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，则不显示它。

尝试带有简单触发器的＃1 会产生错误 'Text'成员无效，因为它没有限定的类型名称。：

 < 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 ，并带有样式触发器产生错误类型'样式'不包含公共类型转换器类：

 < ; 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 和样式的DataTrigger 产生相同的错误类型'样式'不包含公共类型转换器类：

  < 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 ：好的，这是我的愚蠢监督，忘记了 StaticResource ，但即使尝试＃2和尝试＃3都遇到新错误类型为System.Windows.Trigger的样式未知：

 < 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}填充= 10 Background = Yellow Text = {Binding MainMessage} /> 
< / StackPanel> 
< / UserControl> 
  

那我该怎么做？

答案：

好的，所以这是一个令人发狂的语法搜寻，结局不错，这是可行的版本，希望对您有所帮助，经验教训：

• 如果触发，则为 style


• if触发，然后 StaticResource


• 如果绑定，然后 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}填充= 10 Background = Yellow Text = {Binding MainMessage} /> 
< / StackPanel> 
< / UserControl> 
  

解决方案

尝试尝试＃2或尝试＃3都可以-问题出在引用样式的行中-您需要使用'Style = {StaticResource [KeyName]}或'Style = {DynamicResource [KeyName]}'。

尝试一下（在尝试＃2中）：

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

在尝试1中，您揭示了当前WPF版本的局限性：元素不直接支持触发器。 / p>

I want to tell WPF: "If TextBlock contains no data, then don't show it."

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 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 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: 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>

So how do I do this?

ANSWER:

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

• if trigger, then style
• if style, then StaticResource
• if binding, then DataTrigger

code that works:

<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>

解决方案

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]}"'.

Try this (in Try #2):

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

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

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