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Cast to generic type in C#

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野性不改 2021-01-30 20:27

I have a Dictionary to map a certain type to a certain generic object for that type. For example:

typeof(LoginMessage) maps to MessageProcessor
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  • -上瘾入骨i
    -上瘾入骨i (楼主)
    2021-01-30 21:10

    I struggled to solve a similar problem around data table classes instead of messages. The root issue mentioned above of casting a non-generic version of the class to a derived generic version was the same.

    In order to allow injection into a portable class library which did not support database libraries, I introduced a set of interface classes, with the intent that I could pass a type and get a matching generic. It ended up needing to implement a generic method.

    // Interface for injection
public interface IDatabase
{
    // Original, non-functional signature:
    IDatatable GetDataTable(Type dataType);

    // Functional method using a generic method:
    IDatatable GetDataTable();
}



    And this the whole implementation using the generic method above.
    


    The generic class that will be cast from a dictionary.
    


    // Non-generic base class allows listing tables together
abstract class Datatable
{
    Datatable(Type storedClass)
    {
      StoredClass = storedClass;
    }

    Type StoredClass { get; private set; }
}

// Generic inheriting class
abstract class Datatable: Datatable, IDatatable
{
    protected Datatable()
        :base(typeof(T))
    {
    }
}

    


    This is the class that stores the generic class and casts it to satisfy the generic method in the interface
    


    class Database
{
    // Dictionary storing the classes using the non-generic base class
    private Dictionary _tableDictionary;

    protected Database(List tables)
    {
        _tableDictionary = new Dictionary();
        foreach (var table in tables)
        {
            _tableDictionary.Add(table.StoredClass, table);
        }
    }

    // Interface implementation, casts the generic
    public IDatatable GetDataTable()
    {
        Datatable table = null;

        _tableDictionary.TryGetValue(typeof(T), out table);

        return table as IDatatable;
    }
}

    


    And finally the calling of the interface method.
    


    IDatatable table = _database.GetDataTable();

    
    
    
             
    
                                                        
    
            
            
    
              
                
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