MVVM实现ViewModel获取View输入验证状态

由于Binding只把Convert成功的值送往Source，当目标中的值Convert失败时Source的值依然是旧值，所以ViewModel必须获取View的输入验证状态，以下是本人的实现。

当“+”号两边输入正确时，“Add”可用，当所有“+”号两边输入正确时，“Add All”可用。

通过Behavior添加Validation.ErrorEvent路由事件的事件处理器，在该事件处理器中把HasError状态写入自定义的附加属性，附加属性可以绑定。

Behavior派生类引用System.Windows.Interactivity.dll，代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interactivity;

namespace Calculater
{
    public class NotifyErrorBehavior : Behavior<UIElement>
    {
        protected override void OnAttached()
        {
            base.OnAttached();

            this.AssociatedObject.AddHandler(Validation.ErrorEvent, new RoutedEventHandler(HasErrorChanged));
        }

        protected override void OnDetaching()
        {
            base.OnDetaching();
            this.AssociatedObject.RemoveHandler(Validation.ErrorEvent, new RoutedEventHandler(HasErrorChanged));
        }

        private static void HasErrorChanged(object sender, RoutedEventArgs e)
        {
            DependencyObject d = e.OriginalSource as DependencyObject;
            HasErrorHelper.SetHasError(d, Validation.GetHasError(d));
        }
    }
}

附加属性代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;

namespace Calculater
{
    public class HasErrorHelper
    {
        public static bool GetHasError(DependencyObject obj)
        {
            return (bool)obj.GetValue(HasErrorProperty);
        }

        public static void SetHasError(DependencyObject obj, bool value)
        {
            obj.SetValue(HasErrorProperty, value);
        }

        public static readonly DependencyProperty HasErrorProperty =
            DependencyProperty.RegisterAttached("HasError", typeof(bool), typeof(HasErrorHelper), new PropertyMetadata(false));
    }
}

View代码：

<UserControl x:Class="Calculater.ChildCalculater"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:local="clr-namespace:Calculater"
             xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
             mc:Ignorable="d"
             d:DesignHeight="80" d:DesignWidth="500">
    <i:Interaction.Behaviors>
        <local:NotifyErrorBehavior></local:NotifyErrorBehavior>
    </i:Interaction.Behaviors>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition />
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition />
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="Auto"/>
        </Grid.ColumnDefinitions>
        <TextBox Margin="3" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" local:HasErrorHelper.HasError="{Binding Path=HasErrorX,Mode=OneWayToSource}">
            <Binding Path="X" NotifyOnValidationError="True" UpdateSourceTrigger="PropertyChanged" TargetNullValue="" />
        </TextBox>
        <Label Margin="3" VerticalContentAlignment="Center" HorizontalContentAlignment="Center" Grid.Column="1">+</Label>
        <TextBox Margin="3" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" Grid.Column="2" local:HasErrorHelper.HasError="{Binding Path=HasErrorY,Mode=OneWayToSource}">
            <Binding Path="Y" NotifyOnValidationError="True" UpdateSourceTrigger="PropertyChanged" TargetNullValue="" />
        </TextBox>
        <Label Margin="3" VerticalContentAlignment="Center" HorizontalContentAlignment="Center" Grid.Column="3">=</Label>
        <TextBox Margin="3" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" Grid.Column="4" IsReadOnly="True">
            <Binding Path="Sum" TargetNullValue="" />
        </TextBox>
        <Button Margin="3" Grid.Column="5" Padding="3" Command="{Binding CalculateCommand}">Add</Button>
        <Button Margin="3" Grid.Column="6" Padding="3" Command="{Binding ResetCommand}">Reset</Button>
    </Grid>
</UserControl>

ViewModel引用Microsoft.Practices.Prism.dll，代码如下：

using Microsoft.Practices.Prism.Commands;
using Microsoft.Practices.Prism.ViewModel;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Calculater
{
    class ChildCalculaterViewModel : NotificationObject
    {
        public ChildCalculaterViewModel()
        {
            this._calculateCommand = new DelegateCommand(this.Calculate, this.CanCalculate);
            this._resetCommand = new DelegateCommand(this.Reset);

