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！

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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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