在我们绑定完数据后，在用户输入数据后，还需要进行用户输入合法性验证，比如需要判断 必填项，email地址输入格式，日期格式是否正确等。
wpf为我们提供了一种验证用户合法行的方式。依赖于绑定。在将实体数据绑定到视图后，如果用户输入的视图改变，则同时通知实体的属性值改变。先看代码：
1. 构建一个要绑定到界面的实体。该实体实现了IDataErrorInfo接口，在接口里写了验证规则。
代码
// 实体 实现 IDataErrorInfo接口，并在 this[]索引器里定制自己的验证规则
class Person : IDataErrorInfo
{
public string Name { get ; set ; }
public int Age { get ; set ; }
#region IDataErrorInfo 成员
string _err;
public string Error
{
get { return _err; }
}
// 定制验证规则
public string this [ string columnName]
{
get
{
string err = "" ;
switch (columnName)
{
case " Name " :
if ( string .IsNullOrEmpty( this .Name))
{
err = " 名称不能为空 " ;
}
else
{
if ( this .Name.Length > 8 )
{
err = " 名称太长了，不能大于8个字符 " ;
}
}
break ;
case " Age " :
if ( this .Age < 0 || this .Age > 200 )
{
err = " 年龄不合法 " ;
}
break ;
}
_err = err;
return _err;
}
}
#endregion
}
2.页面：
代码
1 < Window x:Class = " WpfApplication3.Window1 "
2 xmlns = " schemas.microsoft.com/winfx/2006/… "
3 xmlns:x = " schemas.microsoft.com/winfx/2006/… "
4 xmlns:local = " clr-namespace:WpfApplication3 "
5 Title = " Window1 " Height = " 298 " Width = " 681 " Loaded = " Window_Loaded " >
6
7 < Grid Name = " grid1 " >
8 < TextBlock Margin = " 25,29,0,0 " Name = " textBlock1 " Height = " 21 " VerticalAlignment = " Top " HorizontalAlignment = " Left " Width = " 38 " >
9 Name:
10 </ TextBlock >
11 < TextBox HorizontalAlignment = " Left " Margin = " 83,29,0,0 " Name = " textBlock2 " VerticalAlignment = " Top " Width = " 120 " >
12 < TextBox.Text >
13 <!-- 启动Binding的绑定方式1 -->
14 < Binding Path = " Name " UpdateSourceTrigger = " PropertyChanged "
15 ValidatesOnDataErrors = " True " />
16 </ TextBox.Text >
17 </ TextBox >
18 < TextBlock Text = " Age: " Height = " 21 " HorizontalAlignment = " Left " Margin = " 25,68,0,0 " Name = " textBlock3 " VerticalAlignment = " Top " Width = " 38 " />
19 < TextBox Height = " 23 " HorizontalAlignment = " Left " Margin = " 83,66,0,0 " Name = " textBox1 " VerticalAlignment = " Top " Width = " 120 " >
20 < TextBox.Text >
21 <!-- 启动Binding的绑定方式2 -->
22 < Binding Path = " Age " UpdateSourceTrigger = " PropertyChanged " >
23 < Binding.ValidationRules >
24 < DataErrorValidationRule />
25 < ExceptionValidationRule ></ ExceptionValidationRule >
26 </ Binding.ValidationRules >
27 </ Binding >
28 </ TextBox.Text >
29 </ TextBox >
30 </ Grid >
31 </ Window >
32
页面的后置代码：
代码
1 /// <summary>
2 /// Window1.xaml 的交互逻辑
3 /// </summary>
4 public partial class Window1 : Window
5 {
6 public Window1()
7 {
8 InitializeComponent();
9 }
10
11 private void Window_Loaded( object sender, RoutedEventArgs e)
12 {
13 grid1.DataContext = GetPersonFromDatabase();
14 }
15
16 private Person GetPersonFromDatabase()
17 {
18 // 从数据库获得数据对象 <演示>
19 return new Person() { Name = " join " , Age = 30 };
20 }
21 }
按F5运行后，尝试输入写不合法数据。可以看到Textbox的边框变成红色。这是一种默认的提示错误的风格方式，我们还可以对这个提示风格进行自定义。
注意Binding的下面两个属性：
| ValidatesOnDataErrors | 获取或设置一个值，该值指示是否包含 DataErrorValidationRule。 |
|---|
| ValidationRules | 获取用于检查用户输入有效性的规则集合。 |
|---|
也就是说当我们设置了 Binding的ValidatesOnDataErrors="True" 时。WPF框架在构造Binding对象时，会自动的添加一个默认的DataErrorValidationRule到ValidationRules 属性值（验证规则列表）内。或者我们直接在ValidationRules 里添加我们需要的规则,比如下面是添加了两个规则：
