WPF:解决数据验证ValidationRule与按钮Canexcute联动的问题

想法是这样的，
如果用户输入有误，界面上显示ValidationRule的提示，并且按钮enabled=false（canExcute=fales）
按钮是在输入信息属性改变时刷新Canexcute方法

实际中validRule:RequiredNumberValidRule ValidatesOnTargetUpdated="True"默认是先验证再赋值，如果验证不通过就不赋值，
这就造成了如果验证不通过不能执行Canexcute而按钮无法enabled=false

此时需要更改ValidationRule的属性，设置ValidationStep="UpdatedValue"或者CommiteVALUE

此时还是不行，设置ValidationStep="UpdatedValue后，绑定的属性就变成了绑定的表达式了，
参考：https://stackoverflow.com/questions/10342715/validationrule-with-validationstep-updatedvalue-is-called-with-bindingexpressi
改写了下代码，成功！

7.31更新 实际中发现第一版的GetBoundValue有问题，不能获取嵌套属性的属性值（A.B.C），遂又找了一个方法：
https://stackoverrun.com/ja/q/2731242
（PS:感谢大学思修的开卷考试，让我练就了一手快速翻书能力）

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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
            string resolvedPropertyName = binding.GetType().GetProperty("ResolvedSourcePropertyName", BindingFlags.Public | BindingFlags.DeclaredOnly | BindingFlags.Instance).GetValue(binding, null).ToString();

            object resolvedSource = binding.GetType().GetProperty("ResolvedSource", BindingFlags.Public | BindingFlags.DeclaredOnly | BindingFlags.Instance).GetValue(binding, null);

            // Extract the value of the property
            object propertyValue = resolvedSource.GetType().GetProperty(resolvedPropertyName).GetValue(resolvedSource, null);

            return propertyValue;
        }
        else
        {
            return value;
        }
    }

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原答案
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 <TextBox  Grid.Column="2" Height="26"  >
                    <Binding Path="Compare_Correlation" UpdateSourceTrigger="PropertyChanged">
                        <Binding.ValidationRules>
                            <validRule:RequiredNumberValidRule ValidatesOnTargetUpdated="True" ValidationStep="UpdatedValue" />
                        </Binding.ValidationRules>
                    </Binding>
                </TextBox>


public class RequiredNumberValidRule : ValidationRule
   {
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)
    {
        if (GetBoundValue(value) is null)
        {
            return new ValidationResult(false, "required field.");
        }
        var temp = GetBoundValue(value).ToString();
        double doubleValue;
        if (double.TryParse(temp, out doubleValue))
        {
            return new ValidationResult(true, null);
        }
        else
        {
            return new ValidationResult(false, "Incorrect number format.");
        }
    }

    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;
        }
    }
}

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