C# - How to XML Deserialize a Dictionary<string>, List<string>>?

Question

Here is what I tried but I get this error:

Error CS0029 Cannot implicitly convert type 'ListBoxAndDictionary.CountriesAndCities' to 'System.Collections.Generic.Dictionary<string, System.Collections.Generic.List>'

Here is my code:

private Dictionary<string, List<string>> dictCountryAndCities = new
      Dictionary<string, List<string>>();

private void button12_Click(object sender, EventArgs e)
{
    SaveFileDialog sfd = new SaveFileDialog();
    sfd.FileName = "CountriesAndCities";
    sfd.DefaultExt = ".xml";
    sfd.Filter = "XML (*.xml)|*.xml|All Files (*.*)|*.*";
    var sfdResult = sfd.ShowDialog();
    if (sfdResult == DialogResult.Cancel) 
        return;
    var container = new CountriesAndCities
    {
        DictCountriesAndCities = dictCountryAndCities
    };
    using (var writer = XmlWriter.Create(sfd.FileName)) 
        (new XmlSerializer(typeof(CountriesAndCities))).Serialize(writer, container);
}

private void button11_Click(object sender, EventArgs e)
{
    OpenFileDialog ofd = new OpenFileDialog();
    ofd.DefaultExt = ".xml";
    ofd.Filter = "XML (*.xml)|*.xml|All Files (*.*)|*.*";
    var ofdResult = ofd.ShowDialog();
    if (ofdResult == DialogResult.Cancel) 
        return;
    dictCountryAndCities = new Dictionary<string, List<string>>();

    XmlSerializer serializer = new XmlSerializer(typeof(CountriesAndCities));
    using (var reader = new StreamReader(ofd.FileName))
    {
        dictCountryAndCities = serializer.Deserialize(reader) as CountriesAndCities;

        //Error CS0029 Cannot implicitly convert type 'ListBoxAndDictionary.CountriesAndCities' to 'System.Collections.Generic.Dictionary<string, System.Collections.Generic.List<string>>'
    }

    //binding DataSource for listBox1
    listBox1.DataSource = dictCountryAndCities.Keys.ToList();
}

[Serializable]
[XmlRoot("CountriesAndCities")]
public class CountriesAndCities
{
    public List<Country> Name
    {
        get { return DictCountriesAndCities.Select(x => new Country { CountryName = x.Key, Cities = x.Value }).ToList(); }
        set { DictCountriesAndCities = value.ToDictionary(x => x.CountryName, x => x.Cities); }
    }
    [XmlIgnore]
    public Dictionary<string, List<string>> DictCountriesAndCities { get; set; }
}

[Serializable]
public class Country
{
    public string CountryName { get; set; }
    public List<string> Cities { get; set; }
}

Answer 1

You have a few problems with your XML serialization code.

Firstly, you need to modify your CountriesAndCities DTO as follows, replacing the List<Country> Name surrogate property with a Country [] Name property instead:

[XmlRoot("CountriesAndCities")]
public class CountriesAndCities
{
    public Country [] Name      // Replace the List<Country> with Country []
    {
        get { return DictCountriesAndCities.Select(x => new Country { CountryName = x.Key, Cities = x.Value }).ToArray(); }
        set { DictCountriesAndCities = value?.ToDictionary(x => x.CountryName, x => x.Cities); }
    }
    [XmlIgnore]
    public Dictionary<string, List<string>> DictCountriesAndCities { get; set; }
}

public class Country
{
    public string CountryName { get; set; }
    public List<string> Cities { get; set; }
}

Secondly, modify your serialization code as follows:

var container = new CountriesAndCities
{
    DictCountriesAndCities = dictCountriesAndCities,
};
using (var writer = XmlWriter.Create(sfd.FileName, new XmlWriterSettings { Indent = true })) // Indentation is for visualization purposes only
    (new XmlSerializer(typeof(CountriesAndCities))).Serialize(writer, container);

Finally, change your deserialization code as follows:

using (var reader = new StreamReader(ofd.FileName))
{
    dictCountriesAndCities = ((new XmlSerializer(typeof(CountriesAndCities))).Deserialize(reader) as CountriesAndCities)
        ?.DictCountriesAndCities;
}

Notes:

• Your "Error CS0029" is caused because you attempt to assign a value of type CountriesAndCities to a Dictionary<string, List<string>>. Instead, you must access the property DictCountriesAndCities.

• In your method button11_Click() you are deserializing your XML into a local variable dictCountryAndCities, then binding to its keys:

   dictCountryAndCities = new Dictionary<string, List<string>>();
  
   XmlSerializer serializer = new XmlSerializer(typeof(CountriesAndCities));
   using (var reader = new StreamReader(ofd.FileName))
   {
       dictCountryAndCities = serializer.Deserialize(reader) as CountriesAndCities;
  
       //Error CS0029 Cannot implicitly convert type 'ListBoxAndDictionary.CountriesAndCities' to 'System.Collections.Generic.Dictionary<string, System.Collections.Generic.List<string>>'
   }
  

  You are not updating the class member dictCountryAndCities at all. This seems wrong. However, it's not clear from your question what you want to be doing there, so I can't really recommend a fix.

• The [Serializable] attribute is not required or used by XmlSerializer, and can be removed.

• For an explanation as to why you should use Country [] instead of List<Country> for your surrogate Name property, see this answer to Cannot deserialize XML into a list using XML Deserializer.

Demo fiddle here.