Using Asynchronous Category Data Source
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Topic Overview


This topic provides an overview of using the asynchronous category data source on the IGChartView™ control and demonstrates their use with a code example.

In this topic


Asynchronous data source summary

The IGAsyncCategoryDataSourceHelper loads a chunk of data into the IGChartView instead of loading all of the data into memory adding a new chunk of data as needed and when the chart zooms in or out, or when the chart pans past a certain threshold.

While loading a new chunk of data, the control displays a UIActivityIndicator. Overriding the viewForAsyncDataSourceLoadIndicator: method can provide a custom view. To add any initializations or clean up on the custom activity view, override the beginAsyncDataSourceRequest: or endAsyncDataSourceRequest: methods.

Currently, the following chart types support IGAsyncCategoryDataSourceHelper.

  • IGAreaSeries
  • IGColumnSeries
  • IGLineSeries
  • IGSplineAreaSeries
  • IGSplineSeries
  • IGStepAreaSeries
  • IGStepLineSeries
  • IGWaterfallSeries

To use the IGAsyncCategoryDataSourceHelper, adoption of the IGAsyncCategoryDataSource protocol is required and requires that the following two methods must be implemented.

  • -(NSInteger)numberOfPointsInAsyncDataSourceHelper: (IGAsyncCategoryDataSourceHelper*)dataSourceHelper series:(IGSeries*)series
  • -(NSArray*)provideValuesAtStartIndex:(NSInteger)startIndex endIndex:(NSInteger)endIndex forAsyncDataSourceHelper:(IGAsyncCategoryDataSourceHelper*)dataSourceHelper series:(IGSeries*)series

These methods specify the number of points total in the data source and when requested the data for a specific range.

Using the Asynchronous Category Data Source – Code Example


The code example below creates an instance of the IGChartView that uses the IGAsyncCategoryDataSourceHelper to load 5000 points as needed into a line series.



This code example requires the inclusion of the IGChart framework; details about adding this framework are available in the Adding the Chart Framework File topic.


In Objective-C:

@interface DataItem : NSObject
@property (nonatomic, copy) NSString *label;
@property (nonatomic, assign) CGFloat value;
@implementation DataItem
@interface igViewController () <IGAsyncCategoryDataSource>
    IGChartView *_chart;
    NSMutableArray *_data;
    IGLineSeries *_series;
    IGAsyncCategoryDataSourceHelper *_source;
@implementation igViewController
- (void)viewDidLoad
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    [self generateData:5000];
    _source = [[IGAsyncCategoryDataSourceHelper alloc]initWithValuePath:@"value" andLabelPath:@"label"];
    _source.delegate = self;
    _chart = [[IGChartView alloc]initWithFrame:CGRectInset(self.view.bounds, 10, 10)];
    _chart.zoomDisplayType = IGChartZoomHorizontal;
    _chart.theme = [IGChartDefaultThemes IGTheme];
    [self.view addSubview:_chart];
    _series = (IGLineSeries *)[_chart addSeriesForType:[IGLineSeries class] usingKey:@"series" withDataSource:_source firstAxisKey:@"xAxis" secondAxisKey:@"yAxis"];
    _series.yAxis.minimum = 0;
    _series.yAxis.maximum = 100;
    _series.yAxis.extent = 40;
    _series.xAxis.extent = 40;
- (void)generateData:(NSInteger)totalItems
    _data = [[NSMutableArray alloc]init];
    for (int i = 0; i < totalItems; i++)
        DataItem *item = [[DataItem alloc]init];
        item.value = arc4random() % 80;
        if (item.value <= 20)
            item.value += 20;
        item.label = [NSString stringWithFormat:@"Item %d", i];
        [_data addObject:item];
- (NSInteger)numberOfPointsInAsyncDataSourceHelper:(IGAsyncCategoryDataSourceHelper *)dataSourceHelper series:(IGSeries *)series
    return 5000;
- (NSArray *)provideValuesAtStartIndex:(NSInteger)startIndex endIndex:(NSInteger)endIndex forAsyncDataSourceHelper:(IGAsyncCategoryDataSourceHelper *)dataSourceHelper series:(IGSeries *)series
    NSRange range = NSMakeRange(startIndex, endIndex - startIndex);
    return [_data subarrayWithRange:range];

In C#:

public class DataItem : NSObject
      public String Label { get; set; }
      public float Value { get; set; }
public class AsyncDataSource : IGAsyncCategoryDataSource
      List<NSObject> _data;
      public AsyncDataSource(List<NSObject> data)
            _data = data;
      public override int NumberOfPoints (IGAsyncCategoryDataSourceHelper dataSourceHelper, IGSeries series)
            return 5000;
      public override NSObject[] ProvideValues (int startIndex, int endIndex, IGAsyncCategoryDataSourceHelper dataSourceHelper, IGSeries series)
            List<NSObject> values = _data.GetRange (startIndex, endIndex - startIndex);
            return values.ToArray ();
public partial class ChartAsyncDataSourceHelper_CSViewController : UIViewController
      IGChartView _chart;
      List<NSObject> _data;
      IGLineSeries _series;
      IGAsyncCategoryDataSourceHelper _source;
      public ChartAsyncDataSourceHelper_CSViewController ()
      public override void ViewDidLoad ()
            base.ViewDidLoad ();
            this.View.BackgroundColor = UIColor.White;
            GenerateData (5000);
            _source = new IGAsyncCategoryDataSourceHelper ("Value", "Label");
            _source.Delegate = new AsyncDataSource(_data);
            _chart = new IGChartView();
            RectangleF chartRect = this.View.Bounds;
            chartRect.Inflate(-10, -10);
            _chart.Frame = chartRect;
            _chart.ZoomDisplayType = IGChartZoom.IGChartZoomHorizontal;
            _chart.Theme = IGChartDefaultThemes.IGTheme();
            this.View.Add (_chart);
            _series = _chart.AddSeries (new Class ("IGLineSeries"), "series", _source, "xAxis", "yAxis") as IGLineSeries;
            _series.YAxis.Minimum = 0;
            _series.YAxis.Maximum = 100;
            _series.YAxis.Extent = 40;
            _series.XAxis.Extent = 40;
      public void GenerateData(int TotalItems)
            _data = new List<NSObject>();
            for (int i = 0; i < TotalItems; i++)
                  DataItem item = new DataItem();
                  item.Value = new Random (i * DateTime.Now.Millisecond).Next (20, 80);
                  item.Label = String.Format ("Item {0}", i);
                  _data.Add (item);

Related Content


The following topic provides additional information related to this topic.



The topics in this group cover enabling, configuring, and using the IGChartView control’s supported features.