我在silverlight应用程序中有一个比较2个字符串的条件,由于某种原因,当我使用==时,它返回false而. equals()返回true。

代码如下:

if (((ListBoxItem)lstBaseMenu.SelectedItem).Content.Equals("Energy Attack"))
{
    // Execute code
}

if (((ListBoxItem)lstBaseMenu.SelectedItem).Content == "Energy Attack")
{
    // Execute code
}

你知道为什么会这样吗?


当前回答

= =操作符

如果操作数为值类型且值相等,则返回true否则为false。 如果操作数是引用类型(string除外),并且都引用同一个实例(同一对象),则返回true否则返回false。 如果操作数为字符串类型且值相等,则返回true否则返回false。

.Equals

如果操作数是引用类型,它执行引用相等,即如果两个操作数都引用同一个实例(同一个对象),则返回true否则返回false。 如果操作数是值类型,那么与==运算符不同,它首先检查它们的类型,如果它们的类型相同,它执行==运算符,否则返回false。

其他回答

非常棒的答案和例子!

我想补充一下两者之间的根本区别,

像==这样的操作符不是多态的,而Equals是

记住这个概念,如果你算出任何例子(通过查看左手和右手引用类型,并检查/知道类型是否确实重载了==操作符和重写了Equals),你肯定会得到正确的答案。

I am a bit confused here. If the runtime type of Content is of type string, then both == and Equals should return true. However, since this does not appear to be the case, then runtime type of Content is not string and calling Equals on it is doing a referential equality and this explains why Equals("Energy Attack") fails. However, in the second case, the decision as to which overloaded == static operator should be called is made at compile time and this decision appears to be ==(string,string). this suggests to me that Content provides an implicit conversion to string.

Equal和==之间的唯一区别是对象类型比较。在其他情况下,例如引用类型和值类型,它们几乎是相同的(要么都是位相等,要么都是引用相等)。

对象: Equals:位的相等 ==:引用相等

String:(equals和==对于String是相同的,但如果字符串中的一个被更改为object,则比较结果将不同) Equals:位的相等 ==:位相等

更多的解释请看这里。

当比较对象引用和字符串时(即使对象引用引用了字符串),特定于字符串类的==操作符的特殊行为将被忽略。

Normally (when not dealing with strings, that is), Equals compares values, while == compares object references. If two objects you are comparing are referring to the same exact instance of an object, then both will return true, but if one has the same content and came from a different source (is a separate instance with the same data), only Equals will return true. However, as noted in the comments, string is a special case because it overrides the == operator so that when dealing purely with string references (and not object references), only the values are compared even if they are separate instances. The following code illustrates the subtle differences in behaviors:

string s1 = "test";
string s2 = "test";
string s3 = "test1".Substring(0, 4);
object s4 = s3;  // Notice: set to object variable!

Console.WriteLine($"{object.ReferenceEquals(s1, s2)} {s1 == s2} {s1.Equals(s2)}");
Console.WriteLine($"{object.ReferenceEquals(s1, s3)} {s1 == s3} {s1.Equals(s3)}");
Console.WriteLine($"{object.ReferenceEquals(s1, s4)} {s1 == s4} {s1.Equals(s4)}");

输出结果为:

True True True     // s1, s2
False True True    // s1, s3
False False True   // s1, s4

简介:

Variables .ReferenceEquals == .Equals
s1, s2 True True True
s1, s3 False True True
s1, s4 False False True

给答案再加一分。

. equalsto()方法提供了比较区域性和区分大小写的方法。