c# - ItemsSource 在 Custom Bound Horizo​​ntal ScrollView 的构造函数中为空

Question

我在将 Cheesebarons 水平 ListView 更新到新的 v3 MvvmCross 时遇到问题。一切似乎都正常工作，除了在我的“BindableHorizo​​ntalListView”控件的构造函数中，适配器的 ItemsSource 为空。这很奇怪，因为上下文显示我试图绑定(bind)的 View 模型属性非常清楚地显示有 3 个项目，绑定(bind)看起来非常简单。我错过了什么？我希望我已经包含了足够多的代码。我还尝试通过对“OnViewModelSet”事件的流畅绑定(bind)来绑定(bind)它，结果相同。

出现警告

[MvxBind]  24.87 Unable to bind: source property source not found Cirrious.MvvmCross.Binding.Parse.PropertyPath.PropertyTokens.MvxPropertyNamePropertyToken on DeviceViewModel

AXML

 <BindableHorizontalListView
        android:id="@+id/listView"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        local:MvxBind="ItemsSource DevicesList; ItemClick ItemSelected"
        local:MvxItemTemplate="@layout/devices_horizontal_list_item" />

BindableHorizo​​ntalListView 控件

using System.Collections;
using System.Windows.Input;
using Android.Content;
using Android.Util;
using Cirrious.MvvmCross.Binding.Attributes;
using Cirrious.MvvmCross.Binding.Droid.Views;

namespace Project.Droid.Controls
{
    public class BindableHorizontalListView
        : HorizontalListView //Which inherits from AdapterView<BaseAdapter>
    {
        public BindableHorizontalListView(Context context, IAttributeSet attrs) 
            : this(context, attrs, new MvxAdapter(context))
        {
        }

        public BindableHorizontalListView(Context context, IAttributeSet attrs, MvxAdapter adapter)
            : base(context, attrs)
        {
            InitView ();
            var itemTemplateId = MvxAttributeHelpers.ReadListItemTemplateId (context, attrs);

            adapter.ItemTemplateId = itemTemplateId;
            Adapter = adapter;
            SetupItemClickListener();

        }

        public new MvxAdapter Adapter
        {
            get { return base.Adapter as MvxAdapter; }
            set
            {
                var existing = Adapter;
                if (existing == value)
                    return;

                if (existing != null && value != null)
                {
                    value.ItemsSource = existing.ItemsSource;
                    value.ItemTemplateId = existing.ItemTemplateId;
                }

                base.Adapter = value;
            }
        }

        [MvxSetToNullAfterBinding]
        public IEnumerable ItemsSource
        {
            get { return Adapter.ItemsSource; }
            set { Adapter.ItemsSource = value; this.Reset (); }
        }

        public int ItemTemplateId
        {
            get { return Adapter.ItemTemplateId; }
            set { Adapter.ItemTemplateId = value; }
        }

        public new ICommand ItemClick { get; set; }

        private void SetupItemClickListener()
        {
            base.ItemClick += (sender, args) =>
            {
                if (null == ItemClick)
                    return;
                var item = Adapter.GetItem(args.Position) as Java.Lang.Object;
                if (item == null)
                    return;

                if (item == null)
                    return;

                if (!ItemClick.CanExecute(item))
                    return;

                ItemClick.Execute(item);
            };
        }
    }
}

查看

[Activity (Label = "Device", ScreenOrientation = ScreenOrientation.Portrait)]
public class DeviceView : MvxActivity
{

    protected override void OnCreate (Bundle bundle)
    {
        base.OnCreate (bundle);
        SetContentView(Resource.Layout.device);
    }

}

ViewModel 上的属性

private Services.Device[] _devicesList;
public Services.Device[] DevicesList {
    get {
        return _devicesList;
    }
    set {
        _devicesList = value;
        RaisePropertyChanged(() => DevicesList);
    }
}

要是 XAM STUDIO 中有 PCL 支持就好了，我会介入看看其他控件是怎么做的!!!!

Answer 1

ItemsSource 在构造函数中将始终为空 - 它是一个通过绑定(bind)设置的属性，并且该属性只能在构造函数完成后设置。

讯息:

[MvxBind]  24.87 Unable to bind: source property source not found Cirrious.MvvmCross.Binding.Parse.PropertyPath.PropertyTokens.MvxPropertyNamePropertyToken on DeviceViewModel

包含错误 - 已在 a recent commit 中修复- 因此消息在未来应该更具可读性。

如果错误不存在，我怀疑消息会说问题出在 DevicesList 中 - 绑定(bind)无法找到该属性。它在那里吗？它有 get 吗？它是 public 吗？