有没有添加到字典℃的项目更优雅的方式;>安全？ [英] Is there a more elegant way of adding an item to a Dictionary<> safely?

问题描述

我需要的键/对象对添加到字典中，但我当然需要首先检查键已经存在，否则我得到一个键已经存在于词典的错误。下面的代码解决了这个，但笨重。

什么是做这个而不做字符串辅助方法，这样更优雅的方式？

 使用系统; 
使用System.Collections.Generic; 
 
命名空间TestDictStringObject 
 {
类节目
 {
静态无效的主要（字串[] args）
 {
字典<串，对象> currentViews =新词典<字符串对象>（）; 
 
 StringHelpers.SafeDictionaryAdd（currentViews，客户，视图1）; 
 StringHelpers.SafeDictionaryAdd（currentViews，客户，视图2）; 
 StringHelpers.SafeDictionaryAdd（currentViews，员工，视图1）; 
 StringHelpers.SafeDictionaryAdd（currentViews，报告，视图1）; 
 
的foreach（KeyValuePair<字符串对象>对在currentViews）
 {
 Console.WriteLine（{0} {1}，pair.Key，pair.Value） ; 
} 
到Console.ReadLine（）; 
} 
} 
 
公共静态类StringHelpers 
 {
公共静态无效SafeDictionaryAdd（词典<字符串对象>字典，串键，对象视图） 
 {
如果
 {
 dict.Add（键，查看）（dict.ContainsKey（密钥）！）; 
} 
，否则
 {
字典[关键] =视图。 
} 
} 
} 
} 
  

解决方案

只需使用索引 - 如果它已经存在，它将覆盖，但它不会的有无的是那里第一次：

 词典<字符串对象> currentViews =新词典<字符串对象>（）; 
 currentViews [客户] =厂景; 
 currentViews [客户] =视图2; 
 currentViews [员工] =厂景; 
 currentViews [报告] =厂景; 
  

基本上使用添加如果的存在键表示一个错误（所以你要扔它），在其它的索引器。 （这是一个有点像铸造和使用为参考转换之间的区别。）

如果您在使用C＃3的和你有一组不同的键的，你可以让这甚至更整洁：

  VAR currentViews =新词典<字符串对象>（）
 {
 {客户，视图2}，
 {员工，视图1}，
 {报告，视图1}，
}; 
  

这不会工作你的情况虽然，因为集合初始化，总是用添加将在第二客户抛出项。

I need to add key/object pairs to a dictionary, but I of course need to first check if the key already exists otherwise I get a "key already exists in dictionary" error. The code below solves this but is clunky.

What is a more elegant way of doing this without making a string helper method like this?

using System;
using System.Collections.Generic;

namespace TestDictStringObject
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<string, object> currentViews = new Dictionary<string, object>();

            StringHelpers.SafeDictionaryAdd(currentViews, "Customers", "view1");
            StringHelpers.SafeDictionaryAdd(currentViews, "Customers", "view2");
            StringHelpers.SafeDictionaryAdd(currentViews, "Employees", "view1");
            StringHelpers.SafeDictionaryAdd(currentViews, "Reports", "view1");

            foreach (KeyValuePair<string, object> pair in currentViews)
            {
                Console.WriteLine("{0} {1}", pair.Key, pair.Value);
            }
            Console.ReadLine();
        }
    }

    public static class StringHelpers
    {
        public static void SafeDictionaryAdd(Dictionary<string, object> dict, string key, object view)
        {
            if (!dict.ContainsKey(key))
            {
                dict.Add(key, view);
            }
            else
            {
                dict[key] = view;
            }
        }
    }
}

解决方案

Just use the indexer - it will overwrite if it's already there, but it doesn't have to be there first:

Dictionary<string, object> currentViews = new Dictionary<string, object>();
currentViews["Customers"] = "view1";
currentViews["Customers"] = "view2";
currentViews["Employees"] = "view1";
currentViews["Reports"] = "view1";

Basically use Add if the existence of the key indicates a bug (so you want it to throw) and the indexer otherwise. (It's a bit like the difference between casting and using as for reference conversions.)

If you're using C# 3 and you have a distinct set of keys, you can make this even neater:

var currentViews = new Dictionary<string, object>()
{
    { "Customers", "view2" },
    { "Employees", "view1" },
    { "Reports", "view1" },
};

That won't work in your case though, as collection initializers always use Add which will throw on the second Customers entry.

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