C# 通用接口中的协方差
我想创建一个可排序的observableCollection 所以我开始创建一个继承observable的类,并使用一些方法对其进行排序,然后我希望该类将索引持久化到child中,因此我创建了一个接口,该接口公开了一个可以写入的索引属性,我对集合类的T进行了成本培训,使其成为我的接口的一部分,然后我希望能够从avery项访问parentCollection,这里问题开始了,因为父集合的类型是泛型的。。。 我尝试过很多解决方案,我认为协方差或不变性是解决方法,但我无法让它工作C# 通用接口中的协方差,c#,.net,generics,variance,C#,.net,Generics,Variance,我想创建一个可排序的observableCollection 所以我开始创建一个继承observable的类,并使用一些方法对其进行排序,然后我希望该类将索引持久化到child中,因此我创建了一个接口,该接口公开了一个可以写入的索引属性,我对集合类的T进行了成本培训,使其成为我的接口的一部分,然后我希望能够从avery项访问parentCollection,这里问题开始了,因为父集合的类型是泛型的。。。 我尝试过很多解决方案,我认为协方差或不变性是解决方法,但我无法让它工作 using Syst
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ClassLibrary1
{
public class SortableCollection<T> : System.Collections.ObjectModel.ObservableCollection<T>, ISortableCollection<T> where T : ISortable<T>
{
public void Sort()
{
//We all know how to sort something
throw new NotImplementedException();
}
protected override void InsertItem(int index, T item)
{
item.Index = index;
item.ParentCollection = this;
base.InsertItem(index, item);
}
}
public interface ISortableCollection<T> : IList<T>
{
void Sort();
}
public interface ISortable<T>
{
Int32 Index { get; set; }
ISortableCollection<T> ParentCollection { get; set; }
}
public class BaseClass : ISortable<BaseClass>
{
public int Index { get; set; }
public ISortableCollection<BaseClass> ParentCollection { get; set; }
}
public class DerivedClass : BaseClass { }
public class Controller
{
SortableCollection<BaseClass> MyBaseSortableList = new SortableCollection<BaseClass>();
SortableCollection<DerivedClass> MyDerivedSortableList = new SortableCollection<DerivedClass>();
public Controller()
{
//do things
}
}
}
使用系统;
使用System.Collections.Generic;
使用System.Linq;
使用系统文本;
使用System.Threading.Tasks;
命名空间类库1
{
公共类SortableCollection:System.Collections.ObjectModel.ObservableCollection,ISortableCollection其中T:ISortable
{
公共无效排序()
{
//我们都知道如何分类
抛出新的NotImplementedException();
}
受保护的覆盖无效插入项(int索引,T项)
{
项目索引=索引;
item.ParentCollection=此;
基本插入项(索引,项目);
}
}
公共接口ISortableCollection:IList
{
无效排序();
}
公共接口可移植
{
Int32索引{get;set;}
ISortableCollection父集合{get;set;}
}
公共类基类:ISortable
{
公共int索引{get;set;}
公共ISortableCollection父集合{get;set;}
}
公共类DerivedClass:基类{}
公共类控制器
{
SortableCollection MyBaseSortableList=新建SortableCollection();
SortableCollection MyDerivedSortableList=新建SortableCollection();
公共控制员()
{
//做事
}
}
}
这或多或少是一种设置。
我希望能够创建一个SortableCollection
,但是类型不匹配。。。做这件事的正确方法是什么
准确的误差是
错误1类型“ClassLibrary1.DerivedClass”不能用作泛型类型或方法中的类型参数“T”“ClassLibrary1.SortableCollection”
。没有从“ClassLibrary1.DerivedClass”到“ClassLibrary1.ISortable”的隐式引用转换。c:\users\luigi.trabacchin\documents\visual studio 2013\Projects\ClassLibrary1\ClassLibrary1\Class1.cs 48 89 ClassLibrary1
您需要DerivedClass
成为一个ISortable
:
问题是您对T
的约束是“T
必须是I
”,并且您已经为T
传递了DerivedClass
,但是DerivedClass
不能转换为I
,它可以转换为I
我不知道你试图用t
成为I
的约束来表示什么。我知道人们经常使用这种模式来表示C#type系统实际上没有实现的约束。有关详细信息,请参阅我的文章:
我鼓励你把事情大大简化;您似乎试图在类型系统中捕获太多内容
I
不能转换为I
的原因是为了使差异生效,接口必须标记为支持差异;将T
标记为out
或in
,具体取决于您想要的是协方差还是反方差
但是,由于IList是不变的,因此使派生接口协变或逆变是不合法的。考虑<代码> iQueDebug <代码>,因为它在代码< t>代码>中是协变的。
为了使接口在T
中是协变的,它只需要在输出位置使用T
<代码>列表
在输入和输出位置都使用T
,因此它不能是协变或逆变的。为了感谢大家,我将发布我最终得到的设计
