added axis titles

example/lib/line_chart/samples/line_chart_sample4.dart

@@ -5,6 +5,8 @@ class LineChartSample4 extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     const cutOffYValue = 5.0;
+    const dateTextStyle = TextStyle(
+        fontSize: 10, color: Colors.purple, fontWeight: FontWeight.bold);
 
     return SizedBox(
       width: 300,
@@ -54,8 +56,8 @@ class LineChartSample4 extends StatelessWidget {
           titlesData: FlTitlesData(
             bottomTitles: SideTitles(
                 showTitles: true,
-                textStyle:
-                    TextStyle(fontSize: 10, color: Colors.purple, fontWeight: FontWeight.bold),
+                reservedSize: 14,
+                textStyle: dateTextStyle,
                 getTitles: (value) {
                   switch (value.toInt()) {
                     case 0:
@@ -93,6 +95,15 @@ class LineChartSample4 extends StatelessWidget {
               },
             ),
           ),
+          axisTitleData: const FlAxisTitleData(
+              leftTitle:
+                  AxisTitle(showTitle: true, titleText: 'Value', margin: 4),
+              bottomTitle: AxisTitle(
+                  showTitle: true,
+                  margin: 0,
+                  titleText: '2019',
+                  textStyle: dateTextStyle,
+                  textAlign: TextAlign.right)),
           gridData: FlGridData(
               show: true,
               checkToShowHorizontalGrid: (double value) {

example/lib/line_chart/samples/line_chart_sample5.dart

@@ -89,6 +89,13 @@ class LineChartSample5 extends StatelessWidget {
                   fontSize: 18,
                 )),
           ),
+          axisTitleData: const FlAxisTitleData(
+              rightTitle: AxisTitle(showTitle: true, titleText: 'count'),
+              leftTitle: AxisTitle(showTitle: true, titleText: 'count'),
+              topTitle: AxisTitle(
+                  showTitle: true,
+                  titleText: 'Wall clock',
+                  textAlign: TextAlign.left)),
           gridData: const FlGridData(show: false),
           borderData: FlBorderData(
             show: true,

lib/src/chart/bar_chart/bar_chart_data.dart

@@ -11,6 +11,7 @@ import 'package:flutter/material.dart';
 /// This class is responsible to holds data to draw Bar Chart
 /// [barGroups] holds list of bar groups to show together,
 /// [groupsSpace] space between groups, it applies only when the [alignment] is [Alignment.center],
+/// [axisTitleData] to show a description of each axis
 /// [alignment] is the alignment of showing groups,
 /// [titlesData] holds data about drawing left and bottom titles.
 class BarChartData extends AxisChartData {
@@ -30,11 +31,13 @@ class BarChartData extends AxisChartData {
       show: false,
     ),
     FlBorderData borderData,
+    FlAxisTitleData axisTitleData = const FlAxisTitleData(),
     double maxY,
     Color backgroundColor,
   }) : super(
           gridData: gridData,
           borderData: borderData,
+          axisTitleData: axisTitleData,
           backgroundColor: backgroundColor,
           touchData: barTouchData,
         ) {
@@ -91,6 +94,7 @@ class BarChartData extends AxisChartData {
     double groupsSpace,
     BarChartAlignment alignment,
     FlTitlesData titlesData,
+    FlAxisTitleData axisTitleData,
     BarTouchData barTouchData,
     FlGridData gridData,
     FlBorderData borderData,
@@ -102,6 +106,7 @@ class BarChartData extends AxisChartData {
       groupsSpace: groupsSpace ?? this.groupsSpace,
       alignment: alignment ?? this.alignment,
       titlesData: titlesData ?? this.titlesData,
+      axisTitleData: axisTitleData ?? this.axisTitleData,
       barTouchData: barTouchData ?? this.barTouchData,
       gridData: gridData ?? this.gridData,
       borderData: borderData ?? this.borderData,
@@ -118,6 +123,7 @@ class BarChartData extends AxisChartData {
         groupsSpace: lerpDouble(a.groupsSpace, b.groupsSpace, t),
         alignment: b.alignment,
         titlesData: FlTitlesData.lerp(a.titlesData, b.titlesData, t),
+        axisTitleData: FlAxisTitleData.lerp(a.axisTitleData, b.axisTitleData, t),
         barTouchData: b.barTouchData,
         gridData: FlGridData.lerp(a.gridData, b.gridData, t),
         borderData: FlBorderData.lerp(a.borderData, b.borderData, t),

lib/src/chart/bar_chart/bar_chart_painter.dart

@@ -41,6 +41,7 @@ class BarChartPainter extends AxisChartPainter<BarChartData> with TouchHandler<B
     groupBarsPosition = calculateGroupAndBarsPosition(size, groupsX, data.barGroups);
 
