WPF-Demo/Waaagh/Converters/DefaultItemsVisibilityConverter.cs

using System.Collections;
using System.Globalization;
using System.Windows;
using System.Windows.Data;
using System.Windows.Markup;

namespace Waaagh.Converters {
    public class DefaultContentVisibilityConverter: MarkupExtension, IValueConverter {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
            // 默认使用 Hidden 作为不显示
            Visibility unvisibility = Visibility.Hidden;
            if (parameter is Visibility mode) {
                unvisibility = mode;
            }
            else if (parameter is bool isCollapsed && isCollapsed) {
                unvisibility = Visibility.Collapsed;
            }
            else if (parameter is string str && bool.TryParse(str, out isCollapsed) && isCollapsed) {
                unvisibility = Visibility.Collapsed;
            }

            // 任意类型为空, 显示默认内容
            if (value == null) {
                return Visibility.Visible;
            }
            // 集合类型且空集合, 显示默认内容
            if (value is ICollection collection && collection.Count == 0) {
                return Visibility.Visible;
            }
            return unvisibility;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
            throw new NotImplementedException();
        }

        public override object ProvideValue(IServiceProvider serviceProvider) {
            return this;
        }
    }
}