Android: Add onScroll event to TextInput

Summary:
Corresponding iOS PR: https://github.com/facebook/react-native/pull/11002

This adds an onScroll event to TextInput which is useful when a multiline TextInput has so much content that it is scrollable.

**Test plan (required)**

Verified the event works properly in a test app. Also, my team uses this event in our app.

Adam Comella
Microsoft Corp.
Closes https://github.com/facebook/react-native/pull/11001

Differential Revision: D4220941

Pulled By: mkonicek

fbshipit-source-id: 7e420579946f2ae840c9e1fcdc8afab68007da17

Libraries/Components/TextInput/TextInput.js

@@ -739,6 +739,7 @@ const TextInput = React.createClass({
         children={children}
         disableFullscreenUI={this.props.disableFullscreenUI}
         textBreakStrategy={this.props.textBreakStrategy}
+        onScroll={this._onScroll}
       />;
 
     return (

ReactAndroid/src/main/java/com/facebook/react/views/textinput/BUCK

@@ -14,6 +14,7 @@ android_library(
     react_native_target('java/com/facebook/react/uimanager:uimanager'),
     react_native_target('java/com/facebook/react/uimanager/annotations:annotations'),
     react_native_target('java/com/facebook/react/views/imagehelper:imagehelper'),
+    react_native_target('java/com/facebook/react/views/scroll:scroll'),
     react_native_target('java/com/facebook/react/views/text:text'),
     react_native_target('java/com/facebook/react/views/view:view'),
   ],

ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactEditText.java

@@ -80,6 +80,7 @@ public class ReactEditText extends EditText {
   private @Nullable String mReturnKeyType;
   private @Nullable SelectionWatcher mSelectionWatcher;
   private @Nullable ContentSizeWatcher mContentSizeWatcher;
+  private @Nullable ScrollWatcher mScrollWatcher;
   private final InternalKeyListener mKeyListener;
   private boolean mDetectScrollMovement = false;
 
@@ -106,6 +107,7 @@ public class ReactEditText extends EditText {
     mTextWatcherDelegator = null;
     mStagedInputType = getInputType();
     mKeyListener = new InternalKeyListener();
+    mScrollWatcher = null;
   }
 
   // After the text changes inside an EditText, TextView checks if a layout() has been requested.
@@ -171,6 +173,15 @@ public class ReactEditText extends EditText {
     return super.onKeyUp(keyCode, event);
   }
 
+  @Override
+  protected void onScrollChanged(int horiz, int vert, int oldHoriz, int oldVert) {
+    super.onScrollChanged(horiz, vert, oldHoriz, oldVert);
+
+    if (mScrollWatcher != null) {
+      mScrollWatcher.onScrollChanged(horiz, vert, oldHoriz, oldVert);
+    }
+  }
+
   @Override
   public void clearFocus() {
     setFocusableInTouchMode(false);
@@ -220,6 +231,10 @@ public class ReactEditText extends EditText {
     mContentSizeWatcher = contentSizeWatcher;
   }
 
+  public void setScrollWatcher(ScrollWatcher scrollWatcher) {
+    mScrollWatcher = scrollWatcher;
+  }
+
   @Override
   public void setSelection(int start, int end) {
     // Skip setting the selection if the text wasn't set because of an out of date value.

ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactTextInputManager.java

@@ -48,6 +48,8 @@ import com.facebook.react.uimanager.annotations.ReactProp;
 import com.facebook.react.uimanager.annotations.ReactPropGroup;
 import com.facebook.react.uimanager.events.EventDispatcher;
 import com.facebook.react.views.imagehelper.ResourceDrawableIdHelper;
+import com.facebook.react.views.scroll.ScrollEvent;
+import com.facebook.react.views.scroll.ScrollEventType;
 import com.facebook.react.views.text.DefaultStyleValuesUtil;
 import com.facebook.react.views.text.ReactFontManager;
 import com.facebook.react.views.text.ReactTextUpdate;
@@ -278,6 +280,15 @@ public class ReactTextInputManager extends BaseViewManager<ReactEditText, Layout
     }
   }
 
+  @ReactProp(name = "onScroll", defaultBoolean = false)
+  public void setOnScroll(final ReactEditText view, boolean onScroll) {
+    if (onScroll) {
+      view.setScrollWatcher(new ReactScrollWatcher(view));
+    } else {
+      view.setScrollWatcher(null);
+    }
+  }
+
   @ReactProp(name = "placeholder")
   public void setPlaceholder(ReactEditText view, @Nullable String placeholder) {
     view.setHint(placeholder);
@@ -772,6 +783,41 @@ public class ReactTextInputManager extends BaseViewManager<ReactEditText, Layout
     }
   }
 
+  private class ReactScrollWatcher implements ScrollWatcher {
+
+    private ReactEditText mReactEditText;
+    private EventDispatcher mEventDispatcher;
+    private int mPreviousHoriz;
+    private int mPreviousVert;
+
+    public ReactScrollWatcher(ReactEditText editText) {
+      mReactEditText = editText;
+      ReactContext reactContext = (ReactContext) editText.getContext();
+      mEventDispatcher = reactContext.getNativeModule(UIManagerModule.class).getEventDispatcher();
+    }
+
+    @Override
+    public void onScrollChanged(int horiz, int vert, int oldHoriz, int oldVert) {
+      if (mPreviousHoriz != horiz || mPreviousVert != vert) {
+        ScrollEvent event = ScrollEvent.obtain(
+          mReactEditText.getId(),
+          ScrollEventType.SCROLL,
+          horiz,
+          vert,
+          0, // can't get content width
+          0, // can't get content height
+          mReactEditText.getWidth(),
+          mReactEditText.getHeight()
+        );
+
+        mEventDispatcher.dispatchEvent(event);
+
+        mPreviousHoriz = horiz;
+        mPreviousVert = vert;
+      }
+    }
+  }
+
   @Override
   public @Nullable Map getExportedViewConstants() {
     return MapBuilder.of(

ReactAndroid/src/main/java/com/facebook/react/views/textinput/ScrollWatcher.java

@@ -0,0 +1,14 @@
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.views.textinput;
+
+public interface ScrollWatcher {
+  public void onScrollChanged(int horiz, int vert, int oldHoriz, int oldVert);
+}