I have the following ViewModifier and it does not work:
import SwiftUI
struct NavLink: ViewModifier {
let title: String
func body(content: Content) -> some View {
NavigationLink(destination: content) {
Text(title)
}
}
}
extension View {
func navLink(title: String) -> some View {
modifier(NavLink(title: title))
}
}
If I use that as follows:
import SwiftUI
struct MainScreen: View {
var body: some View {
NavigationStack() {
VStack {
// This does not work
NavStackScreen()
.navLink(title: "Nav Stack")
// But this does
Helper.linked(to: NavStackScreen(), title: "Nav Stack 2")
}
}
}
}
struct Helper {
static func linked(to destination: some View, title: String) -> some View {
NavigationLink(destination: destination) {
Text(title)
}
}
}
It creates the link and pushes a new view onto the screen if tapped; however, the contents of the NavStackScreen are not displayed, only an empty screen.
Any ideas about what is going on?
Contents of NavStackScreen for reference:
struct NavStackScreen: View {
var body: some View {
Text("Nav Stack Screen")
.font(.title)
.navigationTitle("Navigation Stack")
}
}
If I use a static helper function within a helper struct, then it works correctly:
static func linked(to destination: some View, title: String) -> some View {
NavigationLink(destination: destination) {
Text(title)
}
}
I added the full code of the MainView for reference and updated the example with more detail for easy reproduction.
The modifier doesn't work because the content argument is not the actual view being modified, but instead is a proxy:
content is a proxy for the view that will have the modifier represented by Self applied to it.
Reference.
This is what a quick debugging over the modifier shows:
(lldb) po content
SwiftUI._ViewModifier_Content<SwiftUIApp.NavLink>()
As the proxy is an internal type of SwiftUI, we can't know for sure why NavigationLink doesn't work with it.
A workaround would be to skip the modifier, and only add the extension over View:
extension View {
func navLink(title: String) -> some View {
NavigationLink(destination: content) {
Text(title)
}
}
}
The code below works:
struct ContentView: View {
var body: some View {
Text("Hello, world!")
.customViewModifier(modifier: { view in CustomModifier(content: { view } )} )
}
}
struct CustomModifier<Content: View>: View {
let content: () -> Content
var body: some View {
content()
.foregroundColor(.red)
}
}
extension View {
func customViewModifier<ContentModifier: View>(modifier: (Self) -> ContentModifier) -> some View {
return modifier(self)
}
}
My goal is to be able the code below. Currently, Xcode does not help me to fix the error.
struct ContentView: View {
var body: some View {
Text("Hello, world!")
.customViewModifier(modifier: CustomModifier)
}
}
Is there a way around to make my goal possible?
here was my try to solve the issue:
extension View {
func customViewModifier2<ContentModifier: View>(modifier: (Self) -> ((Self) -> ContentModifier)) -> some View {
return modifier(self)
}
}
Error:
Type '(Self) -> ContentModifier' cannot conform to 'View'
The final real goal is not clear ('cause it is really better to use ViewModifier based approach), but if you want to use a type as argument it can be like the following
*compiled with Xcode 13.2 / iOS 15.2
struct ContentView: View {
var body: some View {
Text("Hello, world!")
.customViewModifier(modifier: CustomModifier.self) // << type !!
}
}
extension View {
func customViewModifier(modifier: CustomModifier<Self>.Type) -> some View {
return modifier.init(content: { self })
}
}
I have a very simple CustomView which it takes a View and modify it! Like this code:
struct CustomView<ViewType: View>: View {
let content: () -> ViewType
var body: some View {
return content()
.foregroundColor(.red)
}
}
So far so good!
Now I want make a CustomModifier out of it, like this:
extension View {
func customModifier<ViewModifierType: View>(viewModifier: () -> ViewModifierType) -> some View {
// how can I import self from here?
return viewModifier()
}
}
use case:
struct ContentView: View {
var body: some View {
Text("Hello, World!")
.customModifier(viewModifier: { CustomView(content: { Text("Hello, World!") } ) }) // <<: Here is the issue!
// How can I satisfy CustomView with self in extension? that could help to cut Text("Hello, World!") to feeding as content for CustomView?
}
}
So if see the codes, all I am trying to do is cut off Text("Hello, World!") with using self from extension and trying to have this form of coding:
.customModifier(viewModifier: { CustomView() })
PS: I know that for having form of CustomView() I have to respect the generic parameter CustomView with word of where but I do not know how can I put these all puzzle together!
If I understand you correctly, then try this
extension View {
func customModifier<ViewModifierType: View>(viewModifier: (Self) -> ViewModifierType) -> some View {
return viewModifier(self)
}
}
Not sure what is your goal but if you just want to add a red foreground to a view you need to implement a view modifier:
struct RedForeground: ViewModifier {
func body(content: Content) -> some View {
content.foregroundColor(.red)
}
}
And then just call it using the modifier method:
Text("Text")
.modifier(RedForeground())
If you want to simplify it further you can extend View and add make it a computed property:
extension View {
var redForeground: some View { modifier(RedForeground()) }
}
usage:
Text("Text")
.redForeground
You can't just init CustomView without a view, but you can pass CustomView initializer as function to customModifier, like this:
struct ContentView: View {
var body: some View {
Text("Hello, World!")
