How to request that two out of three fields need to be populated in a mobile search app

Question

I am developing a new iOS app and I need to let the user commit a search where three fields are shown.

1. a group name (development, marketing etc.)
2. member name
3. project name

the search should be done by choosing only one or two of the three options, with these conditions:

• if group was selected you can only select project (not member)
• if member was selected, you can only select project (not group)
• if project was selected, you have an option to fill out either group or member.

I would like to accomplish that without graying out the fields. I would like to give the app a bit more intuitive and friendly UI. I was thinking more of choosing one, and somehow displaying the relevant field, and I would like the user to somehow understand that the other field is not mandatory, but optional.

Answer 1

I would use enable/disable state on the search button.

1. No fields filled in - disabled
2. One field filled in - enabled
3. Two field filled in - enabled
4. Three field filled in - disabled

^{download bmml source – Wireframes created with Balsamiq Mockups}

Answer 2

I thought of this solution:

Graphically, show the options right after the first choice was made:

After that

Answer 3

If this is advanced search screen, I whould have done it in this way:

Ask how to search on a first screen and choose other data on other steps using scroll list. in this way i user don't have to enter anything.

^{download bmml source – Wireframes created with Balsamiq Mockups}