SwiftFlow: A Swift repository from hlung

Draw flowchart in Swift! 🚀
Built on simple UIKit + NSLayoutConstraint
Define data in flow arrays
Everything is aligned automatically with autolayout
Live editing (by SwiftUI PreviewProvider)
Try it out in example project

Example

Generate this flow chart:

From this code:

import SwiftFlow

let graph = Graph()

// setup configs
var blueConfig = NodeConfig()
blueConfig.backgroundColor = UIColor(red: 0.81, green: 0.96, blue: 1.00, alpha: 1.00)
var redConfig = NodeConfig()
redConfig.backgroundColor = UIColor(red: 1.00, green: 0.80, blue: 0.82, alpha: 1.00)

graph.nodeConfig = blueConfig

// add flows to graph
graph.addFlow([
  Node("Start", shape: .pill),
  Arrow(.down),
  Node("Work\nsuccess?", shape: .diamond, id: "success"), // declare id for later reference
  Arrow(.down, title: "Yes"),
  Node("Go Party!", shape: .rect, id: "party"),
  Arrow(.down),
  Node("End", shape: .pill, id: "end")
])

graph.addFlow([
  NodeShortcut(id: "success"), // refers back to the Node above
  Arrow(.right, title: "No"), // branch out to the right side
  Node("Cry", shape: .rect, config: redConfig), // different color using config
  Arrow(.down),
  Node("Go home", shape: .rect, id: "home"),
  ArrowLoopBack(from: .bottom, to: .right),
  NodeShortcut(id: "end")
])

let graphView = GraphView()
graphView.layoutMargins = UIEdgeInsets(top: 20, left: 20, bottom: 20, right: 20)

// draw the graph!
try! graphView.draw(graph)

How to use

Installation

Search for "SwiftFlow" library in Swift Packages in Xcode 📦

Requirements

iOS 13 and above
I attempted to support macOS, but still doesn't work :(. See more details at the bottom.
Can only draw on iOS / ipadOS simulators for now. You can capture screen to get the output image 😂

Why do you build this?

I often draw a flowchart to help understand some complex logic. It can also serves as a reference document for other engineers and testers. To draw one, I usually use popular tools like https://docs.google.com/drawings or https://app.diagrams.net/. However, I find it slow and tedious to do simple stuff like node alignment, auto text content hugging, adding arrow between nodes, or just adding arrow annotation. Not to mention that most of these styling will be out of place one you insert new nodes in between or update existing text.

Working with UIKit autolayout for years makes me aware that all of these UI styling can be handled in code very easily. Moreover, with the new SwiftUI, we can see live previews of the flowchart as we add each line of code. This will make flowchart drawing much faster and enjoyable.

We can do it better! 💪

Components ✍️

Models

Node - Each rectangle / other shapes boxes you see are backed by this type.
NodeShortcut - A way to refer to an existing Node by id.
Arrow - For chaining nodes together side-by-side. It has direction property for telling which way the arrow is pointing out from a node. You can also add annotations to it.
ArrowLoopBack - Similar to Arrow, but it also support drawing an angled arrow to go around existing nodes, typically for looping back to an existing node above. It can be used for linking further away nodes that would look nicer using an angled arrow than a straight one.
NodeConfig - For customizing a Node properties like background color / border color / distance from other nodes. A Graph can also take this property to apply to all nodes.
ArrowConfig - For customizing an Arrow.
GraphElement - A protocol that all above types conforms to.
Graph - This is the central piece that holds all information on how to draw the flowchart.
- You call addFlow(_:) which takes [GraphElement]. Typically, the array be a sequence of "Node, Arrow, Node, Arrow, ...".
- Finally, you pass this type into GraphView and call graphView.draw(graph) to draw the view.

Layout

I use autolayout to put the nodes in place. The arrows, on the other hand, are drawn directly using exact coordinates derived from nodes already laid out. The GraphView respects layoutMargins, so you can adjust outer edge margins with it.

Future ideas 💡

This project is stil in early stage. Feel free to suggest features and fixes. 🙂

improve syntax using result builders
export as image file
allow multiple arrows in same direction
add font/fontSize to NodeConfig
add bold/italic/underline text
add more node shapes
dotted arrows?
markdown syntax support - convert markdown syntax into SwiftFlow code. A very ambitious goal I would say. Not sure if there's a need for this though.
macOS support - As an iOS developer, I built everything using UIKit. For macOS, those view components and UIBezierPath drawing code has to be translated into AppKit code. I attempted to create AppKit+UIKit.swift extension that would provide AppKit components with UIKit interface. But I'm stuck at creating UIBezierPath cgPath setter. The code compiles on macOS but doesn't draw anything. You can try to fix in feature/macos-support branch. So if you need a bigger canvas for the flowchart, just run it on an "iPad Simulator" for now. 😝

Other Notes

About live preview

In the live preview demo, I'm actually just wrapping GraphView in a SwiftUI's UIViewRepresentable type. While it is not the most optimized way, I think it is good enough for general use.

The name

I know some other library has the same name, like https://github.com/Swift-Kit/Swift-Flow . But I still prefer this name.

Comparison with mermaid 🧜‍♀️

There is a JavaScript library for drawing flowchart in code called mermaid. (There's a live editor you can try.) At first glance it is very powerful. It can draw not only flowcharts, but may other types of diagrams. But I find there are some problems for drawing flowchart...

Node duplication - The syntax is pair-based, meaning each declaration includes 2 nodes and 1 arrow ( A --> B, B --> C, C --> D ). In a long flowchart, most nodes will appear twice (B and C), which is very redundant. This won't happen if the syntax is flow based ( A --> B --> C --> D ) because most nodes will be referenced only once, except at the intersections. I think using flow-based syntax is cleaner and faster to write.
Ugly new line - Need to use <br /> 😫. I could just be \n.
Arrow is long - It uses --> for an arrow. It could have been just -> or >. This adds up with the link-based syntax mentioned.
Cannot specify arrow direction - The graph declaration at the top dictates the arrow direction, e.g. graph TD means going from "top to bottom".

hlung/SwiftFlow