            CalculaterCommand.CalculateAllCommand.RegisterCommand(this.CalculateCommand);
            CalculaterCommand.ResetAllCommand.RegisterCommand(this.ResetCommand);

        }

        private double? _x;

        public double? X
        {
            get { return _x; }
            set
            {
                if (_x != value)
                {
                    _x = value;
                    this.RaisePropertyChanged("X");
                    this.Sum = null;
                    this.CalculateCommand.RaiseCanExecuteChanged();
                }

            }
        }

        private double? _y;

        public double? Y
        {
            get { return _y; }
            set
            {
                if (_y != value)
                {
                    _y = value;
                    this.RaisePropertyChanged("Y");
                    this.Sum = null;
                    this.CalculateCommand.RaiseCanExecuteChanged();
                }

            }
        }

        private double? _sum;

        public double? Sum
        {
            get { return _sum; }
            set
            {
                if (_sum != value)
                {
                    _sum = value;
                    this.RaisePropertyChanged("Sum");
                }

            }
        }

        private bool _hasErrorX;

        public bool HasErrorX
        {
            get { return _hasErrorX; }
            set
            {
                if (_hasErrorX != value)
                {
                    _hasErrorX = value;
                    this.Sum = null;
                    this.CalculateCommand.RaiseCanExecuteChanged();
                }

            }
        }

        private bool _hasErrorY;

        public bool HasErrorY
        {
            get { return _hasErrorY; }
            set
            {
                if (_hasErrorY != value)
                {
                    _hasErrorY = value;
                    this.Sum = null;
                    this.CalculateCommand.RaiseCanExecuteChanged();
                }

            }
        }

        private DelegateCommand _calculateCommand;

        public DelegateCommand CalculateCommand
        {
            get { return _calculateCommand; }
        }

        private bool CanCalculate()
        {
            if (this.HasErrorX || this.HasErrorY || !this.X.HasValue || !this.Y.HasValue)
            {
                return false;
            }

            return true;
        }

        private void Calculate()
        {
            try
            {
                double x = this.X.Value;
                double y = this.Y.Value;

                this.Sum = x + y;
            }
            catch
            {
                return;
            }
        }

        private DelegateCommand _resetCommand;

        public DelegateCommand ResetCommand
        {
            get { return _resetCommand; }
        }

        private void Reset()
        {
            this.X = null;
            this.Y = null;
            this.Sum = null;
        }
    }
}

主窗体代码：

<Window x:Class="Calculater.Shell"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:Calculater"
        xmlns:prism="http://www.codeplex.com/prism"
        Title="Calculater" Height="300" Width="600">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition />
        </Grid.RowDefinitions>
        <local:ChildCalculater></local:ChildCalculater>
        <local:ChildCalculater Grid.Row="1"></local:ChildCalculater>
        <local:ChildCalculater Grid.Row="2"></local:ChildCalculater>
        <Grid Grid.Row="3">
            <Grid.ColumnDefinitions>
                <ColumnDefinition />
                <ColumnDefinition />
            </Grid.ColumnDefinitions>
            <Button Margin="3" HorizontalAlignment="Right" Padding="3" Content="Add All" Command="{x:Static local:CalculaterCommand.CalculateAllCommand}"></Button>
            <Button Margin="3" HorizontalAlignment="Left" Padding="3" Grid.Column="1" Content="Reset All" Command="{x:Static local:CalculaterCommand.ResetAllCommand}"></Button>
        </Grid>
    </Grid>
</Window>

using Microsoft.Practices.Prism.Commands;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Calculater
{
    public static class CalculaterCommand
    {
        private static CompositeCommand _calculateAllCommand = new CompositeCommand();

        public static CompositeCommand CalculateAllCommand
        {
            get { return _calculateAllCommand; }
        }

        private static CompositeCommand _resetAllCommand = new CompositeCommand();

        public static CompositeCommand ResetAllCommand
        {
            get { return _resetAllCommand; }
        }

    }
}