模板中的 TemplateBinding 问题

昨天一个朋友向我求助一个自定义水印控件绑定的问题，问题出在文本框中输入的文本，不能绑定到

相应的依赖属性上（自定义的依赖属性 PassText），他纠结了很久找不出问题所在。问题帮他解决后，这里稍

做总结。

朋友有问题的文本框代码下载

问题描述：

1）默认显示效果：

模板中的 TemplateBinding 问题

2）在“水印密码框”中输入四个 ‘a’:

模板中的 TemplateBinding 问题

3）单击按钮，打印出密码框中的字符串，但是密码框中的文字并没有显示，显示的还是定义依赖属性时

的默认值：

模板中的 TemplateBinding 问题

他的部分源代码：

1）密码框控件类继承自 TextBox ，其中依赖属性 PassText 为绑定到密码框的属性：

public class WaterPasswordBox : TextBox
    {
        public static readonly DependencyProperty PassTextProperty = DependencyProperty.Register(
          "PassText", typeof( string ), typeof( WaterPasswordBox ), new PropertyMetadata( "空" ) );

        public string PassText
        {
            get { return (string)GetValue( PassTextProperty ); }
            set { SetValue( PassTextProperty, value ); }
        }

        public static DependencyProperty WaterContentProprty = DependencyProperty.Register("WaterContent", typeof(object), typeof(WaterPasswordBox), new PropertyMetadata("水印密码框"));

        public object WaterContent
        {
            get
            {
                return GetValue(WaterContentProprty);
            }

            set
            {
                SetValue(WaterContentProprty, value);
            }
        }

        public static DependencyProperty WaterForegroundProprty = DependencyProperty.Register("WaterForeground", typeof(Brush), typeof(WaterPasswordBox), new PropertyMetadata(new SolidColorBrush(Colors.Gray)));

        public Brush WaterForeground
        {
            get
            {
                return (Brush)GetValue(WaterForegroundProprty);
            }

            set
            {
                SetValue(WaterForegroundProprty, value);
            }
        }

        public WaterPasswordBox()
        {
            DefaultStyleKey = typeof(WaterPasswordBox);
        }

        ContentControl WaterContentElement = null;
        PasswordBox PasswordBoxElement = null;

        public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();
            WaterContentElement = this.GetTemplateChild("WaterCoElement") as ContentControl;
            PasswordBoxElement = this.GetTemplateChild("ContentElement") as PasswordBox;
            if (WaterContentElement != null && PasswordBoxElement != null)
            {
                if (string.IsNullOrEmpty(PasswordBoxElement.Password))
                    WaterContentElement.Visibility = System.Windows.Visibility.Visible;
                  
                else
                    WaterContentElement.Visibility = System.Windows.Visibility.Collapsed;
            }
        }

        protected override void OnGotFocus(RoutedEventArgs e)
        {
            if (WaterContentElement != null && string.IsNullOrEmpty(PasswordBoxElement.Password))
                WaterContentElement.Visibility = Visibility.Collapsed;
            base.OnGotFocus(e);
        }
        
     //   public event TextChangedEventHandler TextChanged +=   ;
        protected override void OnLostFocus(RoutedEventArgs e)
        {
          
            if (WaterContentElement != null && string.IsNullOrEmpty(PasswordBoxElement.Password))
                WaterContentElement.Visibility = Visibility.Visible;
            base.OnLostFocus(e);
        }
    }

View Code