Cannot remove an observer for the key path "bounds" because it is not registered as an observer

[nathan-fiscaletti]

• I've read, understood, and done my best to follow the *CONTRIBUTING guidelines.

What did you do?

Trying to add a Chart to a UITableViewCell, and was greeted with an error.

let cell = self.tableView.dequeueReusableCell(withIdentifier: "NetworkStatsGraphCell", for: indexPath) as! ChartCell
cell.initializeChart()
return cell

import UIKit
import Charts

class ChartCell : UITableViewCell
{
    @IBOutlet weak var chart: LineChartView!
    
    func initializeChart()
    {
        chart.backgroundColor = UIColor(white: 1, alpha: 0)
        
        chart.marker = nil;
        chart.xAxis.drawAxisLineEnabled = false
        chart.xAxis.drawGridLinesEnabled = false
        chart.xAxis.drawLabelsEnabled = false
        chart.drawBordersEnabled = false;
        chart.layoutMargins = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
        
        chart.leftAxis.drawAxisLineEnabled = false
        chart.leftAxis.drawGridLinesEnabled = false
        chart.leftAxis.drawLabelsEnabled = false
        
        chart.xAxis.enabled = false
        chart.leftAxis.enabled = false
        chart.rightAxis.enabled = false
        chart.drawBordersEnabled = false
        chart.minOffset = 0
        
        chart.rightAxis.drawAxisLineEnabled = false
        chart.rightAxis.drawGridLinesEnabled = false
        chart.rightAxis.drawLabelsEnabled = false
        chart.legend.enabled = false;
        
        let dataSet1 = LineChartDataSet([
            // First four must be 0 for design.
            ChartDataEntry(x: 0, y: 0),
            ChartDataEntry(x: 1, y: 0),
            ChartDataEntry(x: 2, y: 0),
            
            ChartDataEntry(x: 3, y: 6),
            ChartDataEntry(x: 4, y: 9),
            ChartDataEntry(x: 5, y: 5),
            ChartDataEntry(x: 6, y: 8),
            ChartDataEntry(x: 7, y: 18),
            ChartDataEntry(x: 8, y: 14),
            ChartDataEntry(x: 9, y: 12),
            
            // Last three must be 0 for design
            ChartDataEntry(x: 10, y: 0),
            ChartDataEntry(x: 11, y: 0)
            ])
        
        let dataSet2 = LineChartDataSet(values: [
            // First four must be 0 for design.
            ChartDataEntry(x: 0, y: 0),
            ChartDataEntry(x: 1, y: 0),
            ChartDataEntry(x: 2, y: 0),
            
            ChartDataEntry(x: 3, y: 6),
            ChartDataEntry(x: 4, y: 9),
            ChartDataEntry(x: 5, y: 5),
            ChartDataEntry(x: 6, y: 8),
            ChartDataEntry(x: 7, y: 18),
            ChartDataEntry(x: 8, y: 14),
            ChartDataEntry(x: 9, y: 12),
            
            // Last three must be 0 for design
            ChartDataEntry(x: 10, y: 0),
            ChartDataEntry(x: 11, y: 0)
            ],
                                        label: ""
        )
        
        dataSet1.drawIconsEnabled = false
        dataSet1.drawCirclesEnabled = false
        dataSet1.drawCircleHoleEnabled = false
        dataSet1.drawValuesEnabled = false
        dataSet1.lineCapType = .round
        dataSet1.colors = [rgbToUiColor(rgb: 0xFF0000)]
        dataSet1.highlightEnabled = false
        dataSet1.lineWidth = 2;
        dataSet1.mode = .horizontalBezier
        
        
        dataSet2.drawIconsEnabled = false
        dataSet2.drawCirclesEnabled = false
        dataSet2.drawCircleHoleEnabled = false
        dataSet2.drawValuesEnabled = false
        dataSet2.lineCapType = .round
        dataSet2.highlightEnabled = false
        dataSet2.lineWidth = 2;
        dataSet2.mode = .horizontalBezier
        dataSet2.colors = [rgbToUiColor(rgb: 0x00FF00)]
        
        let data = LineChartData(dataSets: [dataSet1, dataSet2])
        chart.data = data
        //chart.animate(xAxisDuration: 1.0, yAxisDuration: 0)
    }
    
    func rgbToUiColor(rgb: Int) -> UIColor {
        return UIColor(
            red: CGFloat((rgb >> 16) & 0xFF) / 255.0,
            green: CGFloat((rgb >> 8) & 0xFF) / 255.0,
            blue: CGFloat(rgb & 0xFF) / 255.0,
            alpha: 1.0
        );
    }
}

What did you expect to happen?

The chart to display.

What happened instead?

