SwiftUI DatePicker Binding optional Date, valid nil - ios

Question

I'm experimenting code from https://alanquatermain.me/programming/swiftui/2019-11-15-CoreData-and-bindings/
my goal is to have DatePicker bind to Binding< Date? > which allow for nil value instead of initiate to Date(); this is useful, if you have Date attribute in your core data model entity which accept nil as valid value.
Here is my swift playground code:
extension Binding {
init<T>(isNotNil source: Binding<T?>, defaultValue: T) where Value == Bool {
self.init(get: { source.wrappedValue != nil },
set: { source.wrappedValue = $0 ? defaultValue : nil})
}
}
struct LiveView: View {
#State private var testDate: Date? = nil
var body: some View {
VStack {
Text("abc")
Toggle("Has Due Date",
isOn: Binding(isNotNil: $testDate, defaultValue: Date()))
if testDate != nil {
DatePicker(
"Due Date",
selection: Binding($testDate)!,
displayedComponents: .date
)
}
}
}
}
let liveView = LiveView()
PlaygroundPage.current.liveView = UIHostingController(rootView: liveView)
I can't find solution to fix this code. It works when the toggle first toggled to on, but crash when the toggle turned back off.
The code seems to behave properly when I removed the DatePicker, and change the code to following:
extension Binding {
init<T>(isNotNil source: Binding<T?>, defaultValue: T) where Value == Bool {
self.init(get: { source.wrappedValue != nil },
set: { source.wrappedValue = $0 ? defaultValue : nil})
}
}
struct LiveView: View {
#State private var testDate: Date? = nil
var body: some View {
VStack {
Text("abc")
Toggle("Has Due Date",
isOn: Binding(isNotNil: $testDate, defaultValue: Date()))
if testDate != nil {
Text("\(testDate!)")
}
}
}
}
let liveView = LiveView()
PlaygroundPage.current.liveView = UIHostingController(rootView: liveView)
I suspect it's something to do with this part of the code
DatePicker("Due Date", selection: Binding($testDate)!, displayedComponents: .date )
or
problem when the source.wrappedValue set back to nil (refer to Binding extension)

Answer 1

The problem is that DatePicker grabs binding and is not so fast to release it even when you remove it from view, due to Toggle action, so it crashes on force unwrap optional, which becomes nil ...
The solution for this crash is
DatePicker(
"Due Date",
selection: Binding<Date>(get: {self.testDate ?? Date()}, set: {self.testDate = $0}),
displayedComponents: .date
)

Answer 2

An alternative solution that I use in all my SwiftUI pickers...
I learned almost all I know about SwiftUI Bindings (with Core Data) by reading that blog by Jim Dovey. The remainder is a combination of some research and quite a few hours of making mistakes.
So when I use Jim's technique to create Extensions on SwiftUI Binding then we end up with something like this for a deselection to nil...
public extension Binding where Value: Equatable {
init(_ source: Binding<Value>, deselectTo value: Value) {
self.init(get: { source.wrappedValue },
set: { source.wrappedValue = $0 == source.wrappedValue ? value : $0 }
)
}
}
Which can then be used throughout your code like this...
Picker("Due Date",
selection: Binding($testDate, deselectTo: nil),
displayedComponents: .date
)
OR when using .pickerStyle(.segmented)
Picker("Date Format Options", // for example
selection: Binding($selection, deselectTo: -1)) { ... }
.pickerStyle(.segmented)
... which sets the index of the segmented style picker to -1 as per the documentation for UISegmentedControl and selectedSegmentIndex.
The default value is noSegment (no segment selected) until the user
touches a segment. Set this property to -1 to turn off the current
selection.

Answer 3

Here is my solution, I added a button to remove the date and add a default date. All it's wrapped in a new component
https://gist.github.com/Fiser12/62ef54ba0048e5b62cf2f2a61f279492
import SwiftUI
struct NullableBindedValue<T>: View {
var value: Binding<T?>
var defaultView: (Binding<T>, #escaping (T?) -> Void) -> AnyView
var nullView: ( #escaping (T?) -> Void) -> AnyView
init(
_ value: Binding<T?>,
defaultView: #escaping (Binding<T>, #escaping (T?) -> Void) -> AnyView,
nullView: #escaping ( #escaping (T?) -> Void) -> AnyView
) {
self.value = value
self.defaultView = defaultView
self.nullView = nullView
}
func setValue(newValue: T?) {
self.value.wrappedValue = newValue
}
var body: some View {
HStack(spacing: 0) {
if value.unwrap() != nil {
defaultView(value.unwrap()!, setValue)
} else {
nullView(setValue)
}
}
}
}
struct DatePickerNullable: View {
var title: String
var selected: Binding<Date?>
#State var defaultToday: Bool = false
var body: some View {
NullableBindedValue(
selected,
defaultView: { date, setDate in
let setDateNil = {
setDate(nil)
self.defaultToday = false
}
return AnyView(
HStack {
DatePicker(
"",
selection: date,
displayedComponents: [.date, .hourAndMinute]
).font(.title2)
Button(action: setDateNil) {
Image(systemName: "xmark.circle")
.foregroundColor(Color.defaultColor)
.font(.title2)
}
.buttonStyle(PlainButtonStyle())
.background(Color.clear)
.cornerRadius(10)
}
)
},
nullView: { setDate in
let setDateNow = {
setDate(Date())
}
return AnyView(
HStack {
TextField(
title,
text: .constant("Is empty")
).font(.title2).disabled(true).textFieldStyle(RoundedBorderTextFieldStyle())
Button(action: setDateNow) {
Image(systemName: "plus.circle")
.foregroundColor(Color.defaultColor)
.font(.title2)
}
.buttonStyle(PlainButtonStyle())
.background(Color.clear)
.cornerRadius(10)
}.onAppear(perform: {
if self.defaultToday {
setDateNow()
}
})
)
}
)
}
}

Answer 4

Most optional binding problems can be solved with this:
public func ??<T>(lhs: Binding<Optional<T>>, rhs: T) -> Binding<T> {
Binding(
get: { lhs.wrappedValue ?? rhs },
set: { lhs.wrappedValue = $0 }
)
}
Here's how I use it with DatePicker:
DatePicker(
"",
selection: $testDate ?? Date(),
displayedComponents: [.date]
)