当 XAML TextBlock 不包含任何数据时，如何使其折叠? [英] How can you get a XAML TextBlock to collapse when it contains no data?

问题描述

我想告诉 WPF:如果 TextBlock 不包含数据，则不要显示它."

TRY #1 使用简单触发器 会产生错误'Text' 成员无效，因为它没有合格的类型名称.em>":

TRY #1 with a simple trigger produces the error "'Text' member is not valid because it does not have a qualifying type name.":

<StackPanel Margin="10">
    <TextBlock Padding="10" Background="Yellow" Text="{Binding MainMessage}">
        <TextBlock.Triggers>
            <Trigger Property="Text" Value="{x:Null}">
                <Setter Property="Visibility" Value="Collapsed"/>
            </Trigger>
        </TextBlock.Triggers>
    </TextBlock>
</StackPanel>

TRY #2 使用 样式触发器 会产生错误类型样式"不包含公共类型转换器类:

TRY #2 with a style trigger produces the error The type 'style' does not contain a public type-converter class:

<UserControl x:Class="TestItemsSource234.Views.SmartForm"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <UserControl.Resources>
        <Style x:Key="MainMessageStyle" TargetType="TextBlock">
            <Style.Triggers>
                <Trigger>
                    <Trigger Property="Text" Value="{x:Null}">
                        <Setter Property="Visibility" Value="Collapsed"/>
                    </Trigger>
                </Trigger>
            </Style.Triggers>
        </Style>
    </UserControl.Resources>
    <StackPanel Margin="10">        
        <TextBlock Style="MainMessageStyle" Padding="10" Background="Yellow" Text="{Binding MainMessage}"/>
    </StackPanel>
</UserControl>

TRY #3 使用 style DataTrigger 会产生相同的错误类型style"不包含公共类型转换器类:

TRY #3 with a style DataTrigger produces the same error The type 'style' does not contain a public type-converter class:

<UserControl x:Class="TestItemsSource234.Views.SmartForm"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <UserControl.Resources>
        <Style x:Key="MainMessageStyle" TargetType="TextBlock">
            <Style.Triggers>
                <Trigger>
                    <DataTrigger Binding="{Binding MainMessage}" Value="{x:Null}">
                        <Setter Property="Visibility" Value="Collapsed"/>
                    </DataTrigger>
                </Trigger>
            </Style.Triggers>
        </Style>
    </UserControl.Resources>
    <StackPanel Margin="10">        
        <TextBlock Style="MainMessageStyle" Padding="10" Background="Yellow" Text="{Binding MainMessage}"/>
    </StackPanel>
</UserControl>

TRY #4:好吧，这是我的一个愚蠢的疏忽，忘记了 StaticResource，但即便如此，Try #2 和 Try #3 都会出现新错误样式中的 System.Windows.Trigger 类型未知:

TRY #4: OK, that was a dumb oversight of mine, forgot the StaticResource, but even then both Try #2 and Try #3 get a new error The type System.Windows.Trigger in Style is unknown:

<UserControl x:Class="TestItemsSource234.Views.SmartForm"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <UserControl.Resources>
        <Style x:Key="MainMessageStyle" TargetType="TextBlock">
            <Style.Triggers>
                <Trigger>
                    <Trigger Property="Text" Value="">
                        <Setter Property="Visibility" Value="Collapsed"/>
                    </Trigger>
                </Trigger>
            </Style.Triggers>
        </Style>
    </UserControl.Resources>
    <StackPanel Margin="10">        
        <TextBlock Style="{StaticResource MainMessageStyle}" Padding="10" Background="Yellow" Text="{Binding MainMessage}"/>
    </StackPanel>
</UserControl>

那么我该怎么做呢?

好的，这是一个令人抓狂的语法搜索，但有一个快乐的结局，这是有效的版本，希望它对某人有所帮助，吸取了教训:

OK, so that was a maddening syntax hunt with a happy end, here's the version that works, hope it helps somebody, lessons learned:

• 如果触发，则样式
• 如果是样式，则StaticResource
• 如果绑定，则DataTrigger

有效的代码:

<UserControl x:Class="TestItemsSource234.Views.SmartForm"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <UserControl.Resources>
        <Style x:Key="MainMessageStyle" TargetType="TextBlock">
            <Style.Triggers>
                <DataTrigger Binding="{Binding MainMessage}" Value="{x:Null}">
                    <Setter Property="Visibility" Value="Collapsed"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </UserControl.Resources>
    <StackPanel Margin="10">
        <ItemsControl
            ItemsSource="{Binding DataTypeViews}"/>
        <TextBlock Style="{StaticResource MainMessageStyle}" Padding="10" Background="Yellow" Text="{Binding MainMessage}"/>
    </StackPanel>
</UserControl>

推荐答案

Try #2 或 Try #3 应该没问题 - 问题出在您引用样式的行中 - 您需要使用 'Style="{StaticResource [KeyName]}"' 或 'Style="{DynamicResource [KeyName]}"'.

Either Try #2 or Try #3 should be fine - the problem is in the line where you are referencing the style - you need to use either 'Style="{StaticResource [KeyName]}"' or 'Style="{DynamicResource [KeyName]}"'.

试试这个(在尝试 #2 中):

Try this (in Try #2):

<StackPanel Margin="10">        
    <TextBlock Style="{StaticResource MainMessageStyle}" Padding="10" Background="Yellow" Text="{Binding MainMessage}"/>
</StackPanel>

在尝试 1 中，您揭示了当前 WPF 版本的限制:元素不直接支持触发器.

In Try 1 you reveal a limitation of current WPF versions: Triggers are not supported directly on elements.

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