我们发现我们无法绑定密码框的密码，PasswordBox 的 Password 不能绑定。 我们想做 MVVM ，我们需要绑定密码，不能使用前台 xaml.cs 监听 密码改变得到密码的值，传到 ViewModel 。 本文提供一个简单方法来绑定 WPF 的 PasswordBox 的 Password 。这种方法不仅在 WPF 可以使用，在 UWP 也可以使用。关于 UWP 绑定密码，可以在我博客 win10 uwp 绑定密码 查看。
我在网上找的很多大神给出的可以解决绑定密码的方法，下面是我找的一个简单方法。
首先需要新建一个类 PasswordHelper ，他是一个静态类，当然不是静态也没关系，但是一般写静态的可以让我们少犯错，因为我们所有属性等都是需要静态的。
public static class PasswordHelper
{
public static readonly DependencyProperty PasswordProperty =
DependencyProperty.RegisterAttached("Password",
typeof(string), typeof(PasswordHelper),
new FrameworkPropertyMetadata(string.Empty, OnPasswordPropertyChanged));
public static readonly DependencyProperty AttachProperty =
DependencyProperty.RegisterAttached("Attach",
typeof(bool), typeof(PasswordHelper), new PropertyMetadata(false, Attach));
private static readonly DependencyProperty IsUpdatingProperty =
DependencyProperty.RegisterAttached("IsUpdating", typeof(bool),
typeof(PasswordHelper));
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;
if (passwordBox != null)
{
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;
if (passwordBox != null)
{
SetIsUpdating(passwordBox, true);
SetPassword(passwordBox, passwordBox.Password);
SetIsUpdating(passwordBox, false);
}
}
}
写完我们就可以使用他，使用很简单，在我们需要密码框的页面的xaml 上写两行新的代码就好。
<PasswordBox local:PasswordHelper.Attach="True"
local:PasswordHelper.Password="{Binding Password, Mode=TwoWay}"
Width="180" Style="{DynamicResource PasswordBoxStyle}"/>
其中，Password 是 ViewModel 的PassWord，很简单我们把PasswordBox 绑定到ViewModel。
PASSWORDPROPERTY是附加属性，REGISTERATTACHED 就是注册附加。
我们附加属性是回调，当属性变化使用函数。
我们需要设置Attach，设置时调用static void Attach(DependencyObject sender, DependencyPropertyChangedEventArgs e)
在 Attach 触发，首先要判断设置的 sender 是不是 Password
PasswordBox passwordBox = sender as PasswordBox;
if (passwordBox == null)
{
return;
}
判断改变的值，Old是true还是false，如果是true，那么之前用了事件，我们要把事件
passwordBox.PasswordChanged -= PasswordChanged;
如果之前是false，那么没绑定，我们不能删除。
判断要改变的，如果是true，我们就
passwordBox.PasswordChanged += PasswordChanged;
如果不是，我们就不使用。
我们使用了是否存在密码修改就使用PasswordChanged函数。也就是设置了刚才的就可在密码变化使用PasswordChanged。
我们在PasswordChanged判断输入是不是PasswordBox，把密码传进PasswordProperty。
参见：http://www.wpftutorial.net/PasswordBox.html
还有一个简单方法
using System.Windows;
using System.Windows.Controls;
namespace CustomControl
{
public class BindablePasswordBox : Decorator
{
/// <summary>
/// The password dependency property.
/// </summary>
public static readonly DependencyProperty PasswordProperty;
private bool isPreventCallback;
private RoutedEventHandler savedCallback;
/// <summary>
/// Static constructor to initialize the dependency properties.
/// </summary>
static BindablePasswordBox()
{
PasswordProperty = DependencyProperty.Register(
"Password",
typeof(string),
typeof(BindablePasswordBox),
new FrameworkPropertyMetadata("", FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, new PropertyChangedCallback(OnPasswordPropertyChanged))
);
}
/// <summary>
/// Saves the password changed callback and sets the child element to the password box.
/// </summary>
public BindablePasswordBox()
{
savedCallback = HandlePasswordChanged;
PasswordBox passwordBox = new PasswordBox();
passwordBox.PasswordChanged += savedCallback;
Child = passwordBox;
}
/// <summary>
/// The password dependency property.
/// </summary>
public string Password
{
get { return GetValue(PasswordProperty) as string; }
set { SetValue(PasswordProperty, value); }
}
/// <summary>
/// Handles changes to the password dependency property.
/// </summary>
/// <param name="d">the dependency object</param>
/// <param name="eventArgs">the event args</param>
private static void OnPasswordPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs eventArgs)
{
BindablePasswordBox bindablePasswordBox = (BindablePasswordBox) d;
PasswordBox passwordBox = (PasswordBox) bindablePasswordBox.Child;
if (bindablePasswordBox.isPreventCallback)
{
return;
}
passwordBox.PasswordChanged -= bindablePasswordBox.savedCallback;
passwordBox.Password = (eventArgs.NewValue != null) ? eventArgs.NewValue.ToString() : "";
passwordBox.PasswordChanged += bindablePasswordBox.savedCallback;
}
/// <summary>
/// Handles the password changed event.
/// </summary>
/// <param name="sender">the sender</param>
/// <param name="eventArgs">the event args</param>
private void HandlePasswordChanged(object sender, RoutedEventArgs eventArgs)
{
PasswordBox passwordBox = (PasswordBox) sender;
isPreventCallback = true;
Password = passwordBox.Password;
isPreventCallback = false;
}
}
}
