Window sizing constraints by content

Question

I want the window to respect MinWidth/MinHeight and MaxWidth/MaxHeight specifications of the content control inside.

Some suggested using SizeToContent, but this only helps to set the initial window size, not the constraints.

Others suggested overriding MeasureOverride and setting window's Min/Max height and width there, but this seems to be somewhat unclean, considering that such a trivial problem should surely have a purely declarative solution.

Just to mention another solution which seems reasonable but does not work (and had been previously mentioned in an answer which got deleted): binding MinWidth of the window to MinWidth of the control does not take into account window decorations.

Answer 1

Use Binding markup extension. A binding is wpf's way of saying when this property (source) changes update some other property (target). In this case the Grid's MinWidth property is the Source and your window's MinWidth property is the target.

<Window x:Class="MinMaxValuesOnWindows.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="600" Width="800"
    MinWidth="{Binding ElementName=gridy, Path=MinWidth}"
    MinHeight="{Binding ElementName=gridy, Path=MinHeight}"
    MaxWidth="{Binding ElementName=gridy, Path=MaxWidth}"
    MaxHeight="{Binding ElementName=gridy, Path=MaxHeight}">
    <Grid Name="gridy"  MinHeight="80" MinWidth="80" MaxHeight="300" MaxWidth="300"/>
</Window>

As you mentioned in the topic this does not completely work, but you can use a converter on the binding to add on the window frame's height and width before updating the binding target (might require a PInvoke). Since I doubt the window frame thickness is dynamically changing in your application this can probably just be constant value (not necessarily true if user changes themes).

Answer 2

Some suggested using SizeToContent, but this only helps to set the initial window size, not the constraints.

I worked around this by setting the MinWidth and MinHeight properties right after the windows was initialized:

MainWindow.xaml

<Window ... SizeToContent="WidthAndHeight">
    ...
</Window>

MainWindow.xaml.cs

public MainWindow()
{
    InitializeComponent();
    SourceInitialized += (s, e) =>
    {
        MinWidth = ActualWidth;
        MinHeight = ActualHeight;
    };
}

Answer 3

If the initial window size is set so that actual content size is not coerced by the content's MinWidth/MinHeight and MaxWidth/MaxHeight in the initial layout pass (for example, by using Window.SizeToContent="WidthAndHeight"), then following equations are true:

Window.ActualSize - Content.ActualSize = 
      Window.MinSize - Content.MinSize = Window.MaxSize - Content.MaxSize.

Based on these equations you can derive the following code:

public MainWindow()
{
    InitializeComponent();

    this.SizeChanged += OnWindowSizeChanged;
}

private static void OnWindowSizeChanged(object sender, SizeChangedEventArgs e)
{
    var window = (Window)sender;
    var content = (FrameworkElement)window.Content;

    window.MinWidth = window.ActualWidth - content.ActualWidth + content.MinWidth;
    window.MaxWidth = window.ActualWidth - content.ActualWidth + content.MaxWidth;

    window.MinHeight = window.ActualHeight - content.ActualHeight + content.MinHeight;
    window.MaxHeight = window.ActualHeight - content.ActualHeight + content.MaxHeight;

    window.SizeChanged -= OnWindowSizeChanged;
}

I do not know how to achieve this efficiently using the pure declarative approach since the code should be ran just once after the initial layout pass.