Here is an attempt to solve some of the problems with other solutions:
- Using right click context menu for cut/copy/past selects all text even if you didn't select it all.
- When returning from right click context menu, all text is always selected.
- When returning to the application with Alt+Tab, all text is always selected.
- When trying to select only part of the text on the first click, all is always selected (unlike Google chromes address bar for example).
The code I wrote is configurable. You can choose on what actions the select all behavior should occur by setting three readonly fields: SelectOnKeybourdFocus, SelectOnMouseLeftClick, SelectOnMouseRightClick.
The downside of this solution is that it's more complex and static state is stored. Its seems like an ugly struggle with the defaults behavior of the TextBox control. Still, it works and all the code is hidden in the Attached Property container class.
public static class TextBoxExtensions
{
// Configuration fields to choose on what actions the select all behavior should occur.
static readonly bool SelectOnKeybourdFocus = true;
static readonly bool SelectOnMouseLeftClick = true;
static readonly bool SelectOnMouseRightClick = true;
// Remembers a right click context menu that is opened
static ContextMenu ContextMenu = null;
// Remembers if the first action on the TextBox is mouse down
static bool FirstActionIsMouseDown = false;
public static readonly DependencyProperty SelectOnFocusProperty =
DependencyProperty.RegisterAttached("SelectOnFocus", typeof(bool), typeof(TextBoxExtensions), new PropertyMetadata(false, new PropertyChangedCallback(OnSelectOnFocusChanged)));
[AttachedPropertyBrowsableForChildren(IncludeDescendants = false)]
[AttachedPropertyBrowsableForType(typeof(TextBox))]
public static bool GetSelectOnFocus(DependencyObject obj)
{
return (bool)obj.GetValue(SelectOnFocusProperty);
}
public static void SetSelectOnFocus(DependencyObject obj, bool value)
{
obj.SetValue(SelectOnFocusProperty, value);
}
private static void OnSelectOnFocusChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
if (!(d is TextBox textBox)) return;
if (GetSelectOnFocus(textBox))
{
// Register events
textBox.PreviewMouseDown += TextBox_PreviewMouseDown;
textBox.PreviewMouseUp += TextBox_PreviewMouseUp;
textBox.GotKeyboardFocus += TextBox_GotKeyboardFocus;
textBox.LostKeyboardFocus += TextBox_LostKeyboardFocus;
}
else
{
// Unregister events
textBox.PreviewMouseDown -= TextBox_PreviewMouseDown;
textBox.PreviewMouseUp -= TextBox_PreviewMouseUp;
textBox.GotKeyboardFocus -= TextBox_GotKeyboardFocus;
textBox.LostKeyboardFocus -= TextBox_LostKeyboardFocus;
}
}
private static void TextBox_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
if (!(sender is TextBox textBox)) return;
// If mouse clicked and focus was not in text box, remember this is the first click.
// This will enable to prevent select all when the text box gets the keyboard focus
// right after the mouse down event.
if (!textBox.IsKeyboardFocusWithin)
{
FirstActionIsMouseDown = true;
}
}
private static void TextBox_PreviewMouseUp(object sender, MouseButtonEventArgs e)
{
if (!(sender is TextBox textBox)) return;
// Select all only if:
// 1) SelectOnMouseLeftClick/SelectOnMouseRightClick is true and left/right button was clicked
// 3) This is the first click
// 4) No text is selected
if (((SelectOnMouseLeftClick && e.ChangedButton == MouseButton.Left) ||
(SelectOnMouseRightClick && e.ChangedButton == MouseButton.Right)) &&
FirstActionIsMouseDown &&
string.IsNullOrEmpty(textBox.SelectedText))
{
textBox.SelectAll();
}
// It is not the first click
FirstActionIsMouseDown = false;
}
private static void TextBox_GotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
{
if (!(sender is TextBox textBox)) return;
// Select all only if:
// 1) SelectOnKeybourdFocus is true
// 2) Focus was not previously out of the application (e.OldFocus != null)
// 3) The mouse was pressed down for the first after on the text box
// 4) Focus was not previously in the context menu
if (SelectOnKeybourdFocus &&
e.OldFocus != null &&
!FirstActionIsMouseDown &&
!IsObjectInObjectTree(e.OldFocus as DependencyObject, ContextMenu))
{
textBox.SelectAll();
}
// Forget ContextMenu
ContextMenu = null;
}
private static void TextBox_LostKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
{
if (!(sender is TextBox textBox)) return;
// Remember ContextMenu (if opened)
ContextMenu = e.NewFocus as ContextMenu;
// Forget selection when focus is lost if:
// 1) Focus is still in the application
// 2) The context menu was not opened
if (e.NewFocus != null
&& ContextMenu == null)
{
textBox.SelectionLength = 0;
}
}
// Helper function to look if a DependencyObject is contained in the visual tree of another object
private static bool IsObjectInObjectTree(DependencyObject searchInObject, DependencyObject compireToObject)
{
while (searchInObject != null && searchInObject != compireToObject)
{
searchInObject = VisualTreeHelper.GetParent(searchInObject);
}
return searchInObject != null;
}
}
To attache the Attached Property to a TextBox, all you need to do is add the xml namespace (xmlns) of the Attached Property and then use it like this:
<TextBox attachedprop:TextBoxExtensions.SelectOnFocus="True"/>
Some notes about this solution:
- To override the default behavior of a mouse down event and enable selecting only part of the text on the first click, all text is selected on mouse up event.
- I had to deal with the fact the the
TextBox remembers its selection after it loses focus. I actually have overridden this behavior.
- I had to remember if a mouse button down is the first action on the
TextBox (FirstActionIsMouseDown static field).
- I had to remember the context menu opened by a right click (
ContextMenu static field).
The only side effect I found is when SelectOnMouseRightClick is true. Sometimes the right-click context menu flickers when its opened and right-clicking on a blank are in the TextBox does not do "select all".
