Previously, my adorner only supports TextBox, RichTextBox and PasswordBox. I found it limiting, as there are so many controls out there that supports editing text.
One such case is the ComboBox with the IsEditable property set to true. After trying to add a new code brunch to support the case of ComboBox, I bumped into a wall. The IsFocused property of ComboBox is not reporting the right thing! It reports not focused even with my cursor blinking inside the ComboBox. On examining the visual tree, I found the culprit - the TextBox in the ComboBox is having the focus, not the ComboBox itself. Solution? Hunt for this TextBox!
So here comes an updated adorner that searches the visual tree for a TextBox if the attached property is placed on a control other than a TextBox, RichTextBox or PasswordBox. Turned out to be more powerful than originally planned =).
One more feature improvement is to have the option not to hide the placeholder text even if the control have the focus (set HideOnFocus to false). This allows you to focus on the control when the application start up and still have the prompt there to tell your user what to do.
Miles of code coming your way, watch out!
//-----------------------------------------------------------------------
// <copyright file="Placeholder.cs" company="Jeow Li Huan">
// Copyright (c) Jeow Li Huan. All rights reserved.
// </copyright>
//-----------------------------------------------------------------------
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Documents;
using System.Windows.Media;
namespace TetonWhitewaterKayak.WinUI
{
/// <summary>
/// Represents an adorner that adds placeholder text to a <see cref="T:System.Windows.Controls.TextBox"/>,
/// <see cref="T:System.Windows.Controls.RichTextBox"/> or <see cref="T:System.Windows.Controls.PasswordBox"/>.
/// </summary>
public class Placeholder : Adorner
{
#region Dependency Property
/// <summary>
/// Identifies the <see cref="T:Huan.Windows.Documents.Placeholder" />.Text attached property.
/// </summary>
public static readonly DependencyProperty TextProperty = DependencyProperty.RegisterAttached(
"Text",
typeof(string),
typeof(Placeholder),
new FrameworkPropertyMetadata(string.Empty, OnTextChanged));
/// <summary>
/// Identifies the <see cref="T:Huan.Windows.Documents.Placeholder" />.HideOnFocus attached property.
/// </summary>
public static readonly DependencyProperty HideOnFocusProperty = DependencyProperty.RegisterAttached(
"HideOnFocus",
typeof(bool),
typeof(Placeholder),
new FrameworkPropertyMetadata(true, OnHideOnFocusChanged));
#endregion
/// <summary>
/// <see langword="true"/> when the placeholder text is visible, <see langword="false" /> otherwise.
/// Used to avoid calling <see cref="M:System.Windows.UIElement.InvalidateVisual"/> unnecessarily.
/// </summary>
private bool isPlaceholderVisible;
#region Constructors
/// <summary>
/// Initializes static members of the <see cref="T:Huan.Windows.Documents.Placeholder"/> class.
/// </summary>
static Placeholder()
{
IsHitTestVisibleProperty.OverrideMetadata(typeof(Placeholder), new FrameworkPropertyMetadata(false));
ClipToBoundsProperty.OverrideMetadata(typeof(Placeholder), new FrameworkPropertyMetadata(true));
}
/// <summary>
/// Initializes a new instance of the <see cref="T:Huan.Windows.Documents.Placeholder"/> class.
/// </summary>
/// <param name="adornedElement">
/// The element to bind the adorner to.
/// </param>
/// <exception cref="T:System.ArgumentNullException">
/// Raised when adornedElement is null.
/// </exception>
public Placeholder(PasswordBox adornedElement)
: this((Control)adornedElement)
{
if (!(adornedElement.IsFocused && (bool)adornedElement.GetValue(HideOnFocusProperty)))
adornedElement.PasswordChanged += this.AdornedElement_ContentChanged;
}
/// <summary>
/// Initializes a new instance of the <see cref="T:Huan.Windows.Documents.Placeholder"/> class.
/// </summary>
/// <param name="adornedElement">
/// The element to bind the adorner to.
/// </param>
/// <exception cref="T:System.ArgumentNullException">
/// Raised when adornedElement is null.
/// </exception>
public Placeholder(TextBoxBase adornedElement)
: this((Control)adornedElement)
{
if (!(adornedElement.IsFocused && (bool)adornedElement.GetValue(HideOnFocusProperty)))
adornedElement.TextChanged += this.AdornedElement_ContentChanged;
}
/// <summary>
/// Initializes a new instance of the <see cref="T:Huan.Windows.Documents.Placeholder"/> class.
/// </summary>
/// <param name="adornedElement">
/// The element to bind the adorner to.
