C# 物件對比是否相等 工作筆記
阿新 • • 發佈：2018-12-07
需要在Linq 中對比兩個物件是否相等
/// <summary> /// 定義一個點 /// </summary> class Point { public int x { get; set; } public int y { get; set; } public Point(int x, int y) { this.x = x; this.y = y; } }
List<Point> list1 = newList<Point>() { new Point(1,1), new Point(1, 2), new Point(1, 3), new Point(1, 4), new Point(1, 5), new Point(1, 6)}; var result1 = list1.Where(M => M == new Point(1, 3));
三種對比方法均不能
Point p1 = new Point(2, 1); Point p2 = new Point(2, 1); Console.WriteLine(p1 == p2);//False Console.WriteLine(p1.Equals(p2));//False // ReferenceEquals 方法用於物件的引用是否相等 // ReferenceEquals 不能重寫 注意 Console.WriteLine(System.Object.ReferenceEquals(p1, p2));//False p1 = p2; Console.WriteLine(System.Object.ReferenceEquals(p1, p2));//True
由於沒有重寫 == 運算子 和 Equals 方法，不能夠 直接使用否則對比的將是物件的引用地址
需要對類進行重寫，詳細如下
/// <summary>/// 定義一個點,並重寫物件與物件是否相等的方法 /// 可用於判斷物件是否相等 /// eg: /// obj1 == obj2 /// obj1.Equals(obj2) /// </summary> class TestPoint : IEquatable<TestPoint> { public int x { get; set; } public int y { get; set; } public TestPoint(int x, int y) { this.x = x; this.y = y; } /// <summary> /// 過載 == 運算子 /// </summary> /// <param name="p1"></param> /// <param name="p2"></param> /// <returns></returns> public static bool operator ==(TestPoint p1, TestPoint p2) { return (p1.x == p2.x) && (p1.y == p2.y); } /// <summary> /// 過載 != 運算子 /// </summary> /// <param name="p1"></param> /// <param name="p2"></param> /// <returns></returns> public static bool operator !=(TestPoint p1, TestPoint p2) { return (p1.x != p2.x) || (p1.y != p2.y); } /// <summary> /// 重寫Equals(object obj) /// </summary> /// <param name="obj"></param> /// <returns></returns> public override bool Equals(object obj) { return this.Equals(obj as TestPoint); } /// <summary> /// 重寫 計算物件的雜湊值方法（自定義 這裡只是示範）
/// 該方法用於判斷物件的雜湊值是否相等 如物件雜湊值相同 就認為兩個物件 相等 /// </summary> /// <returns></returns> public override int GetHashCode() { return this.x.GetHashCode() + this.y.GetHashCode(); } /// <summary> /// 繼承定義Equals<T>方法 /// 需要繼承介面IEquatable<T> /// </summary> /// <param name="other"></param> /// <returns></returns> public bool Equals(TestPoint other) { return (this.x == other.x) && (this.y == other.y); } }
使用大概示範
Point p1 = new Point(2, 1); Point p2 = new Point(2, 1); Console.WriteLine(p1 == p2);//False Console.WriteLine(p1.Equals(p2));//False // ReferenceEquals 方法用於物件的引用是否相等 // ReferenceEquals 不能重寫 注意 Console.WriteLine(System.Object.ReferenceEquals(p1, p2));//False p1 = p2; Console.WriteLine(System.Object.ReferenceEquals(p1, p2));//True TestPoint p3 = new TestPoint(2, 1); TestPoint p4 = new TestPoint(2, 1); Console.WriteLine(p3 == p4);//True Console.WriteLine(p3.Equals(p4));//True // ReferenceEquals 方法用於物件的引用是否相等 // ReferenceEquals 不能重寫 注意 Console.WriteLine(System.Object.ReferenceEquals(p3, p4));//False p3 = p4; Console.WriteLine(System.Object.ReferenceEquals(p3, p4));//True List<Point> list1 = new List<Point>() { new Point(1,1), new Point(1, 2), new Point(1, 3), new Point(1, 4), new Point(1, 5), new Point(1, 6)}; var result1 = list1.Where(M => M == new Point(1, 3)); List<TestPoint> list2 = new List<TestPoint>() { new TestPoint(1, 1), new TestPoint(1, 2), new TestPoint(1, 3), new TestPoint(1, 4), new TestPoint(1, 5), new TestPoint(1, 6) }; var result2 = list2.Where(M => M == new TestPoint(1, 3));
