c# - 在更改的回调中设置 DependencyProperty 值

Question

我的 UserControl 中有一个 DependencyProperty，它使用 bool 值来触发行为。在这种情况下，它是一个用户控件，旨在公开 SaveFileDialog 的功能，并且它使用 DialogVisible DependencyProperty。当属性设置为 true 时，我在属性更改的回调中调用 SaveFileDialog 上的 ShowDialog 方法，然后尝试将 DialogVisible 属性设置回 false，但这不会传播回绑定(bind)。我希望这是因为我在回调中设置了值。有没有办法解决？

提供的代码:

using System.Windows;

/// <summary>
/// Interaction logic for SaveFileDialog.xaml.
/// NOTE: Bindings for DialogVisible and FileName must
/// use TwoWay mode or dialog will not function as desired.
/// </summary>
public partial class SaveFileDialog
{
    #region Depedancy Properties

    public static readonly DependencyProperty FilterProperty = DependencyProperty.RegisterAttached(
        "Filter",
        typeof(string),
        typeof(SaveFileDialog),
        new PropertyMetadata(FilterProperty_Changed));

    public static readonly DependencyProperty FileNameProperty = DependencyProperty.RegisterAttached(
        "FileName",
        typeof(string),
        typeof(SaveFileDialog),
        new PropertyMetadata(FileNameProperty_Changed));

    public static readonly DependencyProperty InitialDirectoryProperty = DependencyProperty.RegisterAttached(
        "InitialDirectory",
        typeof(string),
        typeof(SaveFileDialog),
        new PropertyMetadata(InitialDirectoryProperty_Changed));

    public static readonly DependencyProperty DefaultExtensionProperty = DependencyProperty.RegisterAttached(
        "DefaultExtension",
        typeof(string),
        typeof(SaveFileDialog),
        new PropertyMetadata(DefaultExtensionProperty_Changed));

    public static readonly DependencyProperty DialogVisibleProperty = DependencyProperty.RegisterAttached(
        "DialogVisible",
        typeof(bool),
        typeof(SaveFileDialog),
        new PropertyMetadata(DialogVisibleProperty_Changed));

    public string Filter
    {
        get { return (string)this.GetValue(FilterProperty); }
        set { this.SetValue(FilterProperty, value); }
    }

    public string FileName
    {
        get { return (string)this.GetValue(FileNameProperty); }
        set { this.SetValue(FileNameProperty, value); }
    }

    public string InitialDirectory
    {
        get { return (string)this.GetValue(InitialDirectoryProperty); }
        set { this.SetValue(InitialDirectoryProperty, value); }
    }

    public string DefaultExtension
    {
        get { return (string)this.GetValue(DefaultExtensionProperty); }
        set { this.SetValue(DefaultExtensionProperty, value); }
    }

    public bool DialogVisible
    {
        get { return (bool)this.GetValue(DialogVisibleProperty); }
        set { this.SetValue(DialogVisibleProperty, value); }
    }

    private static void FilterProperty_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var control = (SaveFileDialog)d;
        control._dialog.Filter = (string)e.NewValue;
    }

    private static void FileNameProperty_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var control = (SaveFileDialog)d;
        control._dialog.FileName = (string)e.NewValue;
    }

    private static void InitialDirectoryProperty_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var control = (SaveFileDialog)d;
        control._dialog.InitialDirectory = (string)e.NewValue;
    }

    private static void DefaultExtensionProperty_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var control = (SaveFileDialog)d;
        control._dialog.DefaultExt = (string)e.NewValue;
    }

    private static void DialogVisibleProperty_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var control = (SaveFileDialog)d;

        if ((bool)e.NewValue)
        {
            control._dialog.ShowDialog();
            control.DialogVisible = false;
            control.FileName = control._dialog.FileName;
        }
    }

    #endregion

    private readonly Microsoft.Win32.SaveFileDialog _dialog = new Microsoft.Win32.SaveFileDialog();

    public SaveFileDialog()
    {
        InitializeComponent();
    }
}

Answer 1

通常，如果您发现自己的代码在 UI 线程上执行，但在它有意义之前，总是可以通过使用 UI 线程的 Dispatcher 将您的工作卸载到将来某个时间点。

例如，如果您有代码在启动时运行，但您希望 UI 元素已加载并准备好进行交互，您可以稍后使用 Dispatcher 执行您的 UI 代码。

为此，首先您必须获取 UI Dispatcher。您可以通过 Application.Current.Dispatcher 进行此操作并通过 BeginInvoke 卸载更新的执行，传入您希望稍后调用的方法或 lambda。

此方法有一个重载，它采用 DispatcherPriority枚举。使用适当的优先级。通常，我使用 priority的 ContextIdle ，它在您需要的几乎所有内容完成后执行。