     drawBars(canvas, size, groupBarsPosition);
+    drawAxisTitles(canvas, size);
     drawTitles(canvas, size, groupBarsPosition);
 
     for (int i = 0; i < targetData.barGroups.length; i++) {

lib/src/chart/base/axis_chart/axis_chart_data.dart

@@ -12,6 +12,7 @@ import 'package:flutter/material.dart';
 /// each child have to set it in their constructor.
 abstract class AxisChartData extends BaseChartData {
   final FlGridData gridData;
+  final FlAxisTitleData axisTitleData;
 
   double minX, maxX;
   double minY, maxY;
@@ -26,6 +27,7 @@ abstract class AxisChartData extends BaseChartData {
     this.gridData = const FlGridData(),
     FlBorderData borderData,
     FlTouchData touchData,
+    this.axisTitleData,
     this.minX,
     this.maxX,
     this.minY,

lib/src/chart/base/axis_chart/axis_chart_painter.dart

@@ -1,3 +1,5 @@
+import 'dart:math' as math;
+
 import 'package:fl_chart/src/chart/bar_chart/bar_chart_painter.dart';
 import 'package:fl_chart/src/chart/base/base_chart/base_chart_painter.dart';
 import 'package:fl_chart/src/chart/line_chart/line_chart_painter.dart';
@@ -28,6 +30,152 @@ abstract class AxisChartPainter<D extends AxisChartData> extends BaseChartPainte
     drawGrid(canvas, size);
   }
 
+
+  void drawAxisTitles(Canvas canvas, Size viewSize) {
+    if (!data.axisTitleData.show) {
+      return;
+    }
+    viewSize = getChartUsableDrawSize(viewSize);
+
+    final axisTitles = data.axisTitleData;
+
+    // Left Title
+    final leftTitle = axisTitles.leftTitle;
+    if (leftTitle.showTitle) {
+      final TextSpan span =
+      TextSpan(style: leftTitle.textStyle, text: leftTitle.titleText);
+      final TextPainter tp = TextPainter(
+          text: span,
+          textAlign: leftTitle.textAlign,
+          textDirection: TextDirection.ltr);
+      tp.layout(minWidth: viewSize.height);
+      canvas.save();
+      canvas.rotate(-math.pi * 0.5);
+      tp.paint(
+          canvas,
+          Offset(-viewSize.height - getTopOffsetDrawSize(),
+              leftTitle.reservedSize - tp.height));
+      canvas.restore();
+    }
+
+    // Top title
+    final topTitle = axisTitles.topTitle;
+    if (topTitle.showTitle) {
+      final TextSpan span =
+      TextSpan(style: topTitle.textStyle, text: topTitle.titleText);
+      final TextPainter tp = TextPainter(
+          text: span,
+          textAlign: topTitle.textAlign,
+          textDirection: TextDirection.ltr);
+      tp.layout(minWidth: viewSize.width);
+      tp.paint(canvas,
+          Offset(getLeftOffsetDrawSize(), topTitle.reservedSize - tp.height));
+    }
+
+    // Right Title
+    final rightTitle = axisTitles.rightTitle;
+    if (rightTitle.showTitle) {
+      final TextSpan span =
+      TextSpan(style: rightTitle.textStyle, text: rightTitle.titleText);
+      final TextPainter tp = TextPainter(
+          text: span,
+          textAlign: rightTitle.textAlign,
+          textDirection: TextDirection.ltr);
+      tp.layout(minWidth: viewSize.height);
+      canvas.save();
+      canvas.rotate(-math.pi * 0.5);
+      tp.paint(
+          canvas,
+          Offset(
+              -viewSize.height - getTopOffsetDrawSize(),
+              viewSize.width +
+                  getExtraNeededHorizontalSpace() -
+                  rightTitle.reservedSize));
+      canvas.restore();
+    }
+
+    // Bottom title
+    final bottomTitle = axisTitles.bottomTitle;
+    if (bottomTitle.showTitle) {
+      final TextSpan span =
+      TextSpan(style: bottomTitle.textStyle, text: bottomTitle.titleText);
+      final TextPainter tp = TextPainter(
+          text: span,
+          textAlign: bottomTitle.textAlign,
+          textDirection: TextDirection.ltr);
+      tp.layout(minWidth: viewSize.width);
+      tp.paint(
+          canvas,
+          Offset(
+              getLeftOffsetDrawSize(),
+              getExtraNeededVerticalSpace() -
+                  bottomTitle.reservedSize +
+                  viewSize.height));
+    }
+  }
+
+  @override
+  double getExtraNeededHorizontalSpace() {
+    double sum = super.getExtraNeededHorizontalSpace();
+
+    if (data.axisTitleData.show) {
+      final leftSide = data.axisTitleData.leftTitle;
+      if (leftSide.showTitle) {
+        sum += leftSide.reservedSize + leftSide.margin;
+      }
+
+      final rightSide = data.axisTitleData.rightTitle;
+      if (rightSide.showTitle) {
+        sum += rightSide.reservedSize + rightSide.margin;
+      }
+    }
+
+    return sum;
+  }
+
+  @override
+  double getExtraNeededVerticalSpace() {
+    double sum = super.getExtraNeededVerticalSpace();
+
+    if (data.axisTitleData.show) {
+      final topSide = data.axisTitleData.topTitle;
+      if (topSide.showTitle) {
+        sum += topSide.reservedSize + topSide.margin;
+      }
+
+      final bottomSide = data.axisTitleData.bottomTitle;
+      if (bottomSide.showTitle) {
+        sum += bottomSide.reservedSize + bottomSide.margin;
+      }
+    }
+
+    return sum;
+  }
+
+  @override
+  double getLeftOffsetDrawSize() {
+    var sum = super.getLeftOffsetDrawSize();
+
+    final leftAxisTitle = data.axisTitleData.leftTitle;
+    if (data.axisTitleData.show && leftAxisTitle.showTitle) {
+      sum += leftAxisTitle.reservedSize + leftAxisTitle.margin;
+    }
+
+    return sum;
+  }
+
+  @override
+  double getTopOffsetDrawSize() {
+    var sum = super.getTopOffsetDrawSize();
+
+    final topAxisTitle = data.axisTitleData.topTitle;
+    if (data.axisTitleData.show && topAxisTitle.showTitle) {
+      sum += topAxisTitle.reservedSize + topAxisTitle.margin;
+    }
+
+    return sum;
+  }
+
   void drawGrid(Canvas canvas, Size viewSize) {
     if (!data.gridData.show || data.gridData == null) {
       return;