<Binding.ValidationRules>
<DataErrorValidationRule />
<ExceptionValidationRule></ExceptionValidationRule>
</Binding.ValidationRules>
这样的写法很有意思，貌似IOC的方式配置文件，比如spring.Net的配置文件，这样的声明ValidationRules的包含的规则。当WPF框架创建对象时自动的完成规则操作，并判断ValidationRules内的规则数量，如果多于0个，就遍历所有的规则集合，如果集合中包含了DataErrorValidationRule 并且实体类显示了IDataErrorInfo
接口，就调用 实体内包含的 验证规则。
ExceptionValidationRule 类是一个内置的规则，它检查在绑定源属性更新过程中引发的异常。这里验证了Age的用户输入不可为空，当为空时，转型成int（Age是int类型）时就会出错。
通过创建一个从 ValidationRule 派生的类，可以创建自定义规则。下面我尝试自定义验证规则。
MSDN里对ValidateionRule的描述如下：
在使用 WPF 数据绑定模型时，可将 ValidationRules 与绑定对象关联。若要创建自定义规则，请创建此类的子类并实现 Validate 方法。也可选择使用内置的 ExceptionValidationRule （该类捕获在源更新期间引发的异常）或 DataErrorValidationRule （该类检查源对象的 IDataErrorInfo 实现所引发的错误）。
绑定引擎在每次将输入值（即绑定目标属性值）传给绑定源属性时将检查与绑定关联的每一个 ValidationRule。
我们写一个类继承自ValidationRule，代码如下：
代码
1 class AgeValidationRule : ValidationRule
2 {
3 // 验证规则
4 public override ValidationResult Validate( object value, System.Globalization.CultureInfo cultureInfo)
5 {
6 if (value == null )
7 {
8 return new ValidationResult( false , " 年龄不能为空 " );
9 }
10 int valNew = 0 ;
11 if ( ! int .TryParse(value.ToString(), out valNew))
12 {
13 return new ValidationResult( false , value + " 不是一个数字类型 " );
14 }
15 else
16 {
17 if (valNew < 0 || valNew > 200 )
18 {
19 return new ValidationResult( false , " 年龄必须在0和200之间 " );
20 }
21 }
22 return ValidationResult.ValidResult;
23 }
实体的代码：
1 // 实体
class Person
3 {
4 public string Name { get ; set ; }
5 public int Age { get ; set ; }
6
7 }
页面xaml代码如下，而后置代码不变。
代码
1 < Window x:Class = " WpfApplication3.Window1 "
2 xmlns = " schemas.microsoft.com/winfx/2006/… "
3 xmlns:x = " schemas.microsoft.com/winfx/2006/… "
4 xmlns:local = " clr-namespace:WpfApplication3 "
5 Title = " Window1 " Height = " 298 " Width = " 681 " Loaded = " Window_Loaded " >
6
7 < Grid Name = " grid1 " >
8 < TextBlock Margin = " 25,29,0,0 " Name = " textBlock1 " Height = " 21 " VerticalAlignment = " Top " HorizontalAlignment = " Left " Width = " 38 " >
9 Name:
10 </ TextBlock >
11 < TextBox HorizontalAlignment = " Left " Margin = " 83,29,0,0 " Name = " textBlock2 " VerticalAlignment = " Top " Width = " 120 " >
12 < TextBox.Text >
13 <!-- 启动Binding的绑定方式1 -->
14 < Binding Path = " Name " UpdateSourceTrigger = " PropertyChanged "
15 ValidatesOnDataErrors = " True " />
16 </ TextBox.Text >
17 </ TextBox >
18 < TextBlock Text = " Age: " Height = " 21 " HorizontalAlignment = " Left " Margin = " 25,68,0,0 " Name = " textBlock3 " VerticalAlignment = " Top " Width = " 38 " />
19 < TextBox Height = " 23 " HorizontalAlignment = " Left " Margin = " 83,66,0,0 " Name = " textBox1 " VerticalAlignment = " Top " Width = " 120 " >
20 < TextBox.Text >
21 <!-- 启动Binding的绑定方式2 -->
22 < Binding Path = " Age " UpdateSourceTrigger = " PropertyChanged " >
23 < Binding.ValidationRules >
24 <!-- 我们自定义的验证规则 -->
25 < local:AgeValidationRule />
26 < ExceptionValidationRule ></ ExceptionValidationRule >
27 </ Binding.ValidationRules >
28 </ Binding >
29 </ TextBox.Text >
30 </ TextBox >
31 </ Grid >
32 </ Window >
33
F5运行。是不是一样呢。我个人不推荐第一种方法。当实体实现了IDataErrorInfo，并在实体的代码里写验证规则时，会把代码搞的非常混杂。网上有推荐利用Attribute的进行验证的，但是好像还要让实体继承一个基类。我更喜欢让实体model干干净净。
下面我们看看如何更改在验证失败时的提示风格。
