • 12571: Usage of XElement with XmlAnyElementAttribute is not supported by XmlSerializer
  • 16628: ilasm crashes on input file
  • 19594: WebException.Response is null when https request needs proxy authentication
  • 34715: HttpClient incorrectly works with multiple headers
  • 34802: Debugger crash on break-all, step into sequence.
  • 35536: Dns.GetHostEntry no longer supports IPv6
  • 35662: Type System.ServiceModel.Security.Tokens.BinarySecretSecurityToken is missing in assembly System.IdentityModel
  • 39444: Action ReflectedType differs from Delegate ReflectedType for virutal methods
  • 39832: SIGSEGV when running roslyn
  • 40603: Mono can't parse Date in DB wich is in format: "2016-02-04 10:39:11Z"
  • 41133: System.MethodAccessException: Method System.Net.WebHeaderCollection:AddValue (string,string)' is inaccessible from method System.Net.Http.HttpClientHandler
  • 41914: Race condition in named mutex
  • 42226: WCF client Expecting FaultException<TDetail> raising NotImplemented Exception instead When <FaultActor> element is provided.
  • 42271: COOP: gc unsafe mode when printing native backtrace causes crash if GC is triggered
  • 42584: InternalError / Crash when using System.Net.Http and PCL library
  • 42715: Directory.GetFiles & AllDirectories might fail
  • 42843: XmlSerializer does not deserialize UTC Time values on Xamarin.Android but works well on windows.
  • 43921: System.Threading.ThreadHelper.ThreadStart_Context tries to allocate, crashes
  • 44025: FTP download issue with IPv6
  • 44109: NetworkCredential does not convert SecureString
  • 44164: gosharp-regexp benchmark triggers unwinding crash when profiling
  • 44168: Can use non-accessible member with nameof
  • 44296: Multicast not working on Android 7.0 devices
  • 44341: No way of updating async method local variables
  • 44381: Debugger crash with domain unloading and VSTU
  • 44402: Array doesn't implement non-generic IEnumerable
  • 44406: Xamarin.Mac.Socket exception:An address incompatible with the requested protocol was used
  • 44413: HttpHeaders.TryAddWithoutValidation behaves differently from .NET
  • 44440: Attempting to JIT error in function with pointer arithmetic
  • 44549: Ide Shuts down: System.ArgumentException: Item has already been added. Key in dictionary: 'XamlG' Key being added: 'XamlG'
  • 44552: Domain end unload event arrives before start unload event
  • 44624: Connecting to SQL Server using IPv4 exception.
  • 44707: RemotingConfiguration.Configure() Throws RemotingException Because it Cannot Load 'machine.config'
  • 44714: xbuild fails to find VB.NET compiler
  • 44729: Type.GetType("blah",true,false) throws TypeLoadException without message
  • 44751: Incorrect code flow analysis with goto and out parameter causes CS0177
  • 44843: SqlCommand.ExecuteReaderAsync throws NotImplementedException
  • 44937: System.Diagnostics.StartProcess does not detect dotnetcore compiled assemblies as managed
  • 44974: [pdb] stepping over is not working
  • 44978: HttpClientHandler.SendAsync should throw HttpRequestException for proxy auth failure
  • 44982: SourceFileFilter does not filter on specific file when static ctor exists
  • 44994: DeflateStream decompression is incomplete if reading byte-by-byte
  • 45108: Proxy credentials not used for https url
  • 45129: Uri.IsWellFormedUriString returns incorrect result for relative uris beginning with slash
  • 45131: Array of double*[] being treated as non-blittable when marshaled
  • 45137: Seeing new AAPT0000 errors when building certain projects against master
  • 45286: C# string interpolation line does not compile on OSX but does on MSBuild
  • 45371: SIGSEGV occurs when making call from native to managed code
  • 45683: Add fallback implementation to compile with glibc that lacks CPU_COUNT
  • 45761: After network reconnected, web request fails for a couple of minutes with a NameResolutionFailure
  • 45774: Wrong scopes in .mdb in case of foreach loop
  • 45788: Marshaling a native NULL pointer to a managed array creates a new zero sized array
  • 45841: x86 codegen produces wrong result for float operation
  • 45994: TLS connections on non-standard ports result in incorrect Server Name Indication value
  • 46175: If the RSA will be used by multiple threads, it has a variety of exceptions.
