blocks|key|286961|text|不要寻找活动的网络连接，要查找目标主机是否为reachable。它并不复杂，所以没有示例代码:-)|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|286962|更新:我想我应该解释一下在这种情况下可达是什么意思。如文档中所述，如果发往远程网络地址的数据包可以通过任何网络接口离开此计算机，则认为该地址是可到达的。粗略地说，这是一个事实的表达，即i/f被配置并能够直接传送到远程系统，或者具有到达它的可用路由。可达性不会描述与远程主机是否“启动”或此计算机与远程计算机之间的网络是否正常工作相关的任何内容。|286963|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/mac/library/documentation/SystemConfiguration/Reference/SCNetworkReachabilityRef/Reference/reference.html^0|M|9|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

Don't look for an active network connection, look for your target host being <a href="http://developer.apple.com/mac/library/documentation/SystemConfiguration/Reference/SCNetworkReachabilityRef/Reference/reference.html" rel="nofollow noreferrer">reachable</a>. It's not complex, so no example code :-)

Update: I think I should have explained what reachable means in this context. As described in the docs, a remote network address is considered reachable if a packet destined for that address could leave this computer via any network interface. This is, roughly speaking, an expression of the fact that the i/f is configured and able to either directly deliver to the remote system, or has a route available to get to it. Reachability doesn't describe anything relating to whether the remote host is 'up' or whether the network between this computer and the remote one is functioning properly.

blocks|key|1588892|text|OSX积极支持网络/连接情况的变化，并在任何时候发生变化时重新配置。因此，它希望应用程序开发人员不要假设网络总是保持不变。您可能会发现System+Configuration+Goals+and+Architecture是一本有趣的读物，同时还可以检查configd的工作原理。(这只是我读到的，我从来没有在mac上编写过这样的程序)|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1588893|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/mac/library/documentation/Networking/Conceptual/SystemConfigFrameworks/SC_Overview/SC_Overview.html#//apple_ref/doc/uid/TP40001065-CH202-CHDDHABI^0|1V|17|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

OSX actively supports changes in the network/connection situation, and reconfigures any time there is a change. As a consequence it expects application developers to not assume the network will always stay the same. You might find <a href="http://developer.apple.com/mac/library/documentation/Networking/Conceptual/SystemConfigFrameworks/SC_Overview/SC_Overview.html#//apple_ref/doc/uid/TP40001065-CH202-CHDDHABI" rel="nofollow noreferrer">System Configuration Goals and Architecture</a> an interesting read, as well as checking up on the workings of configd. (This is just from reading about it, I've never actually programmed anything like this on the mac)

blocks|key|42889|text|还可以通过一个简单的命令行实用程序scutil(8)公开SystemConfiguration框架|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|42890|$+scutil+-r+stackoverflow.com
Reachable|code-block|syntax|javascript|42891|entityMap^0|H|9|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

The SystemConfiguration framework is also exposed through a simple command line utility, <code>scutil(8)</code>:

<pre><code>$ scutil -r stackoverflow.com
Reachable
</code></pre>

blocks|key|1586459|text|如果运行ifconfig命令行工具，则会得到如下输出：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1586460|en0:+flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST>+mtu+1500
++++++++ether+00:0d:93:48:d8:f2+
++++++++media:+autoselect+(none)+status:+inactive
++++++++supported+media:+none+autoselect+10baseT/UTP+<half-duplex>+10baseT/UTP+<full-duplex>+10baseT/UTP+<full-duplex,hw-loopback>+100baseTX+<half-duplex>+100baseTX+<full-duplex>+100baseTX+<full-duplex,hw-loopback>+1000baseT+<full-duplex>+1000baseT+<full-duplex,hw-loopback>+1000baseT+<full-duplex,flow-control>+1000baseT+<full-duplex,flow-control,hw-loopback>
en1:+flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST>+mtu+1500
++++++++inet6+fe80::211:24ff:fe27:385f%25en1+prefixlen+64+scopeid+0x5+
++++++++inet+192.168.1.67+netmask+0xffffff00+broadcast+192.168.1.255
++++++++ether+00:11:24:27:38:5f+
++++++++media:+autoselect+status:+active
++++++++supported+media:+autoselect|code-block|syntax|javascript|1586461|在我的例子中，请注意我的en0没有连接，而我的en1是连接的。相应地，有'status:active‘或'status:+inactive’。您可以运行ifconfig，解析输出，并查看是否有任何活动接口。除了环回。|1586462|可能有更多的API方式可以做到这一点，但我不能告诉你它们是什么！|1586463|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If you run the ifconfig command-line tool, you get output like this:

<pre><code>en0: flags=8863&lt;UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST&gt; mtu 1500
 ether 00:0d:93:48:d8:f2 
 media: autoselect (none) status: inactive
 supported media: none autoselect 10baseT/UTP &lt;half-duplex&gt; 10baseT/UTP &lt;full-duplex&gt; 10baseT/UTP &lt;full-duplex,hw-loopback&gt; 100baseTX &lt;half-duplex&gt; 100baseTX &lt;full-duplex&gt; 100baseTX &lt;full-duplex,hw-loopback&gt; 1000baseT &lt;full-duplex&gt; 1000baseT &lt;full-duplex,hw-loopback&gt; 1000baseT &lt;full-duplex,flow-control&gt; 1000baseT &lt;full-duplex,flow-control,hw-loopback&gt;
en1: flags=8863&lt;UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST&gt; mtu 1500
 inet6 fe80::211:24ff:fe27:385f%en1 prefixlen 64 scopeid 0x5 
 inet 192.168.1.67 netmask 0xffffff00 broadcast 192.168.1.255
 ether 00:11:24:27:38:5f 
 media: autoselect status: active
 supported media: autoselect
</code></pre>

In my case, note that my en0 is not connected, and my en1 is. Correspondingly, there is either 'status:active' or 'status: inactive'. You could run ifconfig, parse the output, and see if there are any active interfaces. Apart from loopback.

There are probably more API-ish ways to do this, but i can't tell you what they are!

I want to provide my user with some meaningful error messages when network requests fail.

On Windows I can call <a href="http://msdn.microsoft.com/en-us/library/aa384702(VS.85).aspx" rel="nofollow noreferrer">InternetGetConnectedState()</a> to see if there is an active network connection. What is the OS X equivalent? 

Bonus points for example code if it's complex.

How does one tell if there is an active network connection on OS X?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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当网络请求失败时，我想为我的用户提供一些有意义的错误消息。在Windows上，我可以调用来查看是否有活动的网络连接。OS X的等价物是什么？加分:如果代码很复杂，就给它加分。

问如何判断OS X上是否有活动的网络连接？
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