Xcode - Picker on select

RussellHarrower
April 30, 2021
200 views
2 votes
3 Answers

I am trying to run a function after a user has selected a picker option.

The idea is that the user can set a default station, so I need to be able to send the selected value to a function so I can save it inside the core data module. How can I achieve this?

import SwiftUI

struct SettingsView: View {
    var frameworks = ["DRN1", "DRN1 Hits", "DRN1 United", "DRN1 Life"]
    @State private var selectedFrameworkIndex = 0
    
    func doSomethingWith(value: String) {
        print(value)
    }
    
    var body: some View {
        NavigationView {
            Form {
                Section {
                    Picker(selection: $selectedFrameworkIndex, label: Text("Favorite Station")) {
                        ForEach(0 ..< frameworks.count) {
                            Text(self.frameworks[$0])
                        }
                    }.onReceive([self.frameworks].publisher.first()) { value in
                        self.doSomethingWith(value: value)
                    }
                }
            }
            .navigationBarTitle("Settings")
        }
    }
}

Answers

- a1cd
- April 30, 2021 at 4:15 am
- 0 votes
0
Instead of using onRecive try using onChange.

Your code:
```
.onReceive([self.frameworks].publisher.first()) { value in
    self.doSomethingWith(value: value)
}
```
Correction:
```
.onChange(of: $selectedFrameworkIndex, perform: { value in
        self.doSomethingWith(value: value)
    })
```
this will trigger every time $selectedFrameworkIndex is changed.
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I would use a simple .onChange(of:) call on the picker. It will pick up on the change of the @State var and allow you to act on it. Use it like this:

import SwiftUI

struct SettingsView: View {
   var frameworks = ["DRN1", "DRN1 Hits", "DRN1 United", "DRN1 Life"]
   @State private var selectedFrameworkIndex = 0

    
    func doSomethingWith(value: String) {
            print(value)
      }
    
   var body: some View {
    NavigationView {
            Form {
                Section {
                    Picker(selection: $selectedFrameworkIndex, label: Text("Favorite Station")) {
                        ForEach(0 ..< frameworks.count) {
                            Text(self.frameworks[$0])
                        }
                    }
                     // Put your function call in here:
                     .onChange(of: selectedFrameworkIndex) { value in
                        print(value)
                    }

                    }
                }
            }
            .navigationBarTitle("Settings")
        }
   }


}

yours:

import SwiftUI

struct SettingsView: View {
   var frameworks = ["DRN1", "DRN1 Hits", "DRN1 United", "DRN1 Life"]
   @State private var selectedFrameworkIndex = 0
   
   func doSomethingWith(value: String) {
       print(value)
   }
    
   var body: some View {
    NavigationView {
            Form {
                Section {
                    Picker(selection: $selectedFrameworkIndex, label: Text("Favorite Station")) {
                        ForEach(0 ..< frameworks.count) {
                            Text(self.frameworks[$0])
                        }
                    }.onReceive([self.frameworks].publisher.first()) { value in
                        self.doSomethingWith(value: value)
                    }
                }
            }
            .navigationBarTitle("Settings")
        }
   }


}

add a variable that checks to see if selectedFrameworkIndex has changed.
change:

import SwiftUI

struct SettingsView: View {
    var frameworks = ["DRN1", "DRN1 Hits", "DRN1 United", "DRN1 Life"]
    @State private var selectedFrameworkIndex = 0
    @State private var savedFrameworkIndex = 0
    
   func handler<Value: Any>(val: Value) -> Value {
       if selectedFrameworkIndex != savedFrameworkIndex {
           self.doSomethingWith(value: self.frameworks[selectedFrameworkIndex])
       }
       return val
   }

    func doSomethingWith(value: String) {
        print(value)
    }
    var body: some View {
        NavigationView {
            Form {
                Section {
                    Picker(selection: handler(val: $selectedFrameworkIndex), label: Text("Favorite Station")) {
                        ForEach(0 ..< frameworks.count) {
                            Text(self.frameworks[$0])
                        }
                    }
                }
            }
            .navigationBarTitle("Settings")
        }
    }
}

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Xcode – Picker on select

Answers