wpf - 将文本绑定(bind)到附加属性

Question

我的问题与此类似:WPF Generate TextBlock Inlines但我没有足够的声誉来发表评论。这是附加的属性类:

public class Attached
{
    public static readonly DependencyProperty FormattedTextProperty = DependencyProperty.RegisterAttached(
        "FormattedText",
        typeof(string),
        typeof(TextBlock),
        new FrameworkPropertyMetadata(string.Empty, FrameworkPropertyMetadataOptions.AffectsMeasure));

    public static void SetFormattedText(DependencyObject textBlock, string value)
    {
        textBlock.SetValue(FormattedTextProperty, value);
    }

    public static string GetFormattedText(DependencyObject textBlock)
    {
        return (string)textBlock.GetValue(FormattedTextProperty);
    }

    private static void FormattedTextPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var textBlock = d as TextBlock;
        if (textBlock == null)
        {
            return;
        }

        var formattedText = (string)e.NewValue ?? string.Empty;
        formattedText = string.Format("<Span xml:space=\"preserve\" xmlns=\"http://schemas.microsoft.com/winfx/2006/xaml/presentation\">{0}</Span>", formattedText);

        textBlock.Inlines.Clear();
        using (var xmlReader = XmlReader.Create(new StringReader(formattedText)))
        {
            var result = (Span)XamlReader.Load(xmlReader);
            textBlock.Inlines.Add(result);
        }
    }
}

我正在使用这个附加的属性类，并尝试将其应用到文本 block ，以使文本识别 View 模型类中字符串中的内联值，例如粗体、下划线等。我的文本 block 中有以下 XAML:

<TextBlock Grid.Row="1" Grid.Column="1" TextWrapping="Wrap" my:Attached.FormattedText="test" />

但是，当我启动程序时，我在文本 block 中什么也没有得到。我还想最终将文本绑定(bind)到我的 View 模型上的属性，但希望首先显示一些内容......

抱歉，这可能是一个新手问题，但我不明白为什么它不起作用。它在这里没有给我任何错误，只是没有显示出来。如果我尝试绑定(bind)，它会给我错误:

{"A 'Binding' cannot be set on the 'SetFormattedText' property of type 'TextBlock'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject."}

Answer 1

首先，属性的类型需要是类名，而不是类型 TextBlock:

public static readonly DependencyProperty FormattedTextProperty = DependencyProperty.RegisterAttached(
    "FormattedText",
    typeof(string),
    typeof(TextBlock), <----- Here

其次，handler没有被调用，它必须在这里注册:

new FrameworkPropertyMetadata(string.Empty, 
                              FrameworkPropertyMetadataOptions.AffectsMeasure,
                              YOUR_PropertyChanged_HANDLER)

第三，一个工作示例，您需要像这样指定输入字符串:

<Bold>My little text</Bold>

工作示例如下:

XAML

<Window x:Class="InlineTextBlockHelp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:this="clr-namespace:InlineTextBlockHelp"
        Title="MainWindow" Height="350" Width="525">

    <Grid>
        <TextBlock Name="TestText"
                   this:AttachedPropertyTest.FormattedText="TestString"
                   Width="200"
                   Height="100" 
                   TextWrapping="Wrap" />

        <Button Name="TestButton"
                Width="100"
                Height="30"
                VerticalAlignment="Top"
                Content="TestClick" 
                Click="Button_Click" />
    </Grid>
</Window>

代码隐藏

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        string inlineExpression = "<Bold>Once I saw a little bird, go hop, hop, hop.</Bold>";
        AttachedPropertyTest.SetFormattedText(TestText, inlineExpression);
    }
}

public class AttachedPropertyTest
{
    public static readonly DependencyProperty FormattedTextProperty = DependencyProperty.RegisterAttached(
        "FormattedText",
        typeof(string),
        typeof(AttachedPropertyTest),
        new FrameworkPropertyMetadata(string.Empty, FrameworkPropertyMetadataOptions.AffectsMeasure, FormattedTextPropertyChanged));

    public static void SetFormattedText(DependencyObject textBlock, string value)
    {
        textBlock.SetValue(FormattedTextProperty, value);
    }