  • 46190: Overload resolution fails in a case where methods use a named parameter in different positions
  • 46250: Type.GetType with throwOnError true doesn't throw for a generic instance type with too few generic arguments
  • 46288: function mono_string_to_byvalwstr may cause access violation
  • 46456: CultureInfo("ug-CN") not found in Xamarin.Android and Xamarin.iOS
  • 46536: [coop] mono_os_mutex_destroy: pthread_mutex_destroy failed with "Device or resource busy" (16)
  • 46538: System.Net.WebClient.OpenReadAsync/OpenReadTaskAsync do not work for file:// URLs
  • 46602: MobileAuthenticatedStream.AuthenticateAsServer() via EndPointListener
  • 46712: btls fails to build with gcc is v4.4.7 or earlier as they lack alignof/alignas
  • 46739: Assembly::Evidence property crashes for unbaked assembly
  • 46806: opspecial011.Program.DynamicCSharpRunTest test in ms-test-suite fails with "Operator '+' cannot be applied to operands"
  • 46929: Datetime error on
  • 47152: AOT attempts at Xamarin.Mac.dll crash mono
  • 47156:
    • Assertion at class.c:2093
  • 47205: Uri.TryCreate throws exception
  • 47221: Thread.Name can only be set once inside async callback
  • 47353: Mono.CSharp.MetadataImporter.set_IgnoreCompilerGeneratedField not found when running Cake on Mono 4.8
  • 47549: Chunked encoding error when writing zero buffer
  • 47672: Invalid error CS0314
  • 47762: EXC_BAD_ACCESS when unloading assembly
  • 47867: assert at sre.c:1553 in System.Reflection.Emit.TypeBuilder.create_runtime_class
  • 48016: System.Net.NetworkInformation.DnsAddresses is always empty. Fix included.
  • 48429: Mono fails to marshal fixed buffer fields as unicode
  • 48516: ZipArchive.Save attempts to set position and seek non-seekable streams
  • 49056: Assertion at /Users/builder/data/lanes/3969/44931ae8/source/xamarin-macios/external/mono/mono/mini/mini-generic-sharing.c:2351, condition `info' not met
  • 49686: System.NotImplementedException at System.Reflection.Emit.DynamicMethod.GetCustomAttributes (System.Type attributeType, Boolean inherit)
  • 50242: Cannot use MSXSL format-date/format-time XPath extension functions on non-Windows platforms
  • 50789: JITting large method fails (condition lvregs_len < 1024 not met)
  • 51166: mcs converts new T[0] into Array.Empty<T>() which is not conform C# spec
  • 51219: ves_icall_System_Threading_ThreadPool_RequestWorkerThread called after threadpool cleanup
  • 51330: Inline Enum::GetHashCode implementation
  • 51506: C# compiler fails for constrained generics with yield return
  • 51545: [Crash] mono_threads_platform_set_priority: unknown policy 3
  • 51562: NullReferenceException in BTLS X509CertificateImplBtls.Import()
  • 51653: mono_thread_info_wait_one_handle ignored alertable argument
  • 52157: SocketTest.ConnectedProperty test fails in FullAOT Linux runs
  • 52345: Process has exited, so the requested information is not available
  • 52429: Shutdown hang then crash in Finalizer thread
  • 52437: Random NullReferenceExceptions in StringBuilder.ThreadSafeCopy
  • 52448: StreamContent apparently needs to rewind stream before sending it
  • 52475: MTOUCH: error MT3001: Could not AOT the assembly
  • 52549: error: mono_w32socket_convert_error: no translation into winsock error for (41) "Protocol wrong type for socket"
  • 52600: Full AOT: Strange combination of structs, generics, and enums causes runtime failure
  • 52845: [Cycle 9] Satellite assemblies not bundled when using "Bundle assemblies into native code" due to "unknown escape sequence" error from gcc during mkbundle step
  • 52866: F# sprintf AOT bug still exists
  • 52899: mprof-report missing filenames in coverage xml output when using portable pdbs
  • 53066: Can't Build Project in Debug with "Could not AOT the assembly"
  • 53231: csc doesn't unify same file passed multiple times when one path is relative
  • 53278: Two coreclr SIMD test failures (one regression from 4.8)
  • 53481: The threadpool crashes on XS CI
  • 53684: Crash when enumerating directory and selecting the first file
  • 53689: [Test] Certificate7 disabled due to SecCertificateCreateWithData does different things on 10.11 vs 10.12 with invalid certificates
  • 53843: Mono deadlocks on shutdown while waiting for a process which has died
  • 53890: Regression: Native crash while running tests with xunit with mono 2017-02 branch, works with
  • 55148: Debugger checks type which is possibly never used

API Changes

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