It seem that GroupBox can only contain one element, if I place more than one it's won't go inside(or get deleted in blend).
Is this by design or am I doing something wrong?
That sounds right to me. You'd need to put a Grid or Panel (StackPanel, WrapPanel, etc) as a child to define the layout.
Yes, in WPF the GroupBox will contain maximum of 1 element. You can include Grid as its child and in grid specify your desired components. For example 1 placed two buttons in GroupBox using Grid.
Document Outline is shown below:
Code is as follow:
<GroupBox
Header="Read Sensor"
HorizontalAlignment="Left"
Margin="485,4,0,0"
VerticalAlignment="Top"
Height="188"
Width="238">
<Grid
HorizontalAlignment="Left"
Height="169"
Margin="0,0,-13,-3"
VerticalAlignment="Top"
Width="229">
<Button
x:Name="btnReadSensor1"
Content="Read Sensor 1"
HorizontalAlignment="Left"
Margin="10,91,0,0"
VerticalAlignment="Top"
Width="207"
Click="btnReadSensor1_Click" />
<Button
x:Name="btnReadSensor2"
Content="Read Sensor 2"
HorizontalAlignment="Left"
Margin="10,64,0,0"
VerticalAlignment="Top"
Width="207"
Click="btnReadSensor2_Click" />
</Grid>
</GroupBox>
Well the real answer is because groupbox inherits from HeaderedContentControl
Take a look here MSDN
You must drag the items: textbox INTO the groupbox and must only have a single groupbox. Cannot drag more than a single groupbox per linear coordinate for it to work. Can have multiple groupboxes on a page, but not more than a single column wide or you will be limited with only having a single item being added to the groupbox.
来源:https://stackoverflow.com/questions/1356036/groupbox-in-wpf-can-only-contain-one-element