.customModifier(viewModifier: CustomView.init)
}
}
struct CustomView<ViewType: View>: View {
let content: ViewType
var body: some View {
return content
.foregroundColor(.red)
}
}
extension View {
func customModifier<ViewModifierType: View>(viewModifier: (Self) -> ViewModifierType) -> some View {
return viewModifier(self)
}
}
I want to make a generic SwiftUI View that I can plug in and out of my controls. More than just passing it data though, I want to be able to pass in subviews like you would to a List like so:
List{
Text("This works")
Text("Hello World")
Text("This works")
}
MyClass {
Text("This works")
Text("Hello World")
Text("This works")
}
Is this possible? And if so, how would I go about declaring this class?
You can use the #ViewBuilder property wrapper:
struct CustomView<Content: View>: View {
var content: () -> Content
init(#ViewBuilder _ content: #escaping () -> Content) {
self.content = content
}
var body: some View {
VStack {
content()
}
}
}
struct ContentView: View {
var body: some View {
CustomView {
Text("hello")
Text("world")
}
}
}
I'm implementing a very custom NavigationLink called MenuItem and would like to reuse it across the project. It's a struct that conforms to View and implements var body : some View which contains a NavigationLink.
I need to somehow store the view that shall be presented by NavigationLink in the body of MenuItem but have yet failed to do so.
I have defined destinationView in MenuItem's body as some View and tried two initializers:
This seemed too easy:
struct MenuItem: View {
private var destinationView: some View
init(destinationView: View) {
self.destinationView = destinationView
}
var body : some View {
// Here I'm passing destinationView to NavigationLink...
}
}
--> Error: Protocol 'View' can only be used as a generic constraint because it has Self or associated type requirements.
2nd try:
struct MenuItem: View {
private var destinationView: some View
init<V>(destinationView: V) where V: View {
self.destinationView = destinationView
}
var body : some View {
// Here I'm passing destinationView to NavigationLink...
}
}
--> Error: Cannot assign value of type 'V' to type 'some View'.
Final try:
struct MenuItem: View {
private var destinationView: some View
init<V>(destinationView: V) where V: View {
self.destinationView = destinationView as View
}
var body : some View {
// Here I'm passing destinationView to NavigationLink...
}
}
--> Error: Cannot assign value of type 'View' to type 'some View'.
I hope someone can help me. There must be a way if NavigationLink can accept some View as an argument.
Thanks ;D
To sum up everything I read here and the solution which worked for me:
struct ContainerView<Content: View>: View {
#ViewBuilder var content: Content
var body: some View {
content
}
}
This not only allows you to put simple Views inside, but also, thanks to #ViewBuilder, use if-else and switch-case blocks:
struct SimpleView: View {
var body: some View {
ContainerView {
Text("SimpleView Text")
}
}
}
struct IfElseView: View {
var flag = true
var body: some View {
ContainerView {
if flag {
Text("True text")
} else {
Text("False text")
}
}
}
}
struct SwitchCaseView: View {
var condition = 1
var body: some View {
ContainerView {
switch condition {
case 1:
Text("One")
case 2:
Text("Two")
default:
Text("Default")
}
}
}
}
Bonus:
If you want a greedy container, which will claim all the possible space (in contrary to the container above which claims only the space needed for its subviews) here it is:
struct GreedyContainerView<Content: View>: View {
#ViewBuilder let content: Content
var body: some View {
content
.frame(maxWidth: .infinity, maxHeight: .infinity)
}
}
If you need an initializer in your view then you can use #ViewBuilder for the parameter too. Even for multiple parameters if you will:
init(#ViewBuilder content: () -> Content) {…}
The way Apple does it is using function builders. There is a predefined one called ViewBuilder. Make it the last argument, or only argument, of your init method for MenuItem, like so:
..., #ViewBuilder builder: #escaping () -> Content)
Assign it to a property defined something like this:
let viewBuilder: () -> Content
Then, where you want to diplay your passed-in views, just call the function like this:
HStack {
viewBuilder()
}
You will be able to use your new view like this:
MenuItem {
Image("myImage")
Text("My Text")
}
This will let you pass up to 10 views and use if conditions etc. though if you want it to be more restrictive you will have to define your own function builder. I haven't done that so you will have to google that.
You should make the generic parameter part of MenuItem:
struct MenuItem<Content: View>: View {
private var destinationView: Content
init(destinationView: Content) {
self.destinationView = destinationView
}
var body : some View {
// ...
