Add docs on building from source

docs/AndroidBuildingFromSource.md

@@ -0,0 +1,106 @@
+---
+id: android-building-from-source
+title: Building React Native from source
+layout: docs
+category: Guides (Android)
+permalink: docs/android-building-from-source
+next: activityindicatorios
+---
+
+You will need to build React Native from source if you want to work on a new feature/bug fix, try out the latest features which are not released yet, or maintain your own fork with patches that cannot be merged to the core.
+
+## Prerequisites
+
+Assuming you have the Android SDK installed, run `android` to open the Android SDK Manager.
+
+Make sure you have the following installed:
+
+1. Android SDK version 23 (compileSdkVersion in [`build.gradle`](https://github.com/facebook/react-native/blob/master/ReactAndroid/build.gradle))
+2. SDK build tools version 23.0.1 (buildToolsVersion in [`build.gradle`](https://github.com/facebook/react-native/blob/master/ReactAndroid/build.gradle)])
+3. Android Support Repository >= 17 (for Android Support Library)
+4. Android NDK (download & extraction instructions [here](http://developer.android.com/ndk/downloads/index.html))
+
+Point Gradle to your Android SDK: either have `$ANDROID_SDK` and `$ANDROID_NDK ` defined, or create a local.properties file in the root of your react-native checkout with the following contents:
+
+```
+sdk.dir=absolute_path_to_android_sdk
+ndk.dir=absolute_path_to_android_ndk
+```
+
+Example:
+
+```
+sdk.dir=/Users/your_unix_name/android-sdk-macosx
+ndk.dir=/Users/your_unix_name/android-ndk/android-ndk-r10e
+```
+
+
+## Building the source
+
+1. Install `react-native` from your fork. For example, to install the master branch from the offcial repo, run the following:
+
+```sh
+npm install --save github:facebook/react-native#master
+```
+
+Alternatively, you can clone the repo to your `node_modules` directory and run `npm install` inside the cloned repo.
+
+2. Add `gradle-download-task` as dependency in `andoid/build.gradle`:
+
+```gradle
+...
+    dependencies {
+        classpath 'com.android.tools.build:gradle:1.3.1'
+        classpath 'de.undercouch:gradle-download-task:2.0.0'
+
+        // NOTE: Do not place your application dependencies here; they belong
+        // in the individual module build.gradle files
+    }
+...
+```
+
+3. Add the `:ReactAndroid` project in `andoid/settings.gradle`:
+
+```gradle
+...
+include ':ReactAndroid'
+
+project(':ReactAndroid').projectDir = new File(rootProject.projectDir, '../node_modules/react-native/ReactAndroid')
+...
+```
+
+4. Modify your `android/app/build.gradle` to use the `:ReactAndroid` project instead of the pre-compiled library, e.g. - replace `compile 'com.facebook.react:react-native:0.16.+'` with `compile project(':ReactAndroid')`:
+
+```gradle
+...
+dependencies {
+    compile fileTree(dir: 'libs', include: ['*.jar'])
+    compile 'com.android.support:appcompat-v7:23.0.1'
+
+    compile project(':ReactAndroid')
+
+    ...
+}
+...
+```
+
+5. If you use 3rd-party React Native modules, modify your `android/app/build.gradle` to override their dependencies so that they don't bundle the pre-compiled library, e.g. - replace `compile project(':react-native-custom-module')` with:
+
+```gradle
+compile(project(':react-native-custom-module')) {
+    exclude group: 'com.facebook.react', module: 'react-native'
+}
+```
+
+
+## Additional notes
+
+Building from source can take a long time, especially for the first build, as it needs to download ~200 MB of files and compile JSC etc. Every time you update the `react-native` version from your repo, the build directory may get deleted, and all the files are re-downloaded. To avoid this, you might want to change your build directory path by editing the `~/.gradle/init.gradle ` file:
+
+```gradle
+gradle.projectsLoaded {
+    rootProject.allprojects {
+        buildDir = "/path/to/build/directory/${rootProject.name}/${project.name}"
+    }
+}
+```