From 1d6813b918b71c9f2d6400b4ae46993d98277d00 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Sat, 19 Mar 2016 16:26:18 +0100
Subject: [PATCH] Handle empty text when double-clicking TextBox.

Fixes #458
---
 src/Perspex.Controls/TextBox.cs           | 35 ++++++++++++-----------
 src/Perspex.Controls/Utils/StringUtils.cs |  5 ++++
 2 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/src/Perspex.Controls/TextBox.cs b/src/Perspex.Controls/TextBox.cs
index 72f32aff1c..e8f150851a 100644
--- a/src/Perspex.Controls/TextBox.cs
+++ b/src/Perspex.Controls/TextBox.cs
@@ -373,23 +373,26 @@ namespace Perspex.Controls
                 var index = CaretIndex = _presenter.GetCaretIndex(point);
                 var text = Text;
 
-                switch (e.ClickCount)
+                if (text != null)
                 {
-                    case 1:
-                        SelectionStart = SelectionEnd = index;
-                        break;
-                    case 2:
-                        if (!StringUtils.IsStartOfWord(text, index))
-                        {
-                            SelectionStart = StringUtils.PreviousWord(text, index, false);
-                        }
-
-                        SelectionEnd = StringUtils.NextWord(text, index, false);
-                        break;
-                    case 3:
-                        SelectionStart = 0;
-                        SelectionEnd = text.Length;
-                        break;
+                    switch (e.ClickCount)
+                    {
+                        case 1:
+                            SelectionStart = SelectionEnd = index;
+                            break;
+                        case 2:
+                            if (!StringUtils.IsStartOfWord(text, index))
+                            {
+                                SelectionStart = StringUtils.PreviousWord(text, index, false);
+                            }
+
+                            SelectionEnd = StringUtils.NextWord(text, index, false);
+                            break;
+                        case 3:
+                            SelectionStart = 0;
+                            SelectionEnd = text.Length;
+                            break;
+                    }
                 }
 
                 e.Device.Capture(_presenter);
diff --git a/src/Perspex.Controls/Utils/StringUtils.cs b/src/Perspex.Controls/Utils/StringUtils.cs
index 6c69085874..e368a5f4b9 100644
--- a/src/Perspex.Controls/Utils/StringUtils.cs
+++ b/src/Perspex.Controls/Utils/StringUtils.cs
@@ -21,6 +21,11 @@ namespace Perspex.Controls.Utils
 
         public static bool IsStartOfWord(string text, int index)
         {
+            if (index >= text.Length)
+            {
+                return false;
+            }
+
             // A 'word' starts with an AlphaNumeric or some punctuation symbols immediately
             // preceeded by lwsp.
             if (index > 0 && !char.IsWhiteSpace(text[index - 1]))