clean up; apply only changed text to editable

src/Android/Avalonia.Android/AndroidInputMethod.cs

@@ -114,16 +114,42 @@ namespace Avalonia.Android
         private void _client_SurroundingTextChanged(object sender, EventArgs e)
         {
             var surroundingText = _client.SurroundingText ?? "";
+            var editableText = _inputConnection.EditableWrapper.ToString();
 
-            _inputConnection.EditableWrapper.IgnoreChange = true;
+            if (editableText != surroundingText)
+            {
+                _inputConnection.EditableWrapper.IgnoreChange = true;
+
+                var diff = GetDiff();
 
-            _inputConnection.Editable.Replace(0, _inputConnection.Editable.Length(), surroundingText);
+                _inputConnection.Editable.Replace(diff.index, editableText.Length, diff.diff);
 
-            _inputConnection.EditableWrapper.IgnoreChange = false;
+                _inputConnection.EditableWrapper.IgnoreChange = false;
+            }
 
             var selection = Client.Selection;
 
             _imm.UpdateSelection(_host, selection.Start, selection.End, selection.Start, selection.End);
+
+            (int index, string diff) GetDiff()
+            {
+                int index = 0;
+
+                var longerLength = Math.Max(surroundingText.Length, editableText.Length);
+
+                for(int i = 0; i < longerLength; i++)
+                {
+                    if (surroundingText.Length == i || editableText.Length == i || surroundingText[i] != editableText[i])
+                    {
+                        index = i;
+                        break;
+                    }
+                }
+
+                var diffString = surroundingText.Substring(index, surroundingText.Length - index);                
+
+                return (index, diffString);
+            }
         }
 
         public void SetCursorRect(Rect rect)

src/Android/Avalonia.Android/Platform/SkiaPlatform/TopLevelImpl.cs

@@ -447,6 +447,8 @@ namespace Avalonia.Android.Platform.SkiaPlatform
     {
         private readonly AvaloniaInputConnection _inputConnection;
 
+        public event EventHandler<int> SelectionChanged;
+
         public EditableWrapper(AvaloniaInputConnection inputConnection)
         {
             _inputConnection = inputConnection;
@@ -458,8 +460,6 @@ namespace Avalonia.Android.Platform.SkiaPlatform
         {
             if (!IgnoreChange && start != end)
             {
-                var text = tb.SubSequence(0, tb.Length());
-
                 SelectSurroundingTextForDeletion(start, end);
             }
 
@@ -470,8 +470,6 @@ namespace Avalonia.Android.Platform.SkiaPlatform
         {
             if (!IgnoreChange && start != end)
             {
-                var text = tb.SubSequence(tbstart, tbend);
-
                 SelectSurroundingTextForDeletion(start, end);
             }
 
@@ -482,6 +480,11 @@ namespace Avalonia.Android.Platform.SkiaPlatform
         {
             _inputConnection.InputMethod.Client.Selection = new TextSelection(start, end);
         }
+
+        public override void SetSpan(Java.Lang.Object what, int start, int end, [GeneratedEnum] SpanTypes flags)
+        {
+            base.SetSpan(what, start, end, flags);
+        }
     }
 
     internal class AvaloniaInputConnection : BaseInputConnection
@@ -548,11 +551,6 @@ namespace Avalonia.Android.Platform.SkiaPlatform
 
             if (_inputMethod.IsActive && !string.IsNullOrEmpty(committedText))
             {
-                if(_composingRegion != null)
-                {
-                    _inputMethod.Client.Selection = new TextSelection(_composingRegion.Value.Start, _composingRegion.Value.End);
-                }
-
                _toplevel.TextInput(committedText);
 
                 _composingRegion = null;