How to set a button size regarding the height of its container in XAML?

Question

I am developping a WPF application in XAML. I am a beginner and I have an issue with my button. I need to set its height as a proportion of its container which is a grid. I saw that the height can be set to a value or to "Auto", but I don't know how to say to my button that his height must be 3/4 of the height of the grid in which it is contained.

Does anybody know how to deal with that ? Is it possible to do that with XAML ?

The objective is that when the grid grows, the button grows with it.

Any help would be appreciate.

Thanks

Here is the code I wrote :

<Window x:Class="WpfAppButtonSize.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:WpfAppButtonSize"
    mc:Ignorable="d"
    Title="MainWindow" Height="450" Width="800">

<Grid>
    <Grid Height="100" Width="250" HorizontalAlignment="Center" VerticalAlignment="Center">
        <Button Content="Button 1" FontSize="30" Height="75" Width="150"/>
    </Grid>
</Grid>

For the button, instead of Height="75", I would like to say Height=0.75 * Grid Height

Answer 1

If you give your Grid and your Button a name by specifying the x:Name attribute, you could set the Button's Height in the code behind whenever the Grid's size changes.

XAML

<Grid x:Name="MyGrid">
    <Button x:Name="MyButton" />
</Grid>

MainWindow.xaml.cs

In WPF you could then do this in the code-behind:

public MainWindow()
{
    InitializeComponent();
    
    MyGrid.SizeChanged += (s,e) =>
    {
        if(e.HeightChanged)
        {
            MyButton.Height = MyGrid.Height * 0.75;
        }
    }
}

while in other .NET technologies, such as Xamarin.Forms or .NET MAUI it would have to look like this:

public MainWindow()
{
    InitializeComponent();
    
    MyGrid.PropertyChanged += (s,e) =>
    {
        if(e.PropertyName == nameof(MyGrid.Height))
        {
            MyButton.Height = MyGrid.Height * 0.75;
        }
    }
}