Question

我正在设计一个可以有两个主要状态的控件。州将通过依赖属性设置。我想通过XAML设置属性。我知道setter只会运行setValue代码，如果它是通过XAML设置的，如下所述：WPF: XAML property declarations not being set via Setters?

所以我尝试设置DependencyPropertyChangedEvent事件，但是当我运行我的代码时出现此错误：

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，它告诉我在我的事件中无法创建我的控件的新实例。 C＃逻辑看起来像这样：

    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。

我觉得我正在正确地关注表单，但它没有运行。有什么想法吗？

Answer 1

您的依赖项属性的类型是枚举，它是ValueType，但您在属性元数据中将null指定为默认属性值。这不起作用，因为null不是ValueType的有效值。

Answer 2

注册依赖项属性时，您将“null”传递给“FrameworkPropertyMetadata”构造函数。

您传递的第一个参数将是Dependency属性的默认值。在您的情况下，您将Null作为类型为ENUM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..

有些事情可能会这样做

new FrameworkPropertyMetadata(VehicleType.Sale,  FrameworkPropertyMetadataOptions.AffectsRender,  new PropertyChangedCallback(OnVehTypeChanged)));

依赖属性，无法创建新的类实例

2 个答案: