WPF在同一个ListCollectionView上使用多个过滤器

Question

我正在使用MVVM设计模式,ListView绑定到ViewModel上的ListCollectionView.我还有几个用于过滤ListView的组合框.当用户从组合框中选择项目时,将针对所选项目筛选ListView.每当我想要在已经过滤的内容之上进行过滤时,它就像从未发生的那样撤消我以前的过滤器.删除过滤器也是如此.删除一个组合框的过滤器将删除所有过滤器并显示原始列表.是否可以在同一个ListCollectionView上拥有多个独立的过滤器？

我做错了什么,或者这根本不受支持？你可以在这里找到我的应用程序的屏幕截图,看看我想要完成什么.这是我的过滤代码......

    /// <summary>
    /// Filter the list
    /// </summary>
    /// <param name="filter">Criteria and Item to filter the list</param>
    [MediatorMessageSink("FilterList", ParameterType = typeof(FilterItem))]
    public void FilterList(FilterItem filter)
    {
        // Make sure the list can be filtered...
        if (Products.CanFilter)
        {
            // Now filter the list
            Products.Filter = delegate(object obj)
            {
                Product product = obj as Product;

                // Make sure there is an object
                if (product != null)
                {
                    bool isFiltered = false;
                    switch (filter.FilterItemName)
                    {
                        case "Category":
                            isFiltered = (product.Category.IndexOf(filter.Criteria, StringComparison.CurrentCultureIgnoreCase)) != -1 ? true : false;
                            break;

                        case "ClothingType":
                            isFiltered = (product.ClothingType.IndexOf(filter.Criteria, StringComparison.CurrentCultureIgnoreCase)) != -1 ? true : false;
                            break;

                        case "ProductName":
                            isFiltered = (product.ProductName.IndexOf(filter.Criteria, StringComparison.CurrentCultureIgnoreCase)) != -1 ? true : false;
                            break;

                        default:
                            break;
                    }

                    return isFiltered;
                }
                else
                    return false;
            };
        }
    }

Answer 1

每次设置Filter属性时,都会重置上一个过滤器.这是事实.现在你怎么能有多个过滤器？

如您所知,有两种方法可以进行过滤:CollectionView和CollectionViewSource.在第一种情况下CollectionView我们使用委托进行过滤,并且要做多个过滤器,我会创建一个类来聚合自定义过滤器,然后逐个为每个过滤器项调用它们.如下面的代码所示:

  public class GroupFilter
  {
    private List<Predicate<object>> _filters;

    public Predicate<object> Filter {get; private set;}

    public GroupFilter()
    {
      _filters = new List<Predicate<object>>();
      Filter = InternalFilter;
    }

    private bool InternalFilter(object o)
    {
      foreach(var filter in _filters)
      {
        if (!filter(o))
        {
          return false;
        }
      }

      return true;
    }

    public void AddFilter(Predicate<object> filter)
    {
      _filters.Add(filter);
    }

    public void RemoveFilter(Predicate<object> filter)
    {
      if (_filters.Contains(filter))
      {
        _filters.Remove(filter);
      }
    }    
  }

  // Somewhere later:
  GroupFilter gf = new GroupFilter();
  gf.AddFilter(filter1);
  listCollectionView.Filter = gf.Filter;

要刷新筛选视图,您可以调用ListCollectionView.Refresh()方法.

在第二种情况下,CollectionViewSource您使用Filter事件来过滤集合.您可以创建多个事件处理程序以按不同条件进行筛选.要了解有关此方法的更多信息,请查看Bea Stollnitz撰写的这篇精彩文章:如何应用多个过滤器？

希望这可以帮助.

干杯,安瓦卡.

Answer 2

每次用户过滤时,您的代码都会使用新的代码替换Filter集合视图中的委托.而且,新的只检查用户刚刚选择的特定标准ComboBox.

你想要的是一个检查所有标准的过滤器处理程序.就像是:

public MyViewModel()
{
    products = new ObservableCollection<Product>();
    productsView = new ListCollectionView(products);
    productsView.Filter += FilterProduct;
}

public Item SelectedItem
{
    //get,set omitted. set needs to invalidate filter with refresh call
}

public Type SelectedType
{
    //get,set omitted. set needs to invalidate filter with refresh call
}

public Category SelectedCategory
{
    //get,set omitted. set needs to invalidate filter with refresh call
}

public ICollection<Product> FilteredProducts
{
    get { return productsView; }
}

private bool FilterProduct(object o)
{
    var product = o as Product;

    if (product == null)
    {
        return false;
    }

    if (SelectedItem != null)
    {
        // filter according to selected item
    }

    if (SelectedType != null)
    {
        // filter according to selected type
    }

    if (SelectedCategory != null)
    {
        // filter according to selected category
    }

    return true;
}

您的视图现在可以绑定到适当的属性,过滤将起作用.