您可以检查 [字符串长度] == 0 。这将检查它是否是有效但空字符串（@）以及它是否为零，因为在nil上调用 length 也将返回0.。

You can check if [string length] == 0. This will check if it's a valid but empty string (@"") as well as if it's nil, since calling length on nil will also return 0.