How to fit the rectangle text annotation in WPF Charts?

7 mins read

This article explains how to automatically resize rectangle annotation text in WPF Chart.

In the following use case, we dynamically change the annotation text and adjust the annotation based on the new text. This is illustrated in the accompanying image.

WPF
Chart Annotation Text Fit

This is achieved by adjusting the X2 and Y2 values of the annotation, based on the measured size of the text entered in a TextBox. See the following code sample for guidance:

XAML

  <Grid x:Name="grid">
        <Grid.DataContext>
            <local:ViewModel/>
        </Grid.DataContext>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="80*"/>
            <ColumnDefinition Width="20*"/>
        </Grid.ColumnDefinitions>
 
        <chart:SfChart x:Name="chart">
            <chart:SfChart.PrimaryAxis>
                <chart:NumericalAxis x:Name="xAxis"/>
            </chart:SfChart.PrimaryAxis>
 
            <chart:SfChart.SecondaryAxis>
                <chart:NumericalAxis x:Name="yAxis" />
            </chart:SfChart.SecondaryAxis>
 
            <chart:ColumnSeries ItemsSource="{Binding Collection}" 
                                XBindingPath="XValue" 
                                YBindingPath="YValue"/>
            <chart:SfChart.Annotations>
                <!-- Text of rectangle annotation has been updated from TextBox -->
                <chart:RectangleAnnotation x:Name="annotation"
                                           HorizontalTextAlignment="Stretch"
                                           VerticalTextAlignment="Stretch"
                                           X1="2.5"
                                           Text="{Binding Source={x:Reference txtBlock},Path=Text}"
                                           Y1="22"
                                           ClipToBounds="True"/>
            </chart:SfChart.Annotations>
        </chart:SfChart>
 
        <StackPanel Orientation="Vertical" Grid.Column="1"
                    HorizontalAlignment="Center" 
                    VerticalAlignment="Center">
            <TextBlock Text="Change the annotation text" Margin="0,0,0,20" 
                       HorizontalAlignment="Center" 
                       VerticalAlignment="Center"/>
            <!-- TextChanged event hook for updating its annotation's X2 and Y2 on every text change -->
            <TextBox x:Name="txtBlock" 
                     TextChanged="txtBlock_TextChanged" />
        </StackPanel>
    </Grid>

private Size MeasuringString(string text)
        {
            if (string.IsNullOrEmpty(text))
            {
                return new Size(0, 0);
            }
 
            var TextBlock = new TextBlock()
            {
                Text = text,
                FontWeight = FontWeights.Bold,
            };
 
            TextBlock.Measure(new Size(Double.PositiveInfinity, Double.PositiveInfinity));
            return new Size(TextBlock.DesiredSize.Width, TextBlock.DesiredSize.Height);
        }
 
        private void UpdateAnnotation()
        {
            // Measure the size of the updated text in the TextBox
            Size desireSize = MeasuringString(txtBlock.Text);
            var point1 = chart.ValueToPoint(xAxis, Convert.ToDouble(annotation.X1));
            var point2 = chart.ValueToPoint(yAxis, Convert.ToDouble(annotation.Y1));
            var point3 = point1 + desireSize.Width;
            var point4 = point2 + desireSize.Height;
            Point x2Points = new Point(point3, point4);
            var x2 = chart.PointToValue(chart.PrimaryAxis, x2Points);
            var y2 = chart.PointToValue(chart.SecondaryAxis, x2Points);
            annotation.X2 = x2;
            annotation.Y2 = y2;
        }
 
 
        private void txtBlock_TextChanged(object sender, TextChangedEventArgs e)
        {
            UpdateAnnotation();
        }

For a detailed view, explore the sample on GitHub.

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Conclusion

I hope you enjoyed learning how to fit the rectangle text annotation in WPF Charts.

You can refer to our WPF Chart feature tour page know about its other groundbreaking feature representations and documentation, and how to quickly get started for configuration specifications. You can also explore our WPF Chart Examples to understand how to create and manipulate data.

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How to fit the rectangle text annotation in WPF Charts?

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