Question

I have this method Verify_X which is called during databind for a listbox selected value. The problem is the strongly typed datasource. I want to use the abstract class BaseDataSource or an interface to call the methods supported: Parameters[] and Select(), Instead of using the most specific implementation as seen below.

This is so one method can be used for all the different types of datasources I have instead of having a method for each. They all inherit the same way.

Here is the chain of inheritance / implementation

public class DseDataSource : ProviderDataSource<SCCS.BLL.Dse, DseKey>  public abstract class ProviderDataSource<Entity, EntityKey> : BaseDataSource<Entity, EntityKey>, ILinkedDataSource, IListDataSource     where Entity : SCCS.BLL.IEntityId<EntityKey>, new()     where EntityKey : SCCS.BLL.IEntityKey, new()  public abstract class BaseDataSource<Entity, EntityKey> : DataSourceControl, IListDataSource, IDataSourceEvents     where Entity : new()     where EntityKey : new() 

The BaseDataSource has the methods and properties I need. DseDataSource is implemented the following way:

public class DseDataSource : ProviderDataSource<SCCS.BLL.Dse, DseKey> 

I know it is possible to edit the class DseDataSource, add an interface to access Parameters[] and Select(), then program against that, which allows what I want, but this requires editing the NetTiers libraries and I am curious to see if this can be done since it seemed so difficult.

    public static string Verify_DSE(string valueToBind, DseDataSource dataSource)     {         if (ListContainsValue(dataSource.GetEntityList(), valueToBind)) return valueToBind;         CustomParameter p = dataSource.Parameters['WhereClause'] as CustomParameter;         if (p != null)         {             p.Value = 'IsActive=true OR Id=' + valueToBind;             dataSource.Select();             return valueToBind;         }         return string.Empty;     }      private static bool ListContainsValue(IEnumerable list, string value)     {         if (value.Length == 0) return true;          foreach (object o in list)         {             IEntity entity = o as IEntity;             if (entity != null)             {                 if (entity.Id.ToString() == value)                     return true;             }         }         return false;     } 

The end result would be code such as:

public static string Verify(string valueToBind, object dataSource) { //what is the correct way to convert from object BaseDataSource baseInstance = dataSource as BaseDataSource;  if baseInstance != null) {     if (ListContainsValue(baseInstance.GetEntityList(), valueToBind)) return valueToBind;     CustomParameter p = baseInstance.Parameters['WhereClause'] as CustomParameter;     if (p != null)     {         p.Value = 'IsActive=true OR Id=' + valueToBind;         baseInstance.Select();         return valueToBind;     } }  return string.Empty; } 

Answer 1

If you are unable to alter the class definition or to use some sort of extension methods, you can use Reflection. Here is a sample that I worked up using assumptions about your code:

    public static string Verify(string valueToBind, object dataSource)     {         ////what is the correct way to convert from object         //BaseDataSource baseInstance = dataSource as BaseDataSource;         Type type = dataSource.GetType();         MethodInfo select = type.GetMethod('Select');         PropertyInfo parameters = type.GetProperty('Parameters');         PropertyInfo parameterGetter = null;         object parametersInstance = null;         if (parameters != null)         {             parametersInstance = parameters.GetValue(dataSource, null);             type = parametersInstance.GetType();             parameterGetter = type.GetProperty('Item');         }          //if baseInstance != null)         if (select != null && parameters != null && parameterGetter != null)         {                 if (ListContainsValue(baseInstance.GetEntityList(), valueToBind)) return valueToBind;                 CustomParameter p = parameterGetter.GetValue(parametersInstance, new object[] {'WhereClause' }) as CustomParameter;                  if (p != null)                 {                         p.Value = 'IsActive=true OR Id=' + valueToBind;                         select.Invoke(dataSource, null);                         return valueToBind;                 }         }          return string.Empty;     }