使Dictionary泛型查询简单化

我们经常使用Dictionary<T> 来做些操作，查询一个object，没有找到就Add它。代码像如样：

private static Dictionary<string,Employee> employees;
…
public static Employee GetByName(string name) {
    Employee employee;
    if (!employees.TryGetValue(name, out employee)) {
        employee = new Employee(whatever);
        employees.Add(name, employee);
    }
    return employee;
}

现在我们写个扩展方法：

        /// <summary>
        /// Gets the or add.
        /// </summary>
        /// <typeparam name="TKey">The type of the key.</typeparam>
        /// <typeparam name="TDictionaryValue">The type of the dictionary value.</typeparam>
        /// <typeparam name="TActualValue">The type of the actual value.</typeparam>
        /// <param name="dictionary">The dictionary.</param>
        /// <param name="key">The key.</param>
        /// <param name="newValue">The new value.</param>
        /// <returns>TActualValue</returns>
        public static TActualValue GetOrAdd<TKey, TDictionaryValue, TActualValue>(this IDictionary<TKey, TDictionaryValue> dictionary,
    TKey key, Func<TActualValue> newValue) where TActualValue : TDictionaryValue
        {
            TDictionaryValue value;
            if (!dictionary.TryGetValue(key, out value))
            {
                value = newValue.Invoke();
                dictionary.Add(key, value);
            }
            return (TActualValue)value;
        }

一个HelpMethod:

        public static Employee GetByName(string name)
        {
            return employees.GetOrAdd(name, () => new Employee(){Name=name});
        }

最后看Test,简化了：

        [Test]
        public void TestDic()
        {
            employees = new Dictionary<string, Employee>();
            var emp=GetByName("Petter");
            Assert.AreEqual("Petter", emp.Name);
            Assert.IsInstanceOf(typeof(Employee), emp);
        }

Employee这个Class用于演示，您可以随意创建，或是其他Object。希望这篇Post对你有帮助.

Author: Petter Liu    http://wintersun.cnblogs.com