Resolving WPF GridSplitter Issues with Column and Row Length Converters

Windows Presentation Foundation (WPF) offers powerful tools for creating dynamic and responsive user interfaces. One common challenge developers face is managing the size and visibility of grid rows and columns, especially when using the GridSplitter control. This article delves into a specific scenario where a WPF converter applied to grid column and row lengths stops functioning correctly after a GridSplitter is used to resize the grid.

The Problem: Converter Invalidation After GridSplitter Interaction

Imagine a WPF application where you use a converter to dynamically show or hide rows and columns in a grid based on boolean values. This setup works perfectly until the user interacts with a GridSplitter to resize the grid. After the resize, the converter no longer updates the column or row lengths as expected. The core issue is that the GridSplitter seems to disrupt the binding between the boolean value and the column/row definition, preventing the converter from functioning correctly.

Understanding the Scenario

Here’s a breakdown of the situation:

• Boolean-to-Length Conversion: A custom converter (BoolToGridLengthConverter) is used to translate a boolean value into a GridLength value. If the boolean is true, the column/row gets a specific length; otherwise, it collapses to zero.
• Dynamic Resizing: The goal is to allow users to "maximize" a section of the grid. This involves setting specific boolean values to false (hiding the elements) and one specific boolean to True (maximizing the specific section).
• GridSplitter Interference: When a GridSplitter is used, the dynamic adjustment breaks. The converter correctly hides and maximized sections of the grid, but after the GridSplitter has been used it changes the column's value to true.

Code Example: The Initial Setup

Here's the initial setup that demonstrates the problem:

[ValueConversion(typeof(bool), typeof(GridLength))]
public class BoolToGridLengthConverter : IValueConverter
{
    public int Length { get; set; }

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return ((bool)value == true) ? new GridLength(Length == 0 ? 1 : Length, GridUnitType.Star) : new GridLength(0);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return null; // Not needed
    }
}

<Grid>
    <Grid.Resources>
        <helpers:BoolToGridLengthConverter x:Key="BoolToGridLengthConverter1" Length="1" />
        <helpers:BoolToGridLengthConverter x:Key="BoolToGridLengthConverter2" Length="2" />
    </Grid.Resources>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="{Binding ShowColumn1, Mode=TwoWay, Converter={StaticResource BoolToGridLengthConverter1}}" />
        <ColumnDefinition Width="5" />
        <ColumnDefinition Width="{Binding ShowColumn2, Mode=TwoWay, Converter={StaticResource BoolToGridLengthConverter1}}" />
        <ColumnDefinition Width="5" />
        <ColumnDefinition Width="{Binding ShowColumn3, Mode=TwoWay, Converter={StaticResource BoolToGridLengthConverter1}}" />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="{Binding ShowRow1, Mode=TwoWay, Converter={StaticResource BoolToGridLengthConverter1}}" />
        <RowDefinition Height="5" />
        <RowDefinition Height="{Binding ShowRow2, Mode=TwoWay, Converter={StaticResource BoolToGridLengthConverter2}}" />
    </Grid.RowDefinitions>
    <Grid Grid.Column="0" Grid.ColumnSpan="5" Grid.Row="0"></Grid>
    <GridSplitter Grid.Column="0" Grid.ColumnSpan="5" Grid.Row="1" ResizeDirection="Rows" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Height="5" />
    <Grid Grid.Column="0" Grid.Row="2"></Grid>
    <GridSplitter Grid.Column="1" Grid.Row="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="5" />
    <Grid Grid.Column="2" Grid.Row="2"></Grid>
    <GridSplitter Grid.Column="3" Grid.Row="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="5" />
    <Grid Grid.Column="4" Grid.Row="2"></Grid>
</Grid>

The Solution: Using MaxWidth/MaxHeight

Instead of directly manipulating the Width or Height properties, a more robust approach is to control the MaxWidth and MaxHeight properties of the ColumnDefinition and RowDefinition respectively.

1. Create a New Converter: Implement a converter that translates the boolean value to a double representing the maximum size.

[ValueConversion(typeof(bool), typeof(double))]
public class BoolToMaxConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return ((bool)value == true) ? double.MaxValue : 0d;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return null; // Not needed
    }
}

2. Modify the XAML: Apply the new converter to the MaxWidth and MaxHeight properties.

<Grid>
    <Grid.Resources>
        <local:BoolToMaxConverter x:Key="BoolToMaxConverter" />
    </Grid.Resources>
    <Grid.ColumnDefinitions>
        <ColumnDefinition MaxWidth="{Binding ShowColumn1, Converter={StaticResource BoolToMaxConverter}}" />
        <ColumnDefinition Width="5" />
        <ColumnDefinition MaxWidth="{Binding ShowColumn2, Converter={StaticResource BoolToMaxConverter}}" />
        <ColumnDefinition Width="5" />
        <ColumnDefinition MaxWidth="{Binding ShowColumn3, Converter={StaticResource BoolToMaxConverter}}" />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition MaxHeight="{Binding ShowRow1, Converter={StaticResource BoolToMaxConverter}}" />
        <RowDefinition Height="5" />
        <RowDefinition MaxHeight="{Binding ShowRow2, Converter={StaticResource BoolToMaxConverter}}" />
    </Grid.RowDefinitions>
    <Grid Grid.Column="0" Grid.ColumnSpan="5" Grid.Row="0"></Grid>
    <GridSplitter Grid.Column="0" Grid.ColumnSpan="5" Grid.Row="1" ResizeDirection="Rows" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Height="5" />
    <Grid Grid.Column="0" Grid.Row="2"></Grid>
    <GridSplitter Grid.Column="1" Grid.Row="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="5" />
    <Grid Grid.Column="2" Grid.Row="2"></Grid>
    <GridSplitter Grid.Column="3" Grid.Row="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="5" />
    <Grid Grid.Column="4" Grid.Row="2"></Grid>
</Grid>

By setting the MaxWidth and MaxHeight to 0 when the boolean is false, the column or row effectively collapses. When the boolean is true, setting these properties to double.MaxValue allows the column or row to expand as needed.

Additional Considerations

• Two-Way Binding: In many cases, the Mode=TwoWay binding is unnecessary and can be removed. Consider if you actually need to update the source property when the MaxWidth or MaxHeight changes. If not, use Mode=OneWay for better performance and to avoid potential binding issues.
• Alternatives to Visibility Converter: While a Visibility Converter might seem like a simple solution, it often doesn't resize the other columns correctly. The MaxWidth/MaxHeight approach provides more consistent and predictable resizing behavior, so is the preferred solution.
• MVVM and INotifyPropertyChanged: Ensure that the boolean properties (ShowColumn1, ShowRow2, etc.) in your ViewModel implement INotifyPropertyChanged correctly. This ensures that the UI updates whenever the boolean values change.

Conclusion

When working with WPF grids and GridSplitters, directly manipulating Width and Height using converters can lead to unexpected behavior. By using the MaxWidth and MaxHeight properties in conjunction with a boolean converter, you can achieve reliable dynamic resizing even after user interaction with the GridSplitter. This approach provides a more robust and maintainable solution for creating flexible and responsive WPF layouts.