sign the release version of the app

app/build.gradle

@@ -14,10 +14,15 @@ android {
         setProperty("archivesBaseName", "contacts")
     }
 
+    signingConfigs {
+        release
+    }
+
     buildTypes {
         release {
             minifyEnabled true
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+            signingConfig signingConfigs.release
         }
     }
 
@@ -42,3 +47,22 @@ dependencies {
     //debugImplementation "com.squareup.leakcanary:leakcanary-android:$leakCanaryVersion"
     //releaseImplementation "com.squareup.leakcanary:leakcanary-android-no-op:$leakCanaryVersion"
 }
+
+Properties props = new Properties()
+def propFile = new File('signing.properties')
+if (propFile.canRead()) {
+    props.load(new FileInputStream(propFile))
+
+    if (props != null && props.containsKey('STORE_FILE') && props.containsKey('KEY_ALIAS') && props.containsKey('PASSWORD')) {
+        android.signingConfigs.release.storeFile = file(props['STORE_FILE'])
+        android.signingConfigs.release.storePassword = props['PASSWORD']
+        android.signingConfigs.release.keyAlias = props['KEY_ALIAS']
+        android.signingConfigs.release.keyPassword = props['PASSWORD']
+    } else {
+        println 'signing.properties found but some entries are missing'
+        android.buildTypes.release.signingConfig = null
+    }
+} else {
+    println 'signing.properties not found'
+    android.buildTypes.release.signingConfig = null
+}

app/proguard-rules.pro

@@ -0,0 +1,5 @@
+# Joda
+-dontwarn org.joda.convert.**
+-dontwarn org.joda.time.**
+-keep class org.joda.time.** { *; }
+-keep interface org.joda.time.** { *; }

signing.properties_sample

@@ -0,0 +1,3 @@
+STORE_FILE=/path/to/your.keystore
+KEY_ALIAS=projectkeyalias
+PASSWORD=yourpass