如何摆脱if-else链？ [英] How to get rid of if-else chain?

问题描述

我目前正在使用Winforms应用程序。我有一个数据库，上面有表格。



我创建了一个表单，负责显示来自此数据表的数据。为此，我在此表单中添加了一个数据网格视图控件。我还创建了一个枚举来指定显示哪些数据。表单从数据库中获取数据并在数据网格视图中显示。



但我有一些问题。



我有很多不同的数据要显示，所以我有很多if-else链。喜欢;

Hi,

I'm currently working on a Winforms application. I have a database and there are tables on it.

I created a Form that responsible for showing data's coming from this data tables. For this purpose I added a Data Grid View control to this form. I also created an 'enum' to specify which data is shown. The form gets the data from the database and show it in Data Grid View.

But I have some problems about it.

I have a lot of different data to show, and so I have a lot of if-else chain. Like;

if(listType == ListViewTypes.Accounts)
{ 
   //get data from database
} else if(listType == ListViewTypes.Persons)
{ 
  // get data from database
} 
//etc...

有没有解决方法呢？



谢谢。



我的尝试：



我想创建一个不同的类来处理这个，但我也在该类中使用这个if-else链。

Is there any solution about that?

Thank you.

What I have tried:

I think about create a different class to handle this but I also use this if-else chain in that class too.

推荐答案

使用开关：

Use a switch:

switch (listType)
   {
   case ListViewTypes.Accounts:
      ...
      break;
   case ListViewTypes.Persons:
      ...
      break;
...
   default:
      ...
      break;
   }

根据执行代码的同质性，你可以使用 Dictionary 委托 s。例如，请参阅： c＃ - 带委托或交换机的词典？ - 堆栈溢出 [ ^ ]。

Depending on the homogenity of the executed code, you could possibly use a Dictionary of delegates. See, for instance: c# - Dictionary with delegate or switch? - Stack Overflow[^].

您可以将if语句移至工厂类

You could move the "if" statement to a factory class

public interface IDataHandler
{
    void PopulateGridView(GridView gridView);
}

public class AccountsHandler : IDataHandler
{
    public void PopulateGridView(GridView gridView)
    {
        // populate gridView with accounts
    }
}

public class PersonsHandler : IDataHandler
{
    public void PopulateGridView(GridView gridView)
    {
        // populate gridView with people
    }
}

public class DataHandlerFactory
{
    public IDataHandler GetDataHandler (ListViewTypes types)
    {
        switch(types)
        {
            case ListViewTypes.Accounts:
                return new AccountsHandler();
            case ListViewTypes.Persons:
                return new PersonsHandler();
            default:
                throw new NotImplementedException();
        }
    }
}

使用

usage

DataHandlerFactory f = new DataHandlerFactory();

IDataHandler dh = f.GetDataHandler(types);

dh.PopulateGridView(GridView1);

您甚至可以做这样的事情来摆脱开关

You could even do something like this to get rid of the switch

public class DataHandlerFactory
{
    private static Dictionary<ListViewTypes, IDataHandler> handlers;

    static DataHandlerFactory()
    {
        handlers = new Dictionary<ListViewTypes, IDataHandler>();

        handlers.Add(ListViewTypes.Accounts, new AccountsHandler());
        handlers.Add(ListViewTypes.Persons, new PersonsHandler());
    }

    public IDataHandler GetDataHandler (ListViewTypes types)
    {
        IDataHandler dh;
            
        if (!handlers.TryGetValue(types, out dh))
        {
            throw new NotImplementedException();
        }

        return dh;

    }
}

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