Was greeted with this error:

2019-05-11 09:03:46.356484-0500 Prototype Settings[25568:4941238] *** Terminating app due to uncaught exception 'NSRangeException', reason: 'Cannot remove an observer <Charts.ChartDataSet 0x600001d20240> for the key path "bounds" from <Charts.ChartDataSet 0x600001d20240> because it is not registered as an observer.'
*** First throw call stack:
(
	0   CoreFoundation                      0x000000010f9976fb __exceptionPreprocess + 331
	1   libobjc.A.dylib                     0x000000010e484ac5 objc_exception_throw + 48
	2   CoreFoundation                      0x000000010f997555 +[NSException raise:format:] + 197
	3   Foundation                          0x000000010df0a5e1 -[NSObject(NSKeyValueObserverRegistration) _removeObserver:forProperty:] + 488
	4   Foundation                          0x000000010df0aa68 -[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:] + 84
	5   Charts                              0x000000010d9f8009 $s6Charts13ChartViewBaseCfD + 105
	6   Prototype Settings                  0x000000010d609adf $s18Prototype_Settings9ChartCellC010initializeC0yyF + 6543
	7   Prototype Settings                  0x000000010d60be55 $s18Prototype_Settings14SessionDetailsC9tableView_12cellForRowAtSo07UITableF4CellCSo0kF0C_10Foundation9IndexPathVtF + 1285
	8   Prototype Settings                  0x000000010d60d5eb $s18Prototype_Settings14SessionDetailsC9tableView_12cellForRowAtSo07UITableF4CellCSo0kF0C_10Foundation9IndexPathVtFTo + 155
	9   UIKitCore                           0x000000011846d62c -[UITableView _createPreparedCellForGlobalRow:withIndexPath:willDisplay:] + 764
	10  UIKitCore                           0x000000011846db65 -[UITableView _createPreparedCellForGlobalRow:willDisplay:] + 73
	11  UIKitCore                           0x0000000118435d20 -[UITableView _updateVisibleCellsNow:isRecursive:] + 2870
	12  UIKitCore                           0x0000000118455e37 -[UITableView layoutSubviews] + 165
	13  UIKitCore                           0x00000001187029c1 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1417
	14  QuartzCore                          0x00000001106a0eae -[CALayer layoutSublayers] + 173
	15  QuartzCore                          0x00000001106a5b88 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 396
	16  QuartzCore                          0x00000001106b1ee4 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 72
	17  QuartzCore                          0x00000001106213aa _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 328
	18  QuartzCore                          0x0000000110658584 _ZN2CA11Transaction6commitEv + 608
	19  UIKitCore                           0x000000011825c3a4 _afterCACommitHandler + 245
	20  CoreFoundation                      0x000000010f8fe0f7 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
	21  CoreFoundation                      0x000000010f8f85be __CFRunLoopDoObservers + 430
	22  CoreFoundation                      0x000000010f8f8c31 __CFRunLoopRun + 1505
	23  CoreFoundation                      0x000000010f8f8302 CFRunLoopRunSpecific + 626
	24  GraphicsServices                    0x000000011462e2fe GSEventRunModal + 65
	25  UIKitCore                           0x0000000118234ba2 UIApplicationMain + 140
	26  Prototype Settings                  0x000000010d60eeab main + 75
	27  libdyld.dylib                       0x0000000111d5e541 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

Charts Environment

Charts version/Branch/Commit Number: 3.2.2
Xcode version: 10.2.1 (10E1001)
Swift version: Swift 5
Platform(s) running Charts: iOS
macOS version running Xcode: Mojave 10.14.3

Demo Project

I don't have the best internet for uploads right now and the project is too large.

[nathan-fiscaletti]

It looks like i get the same problem even if i do not call initializeChart(), so I assume this is an issue with using it in a UITableView

[nathan-fiscaletti]

I've narrowed it down to being something about the way I'm initializing my DataSet, but i'm not sure what specifically.

[nathan-fiscaletti]

I've found that if i comment out .lineCapType = .round and .drawCircleHoleEnabled = false for the data sets i get rid of this error, but then i get a new error which says Fatal error: Datasets for LineChartRenderer must conform to ILineChartDataSet

[nathan-fiscaletti]

Giving the data sets different labels seems to fix the last error, which wasn't very clear. However the issue still persists that if i use lineCapType or drawCircleHoleEnabled, it fails with the Observer bug.

[liuxuan30]

I think you should go to stack overflow for this issue.
I have seen people adding Chart into a cell, but never report something like this.

    deinit
    {
        self.removeObserver(self, forKeyPath: "bounds")
        self.removeObserver(self, forKeyPath: "frame")
    }

the observer is only removed in deinit(), I'm not sure if you already see it's been added. And seems not our scope to investigate.

My bet:
your cell is getting freed very soon as well as the sub views before the chart view add the observer.

[nathan-fiscaletti]

@liuxuan30 I'm not sure how it wouldn't be considered a bug that this only seems to happen when I have .lineCapType = .round and .drawCircleHoleEnabled = false enabled