FileField behavior with multiple files

[Lisa18289]

Uploading multiple files via a FileField (and FileDropZone) is currently only possible when all files are selected in a single upload action. If a user selects one file, then reopens the file picker and selects another file, the previously selected file is overwritten.

In scenarios such as attaching files to a chat message, users might instead expect the newly selected file to be added to the existing selection rather than replacing it.

We should therefore decide whether Flow should natively support this additive upload behavior, or whether Flow should merely provide guidance on how to implement this behavior in applications that use these fields.

[Jan-Eimertenbrink]

In a chat like scenario, my initial expectation was also that selecting another file would simply add it to the existing selection, especially since the files are already represented visually as FileCards.

After doing some research into how React Aria and Polaris handle this, it seems likely that the current behavior of the file trigger is intentional and actually a better fit for a design system. The FileTrigger component itself has no knowledge of how uploaded files are meant to be stored or presented, whether that is in a list, as FileCards, or in some other form. Because of that, supporting additive behavior directly at this level would introduce assumptions that do not necessarily hold across all use cases.

From my point of view, it therefore makes sense that FileTrigger does not expose a built in property for additive uploads. Instead, we should provide guidance in the style guide that shows how applications can temporarily store selected files, render them as FileCards, and then integrate this pattern in contexts like Chat in a way that matches user expectations.

This keeps the core component simple while still enabling additive upload behavior where it actually makes sense.

[Jan-Eimertenbrink]

After a short discussion within the Flow team, we quickly came to the conclusion that the FileTrigger should not support this natively. However, we plan to add a code example to the style guide. We are still undecided about the best place for it.