如何使一个类似Excel的排序按A,然后按一个TObjectList<>使用多个比较器 [英] How to make an Excel-Like Sort By A, Then By B in a TObjectList<> using multiple comparers
问题描述
我刚刚开始使用泛型,我目前在多个字段上进行排序时遇到问题。
案例:
我有一个PeopleList一个TObjectList,我希望能够通过一次选择一个排序字段,然后尽可能多地保留以前的排序,从而形成类似Excel的排序功能。
<编辑:必须在运行时更改字段排序顺序。 (即,在一种情况下,用户想要排序顺序A,B,C - 在另一场景中他想要B,A,C - 在另一个A,C,D)
假设我们有一个未排序的人员列表:
姓氏年龄
------ ---------------
史密斯26
琼斯26
琼斯24
林肯34
现在如果我按姓氏排序:
姓氏▲年龄
---------------------
琼斯26
琼斯24
林肯34
史密斯26
然后如果我按Age排序,我想要这样:
姓氏▲年龄▲
---------------------
琼斯24
琼斯26
史密斯26
林肯34
为了我做了两个比较器 - 一个TLastNameComparer和一个TAgeComparer。
我现在调用
PeopleList.Sort(LastNameCom parer)
PeopleList.Sort(AgeComparer)
现在我的问题是,这不会产生我想要的输出,但是
姓氏?年龄?
---------------------
琼斯24
史密斯26
琼斯26
林肯34
其中Smith,26出现在Jones之前,26代替。所以似乎没有保留以前的排序。
我知道我可以只做一个比较LastName和Age的比较器,但问题是,我必须为TPerson中存在的字段的每个组合进行比较。
是否可以使用多个TComparers做我想要的,或者如何完成我想要的?
谢谢...
新年更新
只是为了参考未来的访客,这是(几乎)我现在使用的代码。
首先我做了一个基类TSortCriterion和一个TSortCriteriaComparer,以便将来可以在多个类中使用这些。
我已将Criterion和列表分别更改为TObject和TObjectList,因为如果objectlist自动处理Criterion的销毁,我发现它更容易。
TSortCriterion< T> = Class(TObject)
Ascending:Boolean;
比较:IComparer< T>;
结束
TSortCriteriaComparer< T> = Class(TComparer< T>)
私人
SortCriteria:TObjectList< TSortCriterion< T>
Public
构造函数创建;
破坏者破坏;覆盖;
函数比较(Const Right,Left:T):整数;覆盖;
过程ClearCriteria;虚拟;
过程AddCriterion(NewCriterion:TSortCriterion< T);虚拟;
结束;
实现
{TSortCriteriaComparer< T> }
procedure TSortCriteriaComparer< T> .AddCriterion(NewCriterion:TSortCriterion< T);
begin
SortCriteria.Add(NewCriterion);
结束
procedure TSortCriteriaComparer< T> .ClearCriteria;
begin
SortCriteria.Clear;
结束
函数TSortCriteriaComparer< T> .Compare(Const Right,Left:T):Integer;
var
条件:TSortCriterion< T>;
begin
在SortCriteria中的条件开始
结果:= Criterion.Comparer.Compare(Right,Left);
如果不是Criterion.Ascending then
结果:= -Result;
如果Result<> 0然后
退出;
结束
结束
构造函数TSortCriteriaComparer< T> .Create;
开始
继承;
SortCriteria:= TObjectList< TSortCriterion< T> .Create(True);
结束
析构函数TSortCriteriaComparer&T; .Destroy;
begin
SortCriteria.Free;
继承;
结束
最后,为了使用排序条件:
(这只是为了这个缘故的例子,因为创建排序顺序的逻辑真的取决于应用程序):
过程TForm1.SortList;
Var
PersonComparer:TSortCriteriaComparer< TPerson> ;;
条件:TSortCriterion< TPerson> ;;
开始
PersonComparer:= TSortCriteriaComparer< TPerson> .Create;
尝试
标准:= TSortCriterion< TPerson>。创建;
Criterion.Ascending:= True;
Criterion.Comparer:= TPersonAgeComparer.Create
PersonComparer.AddCriterion(Criterion);
条件:= TSortCriterion< TPerson>。创建;
Criterion.Ascending:= True;
Criterion.Comparer:= TPersonLastNameComparer.Create
PersonComparer.AddCriterion(Criterion);
PeopleList.Sort(PersonComparer);
//用有序列表的人做某事。
最后
PersonComparer.Free;
结束;
结束;
将排序标准放在包含方向的列表中排序和使用功能来比较项目。这样的记录可以帮助:
type
TSortCriterion< T> = record
Ascending:Boolean;
比较:IComparer< T>;
结束
当用户配置所需的排序时,使用该记录的实例填充列表。
var
SortCriteria:TList< TSortCriterion> ;;
成员将参考功能您已经根据名称和年龄进行比较。现在写一个引用该列表的单一比较函数。这样的东西:
函数比较(const A,B:TPerson):整数;
var
条件:TSortCriterion< TPerson> ;;
begin
在SortCriteria中的条件开始
结果:= Criterion.Comparer.Compare(A,B);
如果不是Criterion.Ascending then
结果:= -Result;
如果Result<> 0然后
退出;
结束
结束
I have just started to use generics, and I am currently having a problem doing sorting on multiple fields.