代码
< Window x:Class = " WpfApplication3.Window1 "
xmlns = " schemas.microsoft.com/winfx/2006/… "
xmlns:x = " schemas.microsoft.com/winfx/2006/… "
xmlns:local = " clr-namespace:WpfApplication3 "
Title = " Window1 " Height = " 298 " Width = " 681 " Loaded = " Window_Loaded " >
< Grid Name = " grid1 " >
< TextBlock Margin = " 25,29,0,0 " Name = " textBlock1 " Height = " 21 " VerticalAlignment = " Top " HorizontalAlignment = " Left " Width = " 38 " >
Name:
</ TextBlock >
< TextBox HorizontalAlignment = " Left " Margin = " 83,29,0,0 " Name = " textBlock2 " VerticalAlignment = " Top " Width = " 120 " >
< TextBox.Text >
<!-- 启动Binding的绑定方式1 -->
< Binding Path = " Name " UpdateSourceTrigger = " PropertyChanged "
ValidatesOnDataErrors = " True " />
</ TextBox.Text >
</ TextBox >
< TextBlock Text = " Age: " Height = " 21 " HorizontalAlignment = " Left " Margin = " 25,68,0,0 " Name = " textBlock3 " VerticalAlignment = " Top " Width = " 38 " />
< TextBox Height = " 23 " HorizontalAlignment = " Left " Margin = " 83,66,0,0 " Name = " textBox1 " VerticalAlignment = " Top " Width = " 120 " >
< TextBox.Text >
<!-- 启动Binding的绑定方式2 -->
< Binding Path = " Age " UpdateSourceTrigger = " PropertyChanged " >
< Binding.ValidationRules >
<!-- 我们自定义的验证规则 -->
< local:AgeValidationRule />
< ExceptionValidationRule ></ ExceptionValidationRule >
</ Binding.ValidationRules >
</ Binding >
</ TextBox.Text >
< Validation.ErrorTemplate >
< ControlTemplate >
<!-- ControlTemplate要求只能有一个子级，所以加个容器控件DockPanel -->
< DockPanel >
<!-- AdornedElementPlaceholder就是要验证的控件本身，本例里是个TextBox -->
< AdornedElementPlaceholder />
< TextBlock Foreground = " Red " FontSize = " 20 " Text = " * " />
</ DockPanel >
</ ControlTemplate >
</ Validation.ErrorTemplate >
</ TextBox >
</ Grid >
</ Window >\
我们注意到Textbox.Validation属性的ErrorTemplate是发生错误时使用的模板，我们重新new了一个ControlTemplate来代替这个模板。在这个模板里我们定义了一个DockPanel作为容器控件，使用 占位标记AdornedElementPlaceholder 标记了TextBox的位置，并在它后面添加两个 字符"*"号。这可能有点难以理解。换个说法是，每个TextBox都有个Validation属性，Validation包含了一些和验证相关的像，包含有个当验证失败时的显示模板。而我们重新定义了个显示模板。这个模板里有个占位符，占位符表示TextBox本身，我们在这个模板的占位符后面添加一些字符 红色的"*" 号。那么当TextBox在执行时，如果失败，就会把 错误模板 显示出来，并在 占位符位置 显示自己。
我们换个另外的方式来改变视图效果，使用style 方式。
在窗体资源里添加一个style,style这个东西呢，类似web开发中的css。他有个属性TargetType 指示了这个样式的作用域。本例中指示了 所有的TextBox,style的强大之处还有个Triggers就是触发器。本例中触发器指向一个属性Validation.HasError属性，当这属性的值为"True"时，触发Trigger包含的样式。当不等于"True"时，自动改回原来的样式。很强大吧。Setter元素提供了设置目标对象属性的方法，我们直接更改了Textbox.ToolTop属性，那么当鼠标移动到控件上时，就会显示发生错误的原因。
代码
1 < Window.Resources >
2 < Style TargetType = " TextBox " >
3 < Style.Triggers >
4 < Trigger Property = " Validation.HasError " Value = " True " >
5 < Setter Property = " Background " Value = " #DDD " />
6 < Setter Property = " Foreground " Value = " Red " />
7 < Setter Property = " ToolTip "
8 Value = " {Binding RelativeSource={RelativeSource Self},Path=(Validation.Errors)[0].ErrorContent} " />
9 </ Trigger >
10 </ Style.Triggers >
11 </ Style >
12 </ Window.Resources >
这句<Setter Property="ToolTip"
Value="{Binding RelativeSource={RelativeSource Self},Path=(Validation.Errors)[0].ErrorContent}"/>
完成了获得关联数据源，并绑定错误提示的操作。
本节完。
待续ing...
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