通过使用样式修改文本框文本绑定的参数

Question

我想要一个以货币格式显示数字的TextBox(通过在绑定上设置StringFormat=c(。当选择TextBox时(当IsKeyboardFocused==true时(，我希望格式化消失，直到失去对TextBox的关注。

我找到了一种方法，代码粘贴在下面。我的问题是绑定是在Style中指定的——这意味着我必须为每个想要执行此操作的TextBox重新键入样式。理想情况下，我想把样式放在中心位置，并为每个TextBox重用它，每个都有不同的绑定目标。

有没有一种方法可以让我使用Style在现有绑定上设置一个参数，比如Text.Binding.StringFormat=""？(与将Text的整个值设置为新定义的Binding相反(

还将感谢为实现这一目标提出的其他建议。

代码(这很有效，只是不方便(：

<TextBox x:Name="ContractAmountTextBox">
<TextBox.Style>
    <Style TargetType="{x:Type TextBox}">                                       
        <Style.Triggers>
            <DataTrigger Binding="{Binding IsKeyboardFocused, ElementName=ContractAmountTextBox}" Value="False">
                <Setter Property="Text" Value="{Binding Path=ContractAmount, UpdateSourceTrigger=LostFocus, StringFormat=c}"/>
            </DataTrigger>
            <DataTrigger Binding="{Binding IsKeyboardFocused, ElementName=ContractAmountTextBox}" Value="True">
                <Setter Property="Text" Value="{Binding Path=ContractAmount, UpdateSourceTrigger=LostFocus}"/>
            </DataTrigger>
        </Style.Triggers>
    </Style>
</TextBox.Style>

Answer 1

使用附加的属性是可行的，但这意味着必须完全替换绑定，然后将其放回。

这里有一个快速而肮脏的实现：

public static class TextBoxBehavior
{
    #region StringFormat
    public static string GetStringFormat(TextBox obj)
    {
        return (string)obj.GetValue(StringFormatProperty);
    }
    public static void SetStringFormat(TextBox obj, string value)
    {
        obj.SetValue(StringFormatProperty, value);
    }

    public static readonly DependencyProperty StringFormatProperty =
        DependencyProperty.RegisterAttached(
          "StringFormat",
          typeof(string),
          typeof(TextBoxBehavior),
          new UIPropertyMetadata(
            null,
            StringFormatChanged));
    // Used to store the original format
    private static readonly DependencyPropertyKey OriginalBindingPropertyKey =
        DependencyProperty.RegisterAttachedReadOnly(
            "OriginalBinding",
            typeof(BindingBase),
            typeof(TextBoxBehavior),
            new UIPropertyMetadata(null));
    private static void StringFormatChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
    {
        TextBox textBox = o as TextBox;
        if (textBox == null)
            return;
        string oldValue = (string)e.OldValue;
        string newValue = (string)e.NewValue;
        if (!string.IsNullOrEmpty(oldValue) && string.IsNullOrEmpty(newValue))
        {
            // Update target for current binding
            UpdateTextBindingSource(textBox);
            // Restore original binding
            var originalBinding = (BindingBase)textBox.GetValue(OriginalBindingPropertyKey.DependencyProperty);
            if (originalBinding != null)
                BindingOperations.SetBinding(textBox, TextBox.TextProperty, originalBinding);
            textBox.SetValue(OriginalBindingPropertyKey, null);
        }
        else if (!string.IsNullOrEmpty(newValue) && string.IsNullOrEmpty(oldValue))
        {
            // Get current binding
            var originalBinding = BindingOperations.GetBinding(textBox, TextBox.TextProperty);
            if (originalBinding != null)
            {
                // Update target for current binding
                UpdateTextBindingSource(textBox);
                // Create new binding
                var newBinding = CloneBinding(originalBinding);
                newBinding.StringFormat = newValue;
                // Assign new binding
                BindingOperations.SetBinding(textBox, TextBox.TextProperty, newBinding);
                // Store original binding
                textBox.SetValue(OriginalBindingPropertyKey, originalBinding);
            }
        }
    }
    private static void UpdateTextBindingSource(TextBox textBox)
    {
        var expr = textBox.GetBindingExpression(TextBox.TextProperty);
        if (expr != null &&
            expr.ParentBinding != null &&
            (expr.ParentBinding.Mode == BindingMode.Default // Text binds two-way by default
            || expr.ParentBinding.Mode == BindingMode.TwoWay
            || expr.ParentBinding.Mode == BindingMode.OneWayToSource))
        {
            expr.UpdateSource();
        }
    }
    private static Binding CloneBinding(Binding original)
    {
        var copy = new Binding
                         {
                             Path = original.Path,
                             XPath = original.XPath,
                             Mode = original.Mode,
                             Converter = original.Converter,
                             ConverterCulture = original.ConverterCulture,
                             ConverterParameter = original.ConverterParameter,
                             FallbackValue = original.FallbackValue,
                             TargetNullValue = original.TargetNullValue,
                             NotifyOnSourceUpdated = original.NotifyOnSourceUpdated,
                             NotifyOnTargetUpdated = original.NotifyOnTargetUpdated,
                             NotifyOnValidationError = original.NotifyOnValidationError,
                             UpdateSourceExceptionFilter = original.UpdateSourceExceptionFilter,
                             UpdateSourceTrigger = original.UpdateSourceTrigger,
                             ValidatesOnDataErrors = original.ValidatesOnDataErrors,
                             ValidatesOnExceptions = original.ValidatesOnExceptions,
                             BindingGroupName = original.BindingGroupName,
                             BindsDirectlyToSource = original.BindsDirectlyToSource,
                             AsyncState = original.AsyncState,
                             IsAsync = original.IsAsync,
                             StringFormat = original.StringFormat
                         };
        if (original.Source != null)
            copy.Source = original.Source;
        if (original.RelativeSource != null)
            copy.RelativeSource = original.RelativeSource;
        if (original.ElementName != null)
            copy.ElementName = original.ElementName;
        foreach (var rule in original.ValidationRules)
        {
            copy.ValidationRules.Add(rule);
        }
        return copy;
    }
    #endregion
}

用法：

<TextBox x:Name="ContractAmountTextBox"
         Text="{Binding Path=ContractAmount, UpdateSourceTrigger=LostFocus, StringFormat=c}">
    <TextBox.Style>
        <Style TargetType="{x:Type TextBox}">                                       
            <Style.Triggers>
                <Trigger Property="IsKeyboardFocused" Value="True">
                    <Setter Property="local:TextBoxBehavior.StringFormat" Value="N"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </TextBox.Style>
</TextBox>

使用它，您还可以为不同的TextBoxes重新使用样式