在 TextBox 条目中的暂停期间引发 PropertyChanged 事件? [英] Raising a PropertyChanged event during a Pause in TextBox entry?
问题描述
我想知道是否可以在用户在 TextBox 中输入文本时暂停时引发 PropertyChanged 事件?或者更具体地说，我想在用户停止在 TextBox 中输入后运行 X 秒的方法.
I was wondering if it's possible to raise a PropertyChanged event when the user pauses while typing text into a TextBox? Or more specifically, I want to run a method X seconds after the user stops typing in a TextBox.
例如，我有一个带有 TextBox 的表单，没有其他任何内容.用户在 TextBox 中键入 1-9 位的 Id 值，一个相当资源密集型的后台进程加载记录.
For example, I have a form with a TextBox and nothing else. The user types in a 1-9 digit Id value into the TextBox, a fairly resource-intensive background process loads the record.
我不想使用 UpdateSouceTrigger=PropertyChanged 因为这会导致资源密集型后台进程在输入字符时运行，因此 9 位 ID 号从其中的 9 个开始过程.
I do not want to use the UpdateSouceTrigger=PropertyChanged because that would cause the resource-intensive background process to run whenever a character gets typed, so a 9-digit ID number starts off 9 of these processes.
我也不想使用 UpdateSourceTrigger=LostFocus 因为表单上没有其他东西可以让 TextBox 失去焦点.
I also don't want to use UpdateSourceTrigger=LostFocus because there is nothing else on the form to make the TextBox lose focus.
那么有没有办法让我的后台进程只在用户输入 ID 号时暂停后运行?
So is there a way to cause my background process to run only after the user pauses when typing in the Id number?
推荐答案
准备代码转储.
我已经使用 WPF Fake Behavior(一个附加的 DP，其行为类似于一种行为)做到了这一点.这段代码有效，但它并不漂亮，可能会导致泄漏.可能需要用弱引用等替换所有引用.
I've done this with a WPF Fake Behavior (an attached DP that acts like a behavior). This code works, but it isn't pretty and it may result in leaks. Probably need to replace all the references with weak references, etc.
这是行为类:
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;
}
}
}
}
这是一个如何使用它的示例:
And here's an example of how it is used:
<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>
这个的要点是...
您在绑定的 UIElement 上设置附加属性，传入您希望延迟的 DP.此时，我有附加属性的目标和要延迟的属性，因此我可以进行设置.我必须等到绑定可用，所以我必须在设置数据绑定后使用 Dispatcher 来实例化我的观察者类.不这样做，您将无法获取绑定表达式.
You set the attached property on the bound UIElement, passing in the DP you wish to delay. At this point, I have the target of the attached property and the property to be delayed, so I can set things up. I do have to wait until the binding is available, so I have to use the Dispatcher to instantiate my watcher class after databinding has been set up. Fail to do this and you can't grab the binding expression.
观察者类获取绑定并向 DependencyProperty 添加更新侦听器.在侦听器中，我设置了一个计时器(如果我们还没有更新)或重置计时器.一旦计时器滴答作响，我就会触发绑定表达式.
The watcher class grabs the binding and adds an update listener to the DependencyProperty. In the listener, I set up a timer (if we haven't updated) or reset the timer. Once the Timer ticks, I fire off the binding expression.
同样，它可以工作，但它肯定需要清理.此外，您可以通过以下代码片段的名称使用 DP:
Again, it works, but it definitely needs cleanup. Also, you can just use the DP via its name with the following code snippet:
FieldInfo fieldInfo = instance.GetType()
.GetField(name,
BindingFlags.Public |
BindingFlags.Static |
BindingFlags.FlattenHierarchy);
return (fieldInfo != null) ? (DependencyProperty)fieldInfo.GetValue(null) : null;
您可能需要将属性"附加到 name 上，但与使用 x:Static 相比，这很容易.
You might have to tack "Property" onto name, but that's easy compared to using x:Static.
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