TextInput: support modifying TextInputs with multiple Fragments (Cxx side)

Summary:
Support for modifying AndroidTextInputs with multiple Fragments was added on the Java side in a previous diff.

This diff adds support on the C++ side for the following scenario:

A <TextInput> is initially given contents via children <Text> notes, which represents multiple Fragments (that could have different TextAttributes like color, font size, backgroundcolor, etc). The Android EditText view must get this initial data, and then all updates after that on the Android side must flow to C++ so that the C++ ShadowNode can perform layout and measurement with up-to-date data.

At the same time, the <TextInput> node could be updated from the JS side. All else equal, this would cause the native Android EditText to be replaced with the old, original contents of the <TextInput> that may not have been updated at all from the JS side.

To mitigate this, we keep track of two AttributedStrings with Fragments on the C++ side: the AttributedString representing the values coming from <TextInput> children, from JS (`treeAttributedString`); and the AttributedString representing the current value the user is interacting with (`attributedString`). If the children from JS don't change, we don't update Android/Java with that AttributedString. If the children from JS do change, we overwrite any user input with the tree from JS.

Changelog: [Internal]

Reviewed By: shergin, mdvacca

Differential Revision: D18785976

fbshipit-source-id: a1f3a935e02379cabca8ab62a39cb3c0cf3fbca5

Author: JoshuaGross

ReactCommon/fabric/components/textinput/androidtextinput/AndroidTextInputShadowNode.cpp

@@ -29,8 +29,7 @@ void AndroidTextInputShadowNode::setContextContainer(
   contextContainer_ = contextContainer;
 }
 
-AttributedString AndroidTextInputShadowNode::getAttributedString(
-    bool usePlaceholders) const {
+AttributedString AndroidTextInputShadowNode::getAttributedString() const {
   // Use BaseTextShadowNode to get attributed string from children
   auto childTextAttributes = TextAttributes::defaultTextAttributes();
   childTextAttributes.apply(getProps()->textAttributes);
@@ -61,16 +60,21 @@ AttributedString AndroidTextInputShadowNode::getAttributedString(
     return attributedString;
   }
 
+  return getPlaceholderAttributedString(false);
+}
+
+// For measurement purposes, we want to make sure that there's at least a
+// single character in the string so that the measured height is greater
+// than zero. Otherwise, empty TextInputs with no placeholder don't
+// display at all.
+AttributedString AndroidTextInputShadowNode::getPlaceholderAttributedString(
+    bool ensureMinimumLength) const {
   // Return placeholder text, since text and children are empty.
   auto textAttributedString = AttributedString{};
   auto fragment = AttributedString::Fragment{};
   fragment.string = getProps()->placeholder;
 
-  // For measurement purposes, we want to make sure that there's at least a
-  // single character in the string so that the measured height is greater
-  // than zero. Otherwise, empty TextInputs with no placeholder don't
-  // display at all.
-  if (fragment.string.empty() && usePlaceholders) {
+  if (fragment.string.empty() && ensureMinimumLength) {
     fragment.string = " ";
   }
 
@@ -92,21 +96,25 @@ void AndroidTextInputShadowNode::setTextLayoutManager(
 void AndroidTextInputShadowNode::updateStateIfNeeded() {
   ensureUnsealed();
 
-  auto attributedString = getAttributedString(false);
+  auto reactTreeAttributedString = getAttributedString();
   auto const &state = getStateData();
 
   assert(textLayoutManager_);
   assert(
       (!state.layoutManager || state.layoutManager == textLayoutManager_) &&
       "`StateData` refers to a different `TextLayoutManager`");
 
-  if (state.attributedString == attributedString &&
+  // Tree is often out of sync with the value of the TextInput.
+  // This is by design - don't change the value of the TextInput in the State,
+  // and therefore in Java, unless the tree itself changes.
+  if (state.reactTreeAttributedString == reactTreeAttributedString &&
       state.layoutManager == textLayoutManager_) {
     return;
   }
 
   setStateData(AndroidTextInputState{state.mostRecentEventCount,
-                                     attributedString,
+                                     reactTreeAttributedString,
+                                     reactTreeAttributedString,
                                      getProps()->paragraphAttributes,
                                      textLayoutManager_});
 }
@@ -115,7 +123,13 @@ void AndroidTextInputShadowNode::updateStateIfNeeded() {
 
 Size AndroidTextInputShadowNode::measure(
     LayoutConstraints layoutConstraints) const {
-  AttributedString attributedString = getAttributedString(true);
+  auto const &state = getStateData();
+
+  AttributedString attributedString = state.attributedString;
+
+  if (attributedString.isEmpty()) {
+    attributedString = getPlaceholderAttributedString(true);
+  }
 
   if (attributedString.isEmpty()) {
     return {0, 0};

ReactCommon/fabric/components/textinput/androidtextinput/AndroidTextInputShadowNode.h

@@ -37,7 +37,9 @@ class AndroidTextInputShadowNode : public ConcreteViewShadowNode<
   /*
    * Returns a `AttributedString` which represents text content of the node.
    */
-  AttributedString getAttributedString(bool usePlaceholders) const;
+  AttributedString getAttributedString() const;
+  AttributedString getPlaceholderAttributedString(
+      bool ensureMinimumLength) const;
 
   /*
    * Associates a shared TextLayoutManager with the node.

ReactCommon/fabric/components/textinput/androidtextinput/AndroidTextInputState.cpp

@@ -15,6 +15,7 @@ namespace react {
 
 #ifdef ANDROID
 folly::dynamic AndroidTextInputState::getDynamic() const {
+  // Java doesn't need all fields, so we don't pass them along.
   folly::dynamic newState = folly::dynamic::object();
   newState["mostRecentEventCount"] = mostRecentEventCount;
   newState["attributedString"] = toDynamic(attributedString);

ReactCommon/fabric/components/textinput/androidtextinput/AndroidTextInputState.h

@@ -31,6 +31,15 @@ class AndroidTextInputState final {
    */
   AttributedString attributedString{};
 
+  /*
+   * All content of <TextInput> component represented as an `AttributedString`.
+   * This stores the previous computed *from the React tree*. This usually
+   * doesn't change as the TextInput contents are being updated. If it does
+   * change, we need to wipe out current contents of the TextInput and replace
+   * with the new value from the tree.
+   */
+  AttributedString reactTreeAttributedString{};
+
   /*
    * Represents all visual attributes of a paragraph of text represented as
    * a ParagraphAttributes.
@@ -79,10 +88,12 @@ class AndroidTextInputState final {
   AndroidTextInputState(
       int64_t mostRecentEventCount,
       AttributedString const &attributedString,
+      AttributedString const &reactTreeAttributedString,
       ParagraphAttributes const &paragraphAttributes,
       SharedTextLayoutManager const &layoutManager)
       : mostRecentEventCount(mostRecentEventCount),
         attributedString(attributedString),
+        reactTreeAttributedString(reactTreeAttributedString),
         paragraphAttributes(paragraphAttributes),
         layoutManager(layoutManager) {}
   AndroidTextInputState() = default;
@@ -92,6 +103,7 @@ class AndroidTextInputState final {
       : mostRecentEventCount((int64_t)data["mostRecentEventCount"].getInt()),
         attributedString(
             updateAttributedString(previousState.attributedString, data)),
+        reactTreeAttributedString(previousState.reactTreeAttributedString),
         paragraphAttributes(previousState.paragraphAttributes),
         layoutManager(previousState.layoutManager){};
   folly::dynamic getDynamic() const;