(转)Silverlight数据校验之INotifyDataErrorInfo

原文地址：http://www.cnblogs.com/PerfectSoft/archive/2012/03/01/2375007.html

   
在Silverlight中，数据实体类的有效性校验有多种方法，比如说：运用TargetNullValue、FailBackValue、ValidatesOnExceptions.....，运用这些方法可以解决常见的问题，但是针对一些复杂性的数据校验，显然不是最有效的利器。比如说：在针对单个属性进行多重有效性验证的情况下，此时，可以灵活的运用INotifyDataErrorInfo接口。

    MSDN INotifyDataErrorInfor的定义如下：

    // Summary:
    //     Defines members that data entity classes can implement to provide custom,
    //     asynchronous validation support.
    public interface INotifyDataErrorInfo
    {
        // Summary:
        //     Gets a value that indicates whether the object has validation errors.
        //
        // Returns:
        //     true if the object currently has validation errors; otherwise, false.
        bool HasErrors { get; }

        // Summary:
        //     Occurs when the validation errors have changed for a property or for the
        //     entire object.
        event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;

        // Summary:
        //     Gets the validation errors for a specified property or for the entire object.
        //
        // Parameters:
        //   propertyName:
        //     The name of the property to retrieve validation errors for, or null or System.String.Empty
        //     to retrieve errors for the entire object.
        //
        // Returns:
        //     The validation errors for the property or object.
        IEnumerable GetErrors(string propertyName);
    }

   
从INotifyDataErrorInfo的定义，就能够了解到它的作用。数据实体类可以继承INotifyDataErrorInfo，实现满足业务需求的有效性校验。下面以Student实体类实现INotifyDataErrorInfo接口为例。

    Student定义：

    public class Student : INotifyPropertyChanged,INotifyDataErrorInfo
    {
        //存放错误信息，一个Property可能对应多个错误信息
        private Dictionary<string, List<string>> errors = new Dictionary<string, List<string>>();

        

        //实现INotifyPropertyChanged
        public event PropertyChangedEventHandler PropertyChanged;

        public void OnPropertyChanged(PropertyChangedEventArgs e)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, e);
            }
        }

        

        //实现INotifyDataErrorInfo
        public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;

        public IEnumerable GetErrors(string propertyName)
        {
            if (string.IsNullOrEmpty(propertyName))
            {
                return null;
            }
            else
            {
                if (errors.ContainsKey(propertyName))
                {
                    return errors[propertyName];
                }
            }
            return null;
        }

        public bool HasErrors
        {
            get
            {
                return (errors.Count > 0);
            }
        }

        private void SetErrors(string propertyName, List<string> propertyErrors)
        {
            errors.Remove(propertyName);
            errors.Add(propertyName, propertyErrors);
            if (ErrorsChanged != null)
            {
                ErrorsChanged(this, new DataErrorsChangedEventArgs(propertyName));
            }
        }

        private void ClearErrors(string propertyName)
        {
            errors.Remove(propertyName);
            if (ErrorsChanged != null)
            {
                ErrorsChanged(this, new DataErrorsChangedEventArgs(propertyName));
            }
        }

        private string name;
        private int age;

        public String Name
        {
            get
            {
                return name;
            }
            set
            {
                name = value;
                List<string> errors = new List<string>();
                bool valid = true;

                //数据校验
                  if (name.Trim().Contains(" "))
                {
                    errors.Add("姓名中不能包含空格");
                    valid = false;
                }
                if (name.Length < 2 || name.Length > 4)
                {
                    errors.Add("姓名的长度不能低于2高于4");
                    valid = false;
                }

                if (!valid)
                {
                    SetErrors("Name", errors);
                }
                else
                {
                    ClearErrors("Name");
                }
            }
        }

        public int Age
        {
            get
            {
                return age;
            }
            set
            {
                age = value;
                if (age < 0 || age > 150)
                {
                    List<string> errors = new List<string>();
                    errors.Add("年龄不能小于0或大于150");
                    SetErrors("Age", errors);
                }
                else
                {
                    ClearErrors("Age");
                }
            }
        }
    }

    在MainPage XAML代码中，执行数据绑定时，必须设置ValidatesOnNotifyDataErrors = True。

<Grid x:Name="LayoutRoot" Background="White" BindingValidationError="LayoutRoot_BindingValidationError">
        <Grid.RowDefinitions>
            <RowDefinition Height="40"></RowDefinition>
            <RowDefinition Height="40"></RowDefinition>
            <RowDefinition Height="40"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition></ColumnDefinition>
            <ColumnDefinition></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <TextBlock Text="姓名：" HorizontalAlignment="Right" VerticalAlignment="Center"></TextBlock>
        <TextBox x:Name="txtName" Text="{Binding Name, Mode=TwoWay, ValidatesOnExceptions=True, 
            ValidatesOnNotifyDataErrors=True, NotifyOnValidationError=True}" Width="150" Grid.Column="1" HorizontalAlignment="Left" VerticalAlignment="Center">
        </TextBox>
        <TextBlock Text="年龄：" HorizontalAlignment="Right" Grid.Row="1" VerticalAlignment="Center"></TextBlock>
        <TextBox x:Name="txtAge" Text="{Binding Age, Mode=TwoWay, ValidatesOnExceptions=True, 
            ValidatesOnNotifyDataErrors=True, NotifyOnValidationError=True}" Width="150" Grid.Column="1" Grid.Row="1" HorizontalAlignment="Left" VerticalAlignment="Center">
        </TextBox>
        <Button x:Name="Submit" Content="Submit The Data" HorizontalAlignment="Left" Grid.Row="2" Grid.Column="1" Click="Submit_Click" VerticalAlignment="Center"></Button>
        <TextBlock x:Name="Summary" Text="无任何错误信息" VerticalAlignment="Center" Grid.Column="1" Grid.Row="3"></TextBlock>
    </Grid>

    MainPage 后台代码：

        public MainPage()
        {
            InitializeComponent();

            Student product = new Student();
            LayoutRoot.DataContext = product;
        }

        private void LayoutRoot_BindingValidationError(object sender, ValidationErrorEventArgs e)
        {
            //可能没有Exception,但是存在错误信息
            if (e.Error.Exception != null)
            {
                //异常处理代码
            }
            else
            {
                Summary.Text = e.Error.ErrorContent.ToString();
                txtName.Focus();
            }
        }

    运行结果：

    如果要实现复杂的数据验证，INotifyDataErrorInfo也是一个不错的选择，有不足之处，请大家指出。