如何自定义的验证属性错误消息？

问题描述

目前，我有一个名为ExistingFileName的自定义验证属​​性的（下同）的但我已经给它的错误消息显示

At the moment I have a custom validation attribute called ExistingFileName (below) but i have given it error messages to display

    protected override System.ComponentModel.DataAnnotations.ValidationResult IsValid(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext)
    {
        if (value!=null)
        {
            string fileName = value.ToString();
            if (FileExists(fileName))
            {
                return new ValidationResult("Sorry but there is already an image with this name please rename your image");
            }
            else
            {
                return ValidationResult.Success;
            }
        }
        else
        {
            return new ValidationResult("Please enter a name for your image");
        }
    }

我已经实现了它，像这样：

I have implemented it like so:

[ExistingFileName]
public string NameOfImage { get; set; }

我敢肯定，一个孤单的方式来定义设置像下面的属性时，错误消息：

Im sure theres a way to define the error message when setting the attribute like below:

[ExistingFileName(errormessage="Blah blah blah")]
public string NameOfImage { get; set; }

但我不知道怎么办？任何帮助是极大AP preciated

But I'm not sure how? Any help is greatly appreciated

推荐答案

为ValidationResult 以predefined字符串，请尝试使用的ErrorMessage 财产，或任何其他自定义属性。例如：

Instead of returning ValidationResult with a predefined string, try using the ErrorMessage property, or any other custom properties. For example:

private const string DefaultFileNotFoundMessage =
    "Sorry but there is already an image with this name please rename your image";

private const string DefaultErrorMessage =
    "Please enter a name for your image";

public string FileNotFoundMessage { get; set; }

protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
    if (value!=null)
    {
        string fileName = value.ToString();
        if (FileExists(fileName))
        {
            return new ValidationResult(FileNotFoundMessage ??
                                        DefaultFileNotFoundMessage);
        }
        else
        {
            return ValidationResult.Success;
        }
    }
    else
    {
        return new ValidationResult(ErrorMessage ??
                                    DefaultErrorMessage);
    }
}

而在你的注释：

[ExistingFileName(FileNotFoundMessage = "Uh oh! Not Found!")]
public string NameOfImage { get; set; }

如果你不明确地设置自定义消息，它会回退到predefined在自定义属性不变。

If you don't explicitely set a custom message, it will fallback to the predefined constant in your custom attribute.

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