MvvmCross iOS UITableView 不会在 Property Changed 上更新

Question

我的表格视图不会在其源属性更改时更新。代码如下：

视图控制器：

    public override void ViewDidLoad()
    {
        base.ViewDidLoad();
        View.BackgroundColor = UIColor.White;

        var table = new UITableView(new RectangleF(0, 80, Device.Width, Device.Height - 80));
        Add(table);
        var source = new MvxStandardTableViewSource(table, "TitleText SessionInfo");
        table.Source = source;

        var set = this.CreateBindingSet<JoinSessionViewController, JoinSessionViewModel>();
        set.Bind(source).To(vm => vm.AvailableServers);
        set.Apply();

        table.ReloadData();
    }

视图模型：

    private readonly INetworkSessionClient _client;

    public JoinSessionViewModel(INetworkSessionClient client)
    {
        _client = client;

        _client.ServerFound += ClientOnServerFound;
        _client.BeginSearchingForServers();
    }

    private void ClientOnServerFound(object sender, ServerFoundEventArgs serverFoundEventArgs)
    {
        if (AvailableServers.Any(s => s.Identifier == serverFoundEventArgs.ServerInfo.Identifier))
            return;

        AvailableServers.Add(serverFoundEventArgs.ServerInfo);
        RaisePropertyChanged(() => AvailableServers);
    }

    private List<ServerInfo> _availableServers;
    public List<ServerInfo> AvailableServers
    {
        get { return _availableServers; }
        set { _availableServers = value; RaisePropertyChanged(() => AvailableServers); }
    }

Answer 1

这是一个棘手的问题。罪魁祸首是 MvxTableViewSource 中的这一行：

https://github.com/MvvmCross/MvvmCross/blob/v3.1/Cirrious/Cirrious.MvvmCross.Binding.Touch/Views/MvxTableViewSource.cs#L56

    public virtual IEnumerable ItemsSource
    {
        get { return _itemsSource; }
        set
        {
            if (_itemsSource == value) // **** This one ****
                return;

            if (_subscription != null)
            {
                _subscription.Dispose();
                _subscription = null;
            }

            _itemsSource = value;

            var collectionChanged = _itemsSource as INotifyCollectionChanged;
            if (collectionChanged != null)
            {
                _subscription = collectionChanged.WeakSubscribe(CollectionChangedOnCollectionChanged);
            }

            ReloadTableData();
        }
    }

由于我只是添加到列表中而不是将其设置为新列表，因此设置器提前返回并且没有触发 ReloadTableData()。解决方法是使用 ObservableCollection（或任何其他实现 INotifyCollectionChanged 的​​东西）而不是 List。

    private void ClientOnServerFound(object sender, ServerFoundEventArgs serverFoundEventArgs)
    {
        if (AvailableServers.Any(s => s.Identifier == serverFoundEventArgs.ServerInfo.Identifier))
            return;

        // CollectionChanged event is not automatically martialed to UI thread
        InvokeOnMainThread(() => AvailableServers.Add(serverFoundEventArgs.ServerInfo));
    }

    private ObservableCollection<ServerInfo> _availableServers;
    public ObservableCollection<ServerInfo> AvailableServers
    {
        get { return _availableServers; }
        set { _availableServers = value; RaisePropertyChanged(() => AvailableServers); }
    }

请注意，由于我的特殊情况，ServerFound 事件是在单独的线程上调用的。这意味着 INotifyCollectionChanged.CollectionChanged 事件也将在单独的线程上调用，因此将服务器添加到列表的操作必须使用 InvokeOnMainThread() 进入主线程，以便 UI 正确更新。

如果 CollectionChanged 事件能在 UI 线程上自动处理就好了，类似于 RaisePropertyChanged() 的工作原理。