获取命令模式中执行方法的结果 [英] Get result of executed method in Command Pattern

问题描述

目前我正在尝试实现事务脚本模式(正是 Martin Fowler 描述的方式通过在一个简单的测试项目中使用 Command Pattern)，一切正常，问题是在继承自 ICommand 接口的具体类中执行指定方法时，我不知道如何获取结果.

Currently I'm trying to implement Transaction Script pattern (Exactly how Martin Fowler described by using Command Pattern) in a simple test project, everything just work fine, the problem is where I don't know how to get result(s) when specified method executed in concrete class which is inherited from ICommand interface.

让我们向您展示一些代码来阐明我有哪些功能.我有一个简单的CalculateSalaryCommand 类，它继承自ICommand 接口

Let's show you some code to clarify what functionality I have. I've a simple CalculateSalaryCommand class which inherited from ICommand interface

public class CalculateSalaryCommand : ICommand
{
    private readonly CalculateSalaryTS _salaryTs;
    private readonly int _hour;
    private readonly int _salaryPerHour;

    public CalculateSalaryCommand(CalculateSalaryTS salaryTs, int hour, int salaryPerHour)
    {
        _salaryTs = salaryTs;
        _hour = hour;
        _salaryPerHour = salaryPerHour;
    }

    public void Execute()
    {
        _salaryTs.CalculateSalary(_hour, _salaryPerHour);
    }
}

和一个名为CalculateSalaryTS的简单事务脚本类

and a simple Transaction Script class named CalculateSalaryTS

public class CalculateSalaryTS {
    public void CalculateSalary(int _hour, int _salaryPerHour) {
        Result = _hour * _salaryPerHour;
    }
}

如您所见，我将 的实例传递给具体的命令类，然后在 Execute 方法中，我从该实例执行操作.好吧，一切看起来都不错.但是有一个问题我不能返回执行方法的结果，它应该是一个整数.为了解决这个问题，我决定在事务脚本层添加一些代码，每个事务都应该从一个通用的ITransactionResult接口继承，如下所示:

as you can see I pass the instance of to concrete command class, then inside the Execute method I execute a operations from that instance. Well, everything just look good. but there is a problem I can't return the result of executed method which is should be a integer. To handle this problem, I decided to add some code to Transaction Script layer which each transaction should inherit from a generic ITransactionResult interface, which is look like following:

public interface ITransactionResult<TResult>
{
    TResult Result { get; set; }
}

然后CalculateSalaryTS类变成了这样:

Then CalculateSalaryTS class became like this :

public class CalculateSalaryTS : ITransactionResult<Int32> {

    public void CalculateSalary(int _hour, int _salaryPerHour) {
        Result = _hour * _salaryPerHour;
    }

    public int Result { get; set; }

}

用法:

    var script = new CalculateSalaryTS();
    var command = new CalculateSalaryCommand(script, 10, 20);           
    command.Execute();
    Console.WriteLine("Salary is {0}", script.Result);

我知道这种方式有其自身的局限性，但我别无选择，除非你给我另一个想法来处理这种情况.

I know this way has its own limitation but I don't have any choice till you give me another idea to handle this situation.

提前致谢.

推荐答案

如果你确实需要在命令执行后立即得到结果，你可以将结果存储在命令对象中:

If you absolutely need to get the result immediately after command execution, you could store the result in the command object:

public interface ICommandWithResult<T> : ICommand
{
  T Result { get; }
}

public class CalculateSalaryCommand : ICommandWithResult<int>
{
  public int Result { get; private set; }

  // ...

  public void Execute()
  {
    _salaryTs.CalculateSalary(_hour, _salaryPerHour);
    this.Result = _salaryTs.Result;
  }
}

// Usage:

var command = new CalculateSalaryCommand(new CalculateSalaryTS(), 10, 20);
command.Execute();
Console.WriteLine("Salary is {0}", command.Result);

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