SwiftUI - How can I call a Function in my View? - ios

Question

I am using SwiftUI/Swift for a week now, and I love it. Now I have a problem. I want to call a Function from my View, but I get this Error
Type '()' cannot conform to 'View'; only struct/enum/class types can conform to protocols
This is the Code:
struct testView: View {
var body: some View {
VStack {
Text("TextBox")
Text("SecondTextBox")
self.testFunction()
}
}
func testFunction() {
print("This is a Text.")
}
}
I don't get it. In other languages its much simpler and could work that way. Can anybody help me please? Swift is pretty new to me :D

Answer 1

Meanwhile here are the places (not all) where/how you can call a function
init() {
self.testFunction() // non always good, but can
}
var body: some View {
self.testFunction() // 1)
return VStack {
Text("TextBox")
.onTapGesture {
self.testFunction() // 2)
}
Text("SecondTextBox")
}
.onAppear {
self.testFunction() // 3)
}
.onDisappear {
self.testFunction() // 4)
}
}
... and so on

Answer 2

An additional method:
Testing with Swift 5.8, you can also stick in a let _ = self.testFunction().
eg
(this is extra-contrived so that it's possible to see the effect in Preview, because print() doesn't happen in Preview, at least for me)
import SwiftUI
class MyClass {
var counter = 0
}
struct ContentView: View {
var myClass: MyClass
var body: some View {
VStack {
Text("TextBox counter = \(myClass.counter)")
// v--------------------------------------------
//
let _ = self.testFunction() // compiles happily
// self.testFunction() // does not compile
//
// ^--------------------------------------------
Text("TextBox counter = \(myClass.counter)")
}
}
func testFunction() {
print("This is a Test.")
myClass.counter += 1
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView(myClass: MyClass())
}
}

Answer 3

Using Swift 5.3 and Xcode 12.4
I use a little extension to debug inside the Views (VStack in the example), e.g. to inspect a geometryReader.size. It could be used to call any function in the View as follows:
NOTE: For debugging purposes only. I don't recommend including code like this in any production code
VStack {
Text.console("Hello, World")
Text("TEXT"
}
extension Text {
static func console<T>(_ value: T) -> EmptyView {
print("\(value)")
return EmptyView()
}
}
This will print "Hello, World" to the console.....

Answer 4

There is a reason, when writing in swift UI (iOS Apps), that there is a View protocol that needs to be followed. Calling functions from inside the structure is not compliant with the protocol.
The best thing you can do is the .on(insertTimeORAction here).
Read more about it here