Swift: Networking: Simple Request with Query

by Annett Schwarze | 2025-08-01

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Performing network communication in Swift is enabled using URLSession. A very simple request can be implemented with the asynchronous method `data(from: URL)` using just a couple of code lines.

Parameters for the request can be sent with query parameters. Use `URLComponents` and `URLQueryItem` for that. These types handle conversion of special characters and save you from implementing complicated checks of edge cases.

For easy testing the Python package FastAPI provides a very simple and quick means. That way handling network requests can be tested in the simulator while the server can be started on the developer computer.

Preparing a FastAPI Server

To handle query parameters one can declare function arguments. They are automatically treated as query parameters by FastAPI. For this test the function just returns an upper-cased string of the argument.

        
@app.get("/text/upcase")
def read_text_upcase(string: str):
    return {"result": string.upper()}
    

Performing the Network Request in Swift

To add the query parameter to the URL, use `URLComponents` and `URLQueryItem` like shown below. It is strongly recommended to not add the query parameters using direct string manipulation of the URL.

        
import SwiftUI

struct SimpleRequestWithQueryView: View {
    @State private var text: String = "a text"
    @State private var response: String = "-"
    @State private var errorInfo: String = "-"

    var body: some View {
        VStack {
            Text("Simple Request with Query")
                .font(.largeTitle)

            Form {
                TextField("Enter text", text: $text)
                Button(action: {
                    sendRequest()
                }, label: {
                    Label("Send", systemImage: "paperplane")
                })
                LabeledContent("Response", value: response)
                LabeledContent("Error Info", value: errorInfo)
            }
        }
    }

    private func sendRequest() {
        Task {
            do {
                guard let url = URL(string: "http://localhost:8000/text/upcase") else { return }
                guard var comps = URLComponents(url: url, resolvingAgainstBaseURL: false) else { return }
                let qi = URLQueryItem(name: "string", value: text)
                comps.queryItems = [qi]
                guard let urlq = comps.url else { return }
                let (data, resp) = try await URLSession.shared.data(from: urlq)
                if let httpResp = resp as? HTTPURLResponse {
                    if httpResp.statusCode != 200 {
                        self.errorInfo = "Error: Expected 200"
                        return
                    }
                }
                guard let string = String(data: data, encoding: .utf8) else { return }
                self.response = string
                self.errorInfo = "-"
            } catch {
                self.response = "-"
                self.errorInfo = "\(error.localizedDescription)"
            }
        }
    }
}

#Preview {
    SimpleRequestWithQueryView()
}