Thanks, I have read the WriteMode link you give, and notice the description in the document.
The description about "ADD" is: Do not overwrite an existing file if there is a conflict. The autorename strategy is to append a number to the file name. For example, "document.txt" might become "document (2).txt".
And description about "OVERWRITE" is: Always overwrite the existing file. The autorename strategy is the same as it is for ADD.
But I still don't konw the difference between these two options. Since both option will create a new file like "document (2).txt", how should I understand the words "Always overwrite the existing file"? If I set write mode to overwrite, will every update from multiple devices be added to the end of "document.txt", and at the same time create "document (2).txt" for every update. And if in add mode, app will only create "document (2).txt", and don't add update to "document.txt" ? Did I understand in the right way? I don't have enough devices to try this, so I sincerely hope you can help me figure this out.