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我正在设计一个可以有两种主要状态的控件。状态将通过依赖属性设置。我想通过 XAML 设置属性。我知道 setter 仅在通过 XAML 设置时才会运行 setValue 代码，如下所述：WPF: XAML property declarations not being set via Setters?

所以我试图设置一个 DependencyPropertyChangedEvent 事件，但是当我运行我的代码时，我得到了这个错误：

XamlParseException Occurred
'The invocation of the constructor on type 'RouteOneClient.VehicleInfoControl'
that matches the specified binding constraints threw an exception.' Line number 
'134' and line position '34'.

当我查看它时，它告诉我我无法在我的事件中创建我的控件的新实例。C# 逻辑如下所示：

    public enum VehicleType
    {
        Sale = 1,
        Trade = 2,
    }

    public static readonly DependencyProperty VehicleTypeProperty =  DependencyProperty.Register(
        "VehicleTYPE", 
        typeof(VehicleType), 
        typeof(VehicleInfoControl), 
        new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.AffectsRender, new PropertyChangedCallback(OnVehTypeChanged)));  // optionally metadata for defaults etc.

    public VehicleInfoControl()
    {
        InitializeComponent();
    }

    public VehicleType VehicleTYPE
    {
        get { return (VehicleType)GetValue(VehicleTypeProperty); }
        set
        {
            SetValue(VehicleTypeProperty, value);
        }          
    }

    private static void OnVehTypeChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        VehicleInfoControl instance = d as VehicleInfoControl;

        if (instance.VehicleTYPE == VehicleType.Sale)
        {
            instance.TitleLabel.Content = "Sale Vehicle";
            instance.IntendedUse.Visibility = System.Windows.Visibility.Visible;
            instance.VehicleNewUsed.Visibility = System.Windows.Visibility.Visible;
            instance.VehicleVin.Visibility = System.Windows.Visibility.Visible;
            instance.VehicleInceptionMiles.Visibility = System.Windows.Visibility.Visible;
            instance.IntendedUseLabel.Visibility = System.Windows.Visibility.Visible;
            instance.VehicleNewUsedLabel.Visibility = System.Windows.Visibility.Visible;
            instance.VehicleVinLabel.Visibility = System.Windows.Visibility.Visible;
            instance.VehicleInceptionMilesLabel.Visibility = System.Windows.Visibility.Visible;
        }
        else
        {
            instance.TitleLabel.Content = "Trade Vehicle";
            instance.IntendedUse.Visibility = System.Windows.Visibility.Hidden;
            instance.VehicleNewUsed.Visibility = System.Windows.Visibility.Hidden;
            instance.VehicleVin.Visibility = System.Windows.Visibility.Hidden;
            instance.VehicleInceptionMiles.Visibility = System.Windows.Visibility.Hidden;
            instance.IntendedUseLabel.Visibility = System.Windows.Visibility.Hidden;
            instance.VehicleNewUsedLabel.Visibility = System.Windows.Visibility.Hidden;
            instance.VehicleVinLabel.Visibility = System.Windows.Visibility.Hidden;
            instance.VehicleInceptionMilesLabel.Visibility = System.Windows.Visibility.Hidden;
        }
    }

和 XAML：

<Expander Header="Vehicle Information" Width="Auto" Height="Auto" Grid.Row="2">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width=".3*" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>

        <custom:VehicleInfoControl x:Name="SaleVeh" Width="Auto" Height="Auto" Grid.Column="0" VehicleTYPE="Sale"/>
        <custom:VehicleInfoControl x:Name="TradeVeh" Width="Auto" Height="Auto" Grid.Column="2" VehicleTYPE="Trade"/>

    </Grid>
</Expander>

上面给出的错误指向该行。

我觉得我正确地遵循了表格，但它没有运行。有任何想法吗？

4

2 回答 2

3

您的依赖属性的类型是一个枚举，它是一个ValueType，但您null在属性元数据中指定为默认属性值。那是行不通的，因为null它不是 ValueType 的有效值。

于 2012-05-25T13:16:22.847 回答
2

在注册您的依赖属性时，您将“null”传递给“FrameworkPropertyMetadata”构造函数。

您传递的第一个参数将是您的 Dependency 属性的默认值。在您的情况下，您将 Null 作为 ENUM 类型的依赖项属性的默认值传递，这是不允许的。

传递有效的默认值可能会解决您的问题..

像这样的事情可能会做

new FrameworkPropertyMetadata(VehicleType.Sale,  FrameworkPropertyMetadataOptions.AffectsRender,  new PropertyChangedCallback(OnVehTypeChanged)));
于 2012-05-25T13:18:30.180 回答