背景

WINUI不提供原生的Trigger支持，推荐使用VisualStateManager进行操作；然对于从WPF转WINUI的开发人员而言，经常会想用Trigger解决问题，鉴于此社区推出了CommunityToolkit.WinUI.Triggers以支持Trigger的使用。

使用方法

1.项目中引入CommunityToolkit.WinUI.Triggers Nuget包。

当前最新稳定版本为8.0.240109，具体见下图：

2. 在Page中引入CommunityToolkit.WinUI

xmlns:triggers="using:CommunityToolkit.WinUI"

3. 在需要的地方编写相应的Trigger

如编写一个校验是否为邮箱的校验,以下为示例截图：

xml中代码如下：

<Page x:Class="TriggersExperiment.Samples.RegexStateTriggerSample"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:local="using:TriggersExperiment.Samples"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      xmlns:triggers="using:CommunityToolkit.WinUI"
      mc:Ignorable="d">

    <Grid>
        <VisualStateManager.VisualStateGroups>
            <VisualStateGroup>
                <VisualState x:Name="validEmail">
                    <VisualState.StateTriggers>
                        <!--  Note: Simple example RegEx, see our IsEmail string extension using emailregex.com for official RFC 5322 support  -->
                        <triggers:RegexStateTrigger Expression="^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$"
                                                    Options="IgnoreCase"
                                                    Value="{Binding Text, ElementName=emailTextBox, Mode=OneWay}" />
                    </VisualState.StateTriggers>
                    <VisualState.Setters>
                        <Setter Target="emailStatus.Text" Value="This is a valid email" />
                        <Setter Target="emailStatus.Foreground" Value="{ThemeResource SystemFillColorSuccessBrush}" />
                        <Setter Target="submitButton.IsEnabled" Value="true" />
                    </VisualState.Setters>
                </VisualState>
            </VisualStateGroup>
        </VisualStateManager.VisualStateGroups>

        <StackPanel MaxWidth="400">
            <TextBox x:Name="emailTextBox"
                     HorizontalAlignment="Stretch"
                     Header="Enter an email" />
            <TextBlock x:Name="emailStatus"
                       Margin="0,4,0,24"
                       Foreground="{ThemeResource SystemFillColorCriticalBrush}"
                       Style="{StaticResource CaptionTextBlockStyle}"
                       Text="Not a valid email" />
            <Button x:Name="submitButton"
                    Content="Submit"
                    IsEnabled="False" />
        </StackPanel>
    </Grid>
</Page>

后台代码如下：

using CommunityToolkit.WinUI;

namespace TriggersExperiment.Samples;

[ToolkitSample(id: nameof(RegexStateTriggerSample), "RegexStateTrigger", description: $"A sample for showing how to create and use a {nameof(RegexStateTrigger)}.")]
public sealed partial class RegexStateTriggerSample : Page
{
    public RegexStateTriggerSample()
    {
        this.InitializeComponent();
    }
}

注：以上示例来源于Github。

实现原理

可以看到Trigger的实现还是借助于VisualState实现，只是自定义了一些相应的校验规则而已。以后再做相应介绍。

参考链接：

GitHub - CommunityToolkit/Windows: Collection of controls for WinUI 2, WinUI 3, and Uno Platform developers. Simplifies and demonstrates common developer tasks building experiences for Windows with .NET.