[英]Dictionary.ContainsKey Always Returns False
好吧,我正在尝试创建一个小应用程序,以节省一些员工姓名,年龄和工资。 所以我决定使用Dictionary
来设置每个员工的薪水,我想出了那个代码
var employeeSalaryDictionary = new Dictionary<Employee, int>();
employeeSalaryDictionary.Add(new Employee { Name = "Chuck", Age = 37 }, 1000);
employeeSalaryDictionary.Add(new Employee { Name = "Norris", Age = 37 }, 2000);
employeeSalaryDictionary.Add(new Employee { Name = "Rocks", Age = 44 }, 3000);
Employee employeeToFind = new Employee { Name = "Chuck", Age = 37 };
//or even
Employee employeeToFind = new Employee { Name = "Chuck"};
//Always False...
bool exists = employeeSalaryDictionary.ContainsKey(employeeToFind);
public class Employee
{
public string Name { get; set; }
public int Age { get; set; }
}
但是,当我注释掉或作为主题标题声明时, .ContainsKey
总是返回False
尽管我尝试了两种方式,如代码中所示。
您没有使用接受IEqualityComparer<T>
的Dictionary
构造函数,也没有在Employee
类上实现自定义相等。
所以现在字典是通过引用比较员工。 当您new
员工时,您有不同的参考,即使名称可能相同。
这里最简单的方法可能是实现你自己的IEqualityComparer<Employee>
,你可以选择哪些成员用于相等比较,并将它传递给字典的构造函数。
[编辑]正如所承诺的,片段:
//ReSharper's courtesy
public sealed class NameAgeEqualityComparer : IEqualityComparer<Employee>
{
public bool Equals(Employee x, Employee y)
{
if (ReferenceEquals(x, y)) return true;
if (ReferenceEquals(x, null)) return false;
if (ReferenceEquals(y, null)) return false;
if (x.GetType() != y.GetType()) return false;
return string.Equals(x.Name, y.Name) && x.Age == y.Age;
}
public int GetHashCode(Employee obj)
{
unchecked
{
return ((obj.Name != null ? obj.Name.GetHashCode() : 0) * 397) ^ obj.Age;
}
}
}
然后:
var employeeSalaryDictionary = new Dictionary<Employee, int>(new NameAgeEqualityComparer());
employeeSalaryDictionary.Add(new Employee { Name = "Chuck", Age = 37 }, 1000);
employeeSalaryDictionary.Add(new Employee { Name = "Norris", Age = 37 }, 2000);
employeeSalaryDictionary.Add(new Employee { Name = "Rocks", Age = 44 }, 3000);
Employee employeeToFind = new Employee { Name = "Chuck", Age = 37 };
bool exists = employeeSalaryDictionary.ContainsKey(employeeToFind); // true!
为了完整,这里只有名称比较器(也是ReSharper的礼貌):
public sealed class NameEqualityComparer : IEqualityComparer<Employee>
{
public bool Equals(Employee x, Employee y)
{
if (ReferenceEquals(x, y)) return true;
if (ReferenceEquals(x, null)) return false;
if (ReferenceEquals(y, null)) return false;
if (x.GetType() != y.GetType()) return false;
return string.Equals(x.Name, y.Name);
}
public int GetHashCode(Employee obj)
{
return (obj.Name != null ? obj.Name.GetHashCode() : 0);
}
}
但是,正如您所注意到的,您必须决定在创建字典时将使用哪个比较器进行键比较。 以后不能改变......
Employee是一种引用类型。 添加新员工时,您的字典键将包含该Employee对象的引用地址。 如果您创建另一个Employee对象,则它具有与第一个Employee对象不同的引用,即使它们包含相同的数据
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