xceed propertygrid: choose between sets of custom propertydefinitions

Question

Until now, I use the Xceed propertygrid with AutoGenerateProperties="True" and specify which properties I don't want to display by using the [Browsable(false)] attribute.

Now I have a case, where I need to show only a subset of properties, depending on the value of an other property.

I think the answer is to use PropertyDefinitions, as shown here.

But the example only shows how to implement a single set of PropertyDefinitions that will be used for every inspected object.

Do you have a hint or an example of how I can define multiple sets of PropertyDefinitions and choose when they should be used?

Answer 1

Sorry this is quite a lengthy answer. I also used to use AutoGenerateProperties="True" however I had a similar issue.

My resulting solution was to populate the PropertyDefinition as you suggested. I did this programmatically as I ended up having some rather special cases with wanting properties created dynamically based on the contents of a collection somewhere. One thing I did notice was that even through programmatically checking through my classes to emulate the AutoGenerateProperties="True" feature mine was much faster than their solution.

In order to deal with the Visibility as you requested though I had to create my own Attribute to make items invisible from the PropertyGrid.

public class VisibilityAttribute : Attribute
{
    public Visibility Visibility { get; private set; }

    public VisibilityAttribute(Visibility visibility)
    {
        this.Visibility = visibility;
    }
}

Each item that can be selected in my project has it's own implementation of a PropertySetBase class that has property definitions like so:

[Category("Appearance"), LocalisedProperty(typeof(PropertySetBase), "LocalBackground", "LocalBackgroundDescription"), Editor(typeof(OptionalBrushEditor), typeof(OptionalBrushEditor)),
        PropertyOrder(0)]
    public virtual OptionalProperty<Brush> LocalBackground { get; set; }

And the logic to then process the PropertySetBases in the currentPropertySelection collection.

private void PreparePropertyGrid()
{
    PropertyDefinitionCollection propertyDefinitions = new PropertyDefinitionCollection();

    // This is how I determine 
    var mainPropertySet = this.currentPropertySelection.FirstOrDefault();

    if (mainPropertySet != null)
    {
        var properties = TypeDescriptor.GetProperties(mainPropertySet.GetType());
        // Allowing for multiple selection, if on further iterations through the selected items we will remove properties that do not exist in both PropertySets
        bool firstIteration = true;

        foreach (var x in this.currentPropertySelection)
        {
            foreach (var p in properties.Cast<PropertyDescriptor>())
            {
                if (!firstIteration)
                {
                    // Perhaps we should be checking a little more safely for TargetProperties but if the collection is empty we have bigger problems.
                    var definition = propertyDefinitions.FirstOrDefault(d => string.Equals(d.TargetProperties[0] as string, p.Name, StringComparison.Ordinal));

                    // Someone in the selection does not have this property so we can ignore it.
                    if (definition == null)
                    {
                        continue;
                    }

                    // If this item doesn't have the property remove it from the display collection and proceed.
                    var localProperty = x.GetType().GetProperty(p.Name);
                    if (localProperty == null)
                    {
                        propertyDefinitions.Remove(definition);
                        continue;
                    }

                    // There is actually no point in proceeding if this is not the first iteration and we have checked whether the property exists.
                    continue;
                }

                string category = p.Category;
                string description = p.Description;
                string displayName = p.DisplayName ?? p.Name;
                int? displayOrder = null;
                bool? isBrowsable = p.IsBrowsable;
                bool? isExpandable = null;

                var orderAttribute = p.Attributes[typeof(PropertyOrderAttribute)] as PropertyOrderAttribute;
                if (orderAttribute != null)
                {
                    displayOrder = orderAttribute.Order;
                }

                var expandableAttribute = p.Attributes[typeof(ExpandableObjectAttribute)] as ExpandableObjectAttribute;
                if (expandableAttribute != null)
                {
                    isExpandable = true;
                }

