c# - 对 BindingList 进行反向排序

Question

我有一个从绑定到DataGrid的BindingList(T)继承的自定义类。

但是，DataGrid是自上而下填充的，我希望它是自下而上填充的。所以底部项目是索引 0 而不是顶部项目。

如何更改我的BindingList(T)以便DataGrid反向读取它？

Answer 1

CodeProject.com上关于实现可排序的 BindingList的这篇文章可能会对您有所帮助。

它有一个很好的用于绑定列表的通用包装器，使其可排序：

public class MySortableBindingList<T> : BindingList<T> {

    // reference to the list provided at the time of instantiation
    List<T> originalList;
    ListSortDirection sortDirection;
    PropertyDescriptor sortProperty;

    // function that refereshes the contents
    // of the base classes collection of elements
    Action<MySortableBindingList<T>, List<T>> 
                   populateBaseList = (a, b) => a.ResetItems(b);

    // a cache of functions that perform the sorting
    // for a given type, property, and sort direction
    static Dictionary<string, Func<List<T>, IEnumerable<T>>> 
       cachedOrderByExpressions = new Dictionary<string, Func<List<T>, 
                                                 IEnumerable<T>>>();

    public MySortableBindingList() {
        originalList = new List<T>();
    }

    public MySortableBindingList(IEnumerable<T> enumerable) {
        originalList = enumerable.ToList();
        populateBaseList(this, originalList);
    }

    public MySortableBindingList(List<T> list) {
        originalList = list;
        populateBaseList(this, originalList);
    }

    protected override void ApplySortCore(PropertyDescriptor prop, 
                            ListSortDirection direction) {
        /*
         Look for an appropriate sort method in the cache if not found .
         Call CreateOrderByMethod to create one. 
         Apply it to the original list.
         Notify any bound controls that the sort has been applied.
         */

        sortProperty = prop;

        var orderByMethodName = sortDirection == 
            ListSortDirection.Ascending ? "OrderBy" : "OrderByDescending";
        var cacheKey = typeof(T).GUID + prop.Name + orderByMethodName;

        if (!cachedOrderByExpressions.ContainsKey(cacheKey)) {
            CreateOrderByMethod(prop, orderByMethodName, cacheKey);
        }

        ResetItems(cachedOrderByExpressions[cacheKey](originalList).ToList());
        ResetBindings();
        sortDirection = sortDirection == ListSortDirection.Ascending ? 
                        ListSortDirection.Descending : ListSortDirection.Ascending;
    }


    private void CreateOrderByMethod(PropertyDescriptor prop, 
                 string orderByMethodName, string cacheKey) {

        /*
         Create a generic method implementation for IEnumerable<T>.
         Cache it.
        */

        var sourceParameter = Expression.Parameter(typeof(List<T>), "source");
        var lambdaParameter = Expression.Parameter(typeof(T), "lambdaParameter");
        var accesedMember = typeof(T).GetProperty(prop.Name);
        var propertySelectorLambda =
            Expression.Lambda(Expression.MakeMemberAccess(lambdaParameter, 
                              accesedMember), lambdaParameter);
        var orderByMethod = typeof(Enumerable).GetMethods()
                                      .Where(a => a.Name == orderByMethodName &&
                                                   a.GetParameters().Length == 2)
                                      .Single()
                                      .MakeGenericMethod(typeof(T), prop.PropertyType);

        var orderByExpression = Expression.Lambda<Func<List<T>, IEnumerable<T>>>(
                                    Expression.Call(orderByMethod,
                                            new Expression[] { sourceParameter, 
                                                               propertySelectorLambda }),
                                            sourceParameter);

        cachedOrderByExpressions.Add(cacheKey, orderByExpression.Compile());
    }

    protected override void RemoveSortCore() {
        ResetItems(originalList);
    }

    private void ResetItems(List<T> items) {

        base.ClearItems();

        for (int i = 0; i < items.Count; i++) {
            base.InsertItem(i, items[i]);
        }
    }

    protected override bool SupportsSortingCore {
        get {
            // indeed we do
            return true;
        }
    }

    protected override ListSortDirection SortDirectionCore {
        get {
            return sortDirection;
        }
    }

    protected override PropertyDescriptor SortPropertyCore {
        get {
            return sortProperty;
        }
    }

    protected override void OnListChanged(ListChangedEventArgs e) {
        originalList = base.Items.ToList();
    }
}

Answer 2

它很简单，但您也可以按相反的顺序填充绑定列表（除非您有其他理由保持当前顺序）。

Answer 3

为什么不在 IBindingList 接口实现上调用 ApplySort 方法BindingList<T>呢？您可以只为第二个参数传递 ListSortDirection.Descending 的值，DataGrid 应该以相反的顺序显示项目。

Answer 4

如果您的列表继承自 Collection 类，则可以使用 Insert(0,item) 方法插入到列表的开头。这样最新的元素就会出现在顶部。不确定 BindingList 是否支持这一点。