Legend and Selection

The legend names what the colors stand for. While a point is selected, the title and the legend show its details. The rules below define when each one appears and what it says.

The shared legend is Legend in charts-core, in internal/composable/Legend.kt. It takes the chart's LegendStyle and hides itself when visible is false or without two items and a name. The selected title and legend values come from selectedTitle and selectedLegendValues in internal/SelectedTitle.kt.

Rules

1. The legend lists what color tells apart. That is the series for line, live line, radar, stacked bar and stacked area, and the categories for pie and ring gauge. Bar and histogram use one color, so they have no legend.
2. A legend needs two or more items and at least one name. One item needs no key, and a list of blank names tells the reader nothing.
3. legend.visible = false always hides it. Every chart with a legend has a legend style block. A hidden legend also hides the selected values of several series; the caller can read selectedIndex from rememberChartSelection() and show them in its own UI.
4. A selection names its category in the title. The title shows the selected category, or the caller's title when the category is blank.
5. One series puts its value in the title, as Category: value. Pie is the exception; see rule 8.
6. Several series put their values in the legend, as Name - value on each item. An item with a blank name shows only its value. The title then shows only the category.
7. Selected values use the chart's selectedValueFormatter. Pie's formats the slice's share, in percent from 0 to 100.
8. Pie shows the slice's share in the title, such as Mobile 42.5%, next to its category, or the caller's title when the category is blank, or alone when both are blank. Its legend does not change.

By Chart

Known Issues

Known issues and limits are listed in Legend and Selection Issues, in the Known Issues section.