WPF 附加属性

Question

我创建了一个简单的测试项目，它创建了一个填充有复选框的列表框。我有一些代码隐藏，只要选中复选框，ListBox 上方的 TextBox 就会显示所有选定项目的文本。一切正常，但我现在正在尝试创建一个允许包含前缀的 Attached 属性（同样在后面的代码中）。最终我希望将其转换为 MVVM 标准，但因为我对 WPF 比较陌生，对 MVVM 也很陌生，所以我喜欢从一个工作示例项目开始工作，并逐渐将每个部分转换为一个 MVVM 项目，因为我发现这有助于我更好地理解什么正在进行。我的代码如下：

xaml:

<Window x:Class="CheckBoxList.MainWindow"
    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:CheckBoxList"
    mc:Ignorable="d"
    Title="MainWindow" Height="400" Width="400">
<Window.Resources>
    <Style x:Key="CheckBoxListStyle" TargetType="{x:Type ListBox}">
        <Setter Property="SelectionMode" Value="Multiple"></Setter>
        <Setter Property="ItemContainerStyle">
            <Setter.Value>
                <Style TargetType="{x:Type ListBoxItem}" >
                    <Setter Property="Margin" Value="2" />
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="{x:Type ListBoxItem}">
                                <CheckBox
                                    IsChecked="{Binding Path=IsSelected,RelativeSource={RelativeSource TemplatedParent},Mode=TwoWay}"
                                    Checked="CheckBox_Checked" Unchecked="CheckBox_Unchecked">
                                    <ContentPresenter></ContentPresenter>
                                </CheckBox>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </Setter.Value>
        </Setter>
    </Style>
</Window.Resources>
<Grid Margin="8">
    <Grid.RowDefinitions>
        <RowDefinition Height="30"/>
        <RowDefinition/>
        <RowDefinition Height="Auto"></RowDefinition>
        <RowDefinition Height="30"/>
    </Grid.RowDefinitions>
    <TextBox Grid.Row="0" x:Name="ListBoxTextBox"/>
    <ListBox Grid.Row="1"  Style="{StaticResource CheckBoxListStyle}" Name="lstProducts" local:MainWindow.PrefixMark=">"
         DisplayMemberPath="ModelName">
    </ListBox>
    <Button Grid.Row="2" Margin="0,5,0,0" Click="cmdGetSelectedItems">Get Selected Items</Button>
    <CheckBox Grid.Row="3" Content="Test" Margin="5"/>
</Grid>

xaml.cs

    public static string GetPrefixMark(DependencyObject obj)
        {
            string t = (string)obj.GetValue(PrefixMarkProperty);
            return (string)obj.GetValue(PrefixMarkProperty);
        }

        public static void SetPrefixMark(DependencyObject obj, string value)
        {
            obj.SetValue(PrefixMarkProperty, value);
            string t = (string)obj.GetValue(PrefixMarkProperty);
        }

        // Using a DependencyProperty as the backing store for PrefixMark.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty PrefixMarkProperty =
            DependencyProperty.RegisterAttached("SetPrefixMark", typeof(string), typeof(MainWindow), new PropertyMetadata("('"));

private void CheckBox_Checked(object sender, RoutedEventArgs e)
        {
            if (sender is FrameworkElement element)
            {
                AddText(element);
            }
        }
private void AddText(FrameworkElement e)
        {
            StringBuilder sB = new StringBuilder("");
            foreach (Product product in lstProducts.SelectedItems)
            {
                sB.Append(product.ModelName).Append(ValueSeparator);
            }
            if (sB.Length > 0)
            {
                sB.Remove(sB.Length - (ValueSeparator).Length, (ValueSeparator).Length);
            }
            if (sB.Length > 0)
            {   
                ListBoxTextBox.Text = GetPrefixMark(e) + sB.ToString();
            }
            else
            {
                ListBoxTextBox.Text = "";
            }
        }

当我运行程序时，虽然 PrefixMark 设置为加载，但每当我选中一个复选框时，它都会恢复为默认值。我只能假设这是创建了两次，但对于我来说，我无法弄清楚为什么以及如何解决这个问题？

Answer 1

您应该将依赖项的实际名称属性传递给 Register 方法以开头：

DependencyProperty.RegisterAttached("PrefixMark", ...

The SetPrefixMark is no longer being fired on startup

不应该。如果你想在启动时设置 TextBox 的 Text 属性，你应该将它绑定到源属性或以编程方式设置它：

public MainWindow()
{
    InitializeComponent();
    ListBoxTextBox.Text = GetPrefixMark(this);
    ...
}

WPF 附加属性

WPF AttachedProperty

wpf

attached-properties