在TextBox条目中暂停期间引发PropertyChanged事件？

Question

我想知道PropertyChanged当用户在输入文本时暂停时是否可以引发事件TextBox？或者更具体地说,我想X在用户停止在TextBox中键入数秒后运行一个方法.

例如,我有一个带有TextBox的表单,没有别的.用户在TextBox中键入1-9位Id值,相当资源密集的后台进程加载记录.

我不想使用,UpdateSouceTrigger=PropertyChanged因为这会导致资源密集型后台进程在键入字符时运行,因此9位ID号从这些进程中的9个开始.

我也不想使用,UpdateSourceTrigger=LostFocus因为表单上没有任何其他内容可以使TextBox失去焦点.

那么有没有办法让我的后台进程只有在用户输入ID号时暂停后才会运行？

Answer 1

设置UpdateSourceTrigger=PropertyChanged,然后每次属性更改时,启动计时器以延迟您的延迟.如果在计时器滴答之前再次更改属性,则取消旧计时器并启动新计时器.如果计时器确实打勾,那么您知道该属性在X秒内没有改变,您可以启动后台进程.

Answer 2

准备代码转储.

我用WPF假行为(一个附加的DP就像一个行为)这样做了.此代码有效,但它不漂亮,可能会导致泄漏.可能需要用弱引用等替换所有引用.

这是Behavior类:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Threading;
using System.Windows.Data;
using System.ComponentModel;

namespace BehaviorForDelayedTrigger
{
    public static class DelayedUpdateBehavior
    {
        #region TargetProperty Attached DependencyProperty
        /// <summary>
        /// An Attached <see cref="DependencyProperty"/> of type <see cref="DependencyProperty"/> defined on <see cref="DependencyObject">DependencyObject instances</see>.
        /// </summary>
        public static readonly DependencyProperty TargetPropertyProperty = DependencyProperty.RegisterAttached(
          TargetPropertyPropertyName,
          typeof(DependencyProperty),
          typeof(DelayedUpdateBehavior),
          new FrameworkPropertyMetadata(null, OnTargetPropertyChanged)
        );

        /// <summary>
        /// The name of the <see cref="TargetPropertyProperty"/> Attached <see cref="DependencyProperty"/>.
        /// </summary>
        public const string TargetPropertyPropertyName = "TargetProperty";

        /// <summary>
        /// Sets the value of the <see cref="TargetPropertyProperty"/> on the given <paramref name="element"/>.
        /// </summary>
        /// <param name="element">The <see cref="DependencyObject">target element</see>.</param>
        public static void SetTargetProperty(DependencyObject element, DependencyProperty value)
        {
            element.SetValue(TargetPropertyProperty, value);
        }

        /// <summary>
        /// Gets the value of the <see cref="TargetPropertyProperty"/> as set on the given <paramref name="element"/>.
        /// </summary>
        /// <param name="element">The <see cref="DependencyObject">target element</see>.</param>
        /// <returns><see cref="DependencyProperty"/></returns>
        public static DependencyProperty GetTargetProperty(DependencyObject element)
        {
            return (DependencyProperty)element.GetValue(TargetPropertyProperty);
        }

        /// <summary>
        /// Called when <see cref="TargetPropertyProperty"/> changes
        /// </summary>
        /// <param name="d">The <see cref="DependencyObject">event source</see>.</param>
        /// <param name="e"><see cref="DependencyPropertyChangedEventArgs">event arguments</see></param>
        private static void OnTargetPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var prop = e.NewValue as DependencyProperty;
            if(prop == null)
                return;
            d.Dispatcher.BeginInvoke(
                (Action<DependencyObject, DependencyProperty>)
                    ((target, p) => new PropertyChangeTimer(target, p)), 
                DispatcherPriority.ApplicationIdle, 
                d, 
                prop);

        }
        #endregion
        #region Milliseconds Attached DependencyProperty
        /// <summary>
        /// An Attached <see cref="DependencyProperty"/> of type <see cref="int"/> defined on <see cref="DependencyObject">DependencyObject instances</see>.
        /// </summary>
        public static readonly DependencyProperty MillisecondsProperty = DependencyProperty.RegisterAttached(
          MillisecondsPropertyName,
          typeof(int),
          typeof(DelayedUpdateBehavior),
          new FrameworkPropertyMetadata(1000)
        );

