使用MvvmCross如何将注释列表绑定到MapView？

Question

假设我有一个包含属性"Annotations"的MapView.要在MapView上获取注释,您必须使用AddAnotation或AddAnotations.

public class SiteItems
{
    public string Title { get; set; }
    public string SubTitle { get; set; }

    public string Phone { get; set; }
    public string Address { get; set; }
    public string Url { get; set; }

    public double Latitude { get; set; }
    public double Longitude { get; set; }
}

然后我有一个ViewModel:

public class SiteViewModel : MvxViewModel
{

    private IObservableCollection<Models.SiteItems> _siteItems;
    public IObservableCollection<Models.SiteItems> SiteItems {
        get{ return _siteItems; }
        set{ _siteItems = value; 
            RaisePropertyChanged (() => SiteItems);
        }
    }
}

我还有一个将SiteItem转换为MKAnnotation的转换器

所以我想我的问题是如何绑定这样的东西,因为我们不能直接绑定到"Annotations"属性？我绑定命令吗？

谢谢,任何帮助表示赞赏!

Answer 1

订阅更改集合是Data-Binding的基石之一,并且依赖于对INotifyCollectionChanged界面的一点了解.

内MvvmCross源,还有一些展示如何订阅集合及其变更通知几个示例类-如MvxViewGroupExtensions.cs在Droid和MvxTableViewSource.cs在触摸

该技术的核心是创建一个Adapter或Source对象,该对象在整个列表或列表的某些部分中监听更改,并相应地采取操作.

相同类型的方法适用于具有多个但是标记的地图 - 尽管我们还没有任何帮助类.

如果没有真正拥有Mac或iOS设备,这里大致是我创建包装器的步骤......

假设我有一个Model对象:

public class House
{
    public double Lat { get; set; }
    public double Lng { get; set; }
    public string Name { get; set; }
}

在ViewModel里面,如:

public class FirstViewModel : MvxViewModel
{
    public ObservableCollection<House> HouseList { get; set; }
}

完成后,在View中我们可以为每个House创建一个注释类 - 例如:

public class HouseAnnotation : MKAnnotation
{
    public HouseAnnotation(House house)
    {
        // Todo - the details of actually using the house here.
        // in theory you could also data-bind to the house too (e.g. if it's location were to move...)
    }

    public override CLLocationCoordinate2D Coordinate { get; set; }
}

然后,我们可以创建一个HouseAnnotationManager谁负责管理HouseList映射到地图上显示的注释中的更改的更改的转换.

要做到这一点,我们会给经理方法:

1. 创建单个注释:

   private MKAnnotation CreateAnnotation(House house)
   {
       return new HouseAnnotation(house);
   }
   

2. 向地图添加注释(以及本地查找表)

   private void AddAnnotationFor(House house)
   {
       var annotation = CreateAnnotation(house);
       _annotations[house] = annotation;
       _mapView.AddAnnotation(annotation);
   }
   

3. 从地图中删除注释(以及从本地查找表中删除)

   private void RemoveAnnotationFor(House house)
   {
       var annotation = _annotations[house];
       _mapView.RemoveAnnotation(annotation);
       _annotations.Remove(house);
   }
   

4. 对列表执行相同的操作:

   private void AddAnnotations(IList newItems)
   {
       foreach (House house in newItems)
       {
           AddAnnotationFor(house);
       }
   }
   
   private void RemoveAnnotations(IList oldItems)
   {
       foreach (House house in oldItems)
       {
           RemoveAnnotationFor(house);
       }
   }
   

5. 回应INotifyCollection变化:

   private void OnItemsSourceCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
   {
       switch (e.Action)
       {
           case NotifyCollectionChangedAction.Add:
               AddAnnotations(e.NewItems);
               break;
           case NotifyCollectionChangedAction.Remove:
               RemoveAnnotations(e.OldItems);
               break;
           case NotifyCollectionChangedAction.Replace:
               RemoveAnnotations(e.OldItems);
               AddAnnotations(e.NewItems);
               break;
           case NotifyCollectionChangedAction.Move:
               // not interested in this
               break;
           case NotifyCollectionChangedAction.Reset:
               ReloadAllAnnotations();
               break;
           default:
               throw new ArgumentOutOfRangeException();
       }
   }
   

6. 回应整个列表更改:

   // MvxSetToNullAfterBinding isn't strictly needed any more 
   // - but it's nice to have for when binding is torn down
   [MvxSetToNullAfterBinding]
   public virtual IEnumerable<House> ItemsSource
   {
       get { return _itemsSource; }
       set { SetItemsSource(value); }
   }
   
   protected virtual void SetItemsSource(IEnumerable<House> value)
   {
       if (_itemsSource == value)
           return;
   
       if (_subscription != null)
       {
           _subscription.Dispose();
           _subscription = null;
       }
       _itemsSource = value;
       if (_itemsSource != null && !(_itemsSource is IList))
           MvxBindingTrace.Trace(MvxTraceLevel.Warning,
                                 "Binding to IEnumerable rather than IList - this can be inefficient, especially for large lists");
   
       ReloadAllAnnotations();
   
       var newObservable = _itemsSource as INotifyCollectionChanged;
       if (newObservable != null)
       {
           _subscription = newObservable.WeakSubscribe(OnItemsSourceCollectionChanged);
       }
   }
   

完成所有这些后,您的ViewModel可以拥有一个私有_manager字段,并可以创建和数据绑定它:

        _manager = new HouseAnnotationManager(myMapView);

        var set = this.CreateBindingSet<FirstView, FirstViewModel>();
        set.Bind(_manager).To(vm => vm.HouseList);
        set.Apply();

总的来说,这可能看起来像:https://gist.github.com/slodge/6070386

免责声明:此代码尚未编译,更不用说运行了,但这种方法基本上是正确的(我认为)

注意:如果这样做/不适用于某些修复,我非常希望它作为样本提交回Mvx社区;)

同样的基本方法也适用于Android - 虽然在Android中你还必须与设置 - Ant,Google Play v2和所有爵士乐进行斗争.

如果你想进行进一步的地图操作 - 例如在添加房屋时更改地图中心和缩放,那么显然可以在管理器中的方法(例如AddAnnotation)的覆盖范围内完成.