c# - 如何在焦点输入控件上抑制 NotifyPropertyChanged 事件？

Question

我的应用程序具有定期数据库同步功能。每当发生同步时，所有输入控件的值都会重置为数据库中的当前值。

但是，当在 TextBox 中键入长文本时发生同步事件时，这非常不方便。

期望的行为是输入控件的值不设置为绑定(bind)属性的值，以防控件当前具有焦点。一旦失去键盘焦点，当前值就应该同步回绑定(bind)的属性，从而同步到数据库(这将是默认行为)。

我的第一个想法是修改我的控件，以便在输入具有键盘焦点时绑定(bind)模式自动设置为 OneWayToSource。目前我没有看到其他选择，只能派生我在我的应用程序中拥有的各种输入控件，这将需要大量工作。

你有没有看到一种在中央位置实现这种行为的方法，以便它被所有 UI 控件使用，最好不要子类化 TextBox、ComboBox 等.?

Answer 1

您可以创建一个帮助器来跟踪 IsKeyboardFocusWithin 属性并仅在目标值不包含键盘焦点时更新目标值。例如，您有每秒更改的特定源:

    public partial class MainWindow {
    public static readonly DependencyProperty DataProperty = DependencyProperty.Register(
        "Data", typeof(string), typeof(MainWindow), new PropertyMetadata(default(string), OnDataChanged));

    static void OnDataChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
        Debug.WriteLine((string)e.NewValue);
    }

    public string Data {
        get { return (string)GetValue(DataProperty); }
        set { SetValue(DataProperty, value); }
    }
    public MainWindow() {
        InitializeComponent();
        DispatcherTimer dt = new DispatcherTimer();
        dt.Interval = TimeSpan.FromMilliseconds(1000);
        dt.Tick += Dt_Tick;
        dt.Start();
    }

    void Dt_Tick(object sender, EventArgs e) {
        Data = new Random().Next(0, 100).ToString();
    }
}

在本例中，这是数据属性。现在， helper 。我决定将其创建为 MarkupExtension 以简化 XAML:

 public class SynchronizationHelperExtension : MarkupExtension {
    public Binding Binding { get; set; }
    class Helper {            
        static int index = 0;
        bool locked = false;
        public static readonly DependencyProperty HelperProperty = DependencyProperty.RegisterAttached(
            "Helper", typeof(Helper), typeof(Helper), new PropertyMetadata(default(Helper)));

        public static void SetHelper(DependencyObject element, Helper value) {
            element.SetValue(HelperProperty, value);
        }

        public static Helper GetHelper(DependencyObject element) {
            return (Helper)element.GetValue(HelperProperty);
        }
        public static readonly DependencyProperty FocusProperty = DependencyProperty.RegisterAttached("FocusProperty", typeof(bool), typeof(Helper), new PropertyMetadata(false, (o, args) => GetHelper(o)?.OnFocusPropertyChanged(o, (bool)args.OldValue, (bool)args.NewValue)));            
        public static readonly DependencyProperty SourceProperty = DependencyProperty.RegisterAttached("SourceProperty", typeof(object), typeof(Helper), new PropertyMetadata(false, (o, args) => GetHelper(o)?.OnSourcePropertyChanged(o, args.OldValue, args.NewValue)));
        public static readonly DependencyProperty TargetProperty = DependencyProperty.RegisterAttached("TargetProperty", typeof(object), typeof(Helper), new PropertyMetadata(false, (o, args) => GetHelper(o)?.OnTargetPropertyChanged(o, args.OldValue, args.NewValue)));

        void OnTargetPropertyChanged(DependencyObject o, object oldValue, object newValue) {
            o.SetValue(SourceProperty, newValue);
        }
        void OnSourcePropertyChanged(DependencyObject o, object oldValue, object newValue) {
            if (locked)
                return;
            o.SetValue(TargetProperty, newValue);
        }
        void OnFocusPropertyChanged(DependencyObject o, bool oldValue, bool newValue) {
            locked = newValue;
        }
    }

    public override object ProvideValue(IServiceProvider serviceProvider) {
        var helper = new Helper();
        var ipwt = serviceProvider.GetService(typeof(IProvideValueTarget)) as IProvideValueTarget;
        var dObj = ipwt.TargetObject as DependencyObject;
        BindingOperations.SetBinding(dObj, Helper.FocusProperty, new Binding() {Path = new PropertyPath(FrameworkElement.IsKeyboardFocusWithinProperty), RelativeSource = RelativeSource.Self});
        Binding.Mode = BindingMode.TwoWay;
        BindingOperations.SetBinding(dObj, Helper.SourceProperty, Binding);
        Helper.SetHelper(dObj, helper);
        return new Binding() {Path = new PropertyPath(Helper.TargetProperty), Mode = BindingMode.TwoWay, UpdateSourceTrigger = UpdateSourceTrigger.LostFocus, RelativeSource = RelativeSource.Self }.ProvideValue(serviceProvider);
    }
}

我们有 3 个属性:一个存储来自源的实际值 (Helper.SourceProperty)第二 - 存储目标值 (Helper.TargetProperty)第三个用于锁定这些属性之间的同步 (Helper.FocusProperty)我们还有 Binding 属性 - 这是用于将 Target 属性与源绑定(bind)的绑定(bind)(例如 TextBox.Text 与 MainWindow.Data)在 ProvideValue 方法中，我们:

1. 将 FrameworkElement.IsKeyboardFocusWithinProperty 与 Helper.FocusProperty 绑定(bind)以锁定更新
2. 更新原始绑定(bind)使其成为 TwoWay(更改后更新 Data 属性)
3. 将 BindingExpression 返回给 Helper.TargetProperty

XAML 将如下所示:

<StackPanel>
    <TextBox Text="{local:SynchronizationHelper Binding={Binding Data, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}}}"/>
    <TextBox Text="{local:SynchronizationHelper Binding={Binding Data, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}}}"/>
    <TextBlock Text="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}, Path=Data}"></TextBlock>
</StackPanel>

And the short video demonstrating the result