[RNMobile] Make placeholder text working on RichText (#13699)

* Make placeholder text working again on RichText

* Make sure the native side is always refreshed when the RichText component is cleared

* Remove placeholder check

packages/editor/src/components/rich-text/index.native.js

@@ -360,7 +360,12 @@ export class RichText extends Component {
  } ) );
 
  // Save back to HTML from React tree
- const html = '<' + tagName + '>' + value + '</' + tagName + '>';
+ let html = '<' + tagName + '>' + value + '</' + tagName + '>';
+ // We need to check if the value is undefined or empty, and then assign it properly otherwise the placeholder is not visible
+ if ( value === undefined || value === '' ) {
+ html = '';
+ this.lastEventCount = undefined; // force a refresh on the native side
+ }
 
  return (
  <View>
@@ -373,6 +378,7 @@ export class RichText extends Component {
  }
  }
  text={ { text: html, eventCount: this.lastEventCount } }
+ placeholder={ this.props.placeholder }
  onChange={ this.onChange }
  onFocus={ this.props.onFocus }
  onBlur={ this.props.onBlur }