ValidationRule with ValidationStep="UpdatedValue";使用 BindingExpression 而不是更新值调用 [英] ValidationRule with ValidationStep="UpdatedValue" is called with BindingExpression instead of updated value
问题描述
我开始在我的 WPF 应用程序中使用 ValidationRules，但很困惑.
I am getting started with using ValidationRules in my WPF application, but quite confused.
我有以下简单的规则:
class RequiredRule : ValidationRule
{
public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
{
if (String.IsNullOrWhiteSpace(value as string))
{
return new ValidationResult(false, "Must not be empty");
}
else
{
return new ValidationResult(true, null);
}
}
}
在 XAML 中使用如下:
Used in XAML as follows:
<TextBox>
<TextBox.Text>
<Binding Path="Identity.Name">
<Binding.ValidationRules>
<validation:RequiredRule/>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
这大部分按我的预期工作.我很惊讶地看到我的源属性 (Identity.Name) 没有被设置；我有一个永远不会看到更改的撤消功能，除了重新键入它之外，没有办法恢复该值(不好).
This mostly works as I would expect. I was surprised to see that my source property (Identity.Name) was not being set; I have an undo function that never sees the change, and there is no way to revert the value other than re-type it (not good).
Microsoft 的数据绑定概述 描述了靠近底部的验证过程，它很好地解释了这种行为.基于此，我希望将 ValidationStep 设置为 UpdatedValue.
Microsoft's Data Binding Overview describes the validation process near the bottom, which explains this behavior very well. Based on this, I would want to have my ValidationStep set to UpdatedValue.
<validation:RequiredRule ValidationStep="UpdatedValue"/>
这就是我觉得奇怪的地方.我得到了一个 System.Windows.Data.BindingExpression，而不是使用对象值作为设置的属性值(即字符串)调用 Validate()！我在 Microsoft 的文档中没有看到任何描述这种行为的内容.
This is where things get weird for me. Instead of Validate() being called with object value being the property value that was set (i.e., a string), I get a System.Windows.Data.BindingExpression! I don't see anything in Microsoft's documentation that describes this behavior.
在调试器中，我可以看到源对象(TextBox 的DataContext)，导航到属性的路径，并看到值已设置.但是，我没有看到在验证规则中获得正确属性的任何好方法.
In the debugger, I can see the source object (the DataContext of the TextBox), navigate the path to the property, and see that the value has been set. However, I don't see any good way to get to the right property within the validation rule.
注意:使用 ValidationStep 作为 ConvertedProposedValue，我得到输入的字符串(我没有使用转换器)，但它也会阻止源属性更新正如预期的那样，验证失败.使用 CommittedValue，我得到 BindingExpression 而不是字符串.
Note: With ValidationStep as ConvertedProposedValue, I get the entered string (I don't have a converter in use), but it also blocks the source property update when validation fails, as expected. With CommittedValue, I get the BindingExpression instead of the string.
这里有几个问题:
为什么根据 ValidationStep 设置传递给 Validate() 的参数类型不一致?
Why do I get an inconsistent argument type being passed to Validate() based on the ValidationStep setting?
如何从 BindingExpression 获取实际值?
How can I get to the actual value from the BindingExpression?
或者，是否有一种好方法可以让用户将 TextBox 恢复到之前的(有效)状态?(正如我所提到的，我自己的撤消功能永远不会看到变化.)
Alternately, is there a good way to allow the user to revert the TextBox to the previous (valid) state? (As I mentioned, my own undo function never sees the change.)
推荐答案
我已经解决了从 BindingExpression 中提取值的问题，有一个小限制.
I have solved the problem of extracting the value from the BindingExpression, with a minor limitation.
