如何知道文本框何时被修改？

Question

我正在使用.Net 4.5的延迟绑定标记,但我想更改文本框的背景颜色,而更改不是"已提交".如何在发生延迟时将IsDirty属性设置为true？

我尝试使用TextChanged事件设置IsDirty标志,然后在绑定属性设置时删除标志.问题是TextChanged会在绑定属性发生更改时触发,而不仅仅是在用户修改文本时触发.

通过监视TextChanged事件和绑定属性,我以一种非常笨重和脆弱的方式"工作".不用说这很容易出错,所以我想要一个更清洁的解决方案.有没有办法知道文本框已被更改但尚未提交(延迟)？

Answer 1

我查看了源代码,它BindingExpressionBase本身通过一个名为的属性了解这一点NeedsUpdate.但是这个属性是内部的,所以你必须使用反射才能得到它.

但是,您将无法以任何简单的方式监视此属性.所以我看到它的方式,你需要使用这两个事件,TextChanged并SourceUpdated知道什么时候NeedsUpdate可能已经改变.

更新
我创建了一个执行此操作的附加行为,它可以用于监视任何挂起的更新DependencyProperty.请注意,NotifyOnSourceUpdated必须设置为true.

在这里上传了一个小样本项目:PendingUpdateExample.zip

例

<TextBox Text="{Binding ElementName=textBoxSource,
                        Path=Text,
                        NotifyOnSourceUpdated=True,
                        UpdateSourceTrigger=PropertyChanged,
                        Delay=1000}"
         ab:UpdatePendingBehavior.MonitorPendingUpdates="{x:Static TextBox.TextProperty}">
    <TextBox.Style>
        <Style TargetType="TextBox">
            <Style.Triggers>
                <Trigger Property="ab:UpdatePendingBehavior.HasPendingUpdates"
                         Value="True">
                    <Setter Property="Background" Value="Green"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </TextBox.Style>
</TextBox>

UpdatePendingBehavior

public class UpdatePendingBehavior
{
    #region MonitorPendingUpdates

    public static DependencyProperty MonitorPendingUpdatesProperty =
        DependencyProperty.RegisterAttached("MonitorPendingUpdates",
                                            typeof(DependencyProperty),
                                            typeof(UpdatePendingBehavior),
                                            new UIPropertyMetadata(null, MonitorPendingUpdatesChanged));

    public static DependencyProperty GetMonitorPendingUpdates(FrameworkElement obj)
    {
        return (DependencyProperty)obj.GetValue(MonitorPendingUpdatesProperty);
    }
    public static void SetMonitorPendingUpdates(FrameworkElement obj, DependencyProperty value)
    {
        obj.SetValue(MonitorPendingUpdatesProperty, value);
    }

    public static void MonitorPendingUpdatesChanged(DependencyObject target, DependencyPropertyChangedEventArgs e)
    {
        DependencyProperty property = e.NewValue as DependencyProperty;
        if (property != null)
        {
            FrameworkElement element = target as FrameworkElement;
            element.SourceUpdated += elementProperty_SourceUpdated;

            if (element.IsLoaded == true)
            {
                SubscribeToChanges(element, property);
            }
            element.Loaded += delegate { SubscribeToChanges(element, property); };
            element.Unloaded += delegate { UnsubscribeToChanges(element, property); };
        }
    }

    private static void SubscribeToChanges(FrameworkElement element, DependencyProperty property)
    {
        DependencyPropertyDescriptor propertyDescriptor =
            DependencyPropertyDescriptor.FromProperty(property, element.GetType());
        propertyDescriptor.AddValueChanged(element, elementProperty_TargetUpdated);
    }

    private static void UnsubscribeToChanges(FrameworkElement element, DependencyProperty property)
    {
        DependencyPropertyDescriptor propertyDescriptor =
                DependencyPropertyDescriptor.FromProperty(property, element.GetType());
        propertyDescriptor.RemoveValueChanged(element, elementProperty_TargetUpdated);
    }

    private static void elementProperty_TargetUpdated(object sender, EventArgs e)
    {
        FrameworkElement element = sender as FrameworkElement;
        UpdatePendingChanges(element);
    }

    private static void elementProperty_SourceUpdated(object sender, DataTransferEventArgs e)
    {
        FrameworkElement element = sender as FrameworkElement;
        if (e.Property == GetMonitorPendingUpdates(element))
        {
            UpdatePendingChanges(element);
        }
    }

    private static void UpdatePendingChanges(FrameworkElement element)
    {
        BindingExpressionBase beb = BindingOperations.GetBindingExpressionBase(element, GetMonitorPendingUpdates(element));
        BindingFlags bindingFlags = BindingFlags.Instance | BindingFlags.NonPublic;
        PropertyInfo needsUpdateProperty = beb.GetType().GetProperty("NeedsUpdate", bindingFlags);
        SetHasPendingUpdates(element, (bool)needsUpdateProperty.GetValue(beb));
    }

    #endregion // MonitorPendingUpdates

    #region HasPendingUpdates

    public static DependencyProperty HasPendingUpdatesProperty =
        DependencyProperty.RegisterAttached("HasPendingUpdates",
                                            typeof(bool),
                                            typeof(UpdatePendingBehavior),
                                            new UIPropertyMetadata(false));

    public static bool GetHasPendingUpdates(FrameworkElement obj)
    {
        return (bool)obj.GetValue(HasPendingUpdatesProperty);
    }
    public static void SetHasPendingUpdates(FrameworkElement obj, bool value)
    {
        obj.SetValue(HasPendingUpdatesProperty, value);
    }

    #endregion // HasPendingUpdates
}

另一种方法是使用一个MultiBinding绑定源和目标的方法,并在转换器中比较它们的值.然后你可以改变Background的Style.这假设您不转换该值.两个例子TextBoxes

<TextBox Text="{Binding ElementName=textBoxSource,
                        Path=Text,
                        UpdateSourceTrigger=PropertyChanged,
                        Delay=2000}">
    <TextBox.Style>
        <Style TargetType="TextBox">
            <Style.Triggers>
                <DataTrigger Value="False">
                    <DataTrigger.Binding>
                        <MultiBinding Converter="{StaticResource IsTextEqualConverter}">
                            <Binding RelativeSource="{RelativeSource Self}"
                                     Path="Text"/>
                            <Binding ElementName="textBoxSource" Path="Text"/>
                        </MultiBinding>
                    </DataTrigger.Binding>
                    <Setter Property="Background" Value="Green"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </TextBox.Style>
</TextBox>
<TextBox Name="textBoxSource"/>

IsTextEqualConverter

public class IsTextEqualConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        return values[0].ToString() == values[1].ToString();
    }
    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}