Add Custom Dimensions plugin support;

Add dimensions id and variable limitations;

README.md

@@ -145,6 +145,20 @@ This method uses ``SharedPreferences`` to ensures that tracking application down
 ((YourApplication) getApplication()).getTracker().trackAppDownload();
 ```
 
+#### Custom Dimensions
+To track [Custom Dimensions](https://plugins.piwik.org/CustomDimensions) in scope Action or Visit
+consider following example:
+
+```java
+
+Tracker tracker = ((YourApplication) getApplication()).getTracker();
+tracker.track(
+    new CustomDimensions()
+        .set(1, "foo")
+        .set(2, "bar")
+);
+```
+
 #### Ecommerce
 
 Piwik provides ecommerce analytics that let you measure items added to carts,

piwik-sdk/src/main/java/org/piwik/sdk/TrackMe.java

@@ -20,6 +20,14 @@ public class TrackMe {
     private final HashMap<String, String> mQueryParams = new HashMap<>(DEFAULT_QUERY_CAPACITY);
     private final CustomVariables mScreenCustomVariable = new CustomVariables();
 
+    protected synchronized TrackMe set(@NonNull String key, String value) {
+        if (value == null)
+            mQueryParams.remove(key);
+        else if (value.length() > 0)
+            mQueryParams.put(key, value);
+        return this;
+    }
+
     /**
      * You can set any additional Tracking API Parameters within the SDK.
      * This includes for example the local time (parameters h, m and s).
@@ -34,10 +42,7 @@ public class TrackMe {
      * @return tracker instance
      */
     public synchronized TrackMe set(@NonNull QueryParams key, String value) {
-        if (value == null)
-            mQueryParams.remove(key.toString());
-        else if (value.length() > 0)
-            mQueryParams.put(key.toString(), value);
+        set(key.toString(), value);
         return this;
     }
 

piwik-sdk/src/main/java/org/piwik/sdk/plugins/CustomDimensions.java

@@ -0,0 +1,35 @@
+package org.piwik.sdk.plugins;
+
+import org.piwik.sdk.Piwik;
+import org.piwik.sdk.tools.Logy;
+import org.piwik.sdk.TrackMe;
+
+/**
+ * This plugins allows you to track any Custom Dimensions.
+ * In order to use this functionality install and configure
+ * https://plugins.piwik.org/CustomDimensions plugin.
+ */
+public class CustomDimensions extends TrackMe {
+    protected static final String LOGGER_TAG = Piwik.LOGGER_PREFIX + "CustomDimensions";
+    /**
+     * This method sets a tracking API parameter dimension%dimensionId%=%dimensionValue%.
+     * Eg dimension1=foo or dimension2=bar.
+     * So the tracking API parameter starts with dimension followed by the set dimensionId.
+     * @param dimensionId  accepts values greater than 0
+     * @param dimensionValue is limited to 255 characters
+     * @return instance of CustomDimensions plugin
+     */
+    public synchronized CustomDimensions set(int dimensionId, String dimensionValue) {
+        if (dimensionId < 1){
+            Logy.w(LOGGER_TAG, "dimensionId should be great than 0");
+            return this;
+        }
+        if (dimensionValue != null && dimensionValue.length() > 255){
+            Logy.w(LOGGER_TAG, "dimensionValue will be truncated to 255 chars");
+            dimensionValue = dimensionValue.substring(0, 255);
+        }
+        set("dimension" + dimensionId, dimensionValue);
+        return this;
+    }
+
+}

piwik-sdk/src/test/java/org/piwik/sdk/TrackerTest.java

@@ -9,6 +9,7 @@
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.piwik.sdk.ecommerce.EcommerceItems;
+import org.piwik.sdk.plugins.CustomDimensions;
 import org.robolectric.Robolectric;
 import org.robolectric.annotation.Config;
 
@@ -834,6 +835,33 @@ public void testPreviousVisit() throws Exception {
         assertEquals(1000l, Long.parseLong(queryParams.get(QueryParams.PREVIOUS_VISIT_TIMESTAMP)));
     }
 
+    @Test
+    public void testSetCustomDimensions() throws Exception {
+        CustomDimensions customDimensions = new CustomDimensions();
+        customDimensions.set(0, "foo");
+        customDimensions.set(1, "foo");
+        customDimensions.set(2, "bar");
+        customDimensions.set(3, "empty").set(3, null);
+        customDimensions.set(4, "");
+
+        QueryHashMap<String, String> queryParams = parseEventUrl(customDimensions.build());
+
+        assertEquals(queryParams.get("dimension1"), "foo");
+        assertEquals(queryParams.get("dimension2"), "bar");
+        assertFalse(queryParams.containsKey("dimension0"));
+        assertFalse(queryParams.containsKey("dimension3"));
+        assertFalse(queryParams.containsKey("dimension4"));
+    }
+
+    @Test
+    public void testSetCustomDimensionsMaxLength() throws Exception {
+        CustomDimensions customDimensions = new CustomDimensions();
+        customDimensions.set(1, new String(new char[1000]));
+
+        QueryHashMap<String, String> queryParams = parseEventUrl(customDimensions.build());
+        assertEquals(queryParams.get("dimension1").length(), 255);
+    }
+
     private static class QueryHashMap<String, V> extends HashMap<String, V> {
 
         private QueryHashMap() {