如何在NuGet Uranium UI的TextField中实现巴西CPF掩码？已试MaskedBehavior无效

方案一：自定义CPF掩码Behavior #

由于Xamarin Community Toolkit的MaskedBehavior和Uranium UI TextField兼容性不佳，直接自定义专属的CPF掩码行为更可靠：

using Microsoft.Maui.Controls;
using System.Text.RegularExpressions;

public class CpfMaskBehavior : Behavior<TextField>
{
    protected override void OnAttachedTo(TextField bindable)
    {
        base.OnAttachedTo(bindable);
        bindable.TextChanged += OnTextChanged;
    }

    protected override void OnDetachingFrom(TextField bindable)
    {
        base.OnDetachingFrom(bindable);
        bindable.TextChanged -= OnTextChanged;
    }

    private void OnTextChanged(object sender, TextChangedEventArgs e)
    {
        if (sender is not TextField textField) return;
        
        // 过滤所有非数字字符
        var cleanText = Regex.Replace(e.NewTextValue ?? string.Empty, @"[^\d]", "");
        var formattedText = string.Empty;

        // 应用CPF格式：XXX.XXX.XXX-XX
        if (cleanText.Length > 0)
        {
            formattedText = cleanText.Substring(0, 1);
            if (cleanText.Length >= 3)
                formattedText = $"{cleanText.Substring(0, 3)}.";
            if (cleanText.Length >= 6)
                formattedText += $"{cleanText.Substring(3, 3)}.";
            if (cleanText.Length >= 9)
                formattedText += $"{cleanText.Substring(6, 3)}-";
            if (cleanText.Length >= 11)
                formattedText += cleanText.Substring(9, 2);
        }

        // 避免循环触发TextChanged
        if (textField.Text != formattedText)
        {
            textField.Text = formattedText;
            // 光标定位到末尾
            textField.CursorPosition = formattedText.Length;
        }
    }
}

在XAML中引用该Behavior：

<material:TextField
    x:Name="txtCpf"
    Title="CPF"
    FontFamily="MontserratMedium"
    TitleColor="#902E2E2E">
    <material:TextField.Behaviors>
        <local:CpfMaskBehavior />
    </material:TextField.Behaviors>
</material:TextField>

（注：local是自定义Behavior所在的命名空间，需在XAML根节点添加声明，例如xmlns:local="clr-namespace:你的应用命名空间"）

方案二：直接在TextChanged事件中处理 #

如果不想自定义Behavior，可直接在已有的txtCpf_TextChanged事件中实现格式化逻辑：

private void txtCpf_TextChanged(object sender, TextChangedEventArgs e)
{
    if (sender is not TextField textField) return;
    
    var cleanText = Regex.Replace(e.NewTextValue ?? string.Empty, @"[^\d]", "");
    var formattedText = string.Empty;

    if (cleanText.Length > 0)
    {
        formattedText = cleanText.Substring(0, 1);
        if (cleanText.Length >= 3)
            formattedText = $"{cleanText.Substring(0, 3)}.";
        if (cleanText.Length >= 6)
            formattedText += $"{cleanText.Substring(3, 3)}.";
        if (cleanText.Length >= 9)
            formattedText += $"{cleanText.Substring(6, 3)}-";
        if (cleanText.Length >= 11)
            formattedText += cleanText.Substring(9, 2);
    }

    if (textField.Text != formattedText)
    {
        textField.Text = formattedText;
        textField.CursorPosition = formattedText.Length;
    }
}

同时记得移除之前无效的MaskedBehavior，避免逻辑冲突。

注意事项 #

• 两种方案都会自动过滤非数字输入，确保用户只能输入数字
• 光标会自动定位到输入末尾，提升输入流畅度
• 若需额外的CPF合法性校验，可在格式化完成后添加对应校验逻辑

内容的提问来源于stack exchange，提问作者Reanii