如何从字符串调用静态类方法？

Question

Excuse my ignorance/mistake as I'm a newbie and learning. I have a static class with the name of the country, Finland , as seen below.

namespace Countries
{
    public static class Finland
    {
        public static int ID { get; set; } = 7;
        public static string nameOfCountry { get; set; } = "Finland";
        public static string abbreviation { get; set; } = "FI";
        public static string flagLocation { get; set; } = "finishFlag.png";
        public static string GetFlag()
        {
            return "finishFlag.png";
        }
    }
}

I'm using HttpClient to do GET request a JSON string from a website. Then I use DeserializeObject to deserialize JSON to an object. One of the variables of the object is string countryName (which exactly matches the string, nameOfCountry). By using this string (countryName), I want to call the GetFlag() method from the respective country class. However, I don't know how to call this static method from the string countryName . I can compare nameOfCountry string in with the countryName string, however I have 24 country classes like the class Finland which means 24 if else if statements.

I saw the Type.GetType() method from one of the answers in StackOverflow but I didn't understand how this can be used here as I'm not creating a instance. Please provide an example to solution so that it's easier to understand. Thank you.

Answer 1

You don't need 24 different classes, you need 1 class with 24 instances.

public class Country
{
    public int ID { get; }
    public string NameOfCountry { get; }
    public string Abbreviation { get; }
    public string FlagLocation { get; }

    public Country(int id, string nameOfCountry, string abbreviation, string flagLocation)
    {
        ID = id;
        NameOfCountry = nameOfCountry;
        Abbreviation = abbreviation;
        FlagLocation = flagLocation;
    }        
}

Notice that if those properties were static as in the question, all instances would share the value, which is something you don't want here.

The best way to store these classes (assuming you cannot use a database) would be to use a Dictionary:

private static Dictionary<string, Country> _countries = new Dictionary<string, Country>
{
    ["Finland"] = new Country(7, "Finland", "FI", "finishFlag.png"),
    ["USA"] = ...
};

You can then access these countries by their name:

Country country = _countries["Finland"];

Adding countries to the dictionary is then much easier than creating a new class and adding a new if case.

Answer 2

Don't create a bunch of static classes. Instead create one Country class then create objects of each country.

public class Country
{
    public int ID { get; set; }
    public string Name { get; set; }
    public tring Abbreviation { get; set; }
    public tring FlagLocation { get; set; }
}

Then you can have a static dictionary

public static Dictionary<string, Country> Countries = 
{
    ["Finland"] = new Country
    {
        ID = 7,
        Name = "Finland",
        Abbreviation = "FI",
        FlagLocation = "finishFlag.png"
    },
    ["Germany"] = new Country
    {
        ID = 8,
        Name = "Germany",
        Abbreviation = "DE",
        FlagLocation = "germanFlag.png"
    }
}

Then given the name of a country you can get the flag location like this

Countries["Finland"].FlagLocation;

Answer 3

If you use only static classes, you cannot rely on any common structure between classes (static classes cannot participate in polymorphism).

Instead, what if you defined your countries using an interface, and somewhere in your code you initialized a singleton instance of each of your country types? Then, when you get a string back, you could search for the instance that has the right country name, and use the rest of the information as you see fit.

As an alternative to @juharr's reply, you could use an interface, and then have each country implement that interface as a dedicated class; this lets you have country-specific behavior, if you were to find that you need it. If you don't, then @juharr's answer is effective.

public interface ICountry
{
    int Id { get; }

    string Name { get; }

    // .. and so on.
}

public class Finland : ICountry
{
    public string Name { get; private set; } = "Finland";

    public int Id { get; private set; } = 7;
}

public class CountryRegistry
{
    private Dictionary<string, ICountry> countryMap;

    public CountryRegistry()
    {
        this.countryMap = new Dictionary<string, ICountry>();

        InitCountries();
    }

    public ICountry FindByName( string searchName )
    {
        ICountry result;
        if( this.countryMap.TryGetValue( searchName, out result ) )
        {
            return result;
        }
        else
        {
            return null;
        }
    }

    private void InitCountries()
    {
        AddCountryToMap( new Finland() );
        // .. and so on
    }

    private void AddCountryToMap( ICountry country )
    {
        this.countryMap.Add( country.Name, country );
    }
}

Answer 4

declaring an object as a class is not common in programmer's world. class is somewhere to define a template (and a collection of behaviors). you can define country class in this way:

public class Country    
{
    public int ID { get; set; };
    public string NameOfCountry { get; set; };
    public string Abbreviation { get; set; };
    public string FlagLocation { get; set; };
}

and then define your countries as static objects:

 static Country Finland = new Country() { ID = 7, 
                                          NameOfCountry="Finland",
                                          Abbreviation  = "FI",
                                          FlagLocation = "finishFlag.png"
                                         };