Swift - Updating Binding<String> stored value programmatically from View extension

Question

So my goal is to have a more convenient method for adding a placeholder text value on SwiftUI's TextEditor, since there doesn't appear to be one. The approach I'm trying has uncovered something I really don't understand around Binding<> wrapped types. (Maybe this is a red flag that I'm doing something not recommended?)

Anyway, on to my question: are we able to programmatically update the underlying values on Bindings? If I accept some Binding<String> value, can I update it from within my method here? If so, will the updated value be referenced by the @State originator? The below example places my placeholder value in as text where I'm trying to type when you click into it, and does not even attempt it again if I clear it out.

Imported this code from other posts I found some time ago to make it display a placeholder if the body is empty.

import Foundation
import SwiftUI

struct TextEditorViewThing: View {
  @State private var noteText = ""
  var body: some View {
    VStack{
      TextEditor(text: $noteText)
        .textPlaceholder(placeholder: "PLACEHOLDER", text: $noteText)
        .padding()
    }
  }
}

extension TextEditor {
  @ViewBuilder func textPlaceholder(placeholder: String, text: Binding<String>) -> some View {
    self.onAppear {
      // remove the placeholder text when keyboard appears
      NotificationCenter.default.addObserver(forName: UIResponder.keyboardWillShowNotification, object: nil, queue: .main) { (noti) in
        withAnimation {
          if text.wrappedValue == placeholder {
            text.wrappedValue = placeholder
          }
        }
      }
      
      // put back the placeholder text if the user dismisses the keyboard without adding any text
      NotificationCenter.default.addObserver(forName: UIResponder.keyboardWillHideNotification, object: nil, queue: .main) { (noti) in
        withAnimation {
          if text.wrappedValue == "" {
            text.wrappedValue = placeholder
          }
        }
      }
    }
  }
}

RTXGamer · Accepted Answer · 2021-07-06 19:57:33Z

1

Customize this setup as per your requirement:

struct ContentView: View {
    @State private var text: String = ""
    
    var body: some View {
        VStack {
            ZStack(alignment: .leading) {
                if self.text.isEmpty {
                    VStack {
                        Text("Placeholder Text")
                            .multilineTextAlignment(.leading)
                            .padding(.leading, 25)
                            .padding(.top, 8)
                            .opacity(0.5)
                        Spacer()
                    }
                }
                TextEditor(text: $text)
                    .padding(.leading, 20)
                    .opacity(self.text.isEmpty ? 0.5 : 1)
            }
            .frame(width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height/2)
            .overlay(
                Rectangle().stroke()
                    .foregroundColor(Color.black)
                    .padding(.horizontal, 15)
            )
        }
    }
}

answered Jul 6, 2021 at 19:57

RTXGamer

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1 Comment

Grant Lindsey Over a year ago

Good enough answer for me! Thanks!

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