SwiftUI：从 ViewModel 更改视图 @State 属性

Question

I have date picker in my view like this:

struct BookTimeView: View {
    @ObservedObject var viewModel: BookTimeViewModel

    @State var startTime = Date.now
    
 
     var body: some View {
         DatePicker(“pick time”, selection: $startTime, displayedComponents: .hourAndMinute)
     }
}

initial startTime depends on data from backend.

So in view model I have API call that loads data from backend.

In success callback I want to change startTime.

Question: How can I change startTime from my ViewModel?

PS: Is that possible to bind DatePicker with ViewModel directly?

I tried to put @State var startTime = Date.now in view model. But it doesn't work, and I see warning in Xcode:

Accessing State's value outside of being installed on a View. This will result in a constant Binding of the initial value and will not update.

Answer 1

You can directly bind to the @Published property with just:

$viewModel.startTime

Which will be of type Binding<Date> , even though we declare it as just a @Published property on BookTimeViewModel .

Example code:

class BookTimeViewModel: ObservableObject {
    @Published var startTime: Date = .now
}

struct BookTimeView: View {
    @ObservedObject var viewModel: BookTimeViewModel

    var body: some View {
        DatePicker("pick time", selection: $viewModel.startTime, displayedComponents: .hourAndMinute)
    }
}

Similar to my answer here .