c#引用相等性比较（ReferenceEquals）

Object.ReferenceEquals方法原型

public static bool ReferenceEquals(
object objA,
object objB
)

namespace TestReferenceEquality
    {
        struct TestStruct
        {
            public int Num { get; private set; }
            public string Name { get; private set; }

            public TestStruct(int i, string s) : this()
            {
                Num = i;
                Name = s;
            }
        }

        class TestClass
        {
            public int Num { get; set; }
            public string Name { get; set; }
        }

        class Program
        {
            static void Main()
            {
                //测试对象相等性
                #region ReferenceTypes

                // 创建具有两个相同值的引用实例。

                TestClass tcA = new TestClass() { Num = 1, Name = "New TestClass" };
                TestClass tcB = new TestClass() { Num = 1, Name = "New TestClass" };

                Console.WriteLine("ReferenceEquals(tcA, tcB) = {0}",
                                    Object.ReferenceEquals(tcA, tcB)); // false 

                // 赋值后, 引用同一对象 
                tcB = tcA;
                Console.WriteLine("After asignment: ReferenceEquals(tcA, tcB) = {0}",
                                    Object.ReferenceEquals(tcA, tcB)); // true 
#endregion

                // 演示两个值类型实例从不具有引用相等性。
                #region ValueTypes

                TestStruct tsC = new TestStruct( 1, "TestStruct 1");

                //虽是拷贝，具有相同的值，但却不是同一对象，涉及装箱
                TestStruct tsD = tsC;
                Console.WriteLine("After asignment: ReferenceEquals(tsC, tsD) = {0}",
                                    Object.ReferenceEquals(tsC, tsD)); // false
                #endregion

                #region stringRefEquality
                //"Hello world!";常量字符串在内存中只有一份，所以两者指向同一内存 
                string strA = "Hello world!";
                string strB = "Hello world!";
                Console.WriteLine("ReferenceEquals(strA, strB) = {0}",
                                 Object.ReferenceEquals(strA, strB)); // true 

                // 改变引用用后，两者不再相等
                strA = "Goodbye world!";
                Console.WriteLine("strA = \"{0}\" strB = \"{1}\"", strA, strB);

                Console.WriteLine("After strA changes, ReferenceEquals(strA, strB) = {0}",
                                Object.ReferenceEquals(strA, strB)); // false 

                //string对象在运行期间被创建，跟strB是完全不同的两个对象，在用 Object.ReferenceEquals判断引用相等时则返回false
                StringBuilder sb = new StringBuilder("Hello world!");
                string stringC = sb.ToString(); 
                // False:
                Console.WriteLine("ReferenceEquals(stringC, strB) = {0}",
                                Object.ReferenceEquals(stringC, strB));

                // 字符串类重载了==运算符来执行相等比较
                Console.WriteLine("stringC == strB = {0}", stringC == strB); // true
                #endregion           
            }
        }
    }

对于值类型的采用ReferenceEquals将返回false,引用类型采用ReferenceEquals比较时，若是引用同一实例则返回true,

判断字符串内容是否相等可直接利用字符串类的重载运算符==来判断

为了最大程度地减小出现错误的可能性，最好在必须确定两个对象是否具有引用相等性时使用 ReferenceEquals。