首先，一些更完整的 XAML:
First, some more complete XAML:
<Window x:Class="ValidationRuleTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:ValidationRuleTest"
Title="MainWindow" Height="100" Width="525">
<Window.DataContext>
<local:MainWindowViewModel/>
</Window.DataContext>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="50"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<TextBlock Text="String 1"/>
<TextBox Grid.Column="1">
<TextBox.Text>
<Binding Path="String1" UpdateSourceTrigger="PropertyChanged">
<Binding.ValidationRules>
<local:RequiredRule ValidationStep="RawProposedValue"/>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
<TextBlock Text="String 2" Grid.Row="1"/>
<TextBox Grid.Column="1" Grid.Row="1">
<TextBox.Text>
<Binding Path="String2" UpdateSourceTrigger="PropertyChanged">
<Binding.ValidationRules>
<local:RequiredRule ValidationStep="UpdatedValue"/>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
</Grid>
</Window>
请注意，第一个 TextBox 使用 ValidationStep="RawProposedValue"(默认值)，而第二个使用 ValidationStep="UpdatedValue"，但两者都使用相同的验证规则.
Note that the first TextBox uses ValidationStep="RawProposedValue" (the default), while the second one uses ValidationStep="UpdatedValue", but both use the same validation rule.
一个简单的 ViewModel(忽略 INPC 和其他有用的东西):
A simple ViewModel (neglecting INPC and other useful stuff):
class MainWindowViewModel
{
public string String1
{ get; set; }
public string String2
{ get; set; }
}
最后，新的RequiredRule:
And finally, the new RequiredRule:
class RequiredRule : ValidationRule
{
public override ValidationResult Validate(object value,
System.Globalization.CultureInfo cultureInfo)
{
// Get and convert the value
string stringValue = GetBoundValue(value) as string;
// Specific ValidationRule implementation...
if (String.IsNullOrWhiteSpace(stringValue))
{
return new ValidationResult(false, "Must not be empty");
}
else
{
return new ValidationResult(true, null);
}
}
private object GetBoundValue(object value)
{
if (value is BindingExpression)
{
// ValidationStep was UpdatedValue or CommittedValue (Validate after setting)
// Need to pull the value out of the BindingExpression.
BindingExpression binding = (BindingExpression)value;
// Get the bound object and name of the property
object dataItem = binding.DataItem;
string propertyName = binding.ParentBinding.Path.Path;
// Extract the value of the property.
object propertyValue = dataItem.GetType().GetProperty(propertyName).GetValue(dataItem, null);
// This is what we want.
return propertyValue;
}
else
{
// ValidationStep was RawProposedValue or ConvertedProposedValue
// The argument is already what we want!
return value;
}
}
}
GetBoundValue() 方法将挖掘出我关心的值，如果它获得 BindingExpression，或者如果它不是，则简单地踢回参数.真正的关键是找到路径"，然后使用它来获取属性及其值.
The GetBoundValue() method will dig out the value I care about if it gets a BindingExpression, or simply kick back the argument if it's not. The real key was finding the "Path", and then using that to get the property and its value.
限制:在我最初的问题中，我的绑定有 Path="Identity.Name"，因为我正在挖掘我的 ViewModel 的子对象.这将不起作用，因为上面的代码期望路径直接指向绑定对象上的属性.幸运的是，我已经扁平化了我的 ViewModel，所以情况不再如此，但一种解决方法是首先将控件的数据上下文设置为子对象.
The limitation: In my original question, my binding had Path="Identity.Name", as I was digging into sub-objects of my ViewModel. This will not work, as the code above expects the path to be directly to a property on the bound object. Fortunately, I have already flattened my ViewModel so this is no longer the case, but a workaround could be to set the control's datacontext to be the sub-object, first.
我想感谢 Eduardo Brites，因为他的回答和讨论让我重新开始深入研究这个问题，并且确实为他的难题提供了一部分.此外，虽然我即将完全放弃 ValidationRules 并使用 IDataErrorInfo，但我喜欢他关于将它们一起用于不同类型和复杂性验证的建议.
I'd like to give some credit to Eduardo Brites, as his answer and discussion got me back to digging on this, and did provide a piece to his puzzle. Also, while I was about to ditch the ValidationRules entirely and use IDataErrorInfo instead, I like his suggestion on using them together for different types and complexities of validation.
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