Template (*) (medium )-优快云博客

participants

The classes and/or objects participating in this pattern are:

AbstractClass (DataObject)
- defines abstract primitive operations that concrete subclasses define to implement steps of an algorithm
- implements a template method defining the skeleton of an algorithm. The template method calls primitive operations as well as operations defined in AbstractClass or those of other objects.
ConcreteClass (CustomerDataObject)
- implements the primitive operations ot carry out subclass-specific steps of the algorithm

This real-world code demonstrates a Template method named Run() which provides a skeleton calling sequence of methods. Implementation of these steps are deferred to the CustomerDataObject subclass which implements the Connect, Select, Process, and Disconnect methods.

Hide code

// Template pattern -- Real World example

using System;
using System.Data;
using System.Data.OleDb;

namespace DoFactory.GangOfFour.Template.RealWorld
{

  // MainApp test application

  class MainApp
  {
    static void Main()
    {
      DataAccessObject dao;

      dao = new Categories();
      dao.Run();

      dao = new Products();
      dao.Run();

      // Wait for user
      Console.Read();
    }
  }

  // "AbstractClass"

  abstract class DataAccessObject
  {
    protected string connectionString;

    protected DataSet dataSet;

    public virtual void Connect()
    {
      // Make sure mdb is on c:/
      connectionString =
        "provider=Microsoft.JET.OLEDB.4.0; " +
        "data source=c://nwind.mdb";
    }

    public abstract void Select();
    public abstract void Process();

    public virtual void Disconnect()
    {
      connectionString = "";
    }

    // The "Template Method"

    public void Run()
    {
      Connect();
      Select();
      Process();
      Disconnect();
    }
  }

  // "ConcreteClass"

  class Categories : DataAccessObject
  {
    public override void Select()
    {
      string sql = "select CategoryName from Categories";
      OleDbDataAdapter dataAdapter = new OleDbDataAdapter(
        sql, connectionString);

      dataSet = new DataSet();
      dataAdapter.Fill(dataSet, "Categories");
    }

    public override void Process()
    {
      Console.WriteLine("Categories ---- ");

      DataTable dataTable = dataSet.Tables["Categories"];
      foreach (DataRow row in dataTable.Rows)
      {
        Console.WriteLine(row["CategoryName"]);
      }
      Console.WriteLine();
    }
  }

  class Products : DataAccessObject
  {
    public override void Select()
    {
      string sql = "select ProductName from Products";
      OleDbDataAdapter dataAdapter = new OleDbDataAdapter(
        sql, connectionString);

      dataSet = new DataSet();
      dataAdapter.Fill(dataSet, "Products");
    }

    public override void Process()
    {
      Console.WriteLine("Products ---- ");
      DataTable dataTable = dataSet.Tables["Products"];
      foreach (DataRow row in dataTable.Rows)
      {
        Console.WriteLine(row["ProductName"]);
      }
      Console.WriteLine();
    }
  }
}

Output

Categories ----
Beverages
Condiments
Confections
Dairy Products
Grains/Cereals
Meat/Poultry
Produce
Seafood

Products ----
Chai
Chang
Aniseed Syrup
Chef Anton's Cajun Seasoning
Chef Anton's Gumbo Mix
Grandma's Boysenberry Spread
Uncle Bob's Organic Dried Pears
Northwoods Cranberry Sauce
Mishi Kobe Niku