【WPF】MVVM模式下的输入校验(IDataErrorInfo + DataAnnotations)

到目前为止,登录窗口的基本功能似乎都完成了。但我们知道,很多时候用户名的格式是有要求的,例如是只有字母数字下划线,或者字数有限制。这要求我们在登录之前,验证输入内容的正确性。在这一节,我们需要验证用户名和密码的正确性,如果上面两个框的输入非法,禁用登录按钮。

在数据验证错误的时候,我们显示一个叹号在输入框的旁边,如下图所示:

数据验证的方法有很多,我们使用了一种比较优雅的。

首先定义一些验证属性:

using System.ComponentModel.DataAnnotations;

namespace LoginDemo.ViewModel.Login
{
    public class NotEmptyCheck : ValidationAttribute
    {
        public override bool IsValid(object value)
        {
            var name = value as string;
            if (string.IsNullOrEmpty(name))
            {
                return false;
            }
            return true;
        }

        public override string FormatErrorMessage(string name)
        {
            return "不能为空";
        }
    }

    public class UserNameExists : ValidationAttribute
    {
        public override bool IsValid(object value)
        {
            var name = value as string;
            if (name.Contains("abc"))
            {
                return true;
            }
            return false;
        }

        public override string FormatErrorMessage(string name)
        {
            return "用户名必须包含abc";
        }
    }
}

第一个验证属性要求宿主的内容不能为空,第二个验证属性要求内容必须含有abc这个字符串。

然后我们又要用到Behavior了。当绑定的内容校验出异常后,它会一起冒泡,只到Window。这时候,Window的Behavior接收到异常,做出相应的处理。

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Interactivity;

namespace LoginDemo.ViewModel.Common
{
    /// <summary>
    /// 验证异常行为
    /// </summary>
    public class ValidationExceptionBehavior : Behavior<FrameworkElement>
    {
        /// <summary>
        /// 记录异常的数量
        /// </summary>
        /// <remarks>在一个页面里面,所有控件的验证错误信息都会传到这个类上,每个控制需不需要显示验证错误,需要分别记录</remarks>
        private Dictionary<UIElement, int> ExceptionCount;
        /// <summary>
        /// 缓存页面的提示装饰器
        /// </summary>
        private Dictionary<UIElement, NotifyAdorner> AdornerDict;

        protected override void OnAttached()
        {
            ExceptionCount = new Dictionary<UIElement, int>();
            AdornerDict = new Dictionary<UIElement, NotifyAdorner>();

            this.AssociatedObject.AddHandler(Validation.ErrorEvent, new EventHandler<ValidationErrorEventArgs>(OnValidationError));
        }

        /// <summary>
        /// 当验证错误信息改变时,首先调用此函数
        /// </summary>
        private void OnValidationError(object sender, ValidationErrorEventArgs e)
        {
            try
            {
                var handler = GetValidationExceptionHandler();//插入<c:ValidationExceptionBehavior></c:ValidationExceptionBehavior>此语句的窗口的DataContext,也就是ViewModel
                var element = e.OriginalSource as UIElement;//错误信息发生改变的控件
                if (handler == null || element == null)
                {
                    return;
                }

                if (e.Action == ValidationErrorEventAction.Added)
                {
                    if (ExceptionCount.ContainsKey(element))
                    {
                        ExceptionCount[element]++;
                    }
                    else
                    {
                        ExceptionCount.Add(element, 1);
                    }
                }
                else if (e.Action == ValidationErrorEventAction.Removed)
                {
                    if (ExceptionCount.ContainsKey(element))
                    {
                        ExceptionCount[element]--;
                    }
                    else
                    {
                        ExceptionCount.Add(element, -1);
                    }
                }

                if (ExceptionCount[element] <= 0)
                {
                    HideAdorner(element);
                }
                else
                {
                    ShowAdorner(element, e.Error.ErrorContent.ToString());
                }

                int TotalExceptionCount = 0;
                foreach (KeyValuePair<UIElement, int> kvp in ExceptionCount)
                {
                    TotalExceptionCount += kvp.Value;
                }

                handler.IsValid = (TotalExceptionCount <= 0);//ViewModel里面的IsValid
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        /// <summary>
        /// 获得行为所在窗口的DataContext
        /// </summary>
        private NotificationObject GetValidationExceptionHandler()
        {
            if (this.AssociatedObject.DataContext is NotificationObject)
            {
                var handler = this.AssociatedObject.DataContext as NotificationObject;

                return handler;
            }

            return null;
        }

        /// <summary>
        /// 显示错误信息提示
        /// </summary>
        private void ShowAdorner(UIElement element, string errorMessage)
        {
            if (AdornerDict.ContainsKey(element))
            {
                AdornerDict[element].ChangeToolTip(errorMessage);
            }
            else
            {
                var adornerLayer = AdornerLayer.GetAdornerLayer(element);
                NotifyAdorner adorner = new NotifyAdorner(element, errorMessage);
                adornerLayer.Add(adorner);
                AdornerDict.Add(element, adorner);
            }
        }

        /// <summary>
        /// 隐藏错误信息提示
        /// </summary>
        private void HideAdorner(UIElement element)
        {
            if (AdornerDict.ContainsKey(element))
            {
                var adornerLayer = AdornerLayer.GetAdornerLayer(element);
                adornerLayer.Remove(AdornerDict[element]);
                AdornerDict.Remove(element);
            }
        }
    }
}

这里异常的处理方式是显示我们最开始戴图的叹号图形。这个图形由NotifyAdnoner完成显示:

