我有一个想要排序的类(补丁),所以我实现了 IComparer。
但是,它需要根据用户的需要进行排序,例如: - key1, key2, key3 - key1, key3, key2
对于每个键比较,我编写了一个 IComparer 类,但是,我想知道如何实现它的连接。即排序时我只能传递一个 IComparer 实例。
或者我应该为每种完整排序创建一个 IComparer 类,即 IComparerKey1Key2Key3、IComparerKey1Key3Key2 等?
您可以制作一个通用比较器,它需要一个委托来选择键:
class ByKeyComparer<T, TKey> : IComparer<T>
{
private readonly Func<T, TKey> _keySelector;
private readonly IComparer<TKey> _keyComparer;
public ByKeyComparer(Func<T, TKey> keySelector, IComparer<TKey> keyComparer = null)
{
if (keySelector == null) throw new ArgumentNullException("keySelector");
_keySelector = keySelector;
_keyComparer = keyComparer ?? Comparer<TKey>.Default;
}
public int Compare(T x, T y)
{
return _keyComparer.Compare(_keySelector(x), _keySelector(y));
}
}
使用辅助类来利用类型推断(因此您无需指定键的类型):
static class ByKeyComparer<T>
{
public static IComparer<T> Create<TKey>(Func<T, TKey> keySelector, IComparer<TKey> keyComparer = null)
{
return new ByKeyComparer<T, TKey>(keySelector, keyComparer);
}
}
你可以像这样使用它:
var patchVersionComparer = ByKeyComparer<Patch>.Create(p => p.Version);
patches.Sort(patchVersionComparer);
如果您需要组合多个比较键,您可以创建一个使用其他比较器的比较器:
class CompositeComparer<T> : IComparer<T>
{
private readonly IEnumerable<IComparer<T>> _comparers;
public CompositeComparer(IEnumerable<IComparer<T>> comparers)
{
if (comparers == null) throw new ArgumentNullException("comparers");
_comparers = comparers;
}
public CompositeComparer(params IComparer<T>[] comparers)
: this((IEnumerable<IComparer<T>>)comparers)
{
}
public int Compare(T x, T y)
{
foreach (var comparer in _comparers)
{
int result = comparer.Compare(x, y);
if (result != 0)
return result;
}
return 0;
}
}
示例用法:
var comparer = new CompositeComparer<Patch>(
ByKeyComparer<Patch>.Create(p => p.Key1),
ByKeyComparer<Patch>.Create(p => p.Key2),
ByKeyComparer<Patch>.Create(p => p.Key3));
patches.Sort(comparer);
编辑:这是一个更流畅的 API:
static class ByKeyComparer<T>
{
public static IComparer<T> CompareBy<TKey>(Func<T, TKey> keySelector, IComparer<TKey> keyComparer = null)
{
return new ByKeyComparer<T, TKey>(keySelector, keyComparer);
}
}
static class ComparerExtensions
{
public static IComparer<T> ThenBy<T, TKey>(this IComparer<T> comparer, Func<T, TKey> keySelector, IComparer<TKey> keyComparer = null)
{
var newComparer = ByKeyComparer<T>.CompareBy(keySelector, keyComparer);
var composite = comparer as CompositeComparer<T>;
if (composite != null)
return new CompositeComparer<T>(composite.Comparers.Concat(new[] { newComparer }));
return new CompositeComparer<T>(comparer, newComparer);
}
}
例子:
var comparer = ByKeyComparer<Patch>.CompareBy(p => p.Key1)
.ThenBy(p => p.Key2)
.ThenBy(p => p.Key3);
patches.Sort(comparer);
(显然,您可能希望添加和方法*Descending
的版本以允许按降序排序)CompareBy
ThenBy
如果您可以使用 LINQ,那么对这样的类进行排序将非常容易。假设您有一个List
of,Patch
List<Patch>
并且您想按 key2、key1 和 key4 对其进行排序。你要做的是:
List<Patch> patches = new List<Patch>();
patches = GetPatches().ToList().OrderBy(p=>p.Key2).ThenBy(p=>p.Key1).ThenBy(p=>p.Key4).ToList();
就这样。我们喜欢linq。:)
ToList
如果函数返回列表本身,则不需要First 。
您还可以使用 LINQ 动态查询库 或查看Dynamic LINQ OrderBy