Is there a way to call a function when a SwiftUI Picker selection changes? - swift

Question

I would like to call a function when selectedOption's value changes. Is there a way to do this in SwiftUI similar to when editing a TextField?
Specifically, I would like to save the selected option when the user changes the selectedOption.
Here is my picker:
struct BuilderPicker: View {
let name: String
let options: Array<String>
#State var selectedOption = 0
var body: some View {
HStack {
Text(name)
.font(.body)
.padding(.leading, 10)
Picker(selection: $selectedOption, label: Text(name)) {
ForEach(0 ..< options.count) {
Text(self.options[$0]).tag($0)
}
}.pickerStyle(SegmentedPickerStyle())
.padding(.trailing, 25)
}.onTapGesture {
self.selectedOption = self.selectedOption == 0 ? 1 : 0
}
.padding(.init(top: 10, leading: 10, bottom: 10, trailing: 0))
.border(Color.secondary, width: 3)
.padding(.init(top: 0, leading: 15, bottom: 0, trailing: 15))
.font(.body)
}
}
I’m still new to SwiftUI and would love some help. Thanks!

Answer 1

If the #State value will be used in a View, you don't need extra variable name
struct BuilderPicker: View {
// let name: String = ""
let options: Array<String> = ["1", "2","3","4","5"]
#State var selectedOption = 0
var body: some View {
HStack {
Text(options[selectedOption])
.font(.body)
.padding(.leading, 10)
Picker(selection: $selectedOption, label: Text(options[selectedOption])) {
ForEach(0 ..< options.count) {
Text(self.options[$0]).tag($0)
}
}.pickerStyle(SegmentedPickerStyle())
.padding(.trailing, 25)}
// }.onTapGesture {
// self.selectedOption = self.selectedOption == 0 ? 1 : 0
// }
.padding(.init(top: 10, leading: 10, bottom: 10, trailing: 0))
.border(Color.secondary, width: 3)
.padding(.init(top: 0, leading: 15, bottom: 0, trailing: 15))
.font(.body)
}
}
If you need separated operation on the #State, the simplest way is adding one line : onReceive() to the view.
HStack {
Text("")
.font(.body)
.padding(.leading, 10)
Picker(selection: $selectedOption, label: Text("")) {
ForEach(0 ..< options.count) {
Text(self.options[$0]).tag($0)
}
}.pickerStyle(SegmentedPickerStyle())
.padding(.trailing, 25)}
// }.onTapGesture {
// self.selectedOption = self.selectedOption == 0 ? 1 : 0
// }
.padding(.init(top: 10, leading: 10, bottom: 10, trailing: 0))
.border(Color.secondary, width: 3)
.padding(.init(top: 0, leading: 15, bottom: 0, trailing: 15))
.font(.body)
.onReceive([self.selectedOption].publisher.first()) { (value) in
print(value)
}

Answer 2

The previous solution will end up in an infinite loop if you update an ObservedObject in the callback since .onReceive is also called when the View got rendered.
→ A better approach is to use a .onChange method on the Binding itself:
Picker(selection: $selectedOption.onChange(doSomething), label: Text("Hello world")) {
// ...
}
To do so you need to write an extension for Binding like described here.