是string.Equals（）和==操作符真的一样吗？ [英] Are string.Equals() and == operator really same?

问题描述

他们是真的一样吗？今天，我遇到了这个问题。这里是从即时窗口转储：

Are they really same? Today, I ran into this problem. Here is the dump from the Immediate Window:

?s 
"Category" 
?tvi.Header 
"Category" 
?s == tvi.Header 
false 
?s.Equals(tvi.Header) 
true 
?s == tvi.Header.ToString() 
true 

那么，s和tvi.Header包含类别，但是==返回false和equals返回true。

So, both s and tvi.Header contain "Category", but == returns false and Equals returns true.

s被定义为字符串，tvi.Header实际上是一个WPF TreeViewItem.Header。那么，为什么他们返回不同的结果？我一直以为他们是在C＃中互换。

s is defined as string, tvi.Header is actually a WPF TreeViewItem.Header. So, why are they returning different results? I always thought that they were interchangable in C#.

任何人能解释这是为什么？

Can anybody explain why this is?

推荐答案

两处不同：

• 等于是多态（即它可以被覆盖，并且所使用的实现将依赖于目标对象的执行时间型），而实施的 == 采用的是基于确定的编译时间的类型的对象：

• Equals is polymorphic (i.e. it can be overridden, and the implementation used will depend on the execution-time type of the target object), whereas the implementation of == used is determined based on the compile-time types of the objects:

// Avoid getting confused by interning
object x = new StringBuilder("hello").ToString();
object y = new StringBuilder("hello").ToString();
if (x.Equals(y)) // Yes


// The compiler doesn't know to call ==(string, string) so it generates
// a reference comparision instead
if (x == y) // No


string xs = (string) x;
string ys = (string) y;


// Now *this* will call ==(string, string), comparing values appropriately
if (xs == ys) // Yes

等于如果你调用它空会去的一声，==不会

Equals will go bang if you call it on null, == won't

string x = null;
string y = null;


if (x.Equals(y)) // Bang


if (x == y) // Yes

请注意，您可以避开后者是使用问题的Object.Equals ：

Note that you can avoid the latter being a problem using object.Equals:

if (object.Equals(x, y)) // Fine even if x or y is null

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