WPF按钮默认情况下处于禁用状态，我无法再次启用它

Question

由于不必烦恼某些人单击链接，因此该窗口的XAML代码共有约80行...

<Window x:Class="TollLicenser.Views.LicenseView"
        x:Name="wdw"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:TollLicenser.Views"
        mc:Ignorable="d"
        Title="License View" Height="300" Width="300"
        xmlns:vm="clr-namespace:TollLicenser.ViewModels"
        d:DataContext="{d:DesignInstance vm:LicenseViewModel}"
        SizeToContent="WidthAndHeight"
        Margin="8">
    <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Button.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Shadows.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.ToggleButton.xaml" />
            </ResourceDictionary.MergedDictionaries>
            <Style TargetType="{x:Type TextBox}" BasedOn="{StaticResource MaterialDesignTextBox}">
                <Setter Property="Margin" Value="0 8 8 8" />
            </Style>
            <Style TargetType="{x:Type DatePicker}">
                <Setter Property="Margin" Value="0 8 8 8" />
            </Style>
            <Style TargetType="{x:Type Label}">
                <Setter Property="Margin" Value="0 8 8 8" />
            </Style>
            <Style TargetType="{x:Type TextBlock}">
                <Setter Property="Margin" Value="8" />
            </Style>
        </ResourceDictionary>
    </Window.Resources>
    <Grid FocusManager.FocusedElement="{Binding ElementName=CountryCode}">
        <Grid.RowDefinitions>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="5"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="auto"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>

        <TextBlock Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2"
               Style="{StaticResource MaterialDesignHeadlineTextBlock}">
            Managing a License
        </TextBlock>

        <Label Grid.Row="1" Grid.Column="0">Country Code</Label>
        <TextBox Grid.Row="1" Grid.Column="1" Name="CountryCode" Text="{Binding CountryCode}"/>

        <Label Grid.Row="2" Grid.Column="0">Plaza Name</Label>
        <TextBox Grid.Row="2" Grid.Column="1" Text="{Binding TollPlazaName}"/>

        <Label Grid.Row="3" Grid.Column="0">Start Date</Label>
        <DatePicker Grid.Row="3" Grid.Column="1" SelectedDate="{Binding StartDate}"/>

        <Label Grid.Row="4" Grid.Column="0">End Date</Label>
        <DatePicker Grid.Row="4" Grid.Column="1" SelectedDate="{Binding EndDate}"/>

        <Label Grid.Row="5" Grid.Column="0">Max Users</Label>
        <TextBox Grid.Row="5" Grid.Column="1" Text="{Binding MaxUsers}"/>

        <GridSplitter Grid.Row="6" Height="5" />

        <Button Grid.Row="7" Grid.Column="0" Content="Save" Margin="8" IsEnabled="True" IsDefault="True"
                Command="{Binding SaveLicenseCommand}" CommandParameter="{Binding ElementName=wdw}" />
    </Grid>
</Window>

基本上，问题在于，甚至从窗口打开时起，该死的按钮（如下所示）就被禁用了。

这似乎正确绑定到the ViewModel。

在视图模型中，只有与按钮真正相关的东西才是命令及其执行的方法，如下所示：

public ICommand SaveLicenseCommand => new AwaitableDelegateCommand<Window>(SaveLicense);
private async Task SaveLicense(Window wdw)
{
    _model.Id = Id;
    _model.CountryCode = Encryption.Encrypt(CountryCode);
    _model.EndDate = Encryption.Encrypt(EndDate.ToString());
    _model.MaxUsers = Encryption.Encrypt(MaxUsers.ToString());
    _model.StartDate = Encryption.Encrypt(StartDate.ToString());
    _model.TollPlazaName = Encryption.Encrypt(TollPlazaName);

    // LYTODO Post the model to the web service.
    if (_model.Id != 0)
    {
        // Editing a license.
        await _apiHelper.PutLicenseAsync(_model);
        await _licenses.Load(); // Reload licenses with the updated item.
    }
    else
    {
        // Adding a license.
        await _apiHelper.PostLicenseAsync(_model);
    }

    wdw.Close();
}

我不知道为什么按钮会被禁用或要提供什么其他信息，所以如果您需要更多信息，请发表评论。

为什么在禁用按钮的情况下打开窗口？