Add drag-drop / swap features on tiles

android/gradle.properties

 org.gradle.jvmargs=-Xmx1536M
 android.useAndroidX=true
 android.enableJetifier=true
-app.versionName=0.0.5
-app.versionCode=5
+app.versionName=0.0.6
+app.versionCode=6

lib/entities/tile.dart

@@ -17,13 +17,60 @@ class Tile {
     @required this.originalRow,
   );
 
-  Container widget() {
+  Container _tileWidget() {
     return Container(
+      decoration: BoxDecoration(
+        color: Colors.black,
+        border: Border.all(
+          color: Colors.black,
+          width: 1,
+        ),
+      ),
       child: Image(
         image: this.image.image,
         width: this.size,
         height: this.size,
         fit: BoxFit.fill
+      ),
+    );
+  }
+
+  Container widget() {
+    return Container(
+      child: DragTarget<List<int>>(
+        builder: (
+          BuildContext context,
+          List<dynamic> accepted,
+          List<dynamic> rejected,
+        ) {
+          return Container(
+            height: this.size,
+            width: this.size,
+            color: Colors.cyan,
+            child: Draggable<List<int>>(
+              data: [
+                this.currentCol,
+                this.currentRow,
+              ],
+
+              // Widget when draggable is stationary
+              child: this._tileWidget(),
+
+              // Widget when draggable is being dragged
+              feedback: this._tileWidget(),
+
+              // Widget to display on original place when being dragged
+              childWhenDragging: Container(
+                height: this.size,
+                width: this.size,
+                color: Colors.pinkAccent,
+              ),
+            ),
+          );
+        },
+        onAccept: (List<int> data) {
+          print(data.toString());
+        },
       )
     );
   }