SwiftUI - How to create TextField that only accepts numbers
Solution 1:
Although showing a number pad is a good first step, it does not actually prevent bad data from being entered:
- The user can paste non-numeric text into the textfield
- iPad users will still get a full keyboard
- Anyone with a Bluetooth keyboard attached can type anything
What you really want to do is sanitize the input, like this:
import SwiftUI
import Combine
struct StackOverflowTests: View {
@State private var numOfPeople = "0"
var body: some View {
TextField("Total number of people", text: $numOfPeople)
.keyboardType(.numberPad)
.onReceive(Just(numOfPeople)) { newValue in
let filtered = newValue.filter { "0123456789".contains($0) }
if filtered != newValue {
self.numOfPeople = filtered
}
}
}
}
Whenever numOfPeople
changes, the non-numeric values are filtered out, and the filtered value is compared to see if numOfPeople
should be updated a second time, overwriting the bad input with the filtered input.
Note that the Just
publisher requires that you import Combine
.
EDIT:
To explain the Just
publisher, consider the following conceptual outline of what occurs when you change the value in the TextField
:
- Because
TextField
takes aBinding
to aString
, when the contents of the field are changed, it also writes that change back to the@State
variable. - When a variable marked
@State
changes, SwiftUI recomputes thebody
property of the view. - During the
body
computation, aJust
publisher is created. Combine has a lot of different publishers to emit values over time, but theJust
publisher takes "just" a single value (the new value ofnumberOfPeople
) and emits it when asked. - The
onReceive
method makes aView
a subscriber to a publisher, in this case, theJust
publisher we just created. Once subscribed, it immediately asks for any available values from the publisher, of which there is only one, the new value ofnumberOfPeople
. - When the
onReceive
subscriber receives a value, it executes the specified closure. Our closure can end one of two ways. If the text is already numeric only, then it does nothing. If the filtered text is different, it is written to the@State
variable, which begins the loop again, but this time the closure will execute without modifying any properties.
Check out Using Combine for more info.
Solution 2:
tl;dr
Checkout John M's solution for a much better way.
One way to do it is that you can set the type of keyboard on the TextField
which will limit what people can type on.
TextField("Total number of people", text: $numOfPeople)
.keyboardType(.numberPad)
Apple's documentation can be found here, and you can see a list of all supported keyboard types here.
However, this method is only a first step and is not ideal as the only solution:
- iPad doesn't have a numberPad so this method won't work on an iPad.
- If the user is using a hardware keyboard then this method won't work.
- It does not check what the user has entered. A user could copy/paste a non-numeric value into the TextField.
You should sanitise the data that is entered and make sure that it is purely numeric.
For a solution that does that checkout John M's solution below. He does a great job explaining how to sanitise the data and how it works.
Solution 3:
A lot easyer in my opinion is to use a custom Binding and convert any Strings into numeric values straight ahead. This way you also have the State variable as a number instead of a string, which is a huge plus IMO.
The following is all code needed. Note, that a default value is used in case a string cannot be converted (zero in this case).
@State private var myValue: Int
// ...
TextField("number", text: Binding(
get: { String(myValue) },
set: { myValue = Int($0) ?? 0 }
))