ScreenView do not include previous screen state (close #363)

snowplow-tracker/src/androidTest/java/com/snowplowanalytics/snowplow/tracker/TrackerTest.java

@@ -277,15 +277,26 @@ public void testTrackScreenView() throws Exception {
         Map<String, Object> screenStateMap = (Map<String, Object>)screenStateMapWrapper.get(Parameters.DATA);
         assertEquals("Unknown", screenStateMap.get(Parameters.SCREEN_NAME));
 
+        // Send screenView
         ScreenView screenView = ScreenView.builder().name("screen1").build();
         String screenId = (String)screenView.getData().getMap().get("id");
-
         tracker.track(screenView);
 
         screenStateMapWrapper = screenState.getCurrentScreen(true).getMap();
         screenStateMap = (Map<String, Object>)screenStateMapWrapper.get(Parameters.DATA);
         assertEquals("screen1", screenStateMap.get(Parameters.SCREEN_NAME));
         assertEquals(screenId, screenStateMap.get(Parameters.SCREEN_ID));
+
+        // Send another screenView
+        screenView = ScreenView.builder().name("screen2").build();
+        String screenId1 = (String)screenView.getData().getMap().get("id");
+        tracker.track(screenView);
+
+        Map<String, Object> payload = (Map<String, Object>)screenView.getPayload().getMap().get("data");
+        assertEquals("screen2", payload.get(Parameters.SCREEN_NAME));
+        assertEquals(screenId1, payload.get(Parameters.SCREEN_ID));
+        assertEquals("screen1", payload.get(Parameters.SV_PREVIOUS_NAME));
+        assertEquals(screenId, payload.get(Parameters.SV_PREVIOUS_ID));
     }
 
     public void testTrackUncaughtException() throws InterruptedException {

snowplow-tracker/src/main/java/com/snowplowanalytics/snowplow/ScreenStatePreviousFields.java

@@ -0,0 +1,7 @@
+package com.snowplowanalytics.snowplow;
+
+public interface ScreenStatePreviousFields {
+    String getPreviousId();
+    String getPreviousName();
+    String getPreviousType();
+}

snowplow-tracker/src/main/java/com/snowplowanalytics/snowplow/tracker/events/ScreenView.java

@@ -211,11 +211,18 @@ protected ScreenView(Builder<?> builder) {
     /**
      * Update the passed screen state with the data related to
      * the current ScreenView event.
+     * @apiNote ScreenState updates back the previous screen fields
+     * in the ScreenView event (if `previousId` not already set).
      * @param screenState The screen state to update.
      */
-    public void updateScreenState(ScreenState screenState) {
+    public synchronized void updateScreenState(ScreenState screenState) {
         if (screenState == null) return;
         screenState.updateScreenState(id, name, type, transitionType, fragmentClassName, fragmentTag, activityClassName, activityTag);
+        if (previousId == null) {
+            previousId = screenState.getPreviousId();
+            previousName = screenState.getPreviousName();
+            previousType = screenState.getPreviousType();
+        }
     }
 
     /**

snowplow-tracker/src/main/java/com/snowplowanalytics/snowplow/tracker/tracker/ScreenState.java

@@ -1,13 +1,13 @@
 package com.snowplowanalytics.snowplow.tracker.tracker;
 
+import com.snowplowanalytics.snowplow.ScreenStatePreviousFields;
 import com.snowplowanalytics.snowplow.tracker.constants.Parameters;
 import com.snowplowanalytics.snowplow.tracker.constants.TrackerConstants;
 import com.snowplowanalytics.snowplow.tracker.payload.SelfDescribingJson;
 import com.snowplowanalytics.snowplow.tracker.payload.TrackerPayload;
 import com.snowplowanalytics.snowplow.tracker.utils.Util;
 
-
-public class ScreenState {
+public class ScreenState implements ScreenStatePreviousFields {
     private String name;
     private String type;
     private String id;
@@ -109,4 +109,20 @@ private String getValidName(String s1, String s2) {
         return null;
     }
 
+    // Implement ScreenStatePreviousFields
+
+    @Override
+    public String getPreviousId() {
+        return previousId;
+    }
+
+    @Override
+    public String getPreviousName() {
+        return previousName;
+    }
+
+    @Override
+    public String getPreviousType() {
+        return previousType;
+    }
 }