}
}
You can create your custom view like this:
struct ENavigationView<Content: View>: View {
let viewBuilder: () -> Content
var body: some View {
NavigationView {
VStack {
viewBuilder()
.navigationBarTitle("My App")
}
}
}
}
struct ENavigationView_Previews: PreviewProvider {
static var previews: some View {
ENavigationView {
Text("Preview")
}
}
}
Using:
struct ContentView: View {
var body: some View {
ENavigationView {
Text("My Text")
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
You can pass a NavigationLink (or any other view widget) as a variable to a subview as follows:
import SwiftUI
struct ParentView: View {
var body: some View {
NavigationView{
VStack(spacing: 8){
ChildView(destinationView: Text("View1"), title: "1st")
ChildView(destinationView: Text("View2"), title: "2nd")
ChildView(destinationView: ThirdView(), title: "3rd")
Spacer()
}
.padding(.all)
.navigationBarTitle("NavigationLinks")
}
}
}
struct ChildView<Content: View>: View {
var destinationView: Content
var title: String
init(destinationView: Content, title: String) {
self.destinationView = destinationView
self.title = title
}
var body: some View {
NavigationLink(destination: destinationView){
Text("This item opens the \(title) view").foregroundColor(Color.black)
}
}
}
struct ThirdView: View {
var body: some View {
VStack(spacing: 8){
ChildView(destinationView: Text("View1"), title: "1st")
ChildView(destinationView: Text("View2"), title: "2nd")
ChildView(destinationView: ThirdView(), title: "3rd")
Spacer()
}
.padding(.all)
.navigationBarTitle("NavigationLinks")
}
}
The accepted answer is nice and simple. The syntax got even cleaner with iOS 14 + macOS 11:
struct ContainerView<Content: View>: View {
#ViewBuilder var content: Content
var body: some View {
content
}
}
Then continue to use it like this:
ContainerView{
...
}
I really struggled to make mine work for an extension of View. Full details about how to call it are seen here.
The extension for View (using generics) - remember to import SwiftUI:
extension View {
/// Navigate to a new view.
/// - Parameters:
/// - view: View to navigate to.
/// - binding: Only navigates when this condition is `true`.
func navigate<SomeView: View>(to view: SomeView, when binding: Binding<Bool>) -> some View {
modifier(NavigateModifier(destination: view, binding: binding))
}
}
// MARK: - NavigateModifier
fileprivate struct NavigateModifier<SomeView: View>: ViewModifier {
// MARK: Private properties
fileprivate let destination: SomeView
#Binding fileprivate var binding: Bool
// MARK: - View body
fileprivate func body(content: Content) -> some View {
NavigationView {
ZStack {
content
.navigationBarTitle("")
.navigationBarHidden(true)
NavigationLink(destination: destination
.navigationBarTitle("")
.navigationBarHidden(true),
isActive: $binding) {
EmptyView()
}
}
}
}
}
Alternatively you can use a static function extension. For example, I make a titleBar extension to Text. This makes it very easy to reuse code.
In this case you can pass a #Viewbuilder wrapper with the view closure returning a custom type that conforms to view. For example:
import SwiftUI
extension Text{
static func titleBar<Content:View>(
titleString:String,
#ViewBuilder customIcon: ()-> Content
)->some View {
HStack{
customIcon()
Spacer()
Text(titleString)
.font(.title)
Spacer()
}
}
}
struct Text_Title_swift_Previews: PreviewProvider {
static var previews: some View {
Text.titleBar(titleString: "title",customIcon: {
Image(systemName: "arrowshape.turn.up.backward")
})
.previewLayout(.sizeThatFits)
}
}
If anyone is trying to pass two different views to other view, and can't do it because of this error:
Failed to produce diagnostic for expression; please submit a bug report...
Because we are using <Content: View>, the first view you passed, the view is going to store its type, and expect the second view you are passing be the same type, this way, if you want to pass a Text and an Image, you will not be able to.
The solution is simple, add another content view, and name it differently.
Example:
struct Collapsible<Title: View, Content: View>: View {
#State var title: () -> Title
#State var content: () -> Content
#State private var collapsed: Bool = true
var body: some View {
VStack {
Button(
action: { self.collapsed.toggle() },
label: {
HStack {
self.title()
Spacer()
Image(systemName: self.collapsed ? "chevron.down" : "chevron.up")
}
.padding(.bottom, 1)
.background(Color.white.opacity(0.01))
}
)
.buttonStyle(PlainButtonStyle())
VStack {
self.content()
}
.frame(minWidth: 0, maxWidth: .infinity, minHeight: 0, maxHeight: collapsed ? 0 : .none)
.clipped()
.animation(.easeOut)
.transition(.slide)
}
}
}
Calling this View:
Collapsible {
Text("Collapsible")
} content: {
ForEach(1..<5) { index in
Text("\(index) test")
}
}
Syntax for 2 Views
struct PopOver<Content, PopView> : View where Content: View, PopView: View {
var isShowing: Bool
#ViewBuilder var content: () -> Content
#ViewBuilder var popover: () -> PopView
var body: some View {
ZStack(alignment: .center) {
self
.content()
.disabled(isShowing)
.blur(radius: isShowing ? 3 : 0)
ZStack {
self.popover()
}
.frame(width: 112, height: 112)
.opacity(isShowing ? 1 : 0)
.disabled(!isShowing)
}
}
}