    public static string GetFormattedText(DependencyObject textBlock)
    {
        return (string)textBlock.GetValue(FormattedTextProperty);
    }

    private static void FormattedTextPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var textBlock = d as TextBlock;

        if (textBlock == null)
        {
            return;
        }

        var formattedText = (string)e.NewValue ?? string.Empty;
        formattedText = string.Format("<Span xml:space=\"preserve\" xmlns=\"http://schemas.microsoft.com/winfx/2006/xaml/presentation\">{0}</Span>", formattedText);

        textBlock.Inlines.Clear();
        using (var xmlReader = XmlReader.Create(new StringReader(formattedText)))
        {
            var result = (Span)XamlReader.Load(xmlReader);
            textBlock.Inlines.Add(result);
        }
    }
}

最初是纯文本，点击按钮后将被分配为内联文本。

MVVM 版本示例

要在 MVVM 风格中使用此示例，您需要在 Model/ViewModel 中创建适当的属性，并将其与附加的依赖属性相关联，如下所示:

<TextBlock Name="TestText"
           PropertiesExtension:TextBlockExt.FormattedText="{Binding Path=InlineText, 
                                                                    Mode=TwoWay,
                                                                    UpdateSourceTrigger=PropertyChanged}"
           Width="200"
           Height="100" 
           TextWrapping="Wrap" />

Model/ViewModel 中的属性必须支持方法 NotifyPropertyChanged。

这是一个完整的示例:

附加属性

public class TextBlockExt
{
    public static readonly DependencyProperty FormattedTextProperty = DependencyProperty.RegisterAttached(
        "FormattedText",
        typeof(string),
        typeof(TextBlockExt),
        new FrameworkPropertyMetadata(string.Empty, FrameworkPropertyMetadataOptions.AffectsMeasure, FormattedTextPropertyChanged));

    public static void SetFormattedText(DependencyObject textBlock, string value)
    {
        textBlock.SetValue(FormattedTextProperty, value);
    }

    public static string GetFormattedText(DependencyObject textBlock)
    {
        return (string)textBlock.GetValue(FormattedTextProperty);
    }

    private static void FormattedTextPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var textBlock = d as TextBlock;

        if (textBlock == null)
        {
            return;
        }

        var formattedText = (string)e.NewValue ?? string.Empty;
        formattedText = string.Format("<Span xml:space=\"preserve\" xmlns=\"http://schemas.microsoft.com/winfx/2006/xaml/presentation\">{0}</Span>", formattedText);

        textBlock.Inlines.Clear();
        using (var xmlReader = XmlReader.Create(new StringReader(formattedText)))
        {
            var result = (Span)XamlReader.Load(xmlReader);
            textBlock.Inlines.Add(result);
        }
    }
}

MainViewModel

public class MainViewModel : NotificationObject
{
    private string _inlineText = "";

    public string InlineText
    {
        get
        {
            return _inlineText;
        }

        set
        {
            _inlineText = value;
            NotifyPropertyChanged("InlineText");
        }
    }
}

MainWindow.xaml

<Window x:Class="InlineTextBlockHelp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:ViewModels="clr-namespace:InlineTextBlockHelp.ViewModels"
        xmlns:PropertiesExtension="clr-namespace:InlineTextBlockHelp.PropertiesExtension"
        Title="MainWindow" Height="350" Width="525"
        ContentRendered="Window_ContentRendered">

    <Window.DataContext>
        <ViewModels:MainViewModel />
    </Window.DataContext>

    <Grid>
        <TextBlock Name="TestText"
                   PropertiesExtension:TextBlockExt.FormattedText="{Binding Path=InlineText, 
                                                                            Mode=TwoWay,
                                                                            UpdateSourceTrigger=PropertyChanged}"
                   Width="200"
                   Height="100" 
                   TextWrapping="Wrap" />
    </Grid>
</Window>

代码隐藏(仅用于测试)

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void Window_ContentRendered(object sender, EventArgs e)
    {
        MainViewModel mainViewModel = this.DataContext as MainViewModel;

        mainViewModel.InlineText = "<Bold>Once I saw a little bird, go hop, hop, hop.</Bold>";
    }
}

This example is available at this link.