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ClassLibrary1
{
public class SortableCollection<T> : System.Collections.ObjectModel.ObservableCollection<T>, ISortableCollection where T : ISortable, IComparable, IComparable<T>
{
public new void Add(T item)
{
if (this.Items.Contains(item))
throw new InvalidOperationException("This list can contain the same item only once");
base.Add(item);
}
public void Sort()
{
var sorted = this.Items.ToList();
sorted.Sort();
for (var i = 0; i < this.Items.Count; i++)
{
if (object.ReferenceEquals(this.Items[i], sorted[i]))
{
this.Items[i].Index = i;
continue;
}
// if u want to support duplicates create a nextIndexOf and start searching from i
var previousIndex = IndexOf(sorted[i]);
Move(previousIndex, i);
}
}
protected override void InsertItem(int index, T item)
{
item.Index = index;
item.ParentCollection = this;
base.InsertItem(index, item);
}
protected override void RemoveItem(int index)
{
this.Items[index].ParentCollection = null;
base.RemoveItem(index);
}
protected override void ClearItems()
{
foreach (var item in this.Items)
item.ParentCollection = null;
base.ClearItems();
}
protected override void SetItem(int index, T item)
{
this.Items[index].ParentCollection = null;
item.Index = index;
item.ParentCollection = this;
base.SetItem(index, item);
}
protected override void MoveItem(int oldIndex, int newIndex)
{
this.Items[oldIndex].Index = newIndex;
this.Items[newIndex].Index = oldIndex;
base.MoveItem(oldIndex, newIndex);
}
}
public interface ISortableCollection : IList
{
void Sort();
}
public interface ISortable
{
Int32 Index { get; set; }
ISortableCollection ParentCollection { get; set; }
}
public class BaseClass : ISortable, IComparable, IComparable<BaseClass>
{
public int Index { get; set; }
public ISortableCollection ParentCollection { get; set; }
public int CompareTo(object obj)
{
return CompareTo(obj as BaseClass);
}
public int CompareTo(BaseClass other)
{
if (other == null)
return 1;
return this.Index.CompareTo(other.Index);
}
}
public class DerivedClass : BaseClass { }
public class Controller
{
SortableCollection<BaseClass> MyBaseSortableList = new SortableCollection<BaseClass>();
SortableCollection<DerivedClass> MyDerivedSortableList = new SortableCollection<DerivedClass>();
public Controller()
{
//do things
MyDerivedSortableList.Add(new DerivedClass());
MyDerivedSortableList.Add(new DerivedClass());
var derivedThing = new DerivedClass();
MyDerivedSortableList.Add(derivedThing);
var sibiling = derivedThing.ParentCollection[derivedThing.Index - 1] as BaseClass; //way easier
// switch the two objects order and call sort
// calling a sort before the operation if indexes have been messed with
// add an event to ISortable to notify the list the index has been changed and mark the list dirty
derivedThing.Index -= 1;
sibiling.Index += 1;
derivedThing.ParentCollection.Sort(); // maybe the list was created where i couldn't access it
}
}
}
使用系统;
使用系统集合;
使用System.Collections.Generic;
使用System.Linq;
使用系统文本;
使用System.Threading.Tasks;
命名空间类库1
{
公共类SortableCollection:System.Collections.ObjectModel.ObservableCollection,ISortableCollection其中T:ISortable,IComparable,IComparable
