在我的 Prism 6 WPF MVVM 应用程序中,我使用自定义模式对话框来登录用户。此对话框产生(在 XAML 中)以下设计时错误:“没有为此对象定义无参数构造函数”。下面是对话框的 XAML 标记:
<UserControl x:Class="FlowmeterConfigurator.Views.LoginView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:prism="http://prismlibrary.com/"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:behavior="clr-namespace:CommonClassLibrary.Behaviors;assembly=CommonClassLibrary"
xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"
prism:ViewModelLocator.AutoWireViewModel="True"
Width="330" Height="175" MaxWidth="400" MaxHeight="300" MinWidth="200" MinHeight="100">
<i:Interaction.Triggers>
<!-- OK-dialog -->
<prism:InteractionRequestTrigger SourceObject="{Binding NotificationRequest, Mode=OneWay}">
<prism:PopupWindowAction IsModal="True" CenterOverAssociatedObject="True"/>
</prism:InteractionRequestTrigger>
</i:Interaction.Triggers>
<Grid >
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="100"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<!--UserName-->
<Label Grid.Row="0" Grid.Column="0" Content="Имя пользователя" VerticalAlignment="Center" HorizontalAlignment="Right" Margin="0 30 0 0"/>
<TextBox Grid.Row="0" Grid.Column="1" Height="30" Margin="0 30 5 0" Text="{Binding Username}" AutomationProperties.AutomationId="UserNameTextBox"/>
<!--Pasword-->
<Label Grid.Row="1" Grid.Column="0" Content="Пароль" VerticalAlignment="Center" HorizontalAlignment="Right" Margin="0 10 0 0"/>
<PasswordBox Grid.Row="1" Grid.Column="1" Height="30" Margin="0 10 5 0" AutomationProperties.AutomationId="UserPasswordBox">
<i:Interaction.Behaviors>
<behavior:PasswordBoxBindingBehavior Password="{Binding Password}"/>
</i:Interaction.Behaviors>
</PasswordBox>
<!--Panel with the buttons 'Authrize' and 'Cancel'-->
<StackPanel Grid.Row="2" Grid.Column="0" Grid.ColumnSpan="2" Orientation="Horizontal" HorizontalAlignment="Center">
<telerik:RadButton x:Name="radButtonAuthorize" Content="Авторизоваться" Height="30" Width="Auto" Margin="5 10 20 5"
Command="{Binding PerformAuthorizationCommand}" AutomationProperties.AutomationId="AuthrizeUserButton"/>
<telerik:RadButton x:Name="radButtonCancel" Content="Отмена" Height="30" Width="Auto" Margin="0 10 5 5"
Command="{Binding СancelAuthorizationCommand}" AutomationProperties.AutomationId="CancelAuthorizationButton"/>
</StackPanel>
</Grid>
</UserControl>
对话框的构造函数(来自其 ViewModel)请参见下文:
public LoginViewModel(IEventAggregator eventAggregator, IAuthorizationService authorizationService)
{
this._eventAggregator = eventAggregator;
this._authorizationService = authorizationService;
this.NotificationRequest = new InteractionRequest<INotification>();
this.PerformAuthorizationCommand = new DelegateCommand(this.performAuthorization, this.performAuthorizationCanExecute);
this.СancelAuthorizationCommand = new DelegateCommand(this.canсelAuthorization, this.canсelAuthorizationCanExecute);
}
从上面对话框的 XAML 中可以看出,我使用行为 (PasswordBoxBindingBehavior) 来使 PasswordBox 的数据绑定成为可能。下面是 PasswordBoxBindingBehavior 类定义:
public class PasswordBoxBindingBehavior : Behavior<PasswordBox>
{
protected override void OnAttached()
{
AssociatedObject.PasswordChanged += OnPasswordBoxValueChanged;
}
public SecureString Password
{
get { return (SecureString)GetValue(PasswordProperty); }
set { SetValue(PasswordProperty, value); }
}
public static readonly DependencyProperty PasswordProperty =
DependencyProperty.Register("Password", typeof(SecureString), typeof(PasswordBoxBindingBehavior), new PropertyMetadata(null));
private void OnPasswordBoxValueChanged(object sender, RoutedEventArgs e)
{
var binding = BindingOperations.GetBindingExpression(this, PasswordProperty);
if (binding != null)
{
PropertyInfo property = binding.DataItem.GetType().GetProperty(binding.ParentBinding.Path.Path);
if (property != null)
property.SetValue(binding.DataItem, AssociatedObject.SecurePassword, null);
}
}
}
我从应用程序主窗口(Shell)调用此对话框。下面是 XAML 标记(与对话框相关)。此标记来自应用程序主窗口(Shell)标记。请参见:
<prism:InteractionRequestTrigger SourceObject="{Binding LoginConfirmationRequest, Mode=OneWay}">
<prism:PopupWindowAction IsModal="True" CenterOverAssociatedObject="True">
<prism:PopupWindowAction.WindowContent>
<views:LoginView/>
</prism:PopupWindowAction.WindowContent>
<prism:PopupWindowAction.WindowStyle>
<Style TargetType="Window">
<Setter Property="ResizeMode" Value="NoResize"/>
<Setter Property="SizeToContent" Value="WidthAndHeight"/>
</Style>
</prism:PopupWindowAction.WindowStyle>
</prism:PopupWindowAction>
</prism:InteractionRequestTrigger>
在这个标记中
<views:LoginView/>
出现以下错误:“没有为此对象定义无参数构造函数”。我尝试在对话框的 ViewModel 中添加第二个构造函数(即无参数),但错误并未消除。虽然这只是设计时错误,但即便如此,它也应该被消除。我该如何纠正这个错误?