How to add marker to center position in ios charts while scrolling horizontally with increasing scaleX and enabling drag

Question

I am using the Charts framework from Daniel Cohen Gindi. I am scrolling chart horizontally by increasing scaleX value and enabled drag as described in answer of this question

Set an horizontal scroll to my Barchart in swift

I want to add marker at center position when user scrolls horizontally. I know "chartTranslated" delegate is called whenever user drags the chart but it doesn't contain the value of "ChartDataEntry" and "Highlighted" like in "chartValueSelected" delegate method.

Answer 1

Unfortunately ChartViewBase.swift is full of private function and internal vars and you can't extend some method or obtain some var to get the values you searching for.

Anyway, you can always improve sources adding some other method you want to use inside the public protocol ChartViewDelegate:

ChartViewBase.swift

under the line:

@objc optional func chartTranslated(_ chartView: ChartViewBase, dX: CGFloat, dY: CGFloat)

add this:

@objc optional func chartTranslated(_ chartView: ChartViewBase, dX: CGFloat, dY: CGFloat, entry: ChartDataEntry?, highlight: Highlight?, centerIndices:Highlight?)

Then , you can easily call this new delegate method to the only source part of the code where chartTranslated is called:

BarLineChartViewBase.swift

search the part of the code where you see these lines:

if delegate !== nil
        {
            delegate?.chartTranslated?(self, dX: translation.x, dY: translation.y)
        }

and change it with:

if delegate !== nil
        {
            delegate?.chartTranslated?(self, dX: translation.x, dY: translation.y)
            var entry: ChartDataEntry?
            var h = self.lastHighlighted

            if h == nil
            {
                _indicesToHighlight.removeAll(keepingCapacity: false)
            }
            else
            {
                // set the indices to highlight
                entry = _data?.entryForHighlight(h!)
                if entry == nil
                {
                    h = nil
                    _indicesToHighlight.removeAll(keepingCapacity: false)
                }
                else
                {
                    _indicesToHighlight = [h!]
                }
            }
            let centerH = getHighlightByTouchPoint(self.center)
            if centerH === nil || centerH!.isEqual(self.lastHighlighted)
            {
                //self.highlightValue(nil, callDelegate: true)
                //self.lastHighlighted = nil
            }
            else
            {
                print("\n in center we have: \(centerH!)")
                self.highlightValue(centerH, callDelegate: true)
                self.lastHighlighted = centerH
                // please comment these lines if you don't want to automatic highlight the center indices.. 
            }
            delegate?.chartTranslated?(self, dX: translation.x, dY: translation.y, entry: entry, highlight: h, centerIndices:centerH) 
     }

Usage:

import Foundation
import UIKit
import Charts

class test: UIViewController, ChartViewDelegate {

    func chartTranslated(_ chartView: ChartViewBase, dX: CGFloat, dY: CGFloat, entry: ChartDataEntry?, highlight: Highlight?, centerIndices:Highlight?) {
        if let entry = entry, let highlight = highlight {
            print("chartTranslated info:\n\(self)\ndX and dY:\(dX)-\(dY)\nentry:\(entry)\nhightlight:\(highlight)")
        if let centerIndices = centerIndices {
            print("\n center indices is:\n\(centerIndices)")
        }
    }
}

Now, with this new delegate method you can make your marker to the center indices.

A gif to show a little demonstration: