在输入无效后在Xamarin.Forms中重置验证

// 创建表单页面
public class MyFormPage : ContentPage
{
    Entry usernameEntry;
    Entry passwordEntry;
    Button resetButton;

    public MyFormPage()
    {
        // 创建输入字段和重置按钮
        usernameEntry = new Entry();
        passwordEntry = new Entry();
        resetButton = new Button { Text = "重置" };
        resetButton.Clicked += ResetButton_Clicked;

        // 添加验证规则
        usernameEntry.Behaviors.Add(new RequiredFieldBehavior { ErrorMessage = "用户名不能为空" });
        passwordEntry.Behaviors.Add(new RequiredFieldBehavior { ErrorMessage = "密码不能为空" });

        // 创建布局并添加组件
        var stackLayout = new StackLayout();
        stackLayout.Children.Add(new Label { Text = "用户名" });
        stackLayout.Children.Add(usernameEntry);
        stackLayout.Children.Add(new Label { Text = "密码" });
        stackLayout.Children.Add(passwordEntry);
        stackLayout.Children.Add(resetButton);

        Content = stackLayout;
    }

    // 重置按钮点击事件处理程序
    private void ResetButton_Clicked(object sender, EventArgs e)
    {
        // 重置所有输入字段
        usernameEntry.Text = string.Empty;
        passwordEntry.Text = string.Empty;
        foreach (var behavior in usernameEntry.Behaviors.Concat(passwordEntry.Behaviors))
        {
            if (behavior is IValidity validity)
            {
                validity.IsValid = true;
                validity.ErrorMessage = string.Empty;
            }
        }
    }
}

// 必填字段验证行为
public class RequiredFieldBehavior : Behavior<Entry>, IValidity
{
    public string ErrorMessage { get; set; }
    public bool IsValid { get; set; } = true;

    protected override void OnAttachedTo(Entry bindable)
    {
        bindable.TextChanged += Bindable_TextChanged;
        base.OnAttachedTo(bindable);
    }

    protected override void OnDetachingFrom(Entry bindable)
    {
        bindable.TextChanged -= Bindable_TextChanged;
        base.OnDetachingFrom(bindable);
    }

    private void Bindable_TextChanged(object sender, TextChangedEventArgs e)
    {
        // 验证字段是否为空
        if (string.IsNullOrWhiteSpace(e.NewTextValue))
        {
            IsValid = false;
            ((Entry)sender).TextColor = Color.Red;
        }
        else
        {
            IsValid = true;
            ((Entry)sender).TextColor = Color.Default;
        }
    }
}