Align items in a stack panel?

I was wondering if I can have 2 controls in a horizontal-oriented StackPanel so that the right item should be docked to the right side of the StackPanel.

I tried the following but it didn't work:

<StackPanel Orientation="Horizontal">
    <TextBlock>Left</TextBlock>
    <Button Width="30" HorizontalAlignment="Right">Right<Button>
</StackPanel>

In the snippet above I want the Button to be docked to the right side of the StackPanel.

Note: I need it to be done with StackPanel, not Grid etc.

You can achieve this with a DockPanel:

<DockPanel Width="300">
    <TextBlock>Left</TextBlock>
    <Button HorizontalAlignment="Right">Right</Button>
</DockPanel>

The difference is that a StackPanel will arrange child elements into single line (either vertical or horizontally) whereas a DockPanel defines an area where you can arrange child elements either horizontally or vertically, relative to each other (the Dock property changes the position of an element relative to other elements within the same container. Alignment properties, such as HorizontalAlignment, change the position of an element relative to its parent element).

Update

As pointed out in the comments you can also use the FlowDirection property of a StackPanel. See @D_Bester's answer.

Yo can set FlowDirection of Stack panel to RightToLeft, and then all items will be aligned to the right side.

For those who stumble upon this question, here's how to achieve this layout with a Grid:

<Grid>
    <TextBlock Text="Server:"/>
    <TextBlock Text="http://127.0.0.1" HorizontalAlignment="Right"/>
</Grid>

creates

Server:                                                                   http://127.0.0.1

Could not get this working using a DockPanel quite the way I wanted and reversing the flow direction of a StackPanel is troublesome. Using a grid is not an option as items inside of it may be hidden at runtime and thus I do not know the total number of columns at design time. The best and simplest solution I could come up with is:

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*" />
        <ColumnDefinition Width="Auto" />
    </Grid.ColumnDefinitions>
    <StackPanel Grid.Column="1" Orientation="Horizontal">
        <!-- Right aligned controls go here -->
    </StackPanel>
</Grid>

This will result in controls inside of the StackPanel being aligned to the right side of the available space regardless of the number of controls - both at design and runtime. Yay! :)

This works perfectly for me. Just put the button first since you're starting on the right. If FlowDirection becomes a problem just add a StackPanel around it and specify FlowDirection="LeftToRight" for that portion. Or simply specify FlowDirection="LeftToRight" for the relevant control.

<StackPanel Orientation="Horizontal" HorizontalAlignment="Right" FlowDirection="RightToLeft">
    <Button Width="40" HorizontalAlignment="Right" Margin="3">Right</Button>
    <TextBlock Margin="5">Left</TextBlock>
	<StackPanel FlowDirection="LeftToRight">
		<my:DatePicker Height="24" Name="DatePicker1" Width="113" xmlns:my="http://schemas.microsoft.com/wpf/2008/toolkit" />    
	</StackPanel>
	<my:DatePicker FlowDirection="LeftToRight" Height="24" Name="DatePicker1" Width="113" xmlns:my="http://schemas.microsoft.com/wpf/2008/toolkit" />    
</StackPanel>

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="*"/>
    </Grid.ColumnDefinitions>
    <TextBlock Text="Left"  />
    <Button Width="30" Grid.Column="1" >Right</Button>
</Grid>

If you are having a problem like the one I had where labels were centered in my vertical stack panel, make sure you use full width controls. Delete the Width property, or put your button in a full-width container that allows internal alignment. WPF is all about using containers to control the layout.

<StackPanel Orientation="Vertical">
    <TextBlock>Left</TextBlock>
    <DockPanel>
        <Button HorizontalAlignment="Right">Right</Button>
    </DockPanel>
</StackPanel>

Vertical StackPanel with Left Label followed by Right Button

I hope this helps.

for windows 10 use relativePanel instead of stack panel, and use

> relativepanel.alignrightwithpanel="true"

for the contained elements.

Maybe not what you want if you need to avoid hard-coding size values, but sometimes I use a "shim" (Separator) for this:

<Separator Width="42"></Separator>