如何通过 tabcontrol tabitem 选择更改重新更新文本框验证

在尝试将我的实体保存到数据库之前，我必须验证一些属性。

问题：

1. 程序启动：tabitem1 中的文本框显示验证错误
2. 用户选择：视图中的 Tabitem2
3. 用户选择：视图中的 Tabitem1
4. tabitem1 中不再显示空文本框的验证错误。

异常行为：

如果用户更改了选定的选项卡，则每次也应显示验证错误。

使用的工具/框架：

1. Prism 6.3（带有模板包 PrismUnity 的新项目
2. Prism.Validation ( https://github.com/mfe-/Prism.Validation )

问题：

1. 为什么在不同选项卡之间选择后不再显示 DataAnnoation？ViewModel 属性 hasErrors 为 true。
2. 如果用户再次选择 tabitem1，我如何重新开始评估？

看法：

<Window x:Class="PrismUnityApp1TestValidation.Views.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:prism="http://prismlibrary.com/"
        prism:ViewModelLocator.AutoWireViewModel="True"
        Title="{Binding Title}" Height="350" Width="525">
    <StackPanel>
        <!--<ContentControl prism:RegionManager.RegionName="ContentRegion" />-->
        <TabControl>
        <TabItem>
         <TabItem.Content>
             <TextBox Height="50" Text="{Binding TestText, ValidatesOnDataErrors=True, NotifyOnValidationError=True, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"></TextBox>
         </TabItem.Content>
        </TabItem>
            <TabItem>
                <TabItem.Content>
                   <TextBlock Text="TabItem2"></TextBlock>
                </TabItem.Content>
            </TabItem>

        </TabControl>
    </StackPanel>
</Window>

视图模型：

using System.ComponentModel.DataAnnotations;
using Prism.Mvvm;
using Prism.Validation;

namespace PrismUnityApp1TestValidation.ViewModels
{
    public class MainWindowViewModel : ValidatableBindableBase
    {
        private string _title = "Prism Unity Application";
        public string Title
        {
            get { return _title; }
            set { SetProperty(ref _title, value); }
        }

        private string _testtext;
        [Required]
        public string TestText
        {
            get { return _testtext; }
            set { SetProperty(ref _testtext, value); }
        }


        public MainWindowViewModel()
        {

        }
    }
}

ValidatableBindableBase (NugetPackage Prism.Validation)：

namespace Prism.Validation
{
    /// <summary>
    /// The IValidatableBindableBase interface was created to add validation support for model classes that contain validation rules.
    /// The default implementation of IValidatableBindableBase is the ValidatableBindableBase class, which contains the logic to run the validation rules of the
    /// instance of a model class and return the results of this validation as a list of properties' errors.
    /// </summary>
    // Documentation on validating user input is at http://go.microsoft.com/fwlink/?LinkID=288817&clcid=0x409
    public class ValidatableBindableBase : BindableBase, IValidatableBindableBase, INotifyDataErrorInfo
    {
        private readonly BindableValidator _bindableValidator;

        /// <summary>
        /// Initializes a new instance of the <see cref="ValidatableBindableBase"/> class.
        /// </summary>
        public ValidatableBindableBase()
        {
            _bindableValidator = new BindableValidator(this);
        }

        /// <summary>
        /// Gets or sets a value indicating whether this instance is validation enabled.
        /// </summary>
        /// <value>
        /// <c>true</c> if validation is enabled for this instance; otherwise, <c>false</c>.
        /// </value>
        public bool IsValidationEnabled
        {
            get { return _bindableValidator.IsValidationEnabled; }
            set { _bindableValidator.IsValidationEnabled = value; }
        }

        /// <summary>
        /// Returns the BindableValidator instance that has an indexer property.
        /// </summary>
        /// <value>
        /// The Bindable Validator Indexer property.
        /// </value>
        public BindableValidator Errors
        {
            get
            {
                return _bindableValidator;
            }
        }
        /// <summary>
        /// Gets a value that indicates whether the entity has validation errors.
        /// </summary>
        /// <value>
        /// <c>true</c> if this instance contains validation errors; otherwise, <c>false</c>.
        /// </value>
        public bool HasErrors
        {
            get
            {
                return !ValidateProperties();
            }
        }

        /// <summary>
        /// Occurs when the Errors collection changed because new errors were added or old errors were fixed.
        /// </summary>
        public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged
        {
            add { _bindableValidator.ErrorsChanged += value; }

            remove { _bindableValidator.ErrorsChanged -= value; }
        }

        /// <summary>
        /// Gets all errors.
        /// </summary>
        /// <returns> A ReadOnlyDictionary that's key is a property name and the value is a ReadOnlyCollection of the error strings.</returns>
        public ReadOnlyDictionary<string, ReadOnlyCollection<string>> GetAllErrors()
        {
            return _bindableValidator.GetAllErrors();
        }

        /// <summary>
        /// Validates the properties of the current instance.
        /// </summary>
        /// <returns>
        /// Returns <c>true</c> if all properties pass the validation rules; otherwise, false.
        /// </returns>
        public bool ValidateProperties()
        {
            return _bindableValidator.ValidateProperties();
        }

        /// <summary>
        /// Validates a single property with the given name of the current instance.
        /// </summary>
        /// <param name="propertyName">The property to be validated.</param>
        /// <returns>Returns <c>true</c> if the property passes the validation rules; otherwise, false.</returns>
        public bool ValidateProperty(string propertyName)
        {
            return !_bindableValidator.IsValidationEnabled // don't fail if validation is disabled
                || _bindableValidator.ValidateProperty(propertyName);
        }

        /// <summary>
        /// Sets the error collection of this instance.
        /// </summary>
        /// <param name="entityErrors">The entity errors.</param>
        public void SetAllErrors(IDictionary<string, ReadOnlyCollection<string>> entityErrors)
        {
            _bindableValidator.SetAllErrors(entityErrors);
        }

        /// <summary>
        /// Checks if a property already matches a desired value. Sets the property and
        /// notifies listeners only when necessary. We are overriding this property to ensure that the SetProperty and the ValidateProperty methods are fired in a
        /// deterministic way.
        /// </summary>
        /// <typeparam name="T">Type of the property.</typeparam>
        /// <param name="storage">Reference to a property with both getter and setter.</param>
        /// <param name="value">Desired value for the property.</param>
        /// <param name="propertyName">Name of the property used to notify listeners. This
        /// value is optional and can be provided automatically when invoked from compilers that
        /// support CallerMemberName.</param>
        /// <returns>
        /// True if the value was changed, false if the existing value matched the
        /// desired value.
        /// </returns>
        protected override bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)
        {
            var result = base.SetProperty(ref storage, value, propertyName);

            if (result && !string.IsNullOrEmpty(propertyName))
            {
                if (_bindableValidator.IsValidationEnabled)
                {
                    _bindableValidator.ValidateProperty(propertyName);
                }
            }
            return result;
        }
        /// <summary>
        /// Gets the validation errors for a specified property or for the entire entity.
        /// </summary>
        /// <param name="propertyName">The name of the property to retrieve validation errors for; or null or Empty, to retrieve entity-level errors.</param>
        /// <returns>The validation errors for the property or entity.</returns>
        public IEnumerable GetErrors(string propertyName)
        {
            if (HasErrors==false)
            {
                return Enumerable.Empty<String>();
            }
            return _bindableValidator[propertyName];
        }
    }
}