传递多种方法（委托？）

Question

I'm trying to develop a framework for several applications we are developing here and one of the framework classes I am trying to build is for creating a database. Ideally, I would have a method where I could pass it the following two methods: CreateDatabaseTables() and ResetDatabaseValues();

For instance, I might have three applications which I'll call Application1, Application2 and Application3; each one these applications would have a different database schema which I would incorporate into code (eg the CreateDatabaseTables has a bunch of "Create Table" commands). I want to create a single database method that can be utilized by each of these so it would look something like:

Application1

BuildLocalDatabase(CreateTablesForApp1(),ResetDatabaseValuesforApp1())

Application2

BuildLocalDatabase(CreateTablesForApp2(),ResetDatabaseValuesforApp2())

Application3

 BuildLocalDatabase(CreateTablesForApp3(),ResetDatabaseValuesforApp3())

The BuildLocalDatabase method would do something like:

publid bool BuildLocalDatabase(CreateTablesForApp(),ResetDatabaseValuesforApp())
{
   - see if database file exists; if it does, delete it
   - create a new database file
   - call CreateTablesForApp
   - if the tables were created successfully, call ResetDatabaseValuesForApp
}

Any thoughts on how I would go able doing this. There's actually a bunch of validation and other stuff that I would want to do in the BuildLocalDatabase function and obviously my goal here is to minimize the amount of duplication code in each application...any suggestions on how one might go about doing this. I think in C++, I could have just passed the CreateTablesForApp and ResetDatabaseValuesForApp methods as function points, but it doesn't seem like there is a way to do this in C#. And delegates does seem to handle it well since I'm really only limited to one method (and the multicast seems to want to run the methods twice).

Answer 1

You'll want to use delegates:

public bool BuildLocalDatabase(Func<Database, bool> createTables, Action<Database> resetValues)
{
     // Do initialization
     if (createTables(db))
     {
           resetValues(db);
     }
}

You'd then call this as:

BuildLocalDatabase( (db) => CreateTablesForApp1(), (db) => ResetDatabaseValuesforApp1() );

(I put in a "Database" parameter in case you need it - if you don't, you can just use Func<bool> and Action , without that parameter, and just pass the method name directly instead of lambdas. Usually methods like this need some form of parameter, such as a DB connection, etc, though- so I put it in.)

Answer 2

Well, basically you can. If the question is about delegate syntac, you need to lose a few () and define a delegate:

public delegate void MyDelegate();

publid bool BuildLocalDatabase(MyDelegate CreateTablesForApp, MyDelegate ResetDatabaseValuesforApp)
{
   CreateTablesForApp();
   ...
   ResetDatabaseValuesforApp();
}

and call it like:

BuildLocalDatabase(CreateTablesForApp1,ResetDatabaseValuesforApp1);

Answer 3

You should try to use the built-in delegates:

• System.Action
• System.Action(T)
• System.Action(T1, T2)
• ...
• System.Func(TResult)
• System.Func(T, TResult)
• ...

Use the Action delegate if the delegate doesn't have a return value, otherwise use the Func delegates, each are overloaded with up to 4 input parameters.