I don't know what to put in the view placeholder - swift

Question

I keep getting an error to insert "proxy: /GeometryProxy/" even when "proxy" is a state variable. I have the code for the preview below. I don't know what to put in the placeholder and I am confused. I have included my full code to review. Please look below.
struct MathematicallyMainController_Previews: PreviewProvider {
static var previews: some View {
MathematicallyMainController(proxy: // what do i put here?)
}
}
My full code:
This is where the problem with the 'var' is happening.
struct MathematicallyMainController: View {
#StateObject var tabBarModel = TabBarViewModel()
#Environment(\.colorScheme) var colorScheme
#State var selectedIndex = 0
#State var isSelectedA = false
#State var isSelectedB = false
#State var isSelectedC = false
#State var isSelectedD = false
#State var isSelectedE = false
#State var proxy: GeometryProxy
var body: some View {
ZStack {
let bottomEdge = proxy.safeAreaInsets.bottom
switch selectedIndex {
case 0:
HomeViewController()
case 1:
BrowseView()
case 2:
RewardsView()
case 3:
EssentialsView()
case 4:
SchoolModeView()
default:
HomeViewController()
}
ZStack {
RoundedRectangle(cornerRadius: 15)
.fill(.regularMaterial)
.colorScheme(colorScheme == .dark ? .dark : .light)
HStack(alignment: .center) {
Button {
selectedIndex = 0
} label: {
if selectedIndex == 0 {
ZStack {
Circle()
.blur(radius: 20)
.foregroundColor(.blue)
.frame(width: 60)
.padding([.leading, .trailing], 5)
Image(systemName: "house.fill")
.font(.title)
.foregroundColor(colorScheme == .dark ? .black : .white)
.padding([.leading, .trailing], 5)
}
} else {
Image(systemName: "house.fill")
.font(.title)
.foregroundColor(colorScheme == .dark ? .white : .black)
}
}
Button {
selectedIndex = 1
} label: {
if selectedIndex == 1 {
ZStack {
Circle()
.blur(radius: 20)
.foregroundColor(.indigo)
.frame(width: 60)
.padding(.leading, 15)
Image(systemName: "rectangle.stack.fill")
.font(.title)
.foregroundColor(colorScheme == .dark ? .black : .white)
.padding(.leading, 15)
}
} else {
Image(systemName: "rectangle.stack.fill")
.font(.title)
.foregroundColor(colorScheme == .dark ? .white : .black)
.padding(.leading, 15)
}
}
Button {
selectedIndex = 2
} label: {
if selectedIndex == 2 {
ZStack {
Circle()
.blur(radius: 20)
.foregroundColor(.orange)
.frame(width: 60)
.padding([.trailing, .leading], 15)
Image(systemName: "circle.dotted")
.font(.title)
.foregroundColor(colorScheme == .dark ? .black : .white)
.padding([.trailing, .leading], 15)
}
} else {
Image(systemName: "circle.dotted")
.font(.title)
.foregroundColor(colorScheme == .dark ? .white : .black)
.padding(.trailing, 15)
.padding(.leading, 15)
}
}
Button {
selectedIndex = 3
} label: {
if selectedIndex == 3 {
ZStack {
Circle()
.blur(radius: 20)
.foregroundColor(.green)
.frame(width: 60)
.padding(.trailing, 15)
Image(systemName: "doc.text.image")
.font(.title)
.foregroundColor(colorScheme == .dark ? .black : .white)
.padding(.trailing, 15)
}
} else {
Image(systemName: "doc.text.image")
.font(.title)
.foregroundColor(colorScheme == .dark ? .white : .black)
.padding(.trailing, 15)
}
}
Button {
selectedIndex = 4
} label: {
if selectedIndex == 4 {
ZStack {
Circle()
.blur(radius: 20)
.foregroundColor(.purple)
.frame(width: 60)
.padding([.leading, .trailing], 5)
Image(systemName: "graduationcap.fill")
.font(.title)
.foregroundColor(colorScheme == .dark ? .black : .white)
.padding([.leading, .trailing], 5)
}
} else {
Image(systemName: "graduationcap.fill")
.font(.title)
.foregroundColor(colorScheme == .dark ? .white : .black)
}
}
}
.colorScheme(colorScheme == .dark ? .dark : .light)
.padding(.horizontal)
}
.frame(height: 60)
.shadow(color: .primary, radius: -10)
.shadow(color: .black, radius: 10)
.padding([.horizontal])
.padding(.bottom)
.frame(maxHeight: .infinity, alignment: .bottom)
.modifier(OffsetModifier())
.environmentObject(tabBarModel)
.offset(y: tabBarModel.tabState == .floating ? 0 : bottomEdge)
}
}
}
This is my ViewModifier I have included to create the scrolling animation.
struct OffsetModifier: ViewModifier {
#EnvironmentObject var model: TabBarViewModel
func body(content: Content) -> some View {
content
.overlay(
GeometryReader { proxy -> Color in
let minY = proxy.frame(in: .global).minY
DispatchQueue.main.async {
let durationOffset: CGFloat = 35
if minY < model.offset {
if model.offset < 0 && -minY > (model.lastStoredOffset + durationOffset) {
withAnimation(.easeOut.speed(1)) {
model.tabState = .floating
}
model.lastStoredOffset = -model.offset
}
}
if minY > model.offset && -minY < (model.lastStoredOffset + durationOffset) {
withAnimation(.easeOut.speed(1)) {
model.tabState = .expanded
}
model.lastStoredOffset = -model.offset
}
model.offset = minY
}
return Color.clear
}
,alignment: .top
)
}
}

Answer 1

The only time you ever use proxy is on this line:
let bottomEdge = proxy.safeAreaInsets.bottom
Therefore, there's no reason to pass in the entire GeometryProxy -- you can just pass in the bottom inset. Also, it definitely doesn't need to be a #State variable -- #State is used when the View needs to mutate its state over time -- this is just a parameter being passed in.
Change this line:
#State var proxy: GeometryProxy
to:
var bottomInset : CGFloat = 0
Because it has a default value, your preview can turn into this:
static var previews: some View {
MathematicallyMainController()
}
If you really wanted to pass a value (say, from the parent of the View), you would do something like this:
GeometryReader { proxy in
//other view code...
MathematicallyMainController(bottomInset: proxy.safeAreaInsets.bottom)
//other code...
}
There's also the option of moving the GeometryReader inside of MathematicallyMainController, but I'm assuming there's a reason you had it outside to begin with.
All of that being said, it looks like you have some unnecessary and unused code that you could clean up. For example, none of the isSelectedA-E variables ever get used. There's probably more here that can be refactored, but is outside of the scope of the present question.