Implement Gesture-Based Interactions in Swift Charts Library

Swift Chart

Line and area charts | Multiple series | Partially filled series | Works with signed Double Touch events

Line and area charts
Multiple series
Partially filled series
  • language: Swift
  • platform: ios
  • device: iphone
  • license: MIT

Getting started

Installing Swift Chart via CocoaPods

SwiftChart is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod "SwiftChart"

Installing Swift Chart manually

  1. Download SwiftChart.zip from the last release and extract its content in your project’s folder.
  2. From the Xcode project, choose Add Files to … from the File menu and add the extracted files.

What’s included in Swift Chart

The library includes:

  • the Chart main class, to initialize and configure the chart’s content, e.g. for adding series or setting up the its appearance
  • the ChartSeries class, for creating datasets and configure their appearance
  • the ChartDelegate protocol, which tells other objects about the chart’s touch events
  • the Chart Color struct, containing some predefined colors

Example

let chart = Chart()
let series = ChartSeries([0, 6, 2, 8, 4, 7, 3, 10, 8])
series.color = ChartColors.greenColor()
chart.add(series)

To run the example project, clone the repo, and run pod install from the Example directory first.

How to use Swift Chart

Initialize a chart from the Interface Builder

The chart can be initialized from the Interface Builder. Drag a normal View into a View Controller and assign to it the Chart Custom Class from the Identity Inspector.

Initialize a chart programmatically

To initialize a chart programmatically, use the Chart(frame: ...) initializer, which requires a frame:

let chart = Chart(frame: CGRect(x: 0, y: 0, width: 200, height: 100))

If you prefer to use Autolayout, set the frame to 0 and add the constraints later:

let chart = Chart(frame: CGRectZero)
// add constraints now

Adding a series to a chart

Initialize each series before adding them to the chart. To do so, pass an array to initialize a ChartSeries object:

let chart = Chart(frame: CGRect(x: 0, y: 0, width: 200, height: 100))
let series = ChartSeries([0, 6.5, 2, 8, 4.1, 7, -3.1, 10, 8])
chart.add(series)

Result:

SwiftChart

As you can see, as default the values on the x-axis are the progressive indexes of the passed array. You can customize those values by passing an array of (x: Double, y: Double) tuples to the series initializer:

let chart = Chart(frame: CGRect(x: 0, y: 0, width: 200, height: 100))
// Create a new series specifying x and y values
let data = [
  (x: 0, y: 0),
  (x: 1, y: 3.1),
  (x: 4, y: 2),
  (x: 5, y: 4.2),
  (x: 7, y: 5),
  (x: 9, y: 9),
  (x: 10, y: 8)
]
let series = ChartSeries(data: data)
chart.add(series)

Result:

SwiftChart

Using partially filled series

Use the chart.xLabels property to make the x-axis showing more labels than those inferred from the actual data. For example,

let chart = Chart(frame: CGRect(x: 0, y: 0, width: 200, height: 100))
let data = [
  (x: 0, y: 0),
  (x: 3, y: 2.5),
  (x: 4, y: 2),
  (x: 5, y: 2.3),
  (x: 7, y: 3),
  (x: 8, y: 2.2),
  (x: 9, y: 2.5)
]
let series = ChartSeries(data: data)
series.area = true

// Use `xLabels` to add more labels, even if empty
chart.xLabels = [0, 3, 6, 9, 12, 15, 18, 21, 24]

// Format the labels with a unit
chart.xLabelsFormatter = { String(Int(round($1))) + "h" }

chart.add(series)

Result:

SwiftChart

Using different colors above and below zero

The chart displays the series in different colors when below or above the zero-axis:

let chart = Chart(frame: CGRect(x: 0, y: 0, width: 200, height: 100))
let data: [Double] = [0, -2, -2, 3, -3, 4, 1, 0, -1]

let series = ChartSeries(data)
series.area = true

chart.add(series)