                propertyDefinitions.Add(new PropertyDefinition
                {
                    Category = category,
                    Description = description,
                    DisplayName = displayName,
                    DisplayOrder = displayOrder,
                    IsBrowsable = isBrowsable,
                    IsExpandable = isExpandable,
                    TargetProperties = new[] { p.Name },
                });
            }
        }

        firstIteration = false;

        this.propertyGrid.PropertyDefinitions = propertyDefinitions;
    }
}

When it came to actually showing/hiding the properties I did the following:

public void UpdateProperties(Tuple<string, bool?, Visibility?>[] newPropertyStates)
{
    // Note this currently works under the assumption that an Item has to be selected in order to have a value changed.
    this.suppressPropertyUpdates = true;

    foreach (var property in newPropertyStates)
    {
        string propertyName = property.Item1;

        string[] splits = propertyName.Split('.');
        if (splits.Length == 1)
        {
            this.propertyGrid.Properties.OfType<PropertyItem>()
                                        .Where(p => string.Equals(p.PropertyDescriptor.Name, propertyName, StringComparison.Ordinal))
                                        .Map(p =>
            {
                if (property.Item2.HasValue)
                {
                    p.IsEnabled = property.Item2.Value;
                }

                if (property.Item3.HasValue)
                {
                    p.Visibility = property.Item3.Value;
                }
            });

        }
        else // We currently don't expect to go any lower than 1 level.
        {
            var parent = this.propertyGrid.Properties.OfType<PropertyItem>()
                                                     .Where(p => string.Equals(p.PropertyDescriptor.Name, splits[0], StringComparison.Ordinal))
                                                     .FirstOrDefault();

            if (parent != null)
            {
                parent.Properties.OfType<PropertyItem>()
                                 .Where(p => string.Equals(p.PropertyDescriptor.Name, splits[1], StringComparison.Ordinal))
                                 .Map(p =>
                {
                    if (property.Item2.HasValue)
                    {
                        p.IsEnabled = property.Item2.Value;
                    }
                    if (property.Item3.HasValue)
                    {
                        p.Visibility = property.Item3.Value;
                    }
                });
            }
        }
    }

    this.suppressPropertyUpdates = false;
}

Then inside the PreparePropertyItem event handler I check for my VisibilityAttribute and update the property item accordingly.

void PropertyGrid_PreparePropertyItem(object sender, PropertyItemEventArgs e)
{
    foreach (var x in this.currentPropertySelection)
    {
        // If we are in read-only mode do not allow the editing of any property.
        if (this.IsReadOnly)
        {
            e.PropertyItem.IsEnabled = false;
        }

        string propertyName = ((PropertyItem)e.PropertyItem).PropertyDescriptor.Name;
        PropertyInfo property = x.GetType().GetProperty(propertyName);
        var propertyItem = e.Item as PropertyItem;

        // If the property doesn't exist then check to see if it is on an expandable item.
        if (property == null)
        {
            property = propertyItem.Instance.GetType().GetProperty(propertyName);
        }

        bool hasProperty = property != null;

        if (hasProperty)
        {
            var browsableAttribute = property.GetCustomAttribute<BrowsableAttribute>(true);
            if (browsableAttribute != null &&
                !browsableAttribute.Browsable)
            {
                e.PropertyItem.Visibility = Visibility.Collapsed;
                e.Handled = true;
                break;
            }

            var visibilityAttribute = property.GetCustomAttribute<VisibilityAttribute>(true);
            if (visibilityAttribute != null)
            {
                e.PropertyItem.Visibility = visibilityAttribute.Visibility;
                e.Handled = true;
            }

            var independentAttribute = property.GetCustomAttribute<IndependentAttribute>(true);
            // If a property is marked as being independent then we do not allow editing if multiple items are selected
            if (independentAttribute != null &&
                this.currentPropertySelection.Length > 1)
            {
                e.PropertyItem.IsEnabled = false;
                e.Handled = true;
                break;
            }
        }
    }
}