swift multiple conditions if statement with && operation

I have 4 text boxes.I don't want to allow user to let all these 4 textfields empty. How can I check multiple conditions in swift. I did like this but it's giving me an error

 if self.txtIncomeAd.text?.isEmpty && self.txtIncomeRec.text?.isEmpty &&

like wise. What is the correct way I can do this? Please help me. Thanks