Xamarin.Android Environment

Execution Environment

The execution environment is the set of environment variables and Android system properties that influence program execution. Android system properties can be set with the adb shell setprop command, while environment variables can be set by setting the debug.mono.env system property:

## Enable GREF logging
adb shell setprop debug.mono.log gref

## Set the MONO_LOG_LEVEL and MONO_LOG_MASK environment variables
## so that additional Mono messages will be written to `adb logcat`.
adb shell setprop debug.mono.env "'MONO_LOG_LEVEL=info|MONO_LOG_MASK=asm'"

Android system properties are set for all processes on the target device.

Starting with Xamarin.Android 4.6, both system properties and environment variables may be set or overridden on a per-app basis by adding an environment file to the project. An environment file is a Unix-formatted plain-text file with a Build action of AndroidEnvironment. The environment file contains lines with the format key=value. Comments are lines which start with #. Blank lines are ignored.

If key starts with an uppercase letter, then key is treated as an environment variable and setenv(3) is used to set the environment variable to the specified value during process startup.

If key starts with a lowercase letter, then key is treated as an Android system property and value is the default value: Android system properties which control Xamarin.Android execution behavior are looked up first from the Android system property store, and if no value is present then the value specified in the environment file is used. This is to permit adb shell setprop to be used to override values which come from the environment file for diagnostic purposes.

Xamarin.Android Environment Variables

Xamarin.Android supports the XA_HTTP_CLIENT_HANDLER_TYPE variable, which may be set either via adb shell setprop debug.mono.env or via the $(AndroidEnvironment) Build action.


The assembly-qualified type which must inherit from HttpMessageHandler and is constructed from the HttpClient() default constructor.

In Xamarin.Android 6.1, this environment variable is not set by default, and HttpClientHandler will be used.

Alternatively, the value Xamarin.Android.Net.AndroidClientHandler may be specified to use java.net.URLConnection for network access, which may permit use of TLS 1.2 when Android supports it.

Added in Xamarin.Android 6.1.

Xamarin.Android System Properties

Xamarin.Android supports the following system properties, which may be set either via adb shell setprop or via the $(AndroidEnvironment) Build action.

  • debug.mono.debug
  • debug.mono.env
  • debug.mono.gc
  • debug.mono.log
  • debug.mono.max_grefc
  • debug.mono.profile
  • debug.mono.runtime_args
  • debug.mono.trace
  • debug.mono.wref


The value of the debug.mono.debug system property is an integer. If 1, then behave "as if" the process were started with mono --debug. This generally shows file and line information in stack traces, etc., without requiring that the app be started from a debugger.


Contains a |-separated list of environment variables.


The value of the debug.mono.gc system property is an integer. If 1, then GC information should be logged.

This is equivalent to having the debug.mono.log system property contain gc.


Controls which additional information Xamarin.Android will log to adb logcat. It is a comma-separated string (,), containing one of the following values:

  • all: Print out all messages. This is seldom a good idea, as it includes lref messages.
  • assembly: Print out .apk and assembly parsing messages.
  • gc: Print out GC-related messages.
  • gref: Print out JNI Global Reference messages.
  • lref: Print out JNI Local Reference messages.


    This will really spam adb logcat. In Xamarin.Android 5.1, this will also create a .__override__/lrefs.txt file, which can get gigantic. Avoid.

  • timing: Print out some method timing information. This will also create the files .__override__/methods.txt and .__override__/counters.txt.


The value of the debug.mono.max_grefc system property is an integer. It's value overrides the default detected maximum GREF count for the target device.

Please note: This is only usable with adb shell setprop debug.mono.max_grefc as the value will not be available in time with an environment.txt file.


The debug.mono.profile system property enables the profiler. It is equivalent to, and uses the same values as, the mono --profile option. (See the mono(1) man page for more information.)


The debug.mono.runtime_args system property contains additional options that should be parsed by mono.


The debug.mono.trace system property enables tracing. It is equivalent to, and uses the same values as, the mono --trace option. (See the mono(1) man page for more information.)

In general, do not use. Use of tracing will spam adb logcat output, severaly slow down program behavior, and alter program behavior (up to and including adding additional error conditions).

Sometimes, however, it allows some additional investigation to be performed...


The debug.mono.wref system property allows overriding the default detected JNI Weak Reference mechanism. There are two supported values:

  • jni: Use JNI weak references, as created by JNIEnv::NewWeakGlobalRef() and destroyed by JNIEnv::DeleteWeakGlobalREf().
  • java: Use JNI Global references which reference java.lang.WeakReference instances.

java is used, by default, up through API-7 and on API-19 (Kit Kat) with ART enabled. (API-8 added jni references, and ART broke jni references.)

This system property is useful for testing and certain forms of investigation. In general, it should not be changed.


First introduced in Xamarin.Android 6.1, this environment variable declares the default HttpMessageHandler implementation that will be used by the HttpClient. By default this variable is not set, and Xamarin.Android will use the HttpClientHandler.



The underlying Android device must support TLS 1.2. Android 5.0 and later support TLS 1.2


## Comments are lines which start with '#'
## Blank lines are ignored.

## Enable GREF messages to `adb logcat`

## Clear out a Mono environment variable to decrease logging