To my surprise, Info Path does not let you select the Attachments field to apply rules, making it a challenge apply validation on attachment fields.
However, you’ll still run into the occasional roadblock while working with Info Path forms. The issue was being able to apply validation rules to the attachments field.
In my case, I called the field I created Attachment Validation.
2.) Drop your field onto the form and remove the borders and background.
Then set the default text to ‘Attachments:’ 3.) Finally, lets apply some validation to this field.
Right click the field on your form and select Rules Manage Rules.
Unfortunately, the given regular expression will work for en-US culture only.
To do this, I used a custom expression: Now with all of that complete you will have a separate field that validates the attachments field and if there are no attachments, the text in the left hand column will be surrounded in the standard red dashed border.
NOTE: To get to the ‘:attachments URL’ field you need to create the validation make sure you go into Advanced View of the fields.
And you can’t apply the regular expression through a Skin file.
Other cultures will need different regular expressions here, and so it looks like some additional strategy would have to be developed to validate currency amounts across cultures.