为什么 WPF PasswordBox 有时会变为空白，但有时却不会？

Question

我包含了一个示例程序：似乎在使用 Tab 键进入 PasswordBox 时，输入文本并退出会导致 PasswordBox 变为空白。但是在 PasswordBox 中双击、输入文本和跳出不会。为什么会这样？

编辑：我发现 TextBox 也会发生这种情况，因此这不是 PasswordBox 特有的错误。

重新创建每个场景的步骤：

使密码消失

• 点击新建。
• 单击名字字段。
• 输入内容
• 按 TAB 键
• 输入内容
• 按 TAB 键
• 按 TAB 键（是两次，否则 Save 事件触发）
• 输入内容
• 注意点而不是文本 -PasswordBox 正在工作！
• 按 TAB 键。
• PasswordBox 变为空白，让您的朋友大吃一惊！

使密码不消失

• 点击新建。
• 单击名字字段。
• 输入内容
• 按 TAB 键
• 输入内容
• 双击密码字段。
• 输入内容
• 注意点而不是文本 -PasswordBox 正在工作！
• 按 TAB 键。
• 让您的朋友大吃一惊……等等，PasswordBox 不是空白的吗？什么鬼？

示例代码：

using System;
using System.Collections.ObjectModel;
namespace WpfApplication1 {
    public sealed class MyData    {
        private ObservableCollection<MyDataRow> dataList;
        public ObservableCollection<MyDataRow> DataList { get { return dataList; } }
        public MyData() { dataList = new ObservableCollection<MyDataRow>(); }
        public void AddBlankRow() { DataList.Add(new MyDataRow(this)); }
    }
    public sealed class MyDataRow     {
        private readonly MyData myData;
        public MyDataRow(MyData myData) { this.myData = myData; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Password { get; set; }
    }
}

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

namespace WpfApplication1 {
    public partial class MainWindow : Window  {
        private MyData Data { get { return (MyData)DataContext; } }

        public MainWindow() { InitializeComponent(); }

        private void PasswordBox_PasswordChanged(object sender, RoutedEventArgs e)  {
            PasswordBox pb = (PasswordBox)sender;
            if (pb != null) {
                MyDataRow row = pb.DataContext as MyDataRow;
                if (row != null) { row.Password = pb.Password; }
            }
        }

        private void Window_Loaded(object sender, RoutedEventArgs e) { DataContext = new MyData(); }
        private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e) { }
        private void SaveExecute(object sender, ExecutedRoutedEventArgs e) { }
        private void NewExecute(object sender, ExecutedRoutedEventArgs e) { Data.AddBlankRow(); }
        private void CancelExecute(object sender, ExecutedRoutedEventArgs e) { Close(); }
    }
}

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" Loaded="Window_Loaded" WindowStartupLocation="CenterScreen" Closing="Window_Closing">
    <Window.CommandBindings>
        <CommandBinding Command="Save" Executed="SaveExecute" />
        <CommandBinding Command="New" Executed="NewExecute" />
        <CommandBinding Command="Close" Executed="CancelExecute" />
    </Window.CommandBindings>
    <Grid Margin="0,10,0,0">
        <DataGrid ItemsSource="{Binding DataList}" ColumnWidth="*" Margin="10,0,9,38" HorizontalAlignment="Stretch" 
                  AutoGenerateColumns="False" GridLinesVisibility="Horizontal"
                  HeadersVisibility="Column" HorizontalGridLinesBrush="LightGray" CanUserReorderColumns="False" Background="White" >
            <DataGrid.Columns>
                <DataGridTextColumn Header="First Name"  Binding="{Binding FirstName}"/>
                <DataGridTextColumn Header="Last Name"  Binding="{Binding LastName}"/>
                <DataGridTemplateColumn Header="Password" >
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <PasswordBox PasswordChanged="PasswordBox_PasswordChanged"   BorderThickness="0"
                                     Height="23" HorizontalAlignment="Stretch"/>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
            </DataGrid.Columns>
        </DataGrid>
        <Button  
            Content="_New" Command="New"
            Width="75" Height="23" Margin="10,10,10,10"
            HorizontalAlignment="Left" VerticalAlignment="Bottom"/>
        <Button 
            Content="_Save" Command="Save"
            IsDefault="True"
            IsEnabled="True"
            Width="75" Height="23" Margin="10,10,91,10"
            HorizontalAlignment="Right" VerticalAlignment="Bottom" />
        <Button
            Content="Cancel" Command="Close"
            IsEnabled="True"
            Width="75" Height="23" Margin="10,10,10,10"
            HorizontalAlignment="Right" VerticalAlignment="Bottom"/>
    </Grid>
</Window>

编辑

使用 CellTemplate 和 EditingCellTemplate 的数据模板， 我的工作只是保持一致 - 总是显示一些东西，（在这种情况下是一个省略号）。这样，无论如何，当 PasswordBox 失去焦点时，它会变回椭圆。我认为这比有时看到子弹字符有时看到空白要好。 David Edey 的 DataGrid_PreparingCellForEdit 非常适合解决双标签问题。

这是我的数据模板。

    <Grid.Resources>
        <DataTemplate x:Key="PasswordTemplate" >
            <Label BorderThickness="0" Height="23" HorizontalAlignment="Stretch" Content="..."/>
        </DataTemplate>
        <DataTemplate x:Key="EditingPasswordTemplate" >
            <PasswordBox PasswordChanged="PasswordBox_PasswordChanged"   BorderThickness="0" 
                                 Height="23" HorizontalAlignment="Stretch" />
        </DataTemplate>
    </Grid.Resources>

