CA-293683: Prevent automatic scrolling when setting text in SmartScrollTextBox

Also fix issue whereby `IsVerticalScrollBarAtBottom` would also return `True`

Signed-off-by: Danilo Del Busso <Danilo.Del.Busso@citrix.com>

XenAdmin/Controls/SmartScrollTextBox.cs

@@ -46,8 +46,19 @@ namespace XenAdmin.Controls
     /// </summary>
     internal class SmartScrollTextBox : TextBox
     {
-        protected internal bool IsVerticalScrollBarAtBottom =>
+        private bool _scrolledProgrammatically;
-            string.IsNullOrEmpty(Text) || GetPositionFromCharIndex(Text.Length).Y < Height;
+
+        protected internal bool IsVerticalScrollBarAtBottom => GetPositionFromCharIndex(Text.Length - 1).Y < Height;
+
+        public void SetTextWithoutScrolling(string text)
+        {
+            var oldVerticalPosition = Win32.GetScrollBarPosition(Handle, Win32.ScrollBarConstants.SB_VERT);
+            Text = text;
+            Win32.SetScrollPos(Handle, (int)Win32.ScrollBarConstants.SB_VERT, oldVerticalPosition, true);
+
+            _scrolledProgrammatically = true;
+            Win32.PostMessageA(Handle, Win32.WM_VSCROLL, (int)Win32.ScrollBarCommands.SB_THUMBPOSITION + 0x10000 * oldVerticalPosition, 0);
+        }
 
         #region Custom Events
 
@@ -76,7 +87,7 @@ namespace XenAdmin.Controls
         #region Control Overrides
         protected override void WndProc(ref Message m)
         {
-            if (OnScrollChange != null)
+            if (OnScrollChange != null && !_scrolledProgrammatically)
             {
                 int newPosition;
                 switch (m.Msg)
@@ -97,6 +108,12 @@ namespace XenAdmin.Controls
 
                 }
             }
+
+            if (_scrolledProgrammatically)
+            {
+                _scrolledProgrammatically = false;
+            }
+
             base.WndProc(ref m);
         }
 

XenAdmin/Wizards/PatchingWizard/AutomatedUpdatesBasePage.cs

@@ -43,6 +43,7 @@ using System.Windows.Forms;
 using XenAdmin.Diagnostics.Problems;
 using XenAdmin.Dialogs;
 using XenAdmin.Wizards.RollingUpgradeWizard.PlanActions;
+using Console = System.Console;
 
 
 namespace XenAdmin.Wizards.PatchingWizard
@@ -316,11 +317,19 @@ namespace XenAdmin.Wizards.PatchingWizard
                 stringBuilder.Append(sb);
             }
 
-            textBoxLog.Text = stringBuilder.ToString();
+            var newText = stringBuilder.ToString();
-            textBoxLog.SelectionStart = textBoxLog.Text.Length;
+            
             if (!_userMovedVerticalScrollbar)
+            {
+                textBoxLog.Text = newText;
+                textBoxLog.SelectionStart = textBoxLog.Text.Length;
                 textBoxLog.ScrollToCaret();
             }
+            else
+            {
+                textBoxLog.SetTextWithoutScrolling(newText);
+            }
+        }
 
         private void WorkerDoWork(object sender, DoWorkEventArgs doWorkEventArgs)
         {

XenCenterLib/Win32.cs

@@ -387,6 +387,9 @@ namespace XenCenterLib
         public static extern bool EnumUILanguages(EnumUILanguagesProc pUILanguageEnumProc,
            uint dwFlags, IntPtr lParam);
 
+        [DllImport("user32.dll")]
+        public static extern int SetScrollPos(IntPtr hWnd, int nBar, int nPos, bool bRedraw);
+
         #region Window scrolling functions
 
         /// <summary>
@@ -499,6 +502,10 @@ namespace XenCenterLib
         [DllImport("user32.dll", SetLastError = true)]
         public static extern bool PostMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
         
+        [return: MarshalAs(UnmanagedType.Bool)]
+        [DllImport("user32.dll")] 
+        public static extern bool PostMessageA(IntPtr hWnd, int nBar, int wParam, int lParam);
+
         #region Disk space functions
 
         /// <summary>