抛出System.ArgumentNullException的JsonConvert.DeserializeObject：'路径不能为null参数名称：path'异常为什么？

问题描述

我的班级结构如下：

class AppDetails
{
    public String companyName { get; set; }
    public String applicationName { get; set; }
    public String version { get; set; }
    public List<File_> fileObjectList { get; set; }

    public AppDetails(String cName,String aName,String v)
    {
        companyName = cName;
        applicationName = aName;
        version = v;
    }
}

class File_
{
    public String filePath { get; set; }
    public FileRecord fileRecord { get; set; }
    public File_(String parent_,String filepath_,Boolean Ignored)
    {
        filePath = filepath_;
        fileRecord = new FileRecord(parent_ + filePath,Ignored);
    }
}

class FileRecord
{
    public Boolean ignored { get; set; }
    public String MD5Checksum { get; set; }
    public int version { get; set; }

    public FileRecord(String filePath,Boolean ignored_)
    {
        ignored = ignored_;
        if (ignored)
        {
            MD5Checksum = null;
        }
        else
        {
            MD5Checksum = CalculateMD5(filePath);
            version = 0;
        }
    }

    static string CalculateMD5(string filePath)
    {
        var md5 = MD5.Create();
        var stream = File.OpenRead(filePath);
        var hash = md5.ComputeHash((System.IO.Stream)stream);
        return BitConverter.ToString(hash).Replace("-","").ToLowerInvariant();

    }

}

我使用这些类生成了Json文件。但是，当我尝试使用上述JSON文件初始化对象时，它将引发System.ArgumentNullException：'路径不能为null。参数名称：路径'异常。这是应该返回对象的函数。

AppDetails ReadJsonFile()
    {
        using (StreamReader r = File.OpenText(parent + "\\AllFilesList.json"))
        {
            string json = r.ReadToEnd();
            var result = JsonConvert.DeserializeObject<AppDetails>(json);
            return result;
        }
    }

我尝试使用在线类生成器从JSON生成类，它与我的类结构匹配。在此行抛出异常：

var result = JsonConvert.DeserializeObject<AppDetails>(json);

Json字符串正好从文件中加载内容（从手表中可以看到）。我找不到与JsonConvert.DeserializeObject相关的Path问题的任何信息。以前的大多数问题似乎与价值错误有关。

编辑：序列化代码

void JsonWriter(AppDetails appDetails,String filename)
    {
        string path = parent + "\\" + filename + ".json";
        File.Delete(path);
        string json = JsonConvert.SerializeObject(appDetails);
        using (var tw = new StreamWriter(path,true))
        {
            tw.WriteLine(json.ToString());
            tw.Close();
        }
    }

示例Json文件：

{"companyName":"Home","applicationName":"Test","version":"V5.0.1","fileObjectList":[{"filePath":"\\bug-tracker.exe","fileRecord":{"ignored":false,"MD5Checksum":"a5254a813a040b429f2288df737a8b9f","version":0}},{"filePath":"\\bug-tracker.exe.config","MD5Checksum":"e5c3e9137dc8fadb57dfc27b0ba6855c",{"filePath":"\\bug-tracker.pdb","MD5Checksum":"9a9dfda29dcaacae82cba7bd7aa97ffa",{"filePath":"\\Caliburn.Micro.dll","MD5Checksum":"aa5f96c02b08d9b33322f3024058dd91",{"filePath":"\\Caliburn.Micro.Platform.Core.dll","MD5Checksum":"ab7867bd44b59879a59b5cb968e15668",{"filePath":"\\Caliburn.Micro.Platform.Core.xml","MD5Checksum":"cdfcbbf70a9a62b92e82a953ab9e7e30",{"filePath":"\\Caliburn.Micro.Platform.dll","MD5Checksum":"a52bdecbc1b7625cb13c9385fad4231b",{"filePath":"\\Caliburn.Micro.Platform.xml","MD5Checksum":"09f258a3aeca7285355d82a66dda2176",{"filePath":"\\Caliburn.Micro.xml","MD5Checksum":"c87ec582a4bfcf2e79e517c689441def",{"filePath":"\\MaterialDesignColors.dll","MD5Checksum":"ad729352a9088b889cc0c4dc7542dcb6",{"filePath":"\\MaterialDesignColors.pdb","MD5Checksum":"7ba70b23e22db9ac155e190860d9a5ec",{"filePath":"\\MaterialDesignThemes.Wpf.dll","MD5Checksum":"e4c790d3af41620dc5ad513ae7fcadac",{"filePath":"\\MaterialDesignThemes.Wpf.pdb","MD5Checksum":"f8113c8ea54896b8150db8e7ebd506ef",{"filePath":"\\MaterialDesignThemes.Wpf.xml","MD5Checksum":"49717f8130b7529ee51fb6bc13f79aa4",{"filePath":"\\ShowMeTheXAML.dll","MD5Checksum":"040b9e80820553a55f13ac19c2036367",{"filePath":"\\System.Windows.Interactivity.dll","MD5Checksum":"580244bc805220253a87196913eb3e5e","version":0}}]}

