密码框密码不能绑定问题解决方案

想要扩展该控件时发现PasswordBox是一个密封类，是不可继承的。

故通过附加属性来实现该功能。

声明了两个附加属性

IsPasswordBindingEnabled：用来指示密码是否可用来绑定，当值发生改变时订阅或者取消订阅当Password改变时同步用于绑定的密码附加属性

BindedPassword：用于绑定的密码，与密码同步，当值发生改变是时与Password同步

/// <summary>
/// 扩展密码框密码可用于绑定的帮助类
/// </summary>
public class BindedPasswordHelper
{
#region 指示密码框的密码是否可以绑定的附加属性

public static bool GetIsPasswordBindingEnabled(DependencyObject obj)
{
return (bool)obj.GetValue(IsPasswordBindingEnabledProperty);
}

public static void SetIsPasswordBindingEnabled(DependencyObject obj, bool value)
{
obj.SetValue(IsPasswordBindingEnabledProperty, value);
}

public static readonly DependencyProperty IsPasswordBindingEnabledProperty =
DependencyProperty.RegisterAttached("IsPasswordBindingEnabled", typeof(bool),
typeof(BindedPasswordHelper),
new UIPropertyMetadata(false, OnIsPasswordBindingEnabledChanged));

private static void OnIsPasswordBindingEnabledChanged(DependencyObject obj,
DependencyPropertyChangedEventArgs e)
{
var passwordBox = obj as PasswordBox;

if (passwordBox != null)
{
passwordBox.PasswordChanged -= PasswordBoxPasswordChanged;

if ((bool)e.NewValue)
{
passwordBox.PasswordChanged += PasswordBoxPasswordChanged;
}

}
}

//当密码发生改变时，更新用于绑定的密码
private static void PasswordBoxPasswordChanged(object sender, RoutedEventArgs e)
{
var passwordBox = (PasswordBox)sender;

if (!string.Equals(GetBindedPassword(passwordBox), passwordBox.Password))
{
SetBindedPassword(passwordBox, passwordBox.Password);
}
}

#endregion

#region 用于绑定的密码的附加属性

public static string GetBindedPassword(DependencyObject obj)
{
return (string)obj.GetValue(BindedPasswordProperty);
}

public static void SetBindedPassword(DependencyObject obj, string value)
{
obj.SetValue(BindedPasswordProperty, value);
}

public static readonly DependencyProperty BindedPasswordProperty =
DependencyProperty.RegisterAttached("BindedPassword", typeof(string),
typeof(BindedPasswordHelper),
new UIPropertyMetadata(string.Empty, OnBindedPasswordChanged));

//当被绑定的密码更新时，更新密码
private static void OnBindedPasswordChanged(DependencyObject obj,
DependencyPropertyChangedEventArgs e)
{
var passwordBox = obj as PasswordBox;
if (passwordBox != null && e.NewValue != null && passwordBox.Password != e.NewValue.ToString())
{
passwordBox.Password = e.NewValue.ToString();
}
}

#endregion
}

使用方法，这里要特别注意，与TextBox类似，一定要声明Mode已经UpdateSourceTrigger，不然绑定的值不会与后台的属性同步

<PasswordBox Style="{StaticResource PasswordBoxStyle}"
helper:BindedPasswordHelper.IsPasswordBindingEnabled="True"
helper:BindedPasswordHelper.BindedPassword="{Binding Password,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>