There is a way to force a textfield to have decimals when the iphone keyboard does not have a decimal. Wavelength did this for their tip calculator. The textfield placeholder prompts the user to enter dollar and cents by using the placeholder "0.00" in the textfield. Then when the user inputs the amount, the decimal remains. In other words, the placeholder text within the textfield does not entirely disappear. The decimal remains while the 0's are replaced with the user's input. How did they do this?
Customer support service by UserEcho