Cant get right label size - wpf

Question

I need to write a control, which will look like this:
Click Here to se callout
Problem is that i cant get label's real size to redraw my rectangle geometry. Label's height is always much bigger then space that it really occupies on the screen. I dont know, what to. Here is code:
<Popup x:Class="Controls.Callout"
x:ClassModifier="internal"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008" >
<Grid>
<Image>
<Image.Source>
<DrawingImage>
<DrawingImage.Drawing >
<GeometryDrawing Brush="Orange" x:Name="geometryDrawing">
<GeometryDrawing.Pen>
<Pen Brush="Black" Thickness="2"/>
</GeometryDrawing.Pen>
<GeometryDrawing.Geometry>
<CombinedGeometry GeometryCombineMode="Union">
<CombinedGeometry.Geometry1>
<RectangleGeometry x:Name="rectangel"
RadiusX="15" RadiusY="15"
Rect="0,30, 300,100"
/>
</CombinedGeometry.Geometry1>
<CombinedGeometry.Geometry2>
<PathGeometry>
<PathFigure StartPoint="30,30" IsClosed="False">
<PolyLineSegment Points="15,0, 90,30"/>
</PathFigure>
</PathGeometry>
</CombinedGeometry.Geometry2>
</CombinedGeometry>
</GeometryDrawing.Geometry>
</GeometryDrawing>
</DrawingImage.Drawing>
</DrawingImage>
</Image.Source>
</Image>
<Label Padding="5 20" MaxWidth="300" Name="myLabel" FontSize="16" >
<!--Content="{Binding}">-->
<!--MaxHeight="100" MaxWidth="300">-->
<AccessText TextWrapping="Wrap" MaxHeight="50"/>
</Label>
</Grid>
</Popup>
Code behind:
internal partial class Callout : Popup
{
public Callout()
{
InitializeComponent();
}
protected override void OnOpened(System.EventArgs e)
{
rectangel = new RectangleGeometry(new Rect(0,30,300, myLabel.Height/2));
}
}

Answer 1

Why not use a Grid with a Rectangle with rounded corners, a TextBlock, and some shape on top of the rectangle to make the callout "pointer"? As a Grid, the rectangle can automatically expand to the full size needed by the TextBlock.
For example, you can create a UserControl (or a full-fledged templated control) and given it a MaxWidth so that the text wraps. Then put the control in a Canvas so that it can determine its own size.
<UserControl MaxWidth="200">
<Grid >
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Rectangle Grid.Row="1" RadiusX="50" RadiusY="50"
StrokeThickness="8" Stroke="Gray" />
<!-- Here will be pointer in Grid.Row="0"-->
<TextBlock Grid.Row="1" Name="myLabel" Margin="20" Foreground="Black"
Text="This is the textblock....." FontSize="20" TextWrapping="Wrap" />
</Grid>
</UserControl>