INT32？与IComparable的 [英] Int32? with IComparable

问题描述

我有一个DataGridView的数据源是一个的BindingList。 MyObj中有一些可为空的属性（如int？和日期？）我要实现排序，以我的绑定列表，所以在DataGridView可以对列进行排序，当用户单击列标题。

经过一番周围挖，我发现，跟着这个问题的答案（<一href="http://stackoverflow.com/questions/280948/datagridview-column-sorting-with-business-objects">http://stackoverflow.com/questions/280948/datagridview-column-sorting-with-business-objects).

我不能让这个解决方案工作的可空类型，因为他们没有实现IComparable。即使对于实现IComparable如String类，ApplySortCore（...）失败时的字符串中有一个空值。

有一个解决方案？还是我必须实现一个包装类的Int32？ ？

例如

 公共类Int32Comparable：IComparable的
{
    公众诠释？值{获得;组; }

    ＃地区IComparable的＆LT;诠释＆GT;会员

    公众诠释的CompareTo（对象等）
    {
        // TODO：在这里实现逻辑
        返回-1;
    }

    #endregion
}
 

解决方案

可空＆LT; INT＆GT; 可能无法实施 IComparable的，但肯定 INT 一样。而可空＆LT; T＆GT; 总是拖曳 T （例如当你施放一个接口，如 IComparable的，这是一个装箱转换）。所以比较/排序可为空的属性不应该是一个问题。

 诠释？值= 1;
IComparable的可比=价值; // 作品;甚至含蓄
 

所以，在顶部的检查样本中不工作的权利。试试这个：

 键入interfaceType = prop.PropertyType.GetInterface（IComparable的）;
//接口未对物业的类型中。也许财产是可为空？
//要做到这一点，它必须是值类型。
如果（interfaceType == NULL和放大器;＆安培; prop.PropertyType.IsValueType）
{
    键入underlyingType = Nullable.GetUnderlyingType（prop.PropertyType）;
    // Nullable.GetUnderlyingType只返回一个非空值，如果
    //提供的类型的确是一个可空类型。
    如果（underlyingType！= NULL）
        interfaceType = underlyingType.GetInterface（IComparable的）;
}
如果（interfaceType！= NULL）
   //样品休息
 

还有一个另外：如果你想空值的工作以及（字符串和可空类型），你可以试试这个重新实施 SortCore（...）的：

 保护覆盖无效ApplySortCore（PropertyDescriptor与道具，ListSortDirection方向）
{
    IEnumerable的＆LT; MyClass的＆GT;查询= base.Items;
    如果（方向== ListSortDirection.Ascending）
        查询= query.OrderBy（ⅰ=＆GT; prop.GetValue（ⅰ））;
    其他
        查询= query.OrderByDescending（ⅰ=＆GT; prop.GetValue（ⅰ））;
    INT newIndex = 0;
    的foreach（查询MyClass的项目）
    {
        this.Items [newIndex] =项目;
        newIndex ++;
    }
    this.OnListChanged（新ListChangedEventArgs（ListChangedType.Reset，-1））;
}
 

有没有必要去寻找 IComparable的直接，只是让排序方法自己梳理出来。

I have a DataGridView whose datasource is a BindingList. MyObj has a few nullable properties (like int? and DateTime?) I want to implement sorting to my binding list, so the DataGridView can sort the column when the user clicks on the column header.

After some digging around, I found and followed the answer of this question (http://stackoverflow.com/questions/280948/datagridview-column-sorting-with-business-objects).

I can't get that solution to work for Nullable types because they don't implement IComparable. Even for classes that implement IComparable like String, ApplySortCore(...) fails when the String has a null value.

Is there a solution for this? Or do I have to implement a wrapper class for "Int32?" ?

eg

public class Int32Comparable : IComparable
{
    public int? Value { get; set; }

    #region IComparable<int?> Members

    public int CompareTo(object other)
    {
        // TODO: Implement logic here
        return -1;
    }

    #endregion
}

解决方案

Nullable<int> may not implement IComparable, but surely int does. And Nullable<T> always boxes to T (for instance when you cast to an interface, such as IComparable, which is a boxing conversion). So comparing/sorting on nullable properties should not be a problem.

int? value = 1;
IComparable comparable = value; // works; even implicitly

So, the check in the sample at the top does not work right. Try this:

Type interfaceType = prop.PropertyType.GetInterface("IComparable");
// Interface not found on the property's type. Maybe the property was nullable?
// For that to happen, it must be value type.
if (interfaceType == null && prop.PropertyType.IsValueType)
{
    Type underlyingType = Nullable.GetUnderlyingType(prop.PropertyType);
    // Nullable.GetUnderlyingType only returns a non-null value if the
    // supplied type was indeed a nullable type.
    if (underlyingType != null)
        interfaceType = underlyingType.GetInterface("IComparable");
}
if (interfaceType != null)
   // rest of sample

One more addition: if you want null values to work as well (both string and nullable types), you could try this re-implementation of SortCore(...):

protected override void ApplySortCore(PropertyDescriptor prop, ListSortDirection direction)
{
    IEnumerable<MyClass> query = base.Items;
    if (direction == ListSortDirection.Ascending)
        query = query.OrderBy( i => prop.GetValue(i) );
    else
        query = query.OrderByDescending( i => prop.GetValue(i) );
    int newIndex = 0;
    foreach (MyClass item in query)
    {
        this.Items[newIndex] = item;
        newIndex++;
    }
    this.OnListChanged(new ListChangedEventArgs(ListChangedType.Reset, -1));
}

There's no need to look for IComparable directly, just let the sorting methods themselves sort it out.

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