A SwiftUI interface for adding tags

SwiftUI Tagger.swift

//
//  TaggerView.swift
//
//  Created by Alex Hay on 21/11/2020.
//
// Simple interface for adding tags to an array in SwiftUI
// Example video: https://imgur.com/gallery/CcA1IXp
// alignmentGuide code from Asperi @ https://stackoverflow.com/a/58876712/11685049

import SwiftUI

/// The main  view to add tags to an array
struct TaggerView: View {
	
	@State var newTag = ""
	@State var tags = ["example","hello world"]
	@State var showingError = false
	@State var errorString = "x" // Can't start empty or view will pop as size changes
	
    var body: some View {
		VStack(alignment: .leading) {
			ErrorMessage(showingError: $showingError, errorString: $errorString)
			TagEntry(newTag: $newTag, tags: $tags, showingError: $showingError, errorString: $errorString)
			TagList(tags: $tags)
		}
		.padding()
		.onChange(of: showingError, perform: { value in
			if value {
				// Hide the error message after a delay
				DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
					showingError = false
				}
			}
		})
    }
}

/// A subview that displays a message when an error occurs
struct ErrorMessage: View {
	
	@Binding var showingError: Bool
	@Binding var errorString: String
	
	var body: some View {
		HStack {
			Image(systemName: "exclamationmark.triangle.fill")
				.foregroundColor(.orange)
			Text(errorString)
				.foregroundColor(.secondary)
				.padding(.leading, -6)
		}
		.font(.caption)
		.opacity(showingError ? 1 : 0)
		.animation(.easeIn(duration: 0.3))
	}
}

/// A subview that contains the text-entry field for entering new tags
struct TagEntry: View {
	
	@Binding var newTag: String
	@Binding var tags: [String]
	@Binding var showingError: Bool
	@Binding var errorString: String
	
	var body: some View {
		HStack {
			TextField("Add Tags", text: $newTag, onCommit: {
				addTag(newTag)
			})
			.textFieldStyle(RoundedBorderTextFieldStyle())
			.autocapitalization(.none)
			Spacer()
			Image(systemName: "plus.circle")
				.foregroundColor(.blue)
				.onTapGesture {
					addTag(newTag)
				}
		}
		.onChange(of: newTag, perform: { value in
			if value.contains(",") {
				// Try to add the tag if user types a comma
				newTag = value.replacingOccurrences(of: ",", with: "")
				addTag(newTag)
			}
		})
	}
	
		/// Checks if the entered text is valid as a tag. Sets the error message if it isn't
	private func tagIsValid(_ tag: String) -> Bool {
		// Invalid tags:
		// - empty strings
		// - tags already in the tag array
		let lowerTag = tag.lowercased()
		if lowerTag == "" {
			showError(.Empty)
			return false
		} else if tags.contains(lowerTag) {
			showError(.Duplicate)
			return false
		} else {
			return true
		}
	}
	
	/// If the tag is valid, it is added to an array, otherwise the error message is shown
	private func addTag(_ tag: String) {
		if tagIsValid(tag) {
			tags.append(newTag.lowercased())
			newTag = ""
		}
	}
	
	private func showError(_ code: ErrorCode) {
		errorString = code.rawValue
		showingError = true
	}
	
	enum ErrorCode: String {
		case Empty = "Tag can't be empty"
		case Duplicate = "Tag can't be a duplicate"
	}
}

/// A subview containing a list of all tags that are in the array. Tags flow onto the next line when wider than the view's width
struct TagList: View {
	
	@Binding var tags: [String]
	
	var body: some View {
		GeometryReader { geo in
			generateTags(in: geo)
			.padding(.top)
		}
	}

	/// Adds a tag view for each tag in the array. Populates from left to right and then on to new rows when too wide for the screen
	private func generateTags(in geo: GeometryProxy) -> some View {
		var width: CGFloat = 0
		var height: CGFloat = 0

		return ZStack(alignment: .topLeading) {
			ForEach(tags, id: \.self) { tag in
				Tag(tag: tag, tags: $tags)
				.alignmentGuide(.leading, computeValue: { tagSize in
					if (abs(width - tagSize.width) > geo.size.width) {
						width = 0
						height -= tagSize.height
					}
					let offset = width
					if tag == tags.last ?? "" {
						width = 0
					} else {
						width -= tagSize.width
					}
					return offset
				})
				.alignmentGuide(.top, computeValue: { tagSize in
					let offset = height
					if tag == tags.last ?? "" {
						height = 0
					}
					return offset
				})
			}
		}
	}
}

/// A subview of a tag shown in a list. When tapped the tag will be removed from the array
struct Tag: View {
	
	var tag: String
	@Binding var tags: [String]
	
	var body: some View {
		HStack {
			Text(tag.lowercased())
				.padding(.leading, 2)
			Image(systemName: "xmark.circle.fill")
				.opacity(0.4)
				.padding(.leading, -6)
		}
		.foregroundColor(.white)
		.font(.caption2)
		.padding(4)
		.background(Color.blue.cornerRadius(5))
		.padding(4)
		.onTapGesture {
			tags = tags.filter({ $0 != tag })
		}
	}
}

struct TaggerView_Previews: PreviewProvider {
	static var previews: some View {
		TaggerView()
	}
}

Great work! A small implementation detail I ran across:
if you want to place a view below the TagList in a VStack, it will end up pushed down because GeometryReader is "greedy" about consuming height.
I worked around this by passing in the width from an external GeometryReader wrapping the whole VStack.

(also resolved with .layoutPriority)

Thanks Alex!

@eliyap any chance you can put your solution? I have run into the same issue and not getting fixed with layoutPriority

@ericagredo apologies, the code never shipped, so I don't have a copy of my solution. SwiftUI's internals may also have changed since 2020, so what worked then may no longer apply :/

How could I change the code to store my Tags using @AppStorage for example... ?
Or could UserDefaults be used? Does anyone have a solution to get my embedded Tags loaded when my app starts?