android - remove zero-width-space character from the input and output

android/src/main/java/com/swmansion/reactnativerichtexteditor/spans/EditorBlockQuoteSpan.kt

@@ -5,10 +5,11 @@ import android.graphics.Paint
 import android.text.Layout
 import android.text.style.LeadingMarginSpan
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorParagraphSpan
+import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorZeroWidthSpaceSpan
 import com.swmansion.reactnativerichtexteditor.styles.RichTextStyle
 
 // https://android.googlesource.com/platform/frameworks/base/+/refs/heads/main/core/java/android/text/style/QuoteSpan.java
-class EditorBlockQuoteSpan(private val richTextStyle: RichTextStyle) : LeadingMarginSpan, EditorParagraphSpan {
+class EditorBlockQuoteSpan(private val richTextStyle: RichTextStyle) : LeadingMarginSpan, EditorParagraphSpan, EditorZeroWidthSpaceSpan {
   override fun getLeadingMargin(p0: Boolean): Int {
     return richTextStyle.blockquoteStripeWidth + richTextStyle.blockquoteGapWidth
   }

android/src/main/java/com/swmansion/reactnativerichtexteditor/spans/EditorCodeBlockSpan.kt

@@ -8,9 +8,10 @@ import android.text.TextPaint
 import android.text.style.CharacterStyle
 import android.text.style.LineBackgroundSpan
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorParagraphSpan
+import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorZeroWidthSpaceSpan
 import com.swmansion.reactnativerichtexteditor.styles.RichTextStyle
 
-class EditorCodeBlockSpan(private val richTextStyle: RichTextStyle) : CharacterStyle(), LineBackgroundSpan, EditorParagraphSpan {
+class EditorCodeBlockSpan(private val richTextStyle: RichTextStyle) : CharacterStyle(), LineBackgroundSpan, EditorParagraphSpan, EditorZeroWidthSpaceSpan {
   override fun updateDrawState(paint: TextPaint?) {
     paint?.typeface = Typeface.MONOSPACE
     paint?.color = richTextStyle.codeBlockColor

android/src/main/java/com/swmansion/reactnativerichtexteditor/spans/EditorH1Span.kt

@@ -3,8 +3,9 @@ package com.swmansion.reactnativerichtexteditor.spans
 import android.text.style.AbsoluteSizeSpan
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorHeadingSpan
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorInlineSpan
+import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorZeroWidthSpaceSpan
 import com.swmansion.reactnativerichtexteditor.styles.RichTextStyle
 
 // Heading spans inherit from EditorInlineSpan because they can be nested inside code block and block quote
-class EditorH1Span(style: RichTextStyle) : AbsoluteSizeSpan(style.h1FontSize), EditorHeadingSpan, EditorInlineSpan {
+class EditorH1Span(style: RichTextStyle) : AbsoluteSizeSpan(style.h1FontSize), EditorHeadingSpan, EditorInlineSpan, EditorZeroWidthSpaceSpan {
 }

android/src/main/java/com/swmansion/reactnativerichtexteditor/spans/EditorH2Span.kt

@@ -3,8 +3,9 @@ package com.swmansion.reactnativerichtexteditor.spans
 import android.text.style.AbsoluteSizeSpan
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorHeadingSpan
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorInlineSpan
+import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorZeroWidthSpaceSpan
 import com.swmansion.reactnativerichtexteditor.styles.RichTextStyle
 
 // Heading spans inherit from EditorInlineSpan because they can be nested inside code block and block quote
-class EditorH2Span(richTextStyle: RichTextStyle) : AbsoluteSizeSpan(richTextStyle.h2FontSize), EditorHeadingSpan, EditorInlineSpan {
+class EditorH2Span(richTextStyle: RichTextStyle) : AbsoluteSizeSpan(richTextStyle.h2FontSize), EditorHeadingSpan, EditorInlineSpan, EditorZeroWidthSpaceSpan {
 }

android/src/main/java/com/swmansion/reactnativerichtexteditor/spans/EditorH3Span.kt

@@ -3,8 +3,9 @@ package com.swmansion.reactnativerichtexteditor.spans
 import android.text.style.AbsoluteSizeSpan
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorHeadingSpan
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorInlineSpan
+import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorZeroWidthSpaceSpan
 import com.swmansion.reactnativerichtexteditor.styles.RichTextStyle
 
