Annotation based developer targeted library. Call any function from anywhere from a nice UI or web interface.
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DevFun - Developer (Fun)ctions

A developer targeted library to facilitate the development and testing of Android apps by enabling the invocation of arbitrary functions and code using tagging annotations.

By tagging (annotating) functions of interest, DevFun provides direct access to these functions at run-time through a number of means - such as an automatically generated "Developer Menu".

While developing some feature Z, there's nothing more annoying than having to go through X, to get to Y, to test your changes on Z. So it's not uncommon for developers to sometimes try and shortcut that process... Which inevitably leads to your humiliation when your colleagues notice you committed said shortcut.

Simply adding the @DeveloperFunction annotation to a function/method is all that is needed.

class MyClass {
    fun someFunction() {
        // ...

See the documentation for advanced usage, including custom names, custom arguments, groups, function processing, etc.

Quick Start

Project Setup

  • REQUIRED Android Gradle 3.0.0+ (due to #37140464 and KT-16589)
  • Recommended to use Kotlin 1.2.51, though should work down to 1.1.1 (somewhat untested)
  • Recommended to use KAPT3 (apply plugin: 'kotlin-kapt'), though KAPT1 also works
  • Compiled with minSdkVersion >= 15
  • Built against Android Support libraries 27.1.1

Build File build.gradle

Add the DevFun Gradle plugin to your build script.

If you can use the Gradle plugins block (which you should be able to do - this locates and downloads it for you):

plugins {
    id 'com.nextfaze.devfun' version '1.2.1'

Or the legacy method using apply;
Add the plugin to your classpath (found in the jcenter() repository):

buildscript {
    dependencies {
        classpath 'com.nextfaze.devfun:devfun-gradle-plugin:1.2.1'

And in your build.gradle:

apply plugin: 'com.nextfaze.devfun'


Can be categorized into 5 types:

  • Main: minimum required libraries (annotations and compiler).
  • Core: extend the functionality or accessibility of DevFun (e.g. add menu/http server).
  • Inject: facilitate dependency injection for function invocation.
  • Util: frequently used or just handy functions (e.g. show Glide memory use).
  • Invoke UI: provide additional views for the invocation UI (e.g. a color picker for int args)

Add jcenter() repository or via bintray directly: (will be put on MavenCentral eventually)

repositories {
    maven { url '' }

Add dependencies to build.gradle:

    // Annotations, Compiler, and Developer Menu
    kaptDebug 'com.nextfaze.devfun:devfun-compiler:1.2.1'
    implementation 'com.nextfaze.devfun:devfun-annotations:1.2.1'
    debugImplementation 'com.nextfaze.devfun:devfun-menu:1.2.1'
    // Dagger 2.x component inspector - only if using Dagger 2.x!
    debugImplementation 'com.nextfaze.devfun:devfun-inject-dagger2:1.2.1'
    // Chrome Dev Tools JavaScript console integration
    debugImplementation 'com.nextfaze.devfun:devfun-stetho:1.2.1'
    // HTTP server and simple index page
    debugImplementation 'com.nextfaze.devfun:devfun-httpd:1.2.1'
    debugImplementation 'com.nextfaze.devfun:devfun-httpd-frontend:1.2.1'
    // Glide util functions
    debugImplementation 'com.nextfaze.devfun:devfun-util-glide:1.2.1'
    // Leak Canary util functions
    debugImplementation 'com.nextfaze.devfun:devfun-util-leakcanary:1.2.1'
     * Transitively included libs - in general you don't need to add these explicitly (except maybe for custom module libs).
    // Adds view factory handler for @ColorPicker for invoke UI - transitively included via devfun-menu
    // debugImplementation 'com.nextfaze.devfun:devfun-invoke-view-colorpicker:1.2.1'
    // DevFun core - transitive included from menu et al.
    // debugImplementation 'com.nextfaze.devfun:devfun:1.2.1' 

That's it!

Start adding @DeveloperFunction annotations to methods (can be private, and arguments will be injected or rendered as needed), and these will be added to the menu.

For advanced uses and configuration such as custom categories, item groups, argument providers, etc.

  • See the wiki, or
  • Extensive (Dokka generated) documentation can be accessed at GitHub Pages.

Key Features

Invocation UI for manual entry

Zero-configuration Setup

A Content Provider is used to automatically initialize DevFun, and most simple Dagger 2.x object graphs should work.
See Initialization for more information or for manual initialization details.

Context Aware

Attempts are made to be aware of the current app state, in that the "Context" category should contain only the items that are relevant to the current screen (i.e. methods tagged in the current Activity and any attached Fragments).

Invocation UI

If an annotated function has argument types that cannot be injected then DevFun will attempt to render a UI for you to manually set them (right). The arguments can be injected or otherwise. Simple types and a color picker UI is provided by default.

Optional annotations can be added to configure/tweak their state and custom types can be added:

  • @From for an initial value.
  • @Ranged on a number type for a constrained value.
  • @ColorPicker on an int types renders a color picker.


DevFun is designed to be modular, in terms of both its dependencies (limiting impact to main source tree) and its plugin-like architecture. See Components for more information.

