.net – LinkedList.Contains.用于比较对象的方法是什么？

发布时间：2020-12-15 08:31:23 所属栏目：Java 来源：网络整理

导读：LinkedList.Contains方法. (.NET 2) 如何在里面比较对象？ (等于？CompareTo？) MSDN对此一无所知. 情况： interface IClass{ string GetName();}class Class1 : IClass,IEquatableClass1{ public string FirstName; public string LastName; string IClass.

LinkedList.Contains方法. (.NET 2)

如何在里面比较对象？ (等于？CompareTo？)

MSDN对此一无所知.

情况：

interface IClass
{
    string GetName();
}

class Class1 : IClass,IEquatable<Class1>
{
    public string FirstName;
    public string LastName;

    string IClass.GetName() { return FirstName; }

    bool IEquatable<Class1>.Equals(Class1 other)
    {
        return FirstName.Equals(other.FirstName);
    }
}

class Class2 : IClass,IEquatable<Class2>
{
    public string FirstName;
    public string LastName;

    string IClass.GetName() { return LastName; }

    bool IEquatable<Class2>.Equals(Class2 other)
    {
        return LastName.Equals(other.LastName);
    }
}

public void TestMethod() 
{
    Class1 c1 = new Class1();
    c1.FirstName = "fn";
    c1.FirstName = "ln";

    Class2 c2 = new Class2();
    c2.FirstName = "fn";
    c2.FirstName = "ln";

    Class1 c3 = new Class1();
    c3.FirstName = "fn";
    c3.FirstName = "ln";

    LinkedList<IClass> myList = new LinkedList<IClass>();
    myList.AddFirst(c1);
    myList.AddFirst(c2);
    // false here
    MessageBox.Show("myList<IClass> contains c3? - " + (myList.Contains(c3)));

    LinkedList<Class1> myList1 = new LinkedList<Class1>();
    myList1.AddFirst(c1);
    myList1.AddFirst(c1);
    // true here
    MessageBox.Show("myList1<Class1> contains c3? - " + (myList1.Contains(c3)));
}

解决方法

由于链表不是字典,我希望它使用EqualityComparer< T> .Default.Equals(x,y).

这支持(按顺序)：

> IEquatable< T> (对于有问题的T)
> object.Equals(默认使用引用相等,或支持重写的Equals(object))

注意EqualityComparer< T>还处理这两个类和Nullable< T>的常用空规则等.

(更新：检查,更正;来自Find(T))

...
EqualityComparer<T> comparer = EqualityComparer<T>.Default;
...
if (comparer.Equals(head.item,value)) {...}
...

更新以证明这在ISomeInterface：IEquatable< ISomeInterface&gt ;,根据评论：

using System;
using System.Collections.Generic;


class Program
{
    static void Main()
    {
        LinkedList<IFoo> foos = new LinkedList<IFoo>();
        foos.AddLast(new Foo1("abc"));
        foos.AddLast(new Foo2("def"));
        Console.WriteLine("checking contains...");
        bool c = foos.Contains(new Foo1("ghi"));
        Console.WriteLine("...done");
    }
}
interface IFoo : IEquatable<IFoo>
{
    void Bar();
}
class Foo1 : IFoo
{
    public string Value { get; set; }
    public Foo1(string value) { Value = value; }
    public override bool Equals(object other)
    {
        Console.WriteLine(Value + " > override Equals");
        return base.Equals(other);
    }
    bool IEquatable<IFoo>.Equals(IFoo other)
    {
        Console.WriteLine(Value + " > explicit Equals");
        return base.Equals(other);
    }
    public void Bar() { }
    public override int GetHashCode() { return base.GetHashCode(); }
}
class Foo2 : IFoo
{
    public string Value { get; set; }
    public Foo2(string value) { Value = value; }
    public override bool Equals(object other)
    {
        Console.WriteLine(Value + " > override Equals");
        return base.Equals(other);
    }
    public bool Equals(IFoo other)
    {
        Console.WriteLine(Value + " > implicit Equals");
        return base.Equals(other);
    }
    public void Bar() { }
    public override int GetHashCode() { return base.GetHashCode(); }
}

（编辑：李大同）

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