lib/src/chart/base/base_chart/base_chart_data.dart

@@ -56,7 +56,7 @@ class FlBorderData {
     );
   }
 
-
+  
 }
 
 /***** TouchData *****/
@@ -72,6 +72,69 @@ class FlTouchData {
   const FlTouchData(this.enabled, this.enableNormalTouch);
 }
 
+///***** AxisTitleData *****/
+
+/// This class holds data about the description for each axis of the chart.
+class FlAxisTitleData {
+  final bool show;
+
+  final AxisTitle leftTitle, topTitle, rightTitle, bottomTitle;
+
+  const FlAxisTitleData({
+    this.show = true,
+    this.leftTitle = const AxisTitle(reservedSize: 16),
+    this.topTitle = const AxisTitle(reservedSize: 16),
+    this.rightTitle = const AxisTitle(reservedSize: 16),
+    this.bottomTitle = const AxisTitle(reservedSize: 16),
+  });
+
+  static FlAxisTitleData lerp(FlAxisTitleData a, FlAxisTitleData b, double t) {
+    return FlAxisTitleData(
+      show: b.show,
+      leftTitle: AxisTitle.lerp(a.leftTitle, b.leftTitle, t),
+      rightTitle: AxisTitle.lerp(a.rightTitle, b.rightTitle, t),
+      bottomTitle: AxisTitle.lerp(a.bottomTitle, b.bottomTitle, t),
+      topTitle: AxisTitle.lerp(a.topTitle, b.topTitle, t),
+    );
+  }
+}
+
+/// specify each axis titles data
+class AxisTitle {
+  final bool showTitle;
+  final double reservedSize;
+  final TextStyle textStyle;
+  final TextAlign textAlign;
+  final double margin;
+  final String titleText;
+
+  const AxisTitle({
+    this.showTitle = false,
+    this.titleText = '',
+    this.reservedSize = 14,
+    this.textStyle = const TextStyle(
+      color: Colors.black,
+      fontSize: 11,
+    ),
+    this.textAlign = TextAlign.center,
+    this.margin = 4,
+  });
+
+  static AxisTitle lerp(AxisTitle a, AxisTitle b, double t) {
+    return AxisTitle(
+      showTitle: b.showTitle,
+      titleText: b.titleText,
+      reservedSize: lerpDouble(a.reservedSize, b.reservedSize, t),
+      textStyle: TextStyle.lerp(
+          a.textStyle.copyWith(fontSize: a.textStyle.fontSize),
+          b.textStyle.copyWith(fontSize: b.textStyle.fontSize),
+          t),
+      textAlign: b.textAlign,
+      margin: lerpDouble(a.margin, b.margin, t),
+    );
+  }
+}
+
 /***** TitlesData *****/
 
 /// we use this typedef to determine which titles