Zoom into a specific x-axis range for iOS Charts

BarLineChartViewBase+Extensions.swift

// For library: https://github.com/danielgindi/Charts

extension BarLineChartViewBase {
    func focusXRange(start: Double, end: Double) {
        guard end > start else {
            return
        }

        // Reset the zoom back to the full chart view, so that the setVisibleXRange call will zoom in to the desired range,
        // setVisibleXRange only zooms in, not out.
        // resetZoom() seems like it should be the right API call, but it doesn't work if the user is already zoomed
        // in closer than the range to focus.
        // zoomToCenter(scaleX: 1, scaleY: 1) similarly doesn't work
        while !isFullyZoomedOut {
            zoomOut()
        }

        let distance = end - start
        // If the distance to focus on is greater than the xAxis maximum, we can't zoom in any further
        guard distance < (xAxis.axisMaximum - xAxis.axisMinimum) else {
            return
        }

        // Set the visible range to the distance between start and end. This will zoom the chart in to a range of that distance
        setVisibleXRange(minXRange: xAxis.axisMinimum, maxXRange: xAxis.axisMinimum + distance)

        // Move the chart to the start point
        moveViewToX(start)

        // Due to the previous setVisibleXRange call, the user cannot zoom back out.
        // Restore the visible range to the full width of the dataset, so that the user can zoom back out.
        // Note: this will not zoom the chart back out; setVisibleXRange will only zoom in, not out
        setVisibleXRange(minXRange: xAxis.axisMinimum, maxXRange: xAxis.axisMaximum)
    }
}

// Use it like
// chartView.focusXRange(0, 10) // Focus on the first ten data points
// chartView.focusXRange(chartView.xAxis.axisMaximum - 10, chartView.xAxis.axisMaximum) // Focus on the last ten data points