        /// <summary>
        /// The name of the <see cref="MillisecondsProperty"/> Attached <see cref="DependencyProperty"/>.
        /// </summary>
        public const string MillisecondsPropertyName = "Milliseconds";

        /// <summary>
        /// Sets the value of the <see cref="MillisecondsProperty"/> on the given <paramref name="element"/>.
        /// </summary>
        /// <param name="element">The <see cref="DependencyObject">target element</see>.</param>
        public static void SetMilliseconds(DependencyObject element, int value)
        {
            element.SetValue(MillisecondsProperty, value);
        }

        /// <summary>
        /// Gets the value of the <see cref="MillisecondsProperty"/> as set on the given <paramref name="element"/>.
        /// </summary>
        /// <param name="element">The <see cref="DependencyObject">target element</see>.</param>
        /// <returns><see cref="int"/></returns>
        public static int GetMilliseconds(DependencyObject element)
        {
            return (int)element.GetValue(MillisecondsProperty);
        }
        #endregion
        private class PropertyChangeTimer
        {
            private DispatcherTimer _timer;
            private BindingExpression _expression;
            public PropertyChangeTimer(DependencyObject target, DependencyProperty property)
            {
                if (target == null)
                    throw new ArgumentNullException("target");
                if (property == null)
                    throw new ArgumentNullException("property");
                if (!BindingOperations.IsDataBound(target, property))
                    return;
                _expression = BindingOperations.GetBindingExpression(target, property);
                if (_expression == null)
                    throw new InvalidOperationException("No binding was found on property "+ property.Name + " on object " + target.GetType().FullName);
                DependencyPropertyDescriptor.FromProperty(property, target.GetType()).AddValueChanged(target, OnPropertyChanged);
            }

            private void OnPropertyChanged(object sender, EventArgs e)
            {
                if (_timer == null)
                {
                    _timer = new DispatcherTimer();
                    int ms = DelayedUpdateBehavior.GetMilliseconds(sender as DependencyObject);
                    _timer.Interval = TimeSpan.FromMilliseconds(ms);
                    _timer.Tick += OnTimerTick;
                    _timer.Start();
                    return;
                }
                _timer.Stop();
                _timer.Start();
            }

            private void OnTimerTick(object sender, EventArgs e)
            {
                _expression.UpdateSource();
                _expression.UpdateTarget();
                _timer.Stop();
                _timer = null;
            }
        }
    }
}

以下是如何使用它的示例:

<Window
    x:Class="BehaviorForDelayedTrigger.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:t="clr-namespace:BehaviorForDelayedTrigger">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition
                Height="auto" />
        </Grid.RowDefinitions>
        <Viewbox>
            <TextBlock
                x:Name="TargetTextBlock"
                Background="Red" />
        </Viewbox>
        <TextBox
            t:DelayedUpdateBehavior.TargetProperty="{x:Static TextBox.TextProperty}"
            t:DelayedUpdateBehavior.Milliseconds="1000"
            Grid.Row="1"
            Text="{Binding Text, ElementName=TargetTextBlock, UpdateSourceTrigger=Explicit}" />
    </Grid>
</Window>

这个要点是......

您在绑定的UIElement上设置附加属性,传入您希望延迟的DP.在这一点上,我有附加属性的目标和要延迟的属性,所以我可以设置.我必须等到绑定可用,所以我必须使用Dispatcher在设置数据绑定后实例化我的观察者类.不能这样做,你不能抓住绑定表达式.

watcher类获取绑定并向DependencyProperty添加更新侦听器.在监听器中,我设置了一个计时器(如果我们没有更新)或重置计时器.一旦Timer滴答,我就会触发绑定表达式.

它再次起作用,但肯定需要清理.此外,您可以通过其名称使用DP以及以下代码段:

FieldInfo fieldInfo = instance.GetType()
                             .GetField(name, 
                                 BindingFlags.Public | 
                                 BindingFlags.Static | 
                                 BindingFlags.FlattenHierarchy);
return (fieldInfo != null) ? (DependencyProperty)fieldInfo.GetValue(null) : null;

您可能需要将"Property"添加到"Property"上name,但与使用相比,这很容易x:Static.

Answer 3

如果您使用 .NET 4.5 或更高版本，则可以使用Binding 的Delay属性。这真的很简单：

<TextBox Text="{Binding Name, Delay=500, UpdateSourceTrigger=PropertyChanged}"/>