为什么WPF PasswordBox有时会变空，但其他情况下不会

我包含了一个示例程序：似乎当选项卡进入PasswordBox时，输入文本并选项卡退出会导致PasswordBox变为空白。但是双击PasswordBox，输入文本并用Tab键弹出却不行。为什么会发生这种情况？

编辑：我发现TextBox也会出现这种情况，所以它不是PasswordBox特有的bug。

重新创建每个场景的步骤：

使密码消失

单击"新建"
单击"名字"字段
键入一些内容
按TAB键
键入一些内容
按TAB键
按TAB键（是两次，否则"保存"事件将触发）
键入一些内容
注意点而不是文本-PasswordBox正在工作
按TAB键
当PasswordBox变为空白时，让你的朋友大吃一惊

使密码不消失

单击"新建"
单击"名字"字段
键入一些内容
按TAB键
键入一些内容
双击密码字段
键入一些内容
注意点而不是文本-PasswordBox正在工作
按TAB键
让你的朋友感到惊讶。。等等，PasswordBox不是空白的吗？WTF

样本代码：

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——总是展示一些东西（在这种情况下是一种幻觉）。这样，无论怎样，当PasswordBox失去焦点时，它都会变回消隐。我认为这比有时看到子弹头和有时看到空白要好。David Edey的DataGrid_PreparaingCellForEdit非常适合解决双选项卡问题。

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>

我认为问题与存在两个独立的模板有关：一个用于编辑（CellEditingTemplate），另一个用于显示（CellTemplate）。通常的解决方法是使用绑定，并让两个单独的模板都绑定到同一条数据，如下所示：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）。如果这不是一个很大的问题（我不完全理解为什么会这样，但我想他们不希望明文密码在人们不知道他们在做什么的情况下绑定在一起），那么你可以按照本文的后半部分创建绑定：http://wpftutorial.net/PasswordBox.html-使用自定义静态依赖项属性。

因此，我已经在下面的代码中实现了该过程，并且我还通过向PreparingCellForEdit事件添加一个处理程序来修复了密码框没有正确聚焦并且需要两个选项卡的错误，如https://stackoverflow.com/a/2835464/3940783

总而言之，我的工作样本的样本代码是：

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>

然后从中添加PasswordHelper类http://wpftutorial.net/PasswordBox.html到您的命名空间，瞧。

使密码消失

使密码不消失

编辑

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