Add mobile html5 dnd support using polyfill (#9282)

First step of mobile DND support.

- Add mobile html5 dnd support using polyfill
- Adds a switch for enabling mobile html5 dnd support
- Adds polyfill only when needed
- Ignore native Android Chrome drag start because doesn't work properly
(no dragend event fired)
- Add documentation on enabling mobile HTML5 DnD support
- Add mention of drag-drop-polyfill license
- Fixed issue in polyfill when not using "snapback"
- Add mention of forked polyfill

Fixes #9174

3 files changed, 26 insertions, 1 deletions

diff --git a/shared/src/main/java/com/vaadin/shared/ApplicationConstants.java b/shared/src/main/java/com/vaadin/shared/ApplicationConstants.java
index bb6ec330f7..b3490a434c 100644
--- a/shared/src/main/java/com/vaadin/shared/ApplicationConstants.java
+++ b/shared/src/main/java/com/vaadin/shared/ApplicationConstants.java
@@ -150,7 +150,7 @@ public class ApplicationConstants implements Serializable {
 
     /**
      * Name of the parameter used to transmit the push connection identifier.
-     * 
+     *
      * @since 8.0.6
      */
     public static final String PUSH_ID_PARAMETER = "v-pushId";
@@ -244,4 +244,11 @@ public class ApplicationConstants implements Serializable {
     public static final String FRONTEND_URL_ES5_DEFAULT_VALUE = VAADIN_PROTOCOL_PREFIX
             + "frontend/es5/";
 
+    /**
+     * Name of the HTML5 DnD Polyfill JavaScript file.
+     *
+     * @since 8.1
+     */
+    public static final String MOBILE_DND_POLYFILL_JS = "drag-drop-polyfill.min.js";
+
 }
diff --git a/shared/src/main/java/com/vaadin/shared/ui/ui/PageClientRpc.java b/shared/src/main/java/com/vaadin/shared/ui/ui/PageClientRpc.java
index acbc41b2c8..15419831e5 100644
--- a/shared/src/main/java/com/vaadin/shared/ui/ui/PageClientRpc.java
+++ b/shared/src/main/java/com/vaadin/shared/ui/ui/PageClientRpc.java
@@ -18,8 +18,21 @@ package com.vaadin.shared.ui.ui;
 
 import com.vaadin.shared.communication.ClientRpc;
 
+/**
+ * Client side rpc class for Page / UI.
+ *
+ * @author Vaadin Ltd
+ * @since 7.0
+ */
 public interface PageClientRpc extends ClientRpc {
 
+    /**
+     * Reloads the page.
+     */
     public void reload();
 
+    /**
+     * Initialize Mobile HTML5 Drag and Drop Polyfill.
+     */
+    public void initializeMobileHtml5DndPolyfill();
 }
diff --git a/shared/src/main/java/com/vaadin/shared/ui/ui/UIState.java b/shared/src/main/java/com/vaadin/shared/ui/ui/UIState.java
index c2c7b5c27a..b1d6be2def 100644
--- a/shared/src/main/java/com/vaadin/shared/ui/ui/UIState.java
+++ b/shared/src/main/java/com/vaadin/shared/ui/ui/UIState.java
@@ -86,6 +86,11 @@ public class UIState extends AbstractSingleComponentContainerState {
         tabIndex = 1;
     }
 
+    /**
+     * Enable Mobile HTML5 DnD support.
+     */
+    public boolean enableMobileHTML5DnD = false;
+
     public static class LoadingIndicatorConfigurationState
             implements Serializable {
         public int firstDelay = 300;