Case: I have a PeopleList as a TObjectList and i want to be able to make an Excel-like sorting function, by selecting one sort-field at a time, but keeping the previous sorting as much as possible.
EDIT: It must be possible to change the field sort sequence at runtime. (Ie. in one scenario, the user wants the sort order A,B,C - in another scenario he wants B,A,C - in yet another A,C,D)
Lets say we have an unsorted list of people :
Lastname Age
---------------------
Smith 26
Jones 26
Jones 24
Lincoln 34
Now if I sort by LastName :
Lastname ▲ Age
---------------------
Jones 26
Jones 24
Lincoln 34
Smith 26
Then if I sort by Age, i want this :
Lastname ▲ Age ▲
---------------------
Jones 24
Jones 26
Smith 26
Lincoln 34
In order to do this, i have made two Comparers - One TLastNameComparer and one TAgeComparer.
I now call
PeopleList.Sort(LastNameComparer)
PeopleList.Sort(AgeComparer)
Now my problem is that this does not produce the output I want, but
Lastname ? Age ?
---------------------
Jones 24
Smith 26
Jones 26
Lincoln 34
where Smith,26 appears before Jones,26 instead. So it seems like it doesn't keep the previous sorting.
I know that i can make just one comparer that compares both LastName and Age - but the problem is, that i then have to make comparers for each combination of the fields present in TPerson.
Is it possible to do what i want using multiple TComparers or how can i accomplish what i want ?
Thanks...
New Years Update
Happy new year to all of you.
Just for reference to future visitors, this is (almost) the code i am using now.
First I made a base class TSortCriterion and a TSortCriteriaComparer in order to be able to use these in multiple classes in the future. I have changed the Criterion and the list to TObject and TObjectList respectively, as I found it easier if the objectlist automatically handles destruction of the Criterion.
TSortCriterion<T> = Class(TObject)
Ascending: Boolean;
Comparer: IComparer<T>;
end;
TSortCriteriaComparer<T> = Class(TComparer<T>)
Private
SortCriteria : TObjectList<TSortCriterion<T>>;
Public
Constructor Create;
Destructor Destroy; Override;
Function Compare(Const Right,Left : T):Integer; Override;
Procedure ClearCriteria; Virtual;
Procedure AddCriterion(NewCriterion : TSortCriterion<T>); Virtual;
End;
implementation
{ TSortCriteriaComparer<T> }
procedure TSortCriteriaComparer<T>.AddCriterion(NewCriterion: TSortCriterion<T>);
begin
SortCriteria.Add(NewCriterion);
end;
procedure TSortCriteriaComparer<T>.ClearCriteria;
begin
SortCriteria.Clear;
end;
function TSortCriteriaComparer<T>.Compare(Const Right, Left: T): Integer;
var
Criterion: TSortCriterion<T>;
begin
for Criterion in SortCriteria do begin
Result := Criterion.Comparer.Compare(Right, Left);
if not Criterion.Ascending then
Result := -Result;
if Result <> 0 then
Exit;
end;
end;
constructor TSortCriteriaComparer<T>.Create;
begin
inherited;
SortCriteria := TObjectList<TSortCriterion<T>>.Create(True);
end;
destructor TSortCriteriaComparer<T>.Destroy;
begin
SortCriteria.Free;
inherited;
end;
Finally, in order to use the sort criteria : (this is just for the sake of the example, as the logic of creating the sort order really depends on the application) :
Procedure TForm1.SortList;
Var
PersonComparer : TSortCriteriaComparer<TPerson>;
Criterion : TSortCriterion<TPerson>;
Begin
PersonComparer := TSortCriteriaComparer<TPerson>.Create;
Try
Criterion:=TSortCriterion<TPerson>.Create;
Criterion.Ascending:=True;
Criterion.Comparer:=TPersonAgeComparer.Create
PersonComparer.AddCriterion(Criterion);
Criterion:=TSortCriterion<TPerson>.Create;
Criterion.Ascending:=True;
Criterion.Comparer:=TPersonLastNameComparer.Create
PersonComparer.AddCriterion(Criterion);
PeopleList.Sort(PersonComparer);
// Do something with the ordered list of people.
Finally
PersonComparer.Free;
End;
End;
Put your sort criteria in a list that includes the direction to sort and the function to use to compare items. A record like this could help:
type
TSortCriterion<T> = record
Ascending: Boolean;
Comparer: IComparer<T>;
end;
As the user configures the desired ordering, populate the list with instances of that record.
var
SortCriteria: TList<TSortCriterion>;
The Comparer
member will refer to the functions you've already written for comparing based on name and age. Now write a single comparison function that refers to that list. Something like this:
function Compare(const A, B: TPerson): Integer;
var
Criterion: TSortCriterion<TPerson>;
begin
for Criterion in SortCriteria do begin
Result := Criterion.Comparer.Compare(A, B);
if not Criterion.Ascending then
Result := -Result;
if Result <> 0 then
Exit;
end;
end;
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