我知道需要调用RemoveValueChanged，但是我一直没有找到一个可靠的地方去调用它。我现在明白了可能没有这样的地方。
看起来我需要找到一种不同的方式来监视更改，而不是使用AddValueChanged添加处理程序。我正在寻求关于实现此目的的最佳建议。我曾经看到过建议在PropertyMetadata中使用PropertyChangedCallback, 但是当我的TextBox和Adorner不是静态时，我不确定如何做到这一点。此外，IsFocused属性不是我类中创建的DependencyProperty。
public sealed class WatermarkTextBoxBehavior
{
private readonly TextBox m_TextBox;
private TextBlockAdorner m_TextBlockAdorner;
private WatermarkTextBoxBehavior(TextBox textBox)
{
if (textBox == null)
throw new ArgumentNullException("textBox");
m_TextBox = textBox;
}
#region Behavior Internals
private static WatermarkTextBoxBehavior GetWatermarkTextBoxBehavior(DependencyObject obj)
{
return (WatermarkTextBoxBehavior)obj.GetValue(WatermarkTextBoxBehaviorProperty);
}
private static void SetWatermarkTextBoxBehavior(DependencyObject obj, WatermarkTextBoxBehavior value)
{
obj.SetValue(WatermarkTextBoxBehaviorProperty, value);
}
private static readonly DependencyProperty WatermarkTextBoxBehaviorProperty =
DependencyProperty.RegisterAttached("WatermarkTextBoxBehavior",
typeof(WatermarkTextBoxBehavior), typeof(WatermarkTextBoxBehavior), new UIPropertyMetadata(null));
public static bool GetEnableWatermark(TextBox obj)
{
return (bool)obj.GetValue(EnableWatermarkProperty);
}
public static void SetEnableWatermark(TextBox obj, bool value)
{
obj.SetValue(EnableWatermarkProperty, value);
}
public static readonly DependencyProperty EnableWatermarkProperty =
DependencyProperty.RegisterAttached("EnableWatermark", typeof(bool),
typeof(WatermarkTextBoxBehavior), new UIPropertyMetadata(false, OnEnableWatermarkChanged));
private static void OnEnableWatermarkChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
if (e.OldValue != null)
{
var enabled = (bool)e.OldValue;
if (enabled)
{
var textBox = (TextBox)d;
var behavior = GetWatermarkTextBoxBehavior(textBox);
behavior.Detach();
SetWatermarkTextBoxBehavior(textBox, null);
}
}
if (e.NewValue != null)
{
var enabled = (bool)e.NewValue;
if (enabled)
{
var textBox = (TextBox)d;
var behavior = new WatermarkTextBoxBehavior(textBox);
behavior.Attach();
SetWatermarkTextBoxBehavior(textBox, behavior);
}
}
}
private void Attach()
{
m_TextBox.Loaded += TextBoxLoaded;
m_TextBox.TextChanged += TextBoxTextChanged;
m_TextBox.DragEnter += TextBoxDragEnter;
m_TextBox.DragLeave += TextBoxDragLeave;
m_TextBox.IsVisibleChanged += TextBoxIsVisibleChanged;
}
private void Detach()
{
m_TextBox.Loaded -= TextBoxLoaded;
m_TextBox.TextChanged -= TextBoxTextChanged;
m_TextBox.DragEnter -= TextBoxDragEnter;
m_TextBox.DragLeave -= TextBoxDragLeave;
m_TextBox.IsVisibleChanged -= TextBoxIsVisibleChanged;
}
private void TextBoxDragLeave(object sender, DragEventArgs e)
{
UpdateAdorner();
}
private void TextBoxDragEnter(object sender, DragEventArgs e)
{
m_TextBox.TryRemoveAdorners<TextBlockAdorner>();
}
private void TextBoxIsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e)
{
UpdateAdorner();
}
private void TextBoxTextChanged(object sender, TextChangedEventArgs e)
{
var hasText = !string.IsNullOrEmpty(m_TextBox.Text);
SetHasText(m_TextBox, hasText);
}
private void TextBoxLoaded(object sender, RoutedEventArgs e)
{
Init();
}
#endregion
#region Attached Properties
public static string GetLabel(TextBox obj)
{
return (string)obj.GetValue(LabelProperty);
}
public static void SetLabel(TextBox obj, string value)
{
obj.SetValue(LabelProperty, value);
}
public static readonly DependencyProperty LabelProperty =
DependencyProperty.RegisterAttached("Label", typeof(string), typeof(WatermarkTextBoxBehavior));
public static Style GetLabelStyle(TextBox obj)
{
return (Style)obj.GetValue(LabelStyleProperty);
}
public static void SetLabelStyle(TextBox obj, Style value)
{
obj.SetValue(LabelStyleProperty, value);
}
public static readonly DependencyProperty LabelStyleProperty =
DependencyProperty.RegisterAttached("LabelStyle", typeof(Style),
typeof(WatermarkTextBoxBehavior));
public static bool GetHasText(TextBox obj)
{
return (bool)obj.GetValue(HasTextProperty);
}
private static void SetHasText(TextBox obj, bool value)
{
obj.SetValue(HasTextPropertyKey, value);
}
private static readonly DependencyPropertyKey HasTextPropertyKey =
DependencyProperty.RegisterAttachedReadOnly("HasText", typeof(bool),
typeof(WatermarkTextBoxBehavior), new UIPropertyMetadata(false));
public static readonly DependencyProperty HasTextProperty =
HasTextPropertyKey.DependencyProperty;
#endregion
private void Init()
{
m_TextBlockAdorner = new TextBlockAdorner(m_TextBox, GetLabel(m_TextBox), GetLabelStyle(m_TextBox));
UpdateAdorner();
DependencyPropertyDescriptor focusProp = DependencyPropertyDescriptor.FromProperty(UIElement.IsFocusedProperty, typeof(FrameworkElement));
if (focusProp != null)
{
focusProp.AddValueChanged(m_TextBox, (sender, args) => UpdateAdorner());
}
DependencyPropertyDescriptor containsTextProp = DependencyPropertyDescriptor.FromProperty(HasTextProperty, typeof(TextBox));
if (containsTextProp != null)
{
containsTextProp.AddValueChanged(m_TextBox, (sender, args) => UpdateAdorner());
}
}
private void UpdateAdorner()
{
if (GetHasText(m_TextBox) ||
m_TextBox.IsFocused ||
!m_TextBox.IsVisible)
{
// Hide the Watermark Label if the adorner layer is visible
m_TextBox.ToolTip = GetLabel(m_TextBox);
m_TextBox.TryRemoveAdorners<TextBlockAdorner>();
}
else
{
// Show the Watermark Label if the adorner layer is visible
m_TextBox.ToolTip = null;
m_TextBox.TryAddAdorner<TextBlockAdorner>(m_TextBlockAdorner);
}
}
}