/// </param>
/// <exception cref="T:System.ArgumentNullException">
/// Raised when adornedElement is null.
/// </exception>
protected Placeholder(Control adornedElement)
: base(adornedElement)
{
if ((bool)adornedElement.GetValue(HideOnFocusProperty))
{
adornedElement.GotFocus += this.AdornedElement_GotFocus;
adornedElement.LostFocus += this.AdornedElement_LostFocus;
}
}
#endregion
#region Attached Property Getters and Setters
/// <summary>
/// Gets the value of the <see cref="T:Huan.Windows.Documents.Placeholder" />.Text attached property for a specified element.
/// </summary>
/// <param name="adornedElement">
/// The element from which the property value is read.
/// </param>
/// <returns>
/// The placeholder text property value for the element.
/// </returns>
/// <exception cref="T:ArgumentNullException">
/// Raised when adornedElement is null.
/// </exception>
public static string GetText(Control adornedElement)
{
if (adornedElement == null)
throw new ArgumentNullException("adornedElement");
return (string)adornedElement.GetValue(TextProperty);
}
/// <summary>
/// Sets the value of the <see cref="T:Huan.Windows.Documents.Placeholder" />.Text attached property to a specified element.
/// </summary>
/// <param name="adornedElement">
/// The element to which the attached property is written.
/// </param>
/// <param name="placeholderText">
/// The needed placeholder text value.
/// </param>
/// <exception cref="T:ArgumentNullException">
/// Raised when adornedElement is null.
/// </exception>
/// <exception cref="T:InvalidOperationException">
/// Raised when adornedElement is not a <see cref="T:System.Windows.Controls.TextBox"/>,
/// <see cref="T:System.Windows.Controls.RichTextBox"/> or <see cref="T:System.Windows.Controls.PasswordBox"/>.
/// </exception>
public static void SetText(Control adornedElement, string placeholderText)
{
if (adornedElement == null)
throw new ArgumentNullException("adornedElement");
adornedElement.SetValue(TextProperty, placeholderText);
}
/// <summary>
/// Gets the value of the <see cref="T:Huan.Windows.Documents.Placeholder" />.HideOnFocus attached property for a specified element.
/// </summary>
/// <param name="adornedElement">
/// The element from which the property value is read.
/// </param>
/// <returns>
/// A value indicating whether the control will be hidden when the element is in focus.
/// </returns>
/// <exception cref="T:ArgumentNullException">
/// Raised when adornedElement is null.
/// </exception>
public static bool GetHideOnFocus(Control adornedElement)
{
if (adornedElement == null)
throw new ArgumentNullException("adornedElement");
return (bool)adornedElement.GetValue(HideOnFocusProperty);
}
/// <summary>
/// Sets the value of the <see cref="T:Huan.Windows.Documents.Placeholder" />.HideOnFocus attached property to a specified element.
/// </summary>
/// <param name="adornedElement">
/// The element to which the attached property is written.
/// </param>
/// <param name="hideOnFocus">
/// A value indicating whether to hide the placeholder text when the element is in focus.
/// </param>
/// <exception cref="T:ArgumentNullException">
/// Raised when adornedElement is null.
/// </exception>
/// <exception cref="T:InvalidOperationException">
/// Raised when adornedElement is not a <see cref="T:System.Windows.Controls.TextBox"/>,
/// <see cref="T:System.Windows.Controls.RichTextBox"/> or <see cref="T:System.Windows.Controls.PasswordBox"/>.
/// </exception>
public static void SetHideOnFocus(Control adornedElement, bool hideOnFocus)
{
if (adornedElement == null)
throw new ArgumentNullException("adornedElement");
adornedElement.SetValue(HideOnFocusProperty, hideOnFocus);
}
#endregion
/// <summary>
/// Draws the content of a <see cref="T:System.Windows.Media.DrawingContext" /> object during the render pass of a <see cref="T:Huan.Windows.Documents.Placeholder"/> element.
/// </summary>
/// <param name="drawingContext">
/// The <see cref="T:System.Windows.Media.DrawingContext" /> object to draw. This context is provided to the layout system.
