Get additional metadata from lineTouchData

^{Originally posted by **KapitanPL** September 3, 2022}
Hi Guys,

I generate my LineChartBarData based on model.

I then want to let user interact with the model via LineTouchData.

`LineTouchData.lineBarSpots!.first.bar` seemed to reference the LineChartBarData.

So I tried to extend LineChartBarData to contain my metadata and set this extended object as LineChartBarData. It works, data is displayed.

```dart
class LineBarDataMeta extends LineChartBarData {
LineBarDataMeta(
{
...
required this.displayed,
required this.dataKey});
bool displayed;
String dataKey;
}
```

However when I try:

```dart
lineTouchData: LineTouchData(
touchCallback: (p0, p1) {
if (p0 is FlTapDownEvent &&
p1 is LineTouchResponse &&
p1.lineBarSpots != null) {
var data = p1.lineBarSpots!.first;
if (p1.lineBarSpots!.first.bar is LineBarDataMeta) {
var spots = (p1.lineBarSpots!.first.bar as LineBarDataMeta);
print("key: ${spots.dataKey}");
}
print("touch!: ${p1.lineBarSpots}");
}
},
)
```

the `if (p1.lineBarSpots!.first.bar is LineBarDataMeta) ` part is never true.

How else can I pass some metadata to the lineTouchData.touchCallback in order to get it when processing the callback?

Edit:

Okay, I get it. There is `p1.lineBarSpots![n].barIndex`

The problem is that if you have two or more spots with the same X-coordinate you do not know which one you tap.
They are ordered by y-value.
And moreover the FlTapDownEvent has coordinates in "screen" coordinates, however the spot is in the chart coordinates. (x/y values).
This is going to be a nightmare!

How to know which one of the spots I clicked?