FCM主题名称存在哪些命名限制？

Hey there, great question about FCM topic name restrictions—let’s clear this up for you since it’s a detail that’s easy to miss in the docs.

From confirmed Firebase guidelines and practical usage:

• Maximum Length: FCM topic names can be up to 256 characters long. This counts every character in the name, so keep that limit in mind if you’re using descriptive or structured names (like combining user IDs or categories).
• Allowed Characters: You can use the following in your topic names:
  • Uppercase and lowercase letters (A-Z, a-z)
  • Numbers (0-9)
  • Special characters: -, _, =, +, ,, ., :
  • Important note: Topic names are case-sensitive! So "Football_News" and "football_news" will be treated as two separate topics.

Avoid using spaces, slashes, or any other special characters not listed above—these will cause errors when trying to subscribe devices to the topic or send messages to it.

内容的提问来源于stack exchange，提问作者Todor Kostov