support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Controls/Attach/PasswordBoxMonitor.cs

@@ -0,0 +1,54 @@
+using System.Windows;
+using HandyControl.Data;
+
+namespace HandyControl.Controls
+{
+    public class PasswordBoxMonitor
+    {
+        /// <summary>
+        ///     密码长度
+        /// </summary>
+        public static readonly DependencyProperty PasswordLengthProperty = DependencyProperty.RegisterAttached(
+            "PasswordLength", typeof(int), typeof(PasswordBoxMonitor), new PropertyMetadata(default(int)));
+
+        public static void SetPasswordLength(DependencyObject element, int value) => element.SetValue(PasswordLengthProperty, value);
+
+        public static int GetPasswordLength(DependencyObject element) => (int)element.GetValue(PasswordLengthProperty);
+
+        /// <summary>
+        ///     是否监测
+        /// </summary>
+        public static readonly DependencyProperty IsMonitoringProperty = DependencyProperty.RegisterAttached(
+            "IsMonitoring", typeof(bool), typeof(PasswordBoxMonitor), new FrameworkPropertyMetadata(ValueBoxes.FalseBox, FrameworkPropertyMetadataOptions.Inherits, OnIsMonitoringChanged));
+
+        private static void OnIsMonitoringChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+        {
+            if (d is System.Windows.Controls.PasswordBox passwordBox)
+            {
+                if (e.NewValue is bool boolValue)
+                {
+                    if (boolValue)
+                    {
+                        passwordBox.PasswordChanged += PasswordChanged;
+                    }
+                    else
+                    {
+                        passwordBox.PasswordChanged -= PasswordChanged;
+                    }
+                }
+            }
+        }
+
+        public static void SetIsMonitoring(DependencyObject element, bool value) => element.SetValue(IsMonitoringProperty, value);
+
+        public static bool GetIsMonitoring(DependencyObject element) => (bool)element.GetValue(IsMonitoringProperty);
+
+        private static void PasswordChanged(object sender, RoutedEventArgs e)
+        {
+            if (sender is System.Windows.Controls.PasswordBox passwordBox)
+            {
+                SetPasswordLength(passwordBox, passwordBox.Password.Length);
+            }
+        }
+    }
+}