WPF ScrollViewer pushing control out of window

Question

I have a DockPanel, which contains some controls including a ScrollViewer.

What I WANT to happen, is for the ScrollViewer to allow the grid to be scrolled, without pushing other controls off the bottom of the form.

Instead, the ScrollViewer expands to the height of the window, rather than the top of the Button, pushing the Button off for the bottom of the form. Why is this? How do I fix it?

<Window x:Class="Class1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:Class1"
    mc:Ignorable="d"
    Title="MainWindow" Height="800" Width="600"
    WindowStartupLocation="CenterScreen">
<DockPanel LastChildFill="False">
    <Menu DockPanel.Dock="Top">
        <MenuItem Header="File">
            <MenuItem Name="miQuit" Header="Quit" Click="miQuit_Click" />
        </MenuItem>
    </Menu>
    <ToolBarTray DockPanel.Dock="Top" IsLocked="True">
        <ToolBar>
            <Button Name="btnQuit" ToolBar.OverflowMode="Never" Click="btnQuit_Click">
                Quit
            </Button>
        </ToolBar>
    </ToolBarTray>
    <ScrollViewer VerticalScrollBarVisibility="Auto" DockPanel.Dock="Top" VerticalAlignment="Stretch">
        <Grid Name="gMainGrid" ScrollViewer.CanContentScroll="True">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
                <RowDefinition />
            </Grid.RowDefinitions>
            <TextBox Grid.Column="0" Grid.Row="0"   Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="1"   Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="2"   Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="3"   Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="4"   Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="5"   Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="6"   Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="7"   Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="8"   Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="9"   Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="10"  Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="11"  Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="12"  Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="13"  Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="14"  Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="15"  Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="16"  Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="17"  Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="18"  Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="19"  Width="100" Margin="10,10,10,10"/>
            <TextBox Grid.Column="0" Grid.Row="20"  Width="100" Margin="10,10,10,10"/>
        </Grid>
    </ScrollViewer>
    <Button Name="btnButton1" DockPanel.Dock="Bottom" Click="btnButton1_Click" >ButtonText</Button>
</DockPanel>

I want the menu bar at the top of the screen, the button at the bottom of the screen, and the grid with the ScrollViewer in the middle. What am I doing wrong?

Answer 1

The problem is that the ScrollViewer doesn't know how much height it should get. ScrollViewer is a control that tries to get as much size as its children need. DockPanel also gives as much size as the ScrollViewer need and therefore your problem. You can fix height of the ScrollViewer with pixels (i.e. Height=100) To make it a fixed height. I don't know your use case so this might be useful if you are showing an image carousel for example.

In more general layout advice I might say that you'd better use a grid instead of a DockPanel:

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="auto" />
        <RowDefinition Height="auto" />
        <RowDefinition Height="auto" />
        <!-- Next one is for middle part of the page -->
        <RowDefinition Height="*" />
        <RowDefinition Height="auto" />
    </Grid.RowDefinitions>
    <!-- your controls here -->
</Grid>

Answer 2

I found that I could have a dynamic height with the DockPanel if I stuck the whole thing in a Grid. This appears to work, as I can now have a dynamic height for the ScrollViewer.

<Window x:Class="Class1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:Class1"
    mc:Ignorable="d"
    Title="MainWindow" Height="800" Width="600"
    WindowStartupLocation="CenterScreen">
  <Grid>
      <Grid.ColumnDefinitions>
          <ColumnDefinition />
      </Grid.ColumnDefinitions>
      <Grid.RowDefinitions>
          <RowDefinition Height="*" />
          <RowDefinition Height="Auto" />
      </Grid.RowDefinitions>
      <DockPanel Grid.Column="0" Grid.Row="0" LastChildFill="False">

Everything is then as normal EXCEPT that I move my button outside of the DockPanel and into the Grid's second row:

        </DockPanel>
    <Button Grid.Column="0" Grid.Row="1" Name="btnButton1" DockPanel.Dock="Bottom" Click="btnButton1_Click" >ButtonText</Button>
</Grid>

The rows with a Height of "Auto" will size to fit their content. The rows with a Height of asterisk (*) will size to fill the remaining space after the size of the Autos has been calculated. Thus everything sizes up correctly and nicely.

Alternatively, at this point I can do-away with the DockPanel entirely and have the Menu, ToolBarTray, ScrollViewer, and Button in their own separate grid rows, like Emad suggests in their answer (although I'm not sure what the extra row is for in their example).

    <Grid.ColumnDefinitions>
        <ColumnDefinition />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="Auto" />
        <RowDefinition Height="*" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>

I ultimately decided to go for that approach, so I'll mark it as the answer, but I'm putting this all here for the full explanation, for completeness (in case people do happen to want to keep their DockPanel).