如何处理 ViewModel 中的 Validation.Error 而不是背后的 View 代码? [英] How can I handle a Validation.Error in my ViewModel instead of my View's code behind?

问题描述

我正在尝试让 WPF 验证在 MVVM 模式中工作.

I'm trying to get WPF validation to work within the MVVM pattern.

在我的视图中，我可以验证这样的文本框，它由代码隐藏方法HandleError"处理，该方法工作正常:

In my View, I can validate a TextBox like this which gets handled by the code-behind method "HandleError", which works fine:

<TextBox Width="200"
         Validation.Error="HandleError">
    <TextBox.Text>
        <Binding Path="FirstName"
             NotifyOnValidationError="True"
             Mode="TwoWay">
            <Binding.ValidationRules>
                <validators:DataTypeLineIsValid/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

但是，我想通过 DelegateCommand 处理我的 ViewModel 中的验证，但是当我使用以下代码尝试时，我收到显式错误'{Binding HandleErrorCommand}' is not a valid event handler method名称.只有生成的或代码隐藏的类上的实例方法才有效."

However, I would like to handle the validation in my ViewModel via a DelegateCommand but when I try it with the following code, I get the explicit error "'{Binding HandleErrorCommand}' is not a valid event handler method name. Only instance methods on the generated or code-behind class are valid."

是否有任何解决方法，以便我们可以在 MVVM 模式中处理验证?

Are there any workaround for this so that we can handle validations within a MVVM pattern?

查看:

<TextBox Width="200"
         Validation.Error="{Binding HandleErrorCommand}">
    <TextBox.Text>
        <Binding Path="FirstName"
             NotifyOnValidationError="True"
             Mode="TwoWay">
            <Binding.ValidationRules>
                <validators:DataTypeLineIsValid/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

视图模型:

#region DelegateCommand: HandleError
private DelegateCommand handleErrorCommand;

public ICommand HandleErrorCommand
{
    get
    {
        if (handleErrorCommand == null)
        {
            handleErrorCommand = new DelegateCommand(HandleError, CanHandleError);
        }
        return handleErrorCommand;
    }
}

private void HandleError()
{
    MessageBox.Show("in view model");
}

private bool CanHandleError()
{
    return true;
}
#endregion

推荐答案

我不知道这是否对您有帮助，但我会提供相同的.

I don't know if this will help you, but I'll offer it all the same.

另外，我使用的是 Silverlight，而不是 WPF.

Also, I'm using Silverlight, not WPF.

我没有在我的视图中指定任何验证，无论是在后面的代码中还是在 xaml 中.我的视图只有数据绑定到 ViewModel 上的属性.

I don't specify any validation in my Views, neither in the code behind nor the xaml. My View has only data bindings to properties on the ViewModel.

我所有的错误检查/验证都由 ViewModel 处理.当我遇到错误时，我设置了一个 ErrorMessage 属性，该属性也绑定到视图.ErrorMessage 文本块(在视图中)有一个值转换器，如果错误为 null 或为空，它将隐藏它.

All my error checking/validation is handled by the ViewModel. When I encounter an error, I set a ErrorMessage property, which is bound to the view as well. The ErrorMessage textblock (in the view) has a value converter which hides it if the error is null or empty.

采用这种方式可以轻松地对输入验证进行单元测试.

Doing things this way makes it easy to unit test input validation.

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