Dynamic graph display

[dayizhang]

Hi, I am using your library and use addEntry function to add data on the graph. The adding rate is about 80Hz, so 125 points per second. I set 400 points display on the window and remove entry outside window.
During the test on iPad mini, the whole app will be slower and slower after about 3 minutes. Maybe the library efficiency could be improved.

[danielgindi]

With your numbers, it means 22,500 data entries after 3 minutes. That will definitely draw slower.
Drawing the viewport as the end portion of the data, means the chart is looping over the data until reaching the data that is in the viewport. As it has no way to know which xIndex is inside the viewport without calculating it first.
We do have performance improvements planned, but it's not magic and sometimes we have to make compromises. In the meantime you can maybe remove some data that you are not using.

[dayizhang]

Hi @danielgindi, thanks for this. I've already tried the approach you have mentioned, and as expected, there was a significant improvement in the performance. I was wondering maybe it would be of value to include this as a note in the docs regarding dynamic drawing?

[tulm00073]

I've got the exactly same function, update LineChartView about 100 times/second. But my problems is the graph seems not to update apparently, Could you point me out what's wrong with this? what is my mistake?

-> these lines of code will be call 100 times/sec
let chartDataSet = self.lineChartView.data?dataSets[0]
var index = chartDataSet?.valueCount

if index > MAX_XVALS {
chartDataSet.removeFirst()
index--
}

let entryData = ChartDataEntry(value: arc4random_uniform(1000) + 1, xIndex: index!)
chartDataSet.addEntry(entry)

self.lineChartView.notifyDataSetChanged()

Thank you.

[liuxuan30]

@tulm00073 would you just check if the drawRect is called and the data you are sure it's updated.

Calling notifyDataSetChanged eventually will invoke setNeedsDisplay, so there should be a redraw of your line chart. You can debug from there.