/// </param>
protected override void OnRender(DrawingContext drawingContext)
{
Control adornedElement = this.AdornedElement as Control;
string placeholderText;
bool hideOnFocus = (bool)adornedElement.GetValue(HideOnFocusProperty);
if (adornedElement == null ||
(adornedElement.IsFocused && hideOnFocus) ||
!this.IsElementEmpty() ||
string.IsNullOrEmpty(placeholderText = (string)adornedElement.GetValue(TextProperty)))
this.isPlaceholderVisible = false;
else
{
this.isPlaceholderVisible = true;
Size size = adornedElement.RenderSize;
double maxHeight = size.Height - adornedElement.BorderThickness.Top - adornedElement.BorderThickness.Bottom - adornedElement.Padding.Top - adornedElement.Padding.Bottom;
double maxWidth = size.Width - adornedElement.BorderThickness.Left - adornedElement.BorderThickness.Right - adornedElement.Padding.Left - adornedElement.Padding.Right - 4.0;
if (maxHeight <= 0 || maxWidth <= 0)
return;
TextAlignment computedTextAlignment = this.ComputedTextAlignment();
// Foreground brush does not need to be dynamic. OnRender called when SystemColors changes.
Brush foreground = SystemColors.GrayTextBrush.Clone();
foreground.Opacity = adornedElement.Foreground.Opacity;
Typeface typeface = new Typeface(adornedElement.FontFamily, FontStyles.Italic, adornedElement.FontWeight, adornedElement.FontStretch);
FormattedText formattedText = new FormattedText(
placeholderText,
CultureInfo.CurrentCulture,
adornedElement.FlowDirection,
typeface,
adornedElement.FontSize,
foreground);
formattedText.TextAlignment = computedTextAlignment;
formattedText.MaxTextHeight = maxHeight;
formattedText.MaxTextWidth = maxWidth;
double left;
double top = 0.0;
if (adornedElement.FlowDirection == FlowDirection.RightToLeft)
left = adornedElement.BorderThickness.Right + adornedElement.Padding.Right + 2.0;
else
left = adornedElement.BorderThickness.Left + adornedElement.Padding.Left + 2.0;
switch (adornedElement.VerticalContentAlignment)
{
case VerticalAlignment.Top:
case VerticalAlignment.Stretch:
top = adornedElement.BorderThickness.Top + adornedElement.Padding.Top;
break;
case VerticalAlignment.Bottom:
top = size.Height - adornedElement.BorderThickness.Bottom - adornedElement.Padding.Bottom - formattedText.Height;
break;
case VerticalAlignment.Center:
top = (size.Height + adornedElement.BorderThickness.Top - adornedElement.BorderThickness.Bottom + adornedElement.Padding.Top - adornedElement.Padding.Bottom - formattedText.Height) / 2.0;
break;
}
if (adornedElement.FlowDirection == FlowDirection.RightToLeft)
{
// Somehow everything got drawn reflected. Add a transform to correct.
drawingContext.PushTransform(new ScaleTransform(-1.0, 1.0, RenderSize.Width / 2.0, 0.0));
drawingContext.DrawText(formattedText, new Point(left, top));
drawingContext.Pop();
}
else
drawingContext.DrawText(formattedText, new Point(left, top));
}
}
/// <summary>
/// Adds a <see cref="T:Huan.Windows.Documents.Placeholder"/> to the adorner layer.
/// </summary>
/// <param name="adornedElement">
/// The adorned element.
/// </param>
private static void AddAdorner(Control adornedElement)
{
AdornerLayer adornerLayer = AdornerLayer.GetAdornerLayer(adornedElement);
if (adornerLayer == null)
return;
Adorner[] adorners = adornerLayer.GetAdorners(adornedElement);
if (adorners != null)
foreach (Adorner adorner in adorners)
if (adorner is Placeholder)
{
adorner.InvalidateVisual();
return;
}
TextBox textBox = adornedElement as TextBox;
if (textBox != null)
{
adornerLayer.Add(new Placeholder(textBox));
return;
}
RichTextBox richTextBox = adornedElement as RichTextBox;
if (richTextBox != null)
{
adornerLayer.Add(new Placeholder(richTextBox));
return;
}
PasswordBox passwordBox = adornedElement as PasswordBox;
if (passwordBox != null)
{
adornerLayer.Add(new Placeholder(passwordBox));
return;
}
// TextBox is hidden in template. Search for it.
TextBox templateTextBox = null;
templateTextBox = FindTextBox(adornedElement);
if (templateTextBox != null)
Placeholder.SetText(templateTextBox, (string)Placeholder.GetText(adornedElement));
}
/// <summary>
/// Finds a <see cref="T:System.Windows.Controls.TextBox"/> in the visual tree of the adorned element using a breadth first search.