 // Heading spans inherit from EditorInlineSpan because they can be nested inside code block and block quote
-class EditorH3Span(richTextStyle: RichTextStyle) : AbsoluteSizeSpan(richTextStyle.h3FontSize), EditorHeadingSpan, EditorInlineSpan {
+class EditorH3Span(richTextStyle: RichTextStyle) : AbsoluteSizeSpan(richTextStyle.h3FontSize), EditorHeadingSpan, EditorInlineSpan, EditorZeroWidthSpaceSpan {
 }

android/src/main/java/com/swmansion/reactnativerichtexteditor/spans/EditorOrderedListSpan.kt

@@ -5,9 +5,10 @@ import android.graphics.Paint
 import android.text.Layout
 import android.text.style.LeadingMarginSpan
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorInlineSpan
+import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorZeroWidthSpaceSpan
 import com.swmansion.reactnativerichtexteditor.styles.RichTextStyle
 
-class EditorOrderedListSpan(private var index: Int, private val richTextStyle: RichTextStyle) : LeadingMarginSpan, EditorInlineSpan {
+class EditorOrderedListSpan(private var index: Int, private val richTextStyle: RichTextStyle) : LeadingMarginSpan, EditorInlineSpan, EditorZeroWidthSpaceSpan {
   override fun getLeadingMargin(first: Boolean): Int {
     return richTextStyle.olMarginLeft + richTextStyle.olGapWidth
   }

android/src/main/java/com/swmansion/reactnativerichtexteditor/spans/EditorUnorderedListSpan.kt

@@ -6,10 +6,11 @@ import android.text.Layout
 import android.text.Spanned
 import android.text.style.LeadingMarginSpan
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorInlineSpan
+import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorZeroWidthSpaceSpan
 import com.swmansion.reactnativerichtexteditor.styles.RichTextStyle
 
 // https://android.googlesource.com/platform/frameworks/base/+/refs/heads/main/core/java/android/text/style/BulletSpan.java
-class EditorUnorderedListSpan(private val richTextStyle: RichTextStyle) : LeadingMarginSpan, EditorInlineSpan {
+class EditorUnorderedListSpan(private val richTextStyle: RichTextStyle) : LeadingMarginSpan, EditorInlineSpan, EditorZeroWidthSpaceSpan {
   override fun getLeadingMargin(p0: Boolean): Int {
     return richTextStyle.ulBulletSize + richTextStyle.ulGapWidth + richTextStyle.ulMarginLeft
   }

android/src/main/java/com/swmansion/reactnativerichtexteditor/spans/interfaces/EditorZeroWidthSpaceSpan.kt

@@ -0,0 +1,5 @@
+package com.swmansion.reactnativerichtexteditor.spans.interfaces
+
+// Spans that are prefixed with zero-width space (\u200B) to ensure that they are visible even when empty.
+interface EditorZeroWidthSpaceSpan {
+}

android/src/main/java/com/swmansion/reactnativerichtexteditor/utils/EditorParser.java

@@ -31,6 +31,7 @@
 import com.swmansion.reactnativerichtexteditor.spans.EditorUnorderedListSpan;
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorParagraphSpan;
 import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorInlineSpan;
+import com.swmansion.reactnativerichtexteditor.spans.interfaces.EditorZeroWidthSpaceSpan;
 import com.swmansion.reactnativerichtexteditor.styles.RichTextStyle;
 
 import org.ccil.cowan.tagsoup.HTMLSchema;
@@ -522,7 +523,10 @@ private static void withinStyle(StringBuilder out, CharSequence text,
                                   int start, int end) {
     for (int i = start; i < end; i++) {
       char c = text.charAt(i);
-      if (c == '<') {
+      if (c == '\u200B') {
+        // Do not output zero-width space characters.
+        continue;
+      } else if (c == '<') {
         out.append("&lt;");
       } else if (c == '>') {
         out.append("&gt;");
@@ -657,6 +661,17 @@ public Spanned convert() {
         mSpannableStringBuilder.setSpan(obj[i], start, end, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
       }
     }
+
+    // Assign zero-width space character to the proper spans.
+    EditorZeroWidthSpaceSpan[] zeroWidthSpaceSpans = mSpannableStringBuilder.getSpans(0, mSpannableStringBuilder.length(), EditorZeroWidthSpaceSpan.class);
+    for (EditorZeroWidthSpaceSpan zeroWidthSpaceSpan : zeroWidthSpaceSpans) {
+      int start = mSpannableStringBuilder.getSpanStart(zeroWidthSpaceSpan);
+      int end = mSpannableStringBuilder.getSpanEnd(zeroWidthSpaceSpan);
+      mSpannableStringBuilder.insert(start, "\u200B");
+      mSpannableStringBuilder.removeSpan(zeroWidthSpaceSpan);
+      mSpannableStringBuilder.setSpan(zeroWidthSpaceSpan, start, end + 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
+    }
+
     return mSpannableStringBuilder;
   }