WPF 绑定 FallbackValue 设置为 Binding

发布于 2024-08-15 01:01:31 字数 247 浏览 9 评论 0原文

有没有办法让另一个绑定作为后备值？

我正在尝试做这样的事情：

<Label Content="{Binding SelectedItem.Name, ElementName=groupTreeView,
                         FallbackValue={Binding RootGroup.Name}}" />

如果有人有另一个技巧来实现它，那就太好了。

原文

Is there a way to have another binding as a fallback value?

I'm trying to do something like this:

<Label Content="{Binding SelectedItem.Name, ElementName=groupTreeView,
                         FallbackValue={Binding RootGroup.Name}}" />

If anyone's got another trick to pull it off, that would be great.

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稍尽春風 2024-08-22 01:01:31

您正在寻找的是称为 PriorityBinding 的东西（此列表）

（来自文章）

PriorityBinding 的要点是
按顺序命名多个数据绑定
从最理想到最不理想。
这样如果第一次绑定失败，
为空和/或默认值，另一个
绑定可以取代它。

例如

<TextBox>
    <TextBox.Text>
        <PriorityBinding>
            <Binding Path="LastNameNonExistant" IsAsync="True" />
            <Binding Path="FirstName" IsAsync="True" />
        </PriorityBinding>
    </TextBox.Text>
</TextBox>

What you are looking for is something called PriorityBinding (#6 on this list)

(from the article)

The point to PriorityBinding is to
name multiple data bindings in order
of most desirable to least desirable.
This way if the first binding fails,
is empty and/or default, another
binding can take it's place.

e.g.

<TextBox>
    <TextBox.Text>
        <PriorityBinding>
            <Binding Path="LastNameNonExistant" IsAsync="True" />
            <Binding Path="FirstName" IsAsync="True" />
        </PriorityBinding>
    </TextBox.Text>
</TextBox>

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诗化ㄋ丶相逢 2024-08-22 01:01:31

如果您在绑定到 null 值和 PriorityBinding 时遇到问题（正如 Shimmy 指出的那样），您可以使用 MultiBinding 和 MultiValueConverter，如下所示

public class PriorityMultiValueConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        return values.FirstOrDefault(o => o != null);
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

：

<TextBox>
    <TextBox.Text>
        <MultiBinding Converter="{StaticResource PriorityMultiValueConverter}">
            <Binding Path="LastNameNull" />
            <Binding Path="FirstName" />
        </MultiBinding>
    </TextBox.Text>
</TextBox>

If you run into problems with binding to null values and PriorityBinding (as Shimmy pointed out) you could go with MultiBinding and a MultiValueConverter like that:

public class PriorityMultiValueConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        return values.FirstOrDefault(o => o != null);
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

Usage:

<TextBox>
    <TextBox.Text>
        <MultiBinding Converter="{StaticResource PriorityMultiValueConverter}">
            <Binding Path="LastNameNull" />
            <Binding Path="FirstName" />
        </MultiBinding>
    </TextBox.Text>
</TextBox>

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