Answer 1

我认为问题与存在两个单独的模板有关：一个用于编辑 (CellEditingTemplate)，另一个用于显示 (CellTemplate)。绕过它的正常方法是使用绑定，并让两个单独的模板都绑定到同一条数据，根据：http://msdn.microsoft.com/en-us/library/system.windows.controls.datagridtemplatecolumn.celltemplate(v=vs.110).aspx

当然，出于安全原因，PasswordBox 不允许您绑定到Password（因为Password 不是依赖属性）。如果这不是一个大问题（我不完全理解为什么会这样，但我猜他们不希望明文密码在绑定中飞来飞去而人们不知道他们在做什么），那么您可以创建一个绑定为根据本文的后半部分：http://wpftutorial.net/PasswordBox.html - 使用自定义静态依赖属性。

所以我已经在下面的代码中实现了该过程，并且我还修复了密码框无法正确聚焦并需要两个选项卡的错误，方法是向PreparingCellForEdit 事件添加一个处理程序，根据@987654323 @

总而言之，我的工作示例的示例代码是：

using System;
using System.Collections.ObjectModel;
namespace WpfApplication1 {
    public sealed class MyData    {
        private ObservableCollection<MyDataRow> dataList;
        public ObservableCollection<MyDataRow> DataList { get { return dataList; } }
        public MyData() { dataList = new ObservableCollection<MyDataRow>(); }
        public void AddBlankRow() { DataList.Add(new MyDataRow(this)); }
    }
    public sealed class MyDataRow     {
        private readonly MyData myData;
        public MyDataRow(MyData myData) { this.myData = myData; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Password { get; set; }
    }
}

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;

namespace WpfApplication1 {
    public partial class MainWindow : Window
    {
        public MainWindow() { InitializeComponent(); }
        private MyData Data { get { return (MyData)DataContext; } }

        void DataGrid_PreparingCellForEdit(object sender, DataGridPreparingCellForEditEventArgs e)
        {
            var inputElement = VisualTreeHelper.GetChild(e.EditingElement, 0) as PasswordBox;
            if (inputElement != null)
            {
                Keyboard.Focus(inputElement);
            }
        }

        private void Window_Loaded(object sender, RoutedEventArgs e) { DataContext = new MyData(); }
        private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e) { }
        private void SaveExecute(object sender, ExecutedRoutedEventArgs e) { }
        private void NewExecute(object sender, ExecutedRoutedEventArgs e) { Data.AddBlankRow(); }
        private void CancelExecute(object sender, ExecutedRoutedEventArgs e) { Close(); }
    }

然后 xaml 是：

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:w="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="525" Loaded="Window_Loaded" WindowStartupLocation="CenterScreen" Closing="Window_Closing">
    <Window.CommandBindings>
        <CommandBinding Command="Save" Executed="SaveExecute" />
        <CommandBinding Command="New" Executed="NewExecute" />
        <CommandBinding Command="Close" Executed="CancelExecute" />
    </Window.CommandBindings>
    <Grid Margin="0,10,0,0">
        <DataGrid ItemsSource="{Binding DataList, Mode=OneTime}" ColumnWidth="*" Margin="10,0,9,38" HorizontalAlignment="Stretch"
                  AutoGenerateColumns="False" GridLinesVisibility="Horizontal"
                  HeadersVisibility="Column" HorizontalGridLinesBrush="LightGray" CanUserReorderColumns="False" Background="White"
                  PreparingCellForEdit="DataGrid_PreparingCellForEdit">
            <DataGrid.Resources>
                <DataTemplate x:Key="PasswordTemplate">
                    <PasswordBox w:PasswordHelper.Attach="True" w:PasswordHelper.Password="{Binding Password, Mode=TwoWay}" 
                                 BorderThickness="0" Height="23" HorizontalAlignment="Stretch" Width="130" />
                </DataTemplate>
            </DataGrid.Resources>
            <DataGrid.Columns>
                <DataGridTextColumn Header="First Name"  Binding="{Binding FirstName}"/>
                <DataGridTextColumn Header="Last Name"  Binding="{Binding LastName}"/>
                <DataGridTemplateColumn Header="Password" CellTemplate="{StaticResource PasswordTemplate}"
                                        CellEditingTemplate="{StaticResource PasswordTemplate}" />
            </DataGrid.Columns>
        </DataGrid>
        <Button
            Content="_New" Command="New"
            Width="75" Height="23" Margin="10,10,10,10"
            HorizontalAlignment="Left" VerticalAlignment="Bottom"/>
        <Button
            Content="_Save" Command="Save"
            IsDefault="True"
            IsEnabled="True"
            Width="75" Height="23" Margin="10,10,91,10"
            HorizontalAlignment="Right" VerticalAlignment="Bottom" />
        <Button
            Content="Cancel" Command="Close"
            IsEnabled="True"
            Width="75" Height="23" Margin="10,10,10,10"
            HorizontalAlignment="Right" VerticalAlignment="Bottom"/>
    </Grid>
</Window>

然后将http://wpftutorial.net/PasswordBox.html 中的PasswordHelper 类添加到您的命名空间，然后瞧。