Component Dependencies

And More

  • Keep your methods private, but be able to easily invoke them when needed.
  • Avoid those one-time development conditions.
  • Provide future developers (undoubtedly yourself) access to these quick dev switches "oh, there's already a way to toggle xyz".


Developer Menu on authenticate screen

Developer Menu

An easy to use developer menu accessible at any time via a floating cog button added by the devfun-menu module (right):

Can be accessed via a floating cog, the tilde/grave key `, or the volume button sequence down, down, up, down.

Invocation UI

When DevFun can't inject a type it will attempt to render a UI for manual entry. By default all simple type are supported. View factories can be provided to allow DevFun to render a custom view for other types.

An example of this is the @ColorPicker annotation used by the menu cog overlay (second right) the renders a color picker view for an int parameter.

Overlay Loggers

Adding @DeveloperLogger to a property, type, or function will generate a floating text overlay that (by default) updates once a second with the .toString() of that reference. The loggers are context-aware with additional configuration options available with a long-press.

This feature is somewhat experimental in that it's quite new and has not been used extensively beyond the demo app and a few in-house apps so please report any issues you have with it.

Adding @DeveloperProperty as well will allow you to tap on the overlay to edit its value using the invocation UI system.

Local HTTP Server (experimental)

Using the HTTPD modules devfun-httpd and devfun-httpd-frontend, a local server can be exported using ADB adb forward tcp:23075 tcp:23075 and accessed via http://localhost:23075 where you can invoke functions from your browser: Authenticate screen via local HTTP server Invocation UI with custom view handling

Stetho Integration (experimental)

With the devfun-stetho module functions are exported and available to be invoked directly from Chrome's Developer Tools console:
Stetho integration function list

Dependency Injection

DevFun uses a simple InstanceProvider interface to source object instances.

Providers are checked most recently added first (i.e. user-supplied providers will be checked first). A number of default providers are added, including;

  • Android Application, Activity, Context (current Activity or Application), Fragment, and View types.
  • All DevFun related objects
  • Support for Kotlin object instances
  • Object instantiation (new instance + DI). (opt-in only)

For more details see wiki entry Dependency Injection.

Dagger 2.x Support

Easiest method is to use devfun-inject-dagger2 module - by default it should work just by adding the dependency depending on your setup (if the components are located in the Application and/or Activity classes). However if you use extension functions to retrieve your components (or you put them in weird places for whatever reason), then you can annotate the functions/properties/getters with @Dagger2Component.

If all else fails you can define your own instance provider with utility functions from devfun-inject-dagger2 (see the demo for an example).

Supported Versions

Dagger has been tested on the demo app from versions 2.4 to 2.16, and various in-house apps on more recent versions, and should function correctly for most simple scopes/graphs.

For reference the demo app uses three scopes; Singleton, Retained (fragments), and an Activity scope. It uses both type-annotated scoping and provides scoping. It keeps component instances in the activity and obtains the singleton scope via an extension function. In general this should cover most use cases - if you encounter any problems please create an issue.


DevFun uses a number of methods iteratively to introspect the generated components/modules, however depending on scoping, visibility, and instantiation of a type it can be difficult to determine the source/scope in initial (but faster) introspection methods.

When all else fails DevFun will use a form of heavy reflection to introspect the generated code - types with a custom scope and no constructor arguments are not necessarily obtainable from Dagger (depends on the version) by any other means. To help with this ensure your scope is @Retention(RUNTIME) so that DevFun wont unintentionally create a new instance when it can't find it right away.

Due to the way Dagger generates/injects it is not possible to obtain the instance of non-scoped types from the generated component/module as its instance is created/injected once (effectively inlined) at the inject site. It is intended to allow finding instances based on the context of the dev. function in the future (i.e. if the dev. function is in a fragment then check for the injected instance in the fragment etc.) - if this is desirable sooner make a comment in the issue #26.

Module Dependencies

Though the inject module uses Dagger, it does not export it as a dependency (declared compileOnly). This is to stop DevFun from affecting your project's version. The inject module only uses references to Dagger's annotations @Component, @Module, and @Provides. It also references annotations from javax.inject (which is pulled in from Dagger). It does not use/generate any other aspect of the Dagger APIs explicitly (only via reflection during introspection) and thus is compatible with all Dagger versions from 2.4.


Java Compatibility

DevFun was design with Kotlin in mind. Having said that, Kotlin is implicitly compatible with Java and thus DevFun should work as expected when used in/with Java code (you will still need to use KAPT however as the generated code is in Kotlin).

Submit an issue if you encounter any problems as it is desirable that there be 100% compatibility.


See the wiki for advanced configuration details.
Documentation (Dokka) can be accessed at GitHub Pages.


SLF4J is used for all logging.

By default trace is disable unless library is a snapshot build (i.e. BuildConfig.VERSION.endsWith("-SNAPSHOT")).
This can also be toggled at any time via devFunVerbose

Kotlin stdlib Conflict

DevFun was compiled using Kotlin 1.2.51.
Earlier versions of Kotlin are largely untested and unsupported (this is unlikely to change unless explicitly requested).

