Fix a crash if volume numbers are the same

Author: h65wang

example/lib/main.dart

@@ -76,6 +76,7 @@ class _MyAppState extends State<MyApp> {
             //   overlayBackgroundColor: Colors.red[900]!.withOpacity(0.6),
             //   overlayTextStyle: TextStyle(color: Colors.red[100]),
             //   timeLabelHeight: 32,
+            //   volumeHeightFactor: 0.2, // volume area is 20% of total height
             // ),
             /** Customize axis labels */
             // timeLabel: (timestamp, visibleDataCount) => "📅",

lib/src/interactive_chart.dart

@@ -150,10 +150,14 @@ class _InteractiveChartState extends State<InteractiveChart> {
             candlesInRange.map(highest).whereType<double>().reduce(max);
         final minPrice =
             candlesInRange.map(lowest).whereType<double>().reduce(min);
-        final maxVol =
-            candlesInRange.map((c) => c.volume).whereType<double>().reduce(max);
-        final minVol =
-            candlesInRange.map((c) => c.volume).whereType<double>().reduce(min);
+        final maxVol = candlesInRange
+            .map((c) => c.volume)
+            .whereType<double>()
+            .fold(double.negativeInfinity, max);
+        final minVol = candlesInRange
+            .map((c) => c.volume)
+            .whereType<double>()
+            .fold(double.infinity, min);
 
         final child = TweenAnimationBuilder(
           tween: PainterParamsTween(

lib/src/painter_params.dart

@@ -59,6 +59,22 @@ class PainterParams {
   double fitVolume(double y) {
     final gap = 12; // the gap between price bars and volume bars
     final baseAmount = 2; // display at least "something" for the lowest volume
+
+    if (maxVol == minVol) {
+      // Apparently max and min values (in the current visible range, at least)
+      // are the same. It's likely they passed in a bunch of zeroes, because
+      // they don't have real volume data or don't want to draw volumes.
+      assert(() {
+        if (style.volumeHeightFactor != 0) {
+          print('If you do not want to show volumes, '
+              'make sure to set `volumeHeightFactor` (ChartStyle) to zero.');
+        }
+        return true;
+      }());
+      // Since they are equal, we just draw all volume bars as half height.
+      return priceHeight + volumeHeight / 2;
+    }
+
     final volGridSize = (volumeHeight - baseAmount - gap) / (maxVol - minVol);
     final vol = (y - minVol) * volGridSize;
     return volumeHeight - vol + priceHeight - baseAmount;