无法使用嵌套的依赖属性初始化 UserControl

Question

我正在尝试公开嵌套控件的两个依赖属性。在这种情况下 Mask 和 DisplayFormatString.

<UserControl
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors"
             xmlns:local="clr-namespace:View.UserControls"
             xmlns:dx="http://schemas.devexpress.com/winfx/2008/xaml/core" x:Class="View.UserControls.DateTimeEdit"
             mc:Ignorable="d" >
    <Grid>
        <dxe:DateEdit x:Name="localDateEdit" Width="200" MaskType="DateTime" 
            ShowEditorButtons="True"
            Mask ="dd MMM yyyy HH:mm" 
            DisplayFormatString = "dd MMM yyyy HH:mm"/>
    </Grid>
</UserControl>

我已将依赖属性添加到父控件

public partial class DateTimeEdit : UserControl
    {    
        public static readonly DependencyProperty DisplayFormatStringProperty =
          DependencyProperty.Register("DisplayFormatString", typeof(string), typeof(DateTimeEdit), new PropertyMetadata(0));

        public static readonly DependencyProperty MaskProperty =
          DependencyProperty.Register("Mask", typeof(string), typeof(DateTimeEdit), new PropertyMetadata(0));


        public string DisplayFormatString
        {
            get { return (string)GetValue(DisplayFormatStringProperty); }
            set { SetValue(DisplayFormatStringProperty, value); }
        }

        public string Mask
        {
            get { return (string)GetValue(MaskProperty); }
            set { SetValue(MaskProperty, value); }
        }

        public static void OnDisplayFormatStringChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            (d as DateTimeEdit).localDateEdit.DisplayFormatString = (string)e.NewValue;
        }

        public static void OnMaskChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            (d as DateTimeEdit).localDateEdit.Mask = (string)e.NewValue;
        }
}

但是，当我尝试在父控件上设置属性时，出现与输入格式不正确有关的异常。 Default value type does not match type of property 'DisplayFormatString'

UserControl 用法。

<userControls:DateTimeEdit
          Mask="dd MMM yyyy" 
          DisplayFormatString="dd MMM yyyy"/>

我是否正确公开了嵌套的依赖属性？

Answer 1

PropertyMetadata(object defaultValue) constructor 使用其 object 参数作为依赖项属性的默认值。这里...

new PropertyMetadata(0)

...您正在传递一个整数作为 String 属性的默认值。这就是异常的意思。

尝试 null 两个属性：

public static readonly DependencyProperty DisplayFormatStringProperty =
  DependencyProperty.Register("DisplayFormatString", typeof(string), 
        typeof(DateTimeEdit), new PropertyMetadata(null));

public static readonly DependencyProperty MaskProperty =
  DependencyProperty.Register("Mask", typeof(string), 
        typeof(DateTimeEdit), new PropertyMetadata(null));

或""，如果合适的话。

无法使用嵌套的依赖属性初始化 UserControl

Unable to initialize UserControl with nested Dependency properties

wpf

user-controls

dependency-properties