Thus if you receive a dependency conflict error such as:
Error: Conflict with dependency 'org.jetbrains.kotlin:kotlin-stdlib' in project ':app'. Resolved versions for app (1.1.2-3) and test app (1.1.1) differ. See for details. The simplest resolution is updating your Kotlin version to match.

If this is not possible, you can force Gradle to use a specific version of Kotlin:

// Force specific Kotlin version
configurations.all {

Gradle Plugin and APT Options

The gradle plugin com.nextfaze.devfun should automatically handle/provide the annotation processor with your project build configuration, but can also be configured within your build file (DevFunExtension):

devFun {
    packageSuffix = "..."
    packageRoot = "..."
    packageOverride = "..."

However due to limitations of the build system this can/is somewhat derived with string splitting and/or by using known relative paths to processor outputs as needed.
e.g. To determine the package/buildType/flavor, is located as:


If your build system has been customised or for whatever reason the processor cannot identify your build information then you can manually specify the required information using annotation processor options (values via APT args will override devFun {} gradle plugin values).
Apply using Android DSL:

 android {
      defaultConfig {
          javaCompileOptions {
              annotationProcessorOptions {
                  argument 'devfun.argument', 'value'

See com.nextfaze.devfun.compiler for list of options.


Support for proguard exists, however it has not been tested extensively beyond the demo app.

If you wish to use DevFun with Proguard you will need to configure your app to keep DevFun related code (the DevFun libraries handle themselves). See the demo for a sample and related details.

Rules that are supplied by DevFun libraries can be found in (the Glide util module also adds a couple).

If everything used by DevFun (the annotated classes and functions) is public or internal (see demo rules otherwise) then all you need to do is keep the generated file:

# Keep DevFun generated class
-keep class** extends com.nextfaze.devfun.generated.DevFunGenerated

For non-public/internal you will need to adjust your proguard config appropriately, or more simply use @Keep on the classes/functions.

Function Transformers

When DevFun processes the generated code (such as when you try to open the DevMenu), functions/references are put through a "transformation" process that results in something the modules use to render their various views. Custom transformers can be specified on the @DeveloperFunction annotation. Thus at the moment transformers needs to be in the main source tree (or wherever it's being used) as its class is referenced in the annotation.

If for some reason you cannot use proguard but need sensitive code/values removed (e.g. auto-login items for test accounts à la SignInFunctionTransformer), then surrounding the values in a if (BuildConfig.DEBUG) { ... } else { .. } block will allow the compiler to remove it as "dead code" during release builds - I'm looking into better ways to handle this (suggestions welcome).

Getting ClassInstanceNotFoundException

When DevFun is unable to find the instance of a type it throws ClassInstanceNotFoundException - this happens when there is no instance provider capable of providing the type to DevFun. If there is a view factory defined for the type the invocation UI will be shown for manual entry, otherwise and error dialog will be shown with the exception details.

See the wiki entry on Dependency Injection for details on how to set up custom instance providers.

For a quick and dirty fix utility functions captureInstance and singletonInstance can create an instance provider that you can give to DevFun devFun.instanceProviders += singletonInstance { ... }.


class SomeType : BaseType

val provider = captureInstance { someObject.someType } // triggers for SomeType or BaseType
val someOtherThing = singletonInstance { MyClass() } // lazy initialization
val anotherThing = singletonInstance { devFun.get<MyType>() } // lazy initialization using DevFun to inject/create type

If you want to reduce the type range then specify its base type manually:

val provider = captureInstance<BaseType> { someObject.someType } // triggers only for BaseType

Be aware of leaks! The lambda could implicitly hold a local this reference.

Missing Items

If you are using Android Gradle versions prior to 3.0.0, then this is likely due to tooling issues where APT generated resources of Application projects were not packaged into the APK (see #37140464 and KT-16589).
The extreme hacks/support for this were removed in DevFun 0.1.2 and are unlikely to be re-implemented.
Android Gradle 3.0.0 and 3.1.0 are quite stable and its unlikely newer versions of Android Studio will support earlier than that anyway.


Open project using Android Studio (usually latest preview). Opening in IntelliJ is untested, though it should work.

git clone
cd dev-fun

Build using standard gradle.

./gradlew build

See the included demo project for a simple app.

./gradlew :demo:installDebug
adb shell monkey -p com.nextfaze.devfun.demo.debug -c android.intent.category.LAUNCHER 1
  • See for building artifacts and documentation.


DevFun is intended for developers (though it can be handy for testers). Because of this the API is intended to be quite open and flexible. So if there is anything you want or think should be added then create an issue or PR and more than likely it will be accepted.

  • Any bugs please report (desirably with reproduction steps) and/or PR/fix them.
  • Any crashes please report with the stack trace (doesn't need to be reproducible) and it'll be fixed (if DevFun's fault) and/or wrapped with proper error handling functionality.

Feel free also to submit your own handy util functions or whatever for addition.


Copyright 2018 NextFaze

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
See the License for the specific language governing permissions and
limitations under the License.