MVVM架构下wpf的密码框绑定

背景：TextBox可以很轻松地对Text使用Binding，绑定ViewModel类里面的属性

        即：

        但是使用PasswordBox的密码框就不行了，因为没有Text这个属性，Password不是依赖属性

那么就要自己实现一个PasswordBox的帮助类了

第一步添加Helper类（创建在WPF用户控件库中）

    public class PasswordBindingHelper
    {
        public static readonly DependencyProperty PasswordProperty =
        DependencyProperty.RegisterAttached("Password",
        typeof(string), typeof(PasswordBindingHelper),
        new FrameworkPropertyMetadata(string.Empty, OnPasswordPropertyChanged));
 
        public static readonly DependencyProperty AttachProperty =
            DependencyProperty.RegisterAttached("Attach",
            typeof(bool), typeof(PasswordBindingHelper), new PropertyMetadata(false, Attach));
 
        private static readonly DependencyProperty IsUpdatingProperty =
           DependencyProperty.RegisterAttached("IsUpdating", typeof(bool),
           typeof(PasswordBindingHelper));
 
 
        public static void SetAttach(DependencyObject dp, bool value)
        {
            dp.SetValue(AttachProperty, value);
        }
 
        public static bool GetAttach(DependencyObject dp)
        {
            return (bool)dp.GetValue(AttachProperty);
        }
 
        public static string GetPassword(DependencyObject dp)
        {
            return (string)dp.GetValue(PasswordProperty);
        }
 
        public static void SetPassword(DependencyObject dp, string value)
        {
            dp.SetValue(PasswordProperty, value);
        }
 
        private static bool GetIsUpdating(DependencyObject dp)
        {
            return (bool)dp.GetValue(IsUpdatingProperty);
        }
 
        private static void SetIsUpdating(DependencyObject dp, bool value)
        {
            dp.SetValue(IsUpdatingProperty, value);
        }
 
        private static void OnPasswordPropertyChanged(DependencyObject sender,
            DependencyPropertyChangedEventArgs e)
        {
            PasswordBox passwordBox = sender as PasswordBox;
            passwordBox.PasswordChanged -= PasswordChanged;
 
            if (!(bool)GetIsUpdating(passwordBox))
            {
                passwordBox.Password = (string)e.NewValue;
            }
            passwordBox.PasswordChanged += PasswordChanged;
        }
 
        private static void Attach(DependencyObject sender,
            DependencyPropertyChangedEventArgs e)
        {
            PasswordBox passwordBox = sender as PasswordBox;
 
            if (passwordBox == null)
                return;
 
            if ((bool)e.OldValue)
            {
                passwordBox.PasswordChanged -= PasswordChanged;
            }
 
            if ((bool)e.NewValue)
            {
                passwordBox.PasswordChanged += PasswordChanged;
            }
        }
 
        private static void PasswordChanged(object sender, RoutedEventArgs e)
        {
            PasswordBox passwordBox = sender as PasswordBox;
            SetIsUpdating(passwordBox, true);
            SetPassword(passwordBox, passwordBox.Password);
            SetIsUpdating(passwordBox, false);
        }
    }

第二步：到xaml中使用帮助类添加PasswordBox的绑定就行了：

local:PasswordBindingHelper.Password="{Binding LoginPwd,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"

这下就可以绑定VeiwModel类下面的LoginPwd了

Attach是一个附加属性（Attached Property），它被用来激活或者禁用该 PasswordBindingHelper 的功能。

参考：mvvmlight下passwordBox绑定的解决方法_azyrg88422的博客-CSDN博客

好像上面的写复杂了，其实就是简单的附加属性就行

帮助类中设置附加属性，附加属性没有指定是在哪个控件，想要在哪个地方用都行

public class APPwd
{
    public static string GetPassword(DependencyObject obj)
    {
        return (string)obj.GetValue(PasswordProperty);
    }
 
    public static void SetPassword(DependencyObject obj, string value)
    {
        obj.SetValue(PasswordProperty, value);
    }
 
    // Using a DependencyProperty as the backing store for Password.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty PasswordProperty =
        DependencyProperty.RegisterAttached("Password", typeof(string), typeof(APPwd), new PropertyMetadata(null, new PropertyChangedCallback((s, e) =>
        {
            var pwd = s as PasswordBox;
            pwd.Password = e.NewValue.ToString();
        })));
}

用上附加属性的PasswordBox就可以用这个附加属性绑定ViewModel的内容了

<PasswordBox local:APPwd.Password="{Binding Password}"/>