// Set minimum and maximum values for y-axis
chart.minY = -7
chart.maxY = 7

// Format y-axis, e.g. with units
chart.yLabelsFormatter = { String(Int($1)) +  "ºC" }

Result:

You can customize the zero-axis and the colors with the colors options in the ChartSeries class.

series.colors = (
  above: ChartColors.greenColor(),
  below: ChartColors.yellowColor(),
  zeroLevel: -1
)

Result:

Chart in swift

Adding multiple series to a chart

Using the chart.add(series: ChartSeries) and chart.add(series: Array<ChartSeries>) methods you can add more series. Those will be indentified with a progressive index in the chart’s series property.

let chart = Chart(frame: CGRect(x: 0, y: 0, width: 200, height: 100))

let series1 = ChartSeries([0, 6, 2, 8, 4, 7, 3, 10, 8])
series1.color = ChartColors.yellowColor()
series1.area = true

let series2 = ChartSeries([1, 0, 0.5, 0.2, 0, 1, 0.8, 0.3, 1])
series2.color = ChartColors.redColor()
series2.area = true

// A partially filled series
let series3 = ChartSeries([9, 8, 10, 8.5, 9.5, 10])
series3.color = ChartColors.purpleColor()

chart.add([series1, series2, series3])

Result:

touch chart

Configuring touch events

To make the chart respond to touch events, implement the ChartDelegate protocol in your class, e.g. a View Controller, and then set the chart’s delegate property:

class MyViewController: UIViewController, ChartDelegate {
  override func viewDidLoad() {
    let chart = Chart(frame: CGRect(x: 0, y: 0, width: 100, height: 200))
    chart.delegate = self
  }

  // Chart delegate
  func didTouchChart(chart: Chart, indexes: Array<Int?>, x: Double, left: CGFloat) {
    // Do something on touch
  }

  func didFinishTouchingChart(chart: Chart) {
    // Do something when finished
  }

  func didEndTouchingChart(chart: Chart) {
    // Do something when ending touching chart
  }
}

The didTouchChart method passes an array of indexes, one for each series, with an optional Int referring to the data’s index:

 func didTouchChart(chart: Chart, indexes: Array<Int?>, x: Double, left: CGFloat) {
    for (seriesIndex, dataIndex) in enumerate(indexes) {
      if dataIndex != nil {
        // The series at `seriesIndex` is that which has been touched
        let value = chart.valueForSeries(seriesIndex, atIndex: dataIndex)
      }
    }
  }

You can use chart.valueForSeries() to access the value for the touched position.

The x: Double argument refers to the value on the x-axis: it is inferred from the horizontal position of the touch event, and may be not part of the series values.

The left: CGFloat is the x position on the chart’s view, starting from the left side. It may be used to set the position for a label moving above the chart:

Configuring touch events

API

Chart class

Use the Chart class to initialize and configure the chart’s content, e.g. for adding series or setting up the its appearance.

Example

let chart = Chart(frame: CGRect(x: 0, y: 0, width: 200, height: 100))

ChartSeries class

Use the ChartSeries class to create a chart series and configure its appearance and behavior.

Example

let data: [Double] = [0, -2, -2, 3, -3, 4, 1, 0, -1]
let series = ChartSeries(data)

ChartColors enum

Shorthands for various colors.

Example

let series = ChartSeries([0, 6, 2, 8, 4, 7, 3, 10, 8])
series.color = ChartColors.blueColor()

Common issues and solutions

If you have issue with this library, please tag your question with swiftchart on Stack Overflow.

The chart is not showing

The Chart class inherits from UIView, so if your chart is not displaying it is likely a problem related to the view’s size. Check your view constraints and make sure you initialize it on viewDidLoad, when UIKit can calculate the view dimensions.
Some tips for debugging an hidden chart:

  • start your app and then debug the UI Hierarchy from the Debug navigator
  • initialize a simple UIView with a colored background instead of the chart to easily see how the view is positioned
  • try to not to nest the chart in a subview for better debugging

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