Flutter CustomPaint Chart Example: From Data to Canvas
A flutter custompaint chart example that draws a real line chart from scratch: axes, labels, shouldRepaint, and hit-testing basics.
If you have ever pulled in a chart package, fought its theming API for an hour, and thought "I could just draw this myself" — this flutter custompaint chart example is for you. Flutter's canvas API is genuinely pleasant to use, and a line chart is the perfect first project: it forces you to learn coordinate mapping, text labels, repaint control, and hit-testing — the four skills behind almost every custom shape you will ever draw. We will build a real line chart from a plain List<double> — no packages. Along the way you will pick up flutter custom shapes in general: circles, arcs, and clipped containers all use the same CustomPainter machinery. What you'll learn How CustomPaint and CustomPainter work together (and how they differ) Mapping data values to canvas coordinates — the step most tutorials gloss over A complete line chart drawn with flutter canvas draw line techniques: axes, grid, points Axis labels with TextPainter ( flutter custompainter text ) shouldRepaint done right — compare fields, never => true Hit-testing basics: tap a data point and highlight it Drawing custom shapes: arcs, circles, and rounded fills Step 0 — CustomPainter basics: the smallest flutter custompainter example CustomPaint is the widget; CustomPainter is the delegate that does the drawing. The widget handles layout and gives your painter a Canvas plus a Size . The painter implements two methods: paint() and shouldRepaint() . import 'package:flutter/material.dart'; class CirclePainter extends CustomPainter { @override void paint(Canvas canvas, Size size) { final paint = Paint() ..color = Colors.blue ..style = PaintingStyle.fill; canvas.drawCircle( Offset(size.width / 2, size.height / 2), 40, paint, ); } @override bool shouldRepaint(covariant CirclePainter oldDelegate) =>…