fix some errors

com.unity.uiwidgets/Runtime/painting/text_painter.cs

             }
         }
 
-        void setPlaceholderDimensions(List<PlaceholderDimensions> value) {
+        public void setPlaceholderDimensions(List<PlaceholderDimensions> value) {
             if (value == null || value.isEmpty() || value.equalsList(_placeholderDimensions)) {
                 return;
             }
         bool _isUnicodeDirectionality(int? value) {
             return value == 0x200F || value == 0x200E;
         }
+        
+         public int getOffsetAfter(int offset) {
+            int? nextCodeUnit = _text.codeUnitAt(offset);
+            if (nextCodeUnit == null)
+                return 0;
+            // TODO(goderbauer): doesn't handle extended grapheme clusters with more than one Unicode scalar value (https://github.com/flutter/flutter/issues/13404).
+            return _isUtf16Surrogate(nextCodeUnit.Value) ? offset + 2 : offset + 1;
+        }
+         
+         public int getOffsetBefore(int offset) {
+             int? prevCodeUnit = _text.codeUnitAt(offset - 1);
+             if (prevCodeUnit == null)
+                 return 0;
+             // TODO(goderbauer): doesn't handle extended grapheme clusters with more than one Unicode scalar value (https://github.com/flutter/flutter/issues/13404).
+             return _isUtf16Surrogate(prevCodeUnit.Value) ? offset - 2 : offset - 1;
+         }
+        
     }
 }

com.unity.uiwidgets/Runtime/rendering/animated_size.cs

             curve = curve ?? Curves.linear;
             D.assert(vsync != null);
             D.assert(duration != null);
-            D.assert(curve != null);
             _vsync = vsync;
             _controller = new AnimationController(
                 vsync: this.vsync,

com.unity.uiwidgets/Runtime/rendering/custom_layout.cs

 
         MultiChildLayoutDelegate _delegate;
         
-        /*public void attach(PipelineOwner owner) {
+        public override void attach(object owner) {
             base.attach(owner);
             _delegate?._relayout?.addListener(markNeedsLayout);
         }
             base.detach();
-        }*/ // [!!!] ???
+        }
 
         Size _getSize(BoxConstraints constraints) {
             D.assert(constraints.debugAssertIsValid());

com.unity.uiwidgets/Runtime/rendering/editable.cs

             _textLayoutLastMinWidth = null;
         }
 
-        /*void _handleSetSelection(TextSelection selection) {
+        void _handleSetSelection(TextSelection selection) {
             _handleSelectionChange(selection, SelectionChangedCause.keyboard);
         }
 
                 }
             }
             return true;
-        }*/ //need?
-        
+        }
+
         public void attach(PipelineOwner owner) {
             _tap = new TapGestureRecognizer(debugOwner: this);
             _tap.onTapDown = _handleTapDown;

com.unity.uiwidgets/Runtime/services/text_editing.cs

         public TextPosition endPos {
             get { return new TextPosition(offset: end, affinity: affinity); }
         }
+        
+        public TextPosition  extent {
+            get { return new TextPosition(offset: extentOffset, affinity: affinity); }
+        }
 
         public bool Equals(TextSelection other) {
             if (ReferenceEquals(null, other)) {