Bar chart floating y position

[nspavlo]

Hello.
I'm using BarChartView with following configuration:

- (BarChartView *)chartView
{
    if (_chartView) {
        return _chartView;
    }
    _chartView = [[BarChartView alloc] initForAutoLayout];
    _chartView.minOffset = 1.0f;
    _chartView.descriptionText = @"";
    _chartView.noDataTextDescription = @"";
    _chartView.maxVisibleValueCount = 20;
    _chartView.drawBarShadowEnabled = NO;
    _chartView.pinchZoomEnabled = NO;
    _chartView.drawGridBackgroundEnabled = NO;
    _chartView.xAxis.enabled = NO;
    _chartView.leftAxis.enabled = NO;
    _chartView.rightAxis.enabled = NO;
    _chartView.legend.enabled = NO;
    _chartView.userInteractionEnabled = NO;
    _chartView.noDataText = @"";    
    return _chartView;
}

BarChartData is updated every second. After a while chart y position is changing. Smth. like +/- 8pt.
Is it configurable?
Thanks in advance.

[liuxuan30]

Not sure what you want to config. x axis is index based, so depends on how many bars you have, the x value position is calculated then.

[nspavlo]

Always same number of items (bars). Only values is changing. sry. not x position but y.

[liuxuan30]

then update your data sets

[nspavlo]

Thanks, but I think we're not on the same page here. I will create example project. :)

[liuxuan30]

maybe screenshots and explaination, demo project is too heavy

[nspavlo]

Initial state:

After a while:

Views:
-root
-- chart subview
-- overlay subview (top, middle, bottom) lines

DataSet:

BarChartDataSet *set = [[BarChartDataSet alloc] initWithYVals:yVals label:@"DataSet"];
set.barSpace = 0.4;
set.colors = @[ color ];
set.drawValuesEnabled = NO;

BarChartData *data = [[BarChartData alloc] initWithXVals:items dataSets:@[ set ]];
self.chartView.data = data;

yVals and items always contains same number of items.

[jleach]

I have the same problem. If I have 10 values along the xAxes, 9 of which are 0 (no bar) and the 10th value is say 20 (anything > 0) then the single bar floats about 10px above the x-axis. If on the other hand, I have 10 values along the xAxes, all of which are > 0 then they all sit right on the x-axis.

You can see this in the image above. In the initial state, the bars are floating ~10 px above the x-axis. However, in the "After a while" graph you can see they're much closer to the x-axis. This happens when some of the bars have a 0 value.

If you can point me to where in the code this might be happening, perhaps I can create a PR with a fix.

[liuxuan30]

could you just turn on displaying the y axis values, so we know the y axis range? Also, which version are you using?
I doubt it's related to recent change about deprecating startAtZeroEnabled and moving to axisMinValue.
Please check.
forcing axisMinValue = 0 will make the y axis always started from 0.

[nspavlo]

Initial:

After a while:

[jleach]

For me I have 24 values; index 0 = 71, the rest are zeros. Also, I have rightAxis.startAtZeroEnabled = true I walked through the render bar method and it looks like it should be drawing ok. Maybe its the axes that is being draw too low?

[danielgindi]

If I understand you correctly, your Y values range is changing. When the max value is getting bigger, the other bars are getting smaller relatively.
You can control the minimum/maximum Y axis values, using axisMinValue.
Or you can use setVisibleYRangeMaximum to limit the Y scale and force the user to pan...

[liuxuan30]

@jleach seems your issue is different? I tried your 71 and 23 zeroes with ChartsDemo, it's fine. I think you got something wrong with your code, or you modified something. The typical work flow is first configure the chart properties, and then setup the data. Make sure chartView.data = yourData is the last line; or you call notifyDataSetChanged() everytime you changed something about axis ranges.

[jleach]

@liuxuan30 I tried moving the chartView.data = to the be the last line and tried calling notifyDataSetChated() - no luck. Here is my method:
https://gist.github.com/jleach/ef831910e5dd16a785361533df73113e

I'll go back and see if I'm messing with the layout or something. The only thing I can think of is that I'm embedding the chart in a UIView. Maybe a constraint is causing me grief?

[liuxuan30]

@jleach constraints should impact the whole chart view, not just axis or a bar, right? unless you separate them..

        chartView.data = BarChartData(xVals: xVals, dataSets: barChartDataSets)
        chartView.notifyDataSetChanged()

the second chartView.notifyDataSetChanged() is not needed as data setter will call it once.

I mean something like:

chartView.leftAxis.enabeld = false
chartView.data = BarChartData(xVals: xVals, dataSets: barChartDataSets)
chartView.leftAxis.enabeld = true
chartView.notifyDataSetChanged() <--- must call this or the chart will mess up, becaues left axis will impact the space calculation

BTW, from your code, I see you only use rightAxis, but you don't assign data set axis dependency to right, and default is left axis. I also suspect your chartView.leftAxis.startAtZeroEnabled is NOT true(though default is true), that's why it will have some gap, at least I can reproduce it with ChartsDemo under this scenario

you can try set.axisDependency = AxisDependencyRight to see if your problem is gone (which I guess will) and turn on startAtZeroEnabled(deprecated in latest release)

[danielgindi]

You have not responded to my reply. Have you checked it out?
Also there are dedicated addEntry/removeEntry functions to add/remove entry without calling notifyDataSetChanged.