{
新增公共作废(T项)
{
如果(本项目包含(项目))
抛出新的InvalidOperationException(“此列表只能包含同一项一次”);
基础。添加(项目);
}
公共无效排序()
{
var sorted=this.Items.ToList();
sorted.Sort();
对于(var i=0;i((dynamic))item).ParentCollection = this;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ClassLibrary1
{
public class SortableCollection<T> : System.Collections.ObjectModel.ObservableCollection<T>, ISortableCollection where T : ISortable, IComparable, IComparable<T>
{
public new void Add(T item)
{
if (this.Items.Contains(item))
throw new InvalidOperationException("This list can contain the same item only once");
base.Add(item);
}
public void Sort()
{
var sorted = this.Items.ToList();
sorted.Sort();
for (var i = 0; i < this.Items.Count; i++)
{
if (object.ReferenceEquals(this.Items[i], sorted[i]))
{
this.Items[i].Index = i;
continue;
}
// if u want to support duplicates create a nextIndexOf and start searching from i
var previousIndex = IndexOf(sorted[i]);
Move(previousIndex, i);
}
}
protected override void InsertItem(int index, T item)
{
item.Index = index;
item.ParentCollection = this;
base.InsertItem(index, item);
}
protected override void RemoveItem(int index)
{
this.Items[index].ParentCollection = null;
base.RemoveItem(index);
}
protected override void ClearItems()
{
foreach (var item in this.Items)
item.ParentCollection = null;
base.ClearItems();
}
protected override void SetItem(int index, T item)
{
this.Items[index].ParentCollection = null;
item.Index = index;
item.ParentCollection = this;
base.SetItem(index, item);
}
protected override void MoveItem(int oldIndex, int newIndex)
{
this.Items[oldIndex].Index = newIndex;
this.Items[newIndex].Index = oldIndex;
base.MoveItem(oldIndex, newIndex);
}
}
public interface ISortableCollection : IList
{
void Sort();
}
public interface ISortable
{
Int32 Index { get; set; }
ISortableCollection ParentCollection { get; set; }
}
public class BaseClass : ISortable, IComparable, IComparable<BaseClass>
{
public int Index { get; set; }
public ISortableCollection ParentCollection { get; set; }
public int CompareTo(object obj)
{
return CompareTo(obj as BaseClass);
}
public int CompareTo(BaseClass other)
{
if (other == null)
return 1;
return this.Index.CompareTo(other.Index);
}
}
public class DerivedClass : BaseClass { }
public class Controller
{
SortableCollection<BaseClass> MyBaseSortableList = new SortableCollection<BaseClass>();
SortableCollection<DerivedClass> MyDerivedSortableList = new SortableCollection<DerivedClass>();
public Controller()
{
//do things
MyDerivedSortableList.Add(new DerivedClass());
MyDerivedSortableList.Add(new DerivedClass());
var derivedThing = new DerivedClass();
MyDerivedSortableList.Add(derivedThing);
var sibiling = derivedThing.ParentCollection[derivedThing.Index - 1] as BaseClass; //way easier
// switch the two objects order and call sort
// calling a sort before the operation if indexes have been messed with
// add an event to ISortable to notify the list the index has been changed and mark the list dirty
derivedThing.Index -= 1;
sibiling.Index += 1;
derivedThing.ParentCollection.Sort(); // maybe the list was created where i couldn't access it
}
}
}