WPF-Demo/WpfSample/ViewModels/MainViewModel.cs

using System.Collections;
using System.Collections.ObjectModel;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using Waaagh.Behaviors;

namespace WpfSample.ViewModels {
    internal partial class MainViewModel: ObservableObject {
        public MainViewModel() {
            Random random = new Random();
            for (int i = random.Next(1, 10); i >= 0; --i) {
                Groups.Add(new DemoGroupViewModel() {
                    Name = $"G{i}",
                });
            }
            for (int i = random.Next(1, 10); i >= 0; --i) {
                Groups2.Add(new DemoGroupViewModel() {
                    Name = $"G{i}",
                });
            }
        }

        [ObservableProperty]
        private string message = string.Empty;

        public ObservableCollection<DemoGroupViewModel> Groups { get; } = new ObservableCollection<DemoGroupViewModel>();
        public ObservableCollection<DemoGroupViewModel> Groups2 { get; } = new ObservableCollection<DemoGroupViewModel>();

        class Test {
            public string Name { get; set; } = string.Empty;
        }

        [RelayCommand]
        private void AddGroup() {
            Groups.Add(new DemoGroupViewModel() {
                Name = $"GX",
            });
            Groups2.Add(new DemoGroupViewModel() {
                Name = $"GY",
            });
        }

        [RelayCommand]
        private void AddItem() {
            Groups[0].AddItemCommand?.Execute(null);
        }

        public ItemsDraggable.DoEffectsCallbackHandler DoMoveEffectFunc { get; } = (object sender, ItemsDraggable.DoEffectsCallbackArgs args) => {
            object sourceData = args.SourceData;
            object? targetData = args.TargetData;
            IList sourceCollection = args.SourceCollection;
            IList targetCollection = args.TargetCollection;

            int oldIndex = sourceCollection.IndexOf(sourceData);
            int newIndex = targetCollection.IndexOf(targetData);
            if (newIndex == -1) {
                newIndex = targetCollection.Count - 1;
            }

            if (object.ReferenceEquals(sourceCollection, targetCollection)) {
                if (oldIndex == newIndex) {
                    return;
                }
                // 同个集合, 移除元素后下标可能变化
                if (oldIndex < newIndex) {
                    newIndex -= 1;
                }
            }
            sourceCollection.RemoveAt(oldIndex);
            targetCollection.Insert(newIndex + 1, sourceData);
        };
    }
}