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Media;
using System.Windows.Media.Imaging;

namespace LoginDemo.ViewModel.Common
{
    /// <summary>
    /// 带有感叹号的提示图形
    /// </summary>
    public class NotifyAdorner : Adorner
    {
        private VisualCollection _visuals;
        private Canvas _canvas;
        private Image _image;
        private TextBlock _toolTip;

        public NotifyAdorner(UIElement adornedElement, string errorMessage) : base(adornedElement)
        {
            _visuals = new VisualCollection(this);

            _image = new Image()
            {
                Width = 16,
                Height = 16,
                Source = new BitmapImage(new Uri("/warning.png", UriKind.RelativeOrAbsolute))
            };

            _toolTip = new TextBlock() { Text = errorMessage };
            _image.ToolTip = _toolTip;

            _canvas = new Canvas();
            _canvas.Children.Add(_image);
            _visuals.Add(_canvas);
        }

        protected override int VisualChildrenCount
        {
            get
            {
                return _visuals.Count;
            }
        }

        protected override Visual GetVisualChild(int index)
        {
            return _visuals[index];
        }

        public void ChangeToolTip(string errorMessage)
        {
            _toolTip.Text = errorMessage;
        }

        protected override Size MeasureOverride(Size constraint)
        {
            return base.MeasureOverride(constraint);
        }

        protected override Size ArrangeOverride(Size finalSize)
        {
            _canvas.Arrange(new Rect(finalSize));
            _image.Margin = new Thickness(finalSize.Width + 3, 0, 0, 0);

            return base.ArrangeOverride(finalSize);
        }
    }
}

我们的ViewModel也要对数据验证做出支持。由于我们先前让ViewModel继承了NotificationObject,它并不是一个接口,我们不能继承两个类。所以,我们在NotificationObject里面加入验证有内容(虽然这样不太好)。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Linq;

namespace LoginDemo.ViewModel.Common
{
    public abstract class NotificationObject : INotifyPropertyChanged, IDataErrorInfo
    {
        #region 属性修改通知

        public event PropertyChangedEventHandler PropertyChanged;

        /// <summary>
        /// 发起通知
        /// </summary>
        /// <param name="propertyName">属性名</param>
        public void RaisePropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

        #endregion

        #region 数据验证

        public string Error
        {
            get { return ""; }
        }

        public string this[string columnName]
        {
            get
            {
                var vc = new ValidationContext(this, null, null);
                vc.MemberName = columnName;
                var res = new List<ValidationResult>();
                var result = Validator.TryValidateProperty(this.GetType().GetProperty(columnName).GetValue(this, null), vc, res);
                if (res.Count > 0)
                {
                    return string.Join(Environment.NewLine, res.Select(r => r.ErrorMessage).ToArray());
                }
                return string.Empty;
            }
        }

        /// <summary>
        /// 页面中是否所有控制数据验证正确
        /// </summary>
        public virtual bool IsValid { get; set; }

        #endregion
    }
}

至此,准备就绪。我们修改ViewModel里面的UserName和Password属性:

/// <summary>
/// 用户名
/// </summary>
[NotEmptyCheck]
[UserNameExists]
public string UserName
{
    get
    {
        return obj.UserName;
    }
    set
    {
        obj.UserName = value;
        this.RaisePropertyChanged("UserName");
    }
}

/// <summary>
/// 密码
/// </summary>
[NotEmptyCheck]
public string Password
{
    get
    {
        return obj.Password;
    }
    set
    {
        obj.Password = value;
        this.RaisePropertyChanged("Password");
    }
}

没错,就是加了头上中括号的内容。这样的话,UserName就被要求非空和包含abc,而密码则被要求非空。由于我们在NotificationObject里加入了IsValid虚属性,还必须实现一下:

/// <summary>
/// 数据填写正确
/// </summary>
public override bool IsValid
{
    get
    {
        return obj.IsValid;
    }
    set
    {
        if (value == obj.IsValid)
        {
            return;
        }
        obj.IsValid = value;
        this.RaisePropertyChanged("IsValid");
    }
}

这个IsValid的设置是在ValidationExceptionBehavior里完成的。登录按钮只要绑定这个属性,就能在出现验证异常时,变成禁用。

我们修改XAML文件的用户名、密码和登录按钮:

<TextBox Grid.Row="0" Grid.Column="1" Margin="5" Text="{Binding UserName,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged, ValidatesOnExceptions=True, ValidatesOnDataErrors=True, NotifyOnValidationError=True}"/>

<PasswordBox Grid.Row="1" Grid.Column="1" Margin="5" c:PasswordBoxHelper.Password="{Binding Password,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged,ValidatesOnExceptions=True,ValidatesOnDataErrors=True,NotifyOnValidationError=True}">
    <i:Interaction.Behaviors>
        <c:PasswordBoxBehavior/>
    </i:Interaction.Behaviors>
</PasswordBox>

<Button Grid.Row="3" Grid.ColumnSpan="2" Content="登录" Width="200" Height="30" IsEnabled="{Binding IsValid}">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="Click">
            <c:EventCommand Command="{Binding LoginClick}"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>
</Button>

窗口刚打开的时候是这样的,登录按钮被禁用:

当数据都输入正确,登录按钮被启用:

至此,登录窗口的所有功能就介绍完了。也恭喜你,你已经能熟练地使用MVVM模式了。

技术交流Q群: 1012481075 群内有各种流行书籍资料
原文链接:https://blog.csdn.net/lweiyue/article/details/88894368?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-3.control&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-3.control

发表评论

您的电子邮箱地址不会被公开。

WeChat
WeChat
QQ
QQ
返回顶部