/// </summary>
/// <param name="adornedElement">The adorned element which visual tree is searched for a <see cref="T:System.Windows.Controls.TextBox"/>.</param>
/// <returns>The <see cref="T:System.Windows.Controls.TextBox"/> if one is found, <see langword="null"/> if none exists.</returns>
private static TextBox FindTextBox(Control adornedElement)
{
TextBox templateTextBox = null;
Queue<DependencyObject> queue = new Queue<DependencyObject>();
queue.Enqueue(adornedElement);
while (queue.Count > 0)
{
DependencyObject element = queue.Dequeue();
templateTextBox = element as TextBox;
if (templateTextBox != null)
break;
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(element); ++i)
queue.Enqueue(VisualTreeHelper.GetChild(element, i));
}
return templateTextBox;
}
/// <summary>
/// Event handler for AdornedElement.Loaded.
/// </summary>
/// <param name="sender">
/// The AdornedElement where the event handler is attached.
/// </param>
/// <param name="e">
/// Provides data about the event.
/// </param>
private static void AdornedElement_Loaded(object sender, RoutedEventArgs e)
{
Control adornedElement = (Control)sender;
adornedElement.Loaded -= AdornedElement_Loaded;
AddAdorner(adornedElement);
}
/// <summary>
/// Invoked whenever <see cref="T:Huan.Windows.Documents.Placeholder" />.Text attached property is changed.
/// </summary>
/// <param name="sender">
/// The object where the event handler is attached.
/// </param>
/// <param name="e">
/// Provides data about the event.
/// </param>
private static void OnTextChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
if (((string)e.OldValue).Equals((string)e.NewValue, StringComparison.Ordinal))
return;
Control adornedElement = sender as Control;
if (adornedElement == null)
return;
if (adornedElement.IsLoaded)
AddAdorner(adornedElement);
else
adornedElement.Loaded += AdornedElement_Loaded;
}
/// <summary>
/// Invoked whenever <see cref="T:Huan.Windows.Documents.Placeholder" />.HideOnFocus attached property is changed.
/// </summary>
/// <param name="sender">
/// The object where the event handler is attached.
/// </param>
/// <param name="e">
/// Provides data about the event.
/// </param>
private static void OnHideOnFocusChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
bool hideOnFocus = (bool)e.NewValue;
if ((bool)e.OldValue == hideOnFocus)
return;
Control adornedElement = sender as Control;
if (!(adornedElement is TextBox || adornedElement is PasswordBox || adornedElement is RichTextBox))
{
if (!adornedElement.IsLoaded)
adornedElement.Loaded += ChangeHideOnFocus;
else
{
TextBox templateTextBox = FindTextBox(adornedElement);
if (templateTextBox != null)
Placeholder.SetHideOnFocus(templateTextBox, (bool)e.NewValue);
}
return;
}
Placeholder placeholder = null;
AdornerLayer adornerLayer = AdornerLayer.GetAdornerLayer(adornedElement);
if (adornerLayer == null)
return;
Adorner[] adorners = adornerLayer.GetAdorners(adornedElement);
if (adorners != null)
foreach (Adorner adorner in adorners)
{
placeholder = adorner as Placeholder;
if (placeholder != null)
break;
}
if (placeholder == null)
return;
if (adornedElement.IsLoaded)
{
if (hideOnFocus)
{
adornedElement.GotFocus += placeholder.AdornedElement_GotFocus;
adornedElement.LostFocus += placeholder.AdornedElement_LostFocus;
if (adornedElement.IsFocused && placeholder.isPlaceholderVisible)
placeholder.InvalidateVisual();
}
else
{
adornedElement.GotFocus -= placeholder.AdornedElement_GotFocus;
adornedElement.LostFocus -= placeholder.AdornedElement_LostFocus;
placeholder.AdornedElement_LostFocus(adornedElement, new RoutedEventArgs(UIElement.LostFocusEvent, placeholder));
}
}
else
adornedElement.Loaded += AdornedElement_Loaded;
}
/// <summary>
/// Changes the HideOnFocus property of the text box in the visual tree of the sender.
/// </summary>
/// <param name="sender">The object where the event handler is attached.</param>
/// <param name="e">Provides data about the event.</param>
private static void ChangeHideOnFocus(object sender, RoutedEventArgs e)
{
Control adornedElement = sender as Control;
if (adornedElement == null)
return;
TextBox templateTextBox = FindTextBox(adornedElement);
if (templateTextBox != null)
Placeholder.SetHideOnFocus(templateTextBox, Placeholder.GetHideOnFocus(adornedElement));
}
#region Event Handlers
/// <summary>
/// Event handler for AdornedElement.GotFocus.
/// </summary>
/// <param name="sender">
/// The AdornedElement where the event handler is attached.
/// </param>
/// <param name="e">
/// Provides data about the event.
