How do I make a image/icon’s opacity change on a tap gesture in SwiftUI

Question

I have a heart image/system image that I want to appear by changing the opacity when you tap it two times, but I cannot figure out how to.

import SwiftUI
import PlaygroundSupport

struct ContentView: View{
    
    var body: some View{
        Image("apple")
            .resizable()
            .scaledToFill()
            .clipShape(Circle())
            .frame(width:200,height:200)
            .overlay(
                Image(systemName: "heart.fill")
                    .font(.system(size:50))
                    .foregroundColor(.red)
                    .opacity(0)
                    .onTapGesture(count:2){
                        
                    }
                
            )
    }
}

I expected by tapping on the image two times:

   Image(systemName: "heart.fill")
                    .font(.system(size:50))
                    .foregroundColor(.red)
                    .opacity(0)
                    .onTapGesture(count:2){
                        opacity(2)
                    }

it will show the heart, by I cannot change anything

Answer 1

In SwiftUI you generally change the state of a variable opacity in this example, to change the view. Try this example code to change the opacity (which is 0...1) of the heart when you double tap on it.

struct ContentView: View {
    @State var opacity = 1.0  // <-- here
    
    var body: some View{
        Image(systemName: "house") // <-- for testing
            .resizable()
            .scaledToFill()
            .clipShape(Circle())
            .frame(width:200,height:200)
            .overlay(
                Image(systemName: "heart.fill")
                    .font(.system(size:50))
                    .foregroundColor(.red)
                    .opacity(opacity)  // <-- here
                    .onTapGesture(count: 2) {
                        opacity = 0.2  // <-- here
                    }
            )
    }
}

EDIT-1:

If you want to show the heart when you double tap on the main image, then put the onTapGesture on that image, as shown in the example code. In this example if you double tap on the house again the heart disappears.

struct ContentView: View {
    @State var showHeart = false  // <--- here
    
    var body: some View{
        Image(systemName: "house") // <-- for testing
            .resizable()
            .scaledToFill()
            .clipShape(Circle())
            .frame(width:200,height:200)
            .onTapGesture(count: 2) {
                showHeart.toggle()  // <--- here
            }
            .overlay(
                Image(systemName: "heart.fill")
                    .font(.system(size:50))
                    .foregroundColor(.red)
                    .opacity(showHeart ? 1.0 : 0.0)  // <--- here
            )
    }
}

Answer 2

Opacity's value range is 0.0(invisible) to 1.0(fully opaque). A @State property can be used to record the current state of opacity and the double-tap can be used to toggle between two opacity values. The onTapGesture was placed on the apple image as the tap gesture won't respond when placed on the heart if the heart isn't visible.:

struct ContentView: View{
    
    @State private var isHidden = true
    
    var body: some View{
        Image("apple")
            .resizable()
            .scaledToFill()
            .clipShape(Circle())
            .frame(width:200,height:200)
            .overlay(
                Image(systemName: "heart.fill")
                    .font(.system(size:50))
                    .foregroundColor(.red)
                    .opacity(isHidden ? 0.0 : 1.0)
            )
            .onTapGesture(count:2){
                isHidden.toggle()
            }
    }
}

Edit: meant to move the tapGesture not copy it.