Expanding usercontrol below GridSplitter

Question

I have an application with simple LogView. Messages from program are collected to this log and log is scrolling so the last message is always visible to the user. In the ApplicationMainView there is a grid with few rows and GridSplitter between two rows. The log is at the bottom of the screen and GridSplitter is above the log (user can resize the log window size).

Here comes the problem: When application starts and messages are added to the log window, GridSplitter starts moving up and the log window starts to grow. When user changes the log size with GridSplitter and messages are added to the window, GridSplitter does not move and the log window remains its size. Here is a gif image showing the situation.

Where should I change the code so that LogView remains its size from the application start and user don’t have to move the GridSplitter?

Code for ApplicationMainView where the LogView is:

<Window
    x:Class="UI.ApplicationMainView"
    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:UI">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition
                Height="Auto" />
            <RowDefinition
                Height="Auto" />
            <RowDefinition
                Height="*" />
            <RowDefinition
                Height="Auto" />
            <RowDefinition
                Height="Auto" />
        </Grid.RowDefinitions>
        <!-- Other controls removed for simplifaction-->
        <local:FilesView
            Grid.Row="2"
            DataContext="{Binding Files}" />
        <GridSplitter
            Grid.Row="3"
            Height="5"
            ResizeDirection="Rows"
            ResizeBehavior="PreviousAndNext"
            HorizontalAlignment="Stretch"
            VerticalAlignment="Center"
            ShowsPreview="True" />
        <!-- Here is the log -->
        <local:LogView
            Grid.Row="4"
            DataContext="{Binding Log}" />
    </Grid>
</Window>

Code for LogView:

<UserControl
    x:Class="UI.LogView"
    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"
    xmlns:local="clr-namespace: UI">
    <HeaderedContentControl>
        <HeaderedContentControl.Template>
            <ControlTemplate
                TargetType="HeaderedContentControl">
                <DockPanel>
                    <ContentPresenter
                        DockPanel.Dock="Top"
                        ContentSource="Header" />
                    <ContentPresenter />
                </DockPanel>
            </ControlTemplate>
        </HeaderedContentControl.Template>
        <HeaderedContentControl.Header>
            <Border
                Background="Gray"
                CornerRadius="0,20,0,0">
                <Label
                    Content="Log" />
            </Border>
        </HeaderedContentControl.Header>
        <Border
            BorderThickness="2,0,2,2"
            BorderBrush="Gray">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition
                        Height="*" />
                    <RowDefinition
                        Height="Auto" />
                </Grid.RowDefinitions>
                <DataGrid
                    x:Name="LogGrid"
                    Grid.Row="0"
                    AutoGenerateColumns="False"
                    CanUserAddRows="False"
                    IsReadOnly="True"
                    GridLinesVisibility="None"
                    MinHeight="50"
                    ItemsSource="{Binding AllMessages}">
                    <DataGrid.Columns>
                        <DataGridTextColumn
                            Binding="{Binding Time}"
                            CanUserSort="False"
                            CanUserReorder="False"
                            IsReadOnly="True"
                            Header="Time" />
                        <DataGridTextColumn
                            Binding="{Binding Message}"
                            Width="*"
                            CanUserSort="False"
                            CanUserReorder="False"
                            IsReadOnly="True"
                            Header="Message" />
                    </DataGrid.Columns>
                </DataGrid>
                <DockPanel
                    Grid.Row="1"
                    LastChildFill="False">
                    <Button
                        Content="Clear"
                        Command="{Binding ClearLogCommand}" />
                    <Button
                        Content="Copy clipboard"
                        Command="{Binding CopyLogClipboardCommand}" />
                </DockPanel>
            </Grid>
        </Border>
    </HeaderedContentControl>
</UserControl>

Code behind the LogView (for scrolling the log):

using System.Collections.Specialized;
using System.Windows.Controls;

namespace UI
{
    public partial class LogView : UserControl
    {
        public LogView()
        {
            InitializeComponent();
            ((INotifyCollectionChanged)LogGrid.Items).CollectionChanged += OnLogViewCollectionChanged;
        }

        private void OnLogViewCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            if (LogGrid.Items.Count > 0)
            {
                LogGrid.ScrollIntoView(LogGrid.Items[LogGrid.Items.Count - 1]);
            }
        }
    }
}

Answer 1

You defined the bottom row of the grid:

<RowDefinition Height="Auto" />

This is making the LogView grow.

You must define Height either as a fixed size

Height="200"

or as a percentage of the screen

Height="*" or Height="2*"