编辑2：观看Json String

"{\"companyName\":\"Home\",\"applicationName\":\"Test\",\"version\":\"V5.0.1\",\"fileObjectList\":[{\"filePath\":\"\\\\bug-tracker.exe\",\"fileRecord\":{\"ignored\":false,\"MD5Checksum\":\"a5254a813a040b429f2288df737a8b9f\",\"version\":0}},{\"filePath\":\"\\\\bug-tracker.exe.config\",\"MD5Checksum\":\"e5c3e9137dc8fadb57dfc27b0ba6855c\",{\"filePath\":\"\\\\bug-tracker.pdb\",\"MD5Checksum\":\"9a9dfda29dcaacae82cba7bd7aa97ffa\",{\"filePath\":\"\\\\Caliburn.Micro.dll\",\"MD5Checksum\":\"aa5f96c02b08d9b33322f3024058dd91\",{\"filePath\":\"\\\\Caliburn.Micro.Platform.Core.dll\",\"MD5Checksum\":\"ab7867bd44b59879a59b5cb968e15668\",{\"filePath\":\"\\\\Caliburn.Micro.Platform.Core.xml\",\"MD5Checksum\":\"cdfcbbf70a9a62b92e82a953ab9e7e30\",{\"filePath\":\"\\\\Caliburn.Micro.Platform.dll\",\"MD5Checksum\":\"a52bdecbc1b7625cb13c9385fad4231b\",{\"filePath\":\"\\\\Caliburn.Micro.Platform.xml\",\"MD5Checksum\":\"09f258a3aeca7285355d82a66dda2176\",{\"filePath\":\"\\\\Caliburn.Micro.xml\",\"MD5Checksum\":\"c87ec582a4bfcf2e79e517c689441def\",{\"filePath\":\"\\\\MaterialDesignColors.dll\",\"MD5Checksum\":\"ad729352a9088b889cc0c4dc7542dcb6\",{\"filePath\":\"\\\\MaterialDesignColors.pdb\",\"MD5Checksum\":\"7ba70b23e22db9ac155e190860d9a5ec\",{\"filePath\":\"\\\\MaterialDesignThemes.Wpf.dll\",\"MD5Checksum\":\"e4c790d3af41620dc5ad513ae7fcadac\",{\"filePath\":\"\\\\MaterialDesignThemes.Wpf.pdb\",\"MD5Checksum\":\"f8113c8ea54896b8150db8e7ebd506ef\",{\"filePath\":\"\\\\MaterialDesignThemes.Wpf.xml\",\"MD5Checksum\":\"49717f8130b7529ee51fb6bc13f79aa4\",{\"filePath\":\"\\\\ShowMeTheXAML.dll\",\"MD5Checksum\":\"040b9e80820553a55f13ac19c2036367\",{\"filePath\":\"\\\\System.Windows.Interactivity.dll\",\"MD5Checksum\":\"580244bc805220253a87196913eb3e5e\",\"version\":0}}]}\r\n"

解决方法

实际的问题是您在构造函数中具有参数：

public FileRecord(String filePath,Boolean ignored_)

然后 JsonConvert 将默认值（null，false）放在此处，从而触发代码：

else
{
    MD5Checksum = CalculateMD5(filePath);
    version = 0;
}

依次尝试使用 null 路径参数从文件读取：

static string CalculateMD5(string filePath)
    {
        var md5 = MD5.Create();
        var stream = File.OpenRead(filePath); // <- HERE!!!!
        var hash = md5.ComputeHash((System.IO.Stream)stream);
        return BitConverter.ToString(hash).Replace("-","").ToLowerInvariant();

    }

我看到有两种解决方案

创建无参数构造函数，在其中初始化所需的所有内容，或使用默认值为：this（）的参数调用构造函数：

public FileRecord（）：this（null，true） { }

重命名属性以匹配参数名称，例如：

 public bool Ignored { get; set; }

 public FileRecord(string filePath,bool ignored)
 {
      this.Ingnoerd = ignored;
      ....
 }

c#c#json json-deserialization serialization serialization visual-studio