/// </param>
private void AdornedElement_GotFocus(object sender, RoutedEventArgs e)
{
TextBoxBase textBoxBase = AdornedElement as TextBoxBase;
if (textBoxBase != null)
textBoxBase.TextChanged -= this.AdornedElement_ContentChanged;
else
{
PasswordBox passwordBox = AdornedElement as PasswordBox;
if (passwordBox != null)
passwordBox.PasswordChanged -= this.AdornedElement_ContentChanged;
}
if (this.isPlaceholderVisible)
this.InvalidateVisual();
}
/// <summary>
/// Event handler for AdornedElement.LostFocus.
/// </summary>
/// <param name="sender">
/// The AdornedElement where the event handler is attached.
/// </param>
/// <param name="e">
/// Provides data about the event.
/// </param>
private void AdornedElement_LostFocus(object sender, RoutedEventArgs e)
{
TextBoxBase textBoxBase = AdornedElement as TextBoxBase;
if (textBoxBase != null)
textBoxBase.TextChanged += this.AdornedElement_ContentChanged;
else
{
PasswordBox passwordBox = AdornedElement as PasswordBox;
if (passwordBox != null)
passwordBox.PasswordChanged += this.AdornedElement_ContentChanged;
}
if (!this.isPlaceholderVisible && this.IsElementEmpty())
this.InvalidateVisual();
}
/// <summary>
/// Event handler for AdornedElement.ContentChanged.
/// </summary>
/// <param name="sender">
/// The AdornedElement where the event handler is attached.
/// </param>
/// <param name="e">
/// Provides data about the event.
/// </param>
private void AdornedElement_ContentChanged(object sender, RoutedEventArgs e)
{
if (this.isPlaceholderVisible ^ this.IsElementEmpty())
this.InvalidateVisual();
}
#endregion
/// <summary>
/// Checks if the content of the adorned element is empty.
/// </summary>
/// <returns>
/// Returns <see langword="true" /> if the content is empty, <see langword="false" /> otherwise.
/// </returns>
private bool IsElementEmpty()
{
UIElement adornedElement = AdornedElement;
TextBox textBox = adornedElement as TextBox;
if (textBox != null)
return string.IsNullOrEmpty(textBox.Text);
PasswordBox passwordBox = adornedElement as PasswordBox;
if (passwordBox != null)
return string.IsNullOrEmpty(passwordBox.Password);
RichTextBox richTextBox = adornedElement as RichTextBox;
if (richTextBox != null)
{
BlockCollection blocks = richTextBox.Document.Blocks;
if (blocks.Count == 0)
return true;
if (blocks.Count == 1)
{
Paragraph paragraph = blocks.FirstBlock as Paragraph;
if (paragraph == null)
return false;
if (paragraph.Inlines.Count == 0)
return true;
if (paragraph.Inlines.Count == 1)
{
Run run = paragraph.Inlines.FirstInline as Run;
return run != null && string.IsNullOrEmpty(run.Text);
}
}
return false;
}
return false;
}
/// <summary>
/// Computes the text alignment of the adorned element.
/// </summary>
/// <returns>
/// Returns the computed text alignment.
/// </returns>
private TextAlignment ComputedTextAlignment()
{
Control adornedElement = AdornedElement as Control;
TextBox textBox = adornedElement as TextBox;
if (textBox != null)
{
if (DependencyPropertyHelper.GetValueSource(textBox, TextBox.HorizontalContentAlignmentProperty)
.BaseValueSource != BaseValueSource.Local ||
DependencyPropertyHelper.GetValueSource(textBox, TextBox.TextAlignmentProperty)
.BaseValueSource == BaseValueSource.Local)
// TextAlignment dominates
return textBox.TextAlignment;
}
RichTextBox richTextBox = adornedElement as RichTextBox;
if (richTextBox != null)
{
BlockCollection blocks = richTextBox.Document.Blocks;
TextAlignment textAlignment = richTextBox.Document.TextAlignment;
if (blocks.Count == 0)
return textAlignment;
if (blocks.Count == 1)
{
Paragraph paragraph = blocks.FirstBlock as Paragraph;
if (paragraph == null)
return textAlignment;
return paragraph.TextAlignment;
}
return textAlignment;
}
switch (adornedElement.HorizontalContentAlignment)
{
case HorizontalAlignment.Left:
return TextAlignment.Left;
case HorizontalAlignment.Right:
return TextAlignment.Right;
case HorizontalAlignment.Center:
return TextAlignment.Center;
case HorizontalAlignment.Stretch:
return TextAlignment.Justify;
}
return TextAlignment.Left;
}
}
}