完整程式碼
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace ConsoleApplication1 { /// <summary> /// 定義一個點 /// </summary> class Point { public int x { get; set; } public int y { get; set; } public Point(int x, int y) { this.x = x; this.y = y; } } /// <summary> /// 定義一個點,並重寫物件與物件是否相等的方法 /// 可用於判斷物件是否相等 /// eg: /// obj1 == obj2 /// obj1.Equals(obj2) /// </summary> class TestPoint : IEquatable<TestPoint> { public int x { get; set; } public int y { get; set; } public TestPoint(int x, int y) { this.x = x; this.y = y; } /// <summary> /// 過載 == 運算子 /// </summary> /// <param name="p1"></param> /// <param name="p2"></param> /// <returns></returns> public static bool operator ==(TestPoint p1, TestPoint p2) { return (p1.x == p2.x) && (p1.y == p2.y); } /// <summary> /// 過載 != 運算子 /// </summary> /// <param name="p1"></param> /// <param name="p2"></param> /// <returns></returns> public static bool operator !=(TestPoint p1, TestPoint p2) { return (p1.x != p2.x) || (p1.y != p2.y); } /// <summary> /// 重寫Equals(object obj) /// </summary> /// <param name="obj"></param> /// <returns></returns> public override bool Equals(object obj) { return this.Equals(obj as TestPoint); } /// <summary> /// 重寫 計算物件的雜湊值方法（自定義 這裡只是示範） /// </summary> /// <returns></returns> public override int GetHashCode() { return this.x.GetHashCode() + this.y.GetHashCode(); } /// <summary> /// 繼承定義Equals<T>方法 /// 需要繼承介面IEquatable<T> /// </summary> /// <param name="other"></param> /// <returns></returns> public bool Equals(TestPoint other) { return (this.x == other.x) && (this.y == other.y); } } class Program { static void Main(string[] args) { Point p1 = new Point(2, 1); Point p2 = new Point(2, 1); Console.WriteLine(p1 == p2);//False Console.WriteLine(p1.Equals(p2));//False // ReferenceEquals 方法用於物件的引用是否相等 // ReferenceEquals 不能重寫 注意 Console.WriteLine(System.Object.ReferenceEquals(p1, p2));//False p1 = p2; Console.WriteLine(System.Object.ReferenceEquals(p1, p2));//True TestPoint p3 = new TestPoint(2, 1); TestPoint p4 = new TestPoint(2, 1); Console.WriteLine(p3 == p4);//True Console.WriteLine(p3.Equals(p4));//True // ReferenceEquals 方法用於物件的引用是否相等 // ReferenceEquals 不能重寫 注意 Console.WriteLine(System.Object.ReferenceEquals(p3, p4));//False p3 = p4; Console.WriteLine(System.Object.ReferenceEquals(p3, p4));//True List<Point> list1 = new List<Point>() { new Point(1,1), new Point(1, 2), new Point(1, 3), new Point(1, 4), new Point(1, 5), new Point(1, 6)}; var result1 = list1.Where(M => M == new Point(1, 3)); List<TestPoint> list2 = new List<TestPoint>() { new TestPoint(1, 1), new TestPoint(1, 2), new TestPoint(1, 3), new TestPoint(1, 4), new TestPoint(1, 5), new TestPoint(1, 6) }; var result2 = list2.Where(M => M == new TestPoint(1, 3)); Console.Read(); } } }
ReferenceEquals 不能重寫 注意
用於工作記錄
2018年12月7日13:22:13
lxp