WPF MVVM验证数据网格和禁用命令按钮

要使Button正确响应，我们需要将4个东西粘合在一起;ViewModel、Button、ValidationRules和DataGrid的模板列的文本框。否则,视图模型。CanHello属性不能正确设置，从而使RelayCommand不起作用。现在ValidationRules: CustomValidRule和NegValidRule还没有粘到ViewModel上。为了让它们通知ViewModel它们的验证结果，它们需要触发一些事件。我们将使用InotifyPropertyChanged来使用WPF遵循的通知模式。我们将为UI级验证规则创建一个接口iviewmodeluirrule，以便与ViewModel交互。

ViewModelUIRuleEvent.cs

using System;
    namespace BusinessLogic
    {
        public interface IViewModelUIRule
        {
            event ViewModelValidationHandler ValidationDone;
        }
        public delegate void ViewModelValidationHandler(object sender, ViewModelUIValidationEventArgs e);
        public class ViewModelUIValidationEventArgs : EventArgs
        {
            public bool IsValid { get; set; }
            public ViewModelUIValidationEventArgs(bool valid) { IsValid = valid; }
        }
    }

我们的验证规则现在将实现这个接口。

public class CustomValidRule : ValidationRule, IViewModelUIRule
    {
        bool _isValid = true;
        public bool IsValid { get { return _isValid; } set { _isValid = value; } }
        public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
        {
            int? a = value as int?;
            ValidationResult result = null;
            if (a.HasValue)
            {
                if (a.Value > 0 && a.Value < 10)
                {
                    _isValid = true;
                    result = new ValidationResult(true, "");
                }
                else
                {
                    _isValid = false;
                    result = new ValidationResult(false, "must be > 0 and < 10 ");
                }
            }
            OnValidationDone();
            return result;
        }
        private void OnValidationDone()
        {
            if (ValidationDone != null)
                ValidationDone(this, new ViewModelUIValidationEventArgs(_isValid));
        }
        public event ViewModelValidationHandler ValidationDone;
    }

///////////////////////////

    public class NegValidRule : ValidationRule, IViewModelUIRule
{
    bool _isValid = true;
    public bool IsValid { get { return _isValid; } set { _isValid = value; } }
    ValidationResult result = null;
    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
    {
        int? a = value as int?;
        if (a.HasValue)
        {
            if (a.Value < 0)
            {
                _isValid = true;
                result = new ValidationResult(true, "");
            }
            else
            {
                _isValid = false;
                result = new ValidationResult(false, "must be negative ");
            }
        }
        OnValidationDone();
        return result;
    }
    private void OnValidationDone()
    {
        if (ValidationDone != null)
            ValidationDone(this, new ViewModelUIValidationEventArgs(_isValid));
    }
    public event ViewModelValidationHandler ValidationDone;
}

现在，我们需要更新ViewModel类来维护验证规则集合。并处理由自定义验证规则触发的ValidationDone事件。

namespace BusinessLogic
{
    public class ViewModel : INotifyPropertyChanged
    {
        private ObservableCollection<ValidationRule> _rules;
        public ObservableCollection<ValidationRule> Rules { get { return _rules; } }
        public ViewModel()
        {
            _rules = new ObservableCollection<ValidationRule>();
            Rules.CollectionChanged += Rules_CollectionChanged;
            MyCollection.CollectionChanged += MyCollection_CollectionChanged;            
            MyCollection.Add(new Class1("Eins", 1));
            MyCollection.Add(new Class1("Zwei", 2));
            MyCollection.Add(new Class1("Drei", 3));
        }
        void Rules_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
        {
            foreach (var v in e.NewItems)
                ((IViewModelUIRule)v).ValidationDone += ViewModel_ValidationDone;
        }
        void ViewModel_ValidationDone(object sender, ViewModelUIValidationEventArgs e)
        {
            canHello = e.IsValid;
        }
        void MyCollection_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
        {
            foreach (var v in e.NewItems)
                ((Class1)v).PropertyChanged += ViewModel_PropertyChanged;
        }
        void ViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {            
            // if all validations runs good here
            // canHello = true;
        }
        ……

现在我们已经添加了Rules集合，我们需要向其中添加验证规则。为此，我们需要引用我们的验证规则。我们现在使用XAML添加这些规则，所以我们将使用TextBox的Loaded事件来访问绑定到ID字段的TextBox，如下所示

<TextBox VerticalAlignment="Stretch" VerticalContentAlignment="Center" Loaded="TextBox_Loaded">
                            <TextBox.Text>
                                    <Binding Path="ID" UpdateSourceExceptionFilter="ReturnExceptionHandler" UpdateSourceTrigger="PropertyChanged" ValidatesOnDataErrors="True" ValidatesOnExceptions="True" >
                                        <Binding.ValidationRules>
                                            <b:CustomValidRule ValidationStep="ConvertedProposedValue"></b:CustomValidRule>
                                        </Binding.ValidationRules>
                                    </Binding>
                            </TextBox.Text>
                        </TextBox>

//////////////////////

private void TextBox_Loaded(object sender, RoutedEventArgs e)
        {
            Collection<ValidationRule> rules= ((TextBox)sender).GetBindingExpression(TextBox.TextProperty).ParentBinding.ValidationRules;
            foreach (ValidationRule rule in rules)
                vm.Rules.Add(rule);
        }

void ViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
{            
    // if all back-end last level validations run good here
    // canHello = true;
}