Validation Errors

A chart shows a validation error instead of drawing when its input has no correct fallback. The chart draws the errors as text in its container with ChartErrors, one error per line.

What is an error

Data problems: too few values, series of different lengths, values that are not finite, and negative values in charts that need positive ones.
Counts that must match: categories that do not match the value count, and colors that do not match what they color.
Settings with no fallback: non-finite range bounds and invalid axis label settings.

Style values such as alphas, sizes, and grid steps are never errors. They are clamped instead, as Style Clamping describes.

Messages

Every message comes from ValidationErrors in DataValidation.kt in charts-core, so the same rule reads the same way in every chart.

Rule	Message	Charts
No series	At least one series is required.	Line, radar, stacked bar, stacked area
Wrong series count	Exactly one series is required; got 2.	Bar, histogram
Too few values	At least 2 values are required. (3 on radar)	All
Category count	Category count (3) must match value count (4).	Bar, histogram, line, radar, stacked bar, stacked area
Color count	Color count (2) must match series count (3).	All with a color list
Series length	Series 1 is not aligned with the first series.	Line, radar, stacked bar, stacked area
Not finite	Series 0 contains a non-finite value.	Line, radar, stacked bar, stacked area
Not finite	Value at index 2 is not finite.	Bar, histogram, pie
Negative	Series 0 contains a negative value.	Stacked bar, stacked area
Negative	Value at index 2 is negative.	Histogram, pie

The color message names what the colors are matched to: value on bar and histogram, and series on line, radar, and the stacked charts.

Charts that draw several series report a problem once per series. Charts with one series report it per value, with its index.

Where it happens

All checks live in DataValidation.kt in charts-core. Charts have no validation code of their own; each chart combines these functions where it validates its input:

Function	Checks	Charts
`validateSeries`	No series, too few values, category count, series length, non-finite values, negative values with `allowNegative = false`, and the series color count	Line, radar, stacked bar, stacked area
`validateSingleSeries`	One series, too few values, color count, category count, and each bad value	Bar, histogram
`validateValues`	Each non-finite value, and each negative value with `allowNegative = false`	Pie, and inside `validateSingleSeries`
`validateColorCount`	A color list that does not match what it colors	Inside the two series checks
`validateRange`	Non-finite range bounds	Bar, histogram, line

Axis label settings are checked by validateAxisLabels in AxisLabelValidation.kt.

For example, stacked bar validates its input with:

validateSeries(
    data = data,
    minValues = ValidationErrors.MIN_VALUES,
    allowNegative = false,
    colorCount = style.segments.colors.size,
) + validateAxisLabels(style.axis.xLabels, style.axis.yLabels, density)

Line keeps this combination in validateLineInput in LineChartEntry.kt, because LineChart and LiveLineChart share it.

The minimums are ValidationErrors.MIN_VALUES (2) and ValidationErrors.MIN_RADAR_VALUES (3). With no series, validateSeries reports only that error, and validateSingleSeries stops at the first shape problem.

Adding a rule

Add the message to ValidationErrors and the check to DataValidation.kt. Do not write message text or checks in a chart.
If the rule applies to more than one chart, add it to the function those charts already call.
Keep messages short, name the value or series, and say what is expected.

Tests

DataValidationTest in charts-core covers every function and the message text. Each chart's tests check that its errors are shown for invalid input.