Hi Rahul,
Greetings from Syncfusion support.
We were unable to predict your exact requirement details.
Query: I need to open a custom dialog box first with fields that needs to be added and then based on that, I need to select the files from the system to upload.
We can restrict the file upload based on the file type and size before uploading any file into the file system using FileManager, are you expecting perform such validation? If you are requirement is to validate the file before uploading then we can achieve it. We can achieve the use cases in the following documentation link in FileManager upload action.
If this is not your expected requirement, then please share us more details regarding your requirement with video/screenshots which help us to understand your requirement to provide you a prompt solution.
Regards,
Shameer Ali Baig S.
