#50 Fixed gson serialization issue when building release version of t…

…he app(prevent R8 from obfuscating serialization too much)

app/proguard-rules.pro

@@ -1,24 +1,14 @@
-# Add project specific ProGuard rules here.
-# You can control the set of applied configuration files using the
-# proguardFiles setting in build.gradle.
-#
-# For more details, see
-#   http://developer.android.com/guide/developing/tools/proguard.html
+# Preserve information about line numbers, exception etc. for debugging purposes
+-keepattributes SourceFile, LineNumberTable, Exceptions
 
-# If your project uses WebView with JS, uncomment the following
-# and specify the fully qualified class name to the JavaScript interface
-# class:
-#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
-#   public *;
-#}
+# Hide original source file names
+-renamesourcefileattribute SourceFile
 
-# Uncomment this to preserve the line number information for
-# debugging stack traces.
-#-keepattributes SourceFile,LineNumberTable
-
-# If you keep the line number information, uncomment this to
-# hide the original source file name.
-#-renamesourcefileattribute SourceFile
-
-# Enumerations must be kept
+# Keep enumerations
 -keepclassmembers enum ax.stardust.runcalc.** { *; }
+
+# Proguard configuration for Gson
+# Prevent R8 from leaving Data object members always null
+-keepclassmembers,allowobfuscation class * {
+  @com.google.gson.annotations.SerializedName <fields>;
+}

app/src/main/java/ax/stardust/runcalc/pojo/FinishTimePredictions.java

@@ -2,13 +2,16 @@
 
 import androidx.annotation.NonNull;
 
+import com.google.gson.annotations.SerializedName;
+
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Optional;
 
 import ax.stardust.runcalc.function.PredictionDistance;
 
 public class FinishTimePredictions {
+    @SerializedName("finishTimePredictions")
     private final List<FinishTimePrediction> finishTimePredictions = new ArrayList<>();
 
     public void addPrediction(FinishTimePrediction finishTimePrediction) {

app/src/main/java/ax/stardust/runcalc/pojo/HeartRateZones.java

@@ -2,6 +2,8 @@
 
 import androidx.annotation.NonNull;
 
+import com.google.gson.annotations.SerializedName;
+
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
@@ -15,6 +17,7 @@ public class HeartRateZones {
     public static final String ZONE_2 = "z2";
     public static final String ZONE_1 = "z1";
 
+    @SerializedName("heartRateZones")
     private final List<HeartRateZone> heartRateZones = new ArrayList<>();
 
     public void addZone(HeartRateZone heartRateZone) {