【发布时间】：2017-07-21 09:14:58
【问题描述】：
在尝试将实体保存到数据库之前，我必须验证一些属性。
问题：
- Programmstart：tabitem1 中的文本框显示验证错误
- 用户选择：视图中的 Tabitem2
- 用户选择：视图中的 Tabitem1
- 空文本框的验证错误不再显示在 tabitem1 中。
异常行为：
如果用户更改所选的tabitem，每次都会显示验证错误。
使用的工具/框架：
- Prism 6.3（使用 Templatepack PrismUnity 的新项目
- Prism.Validation (https://github.com/mfe-/Prism.Validation)
问题：
- 为什么在不同的 tabitem 之间选择后 DataAnnoation 不再显示？ ViewModel 属性 hasErrors 为 true。
- 如果用户再次选择了 tabitem1，我如何重新开始评估？
查看：
<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];
}
}
}
【问题讨论】：