Delphi之For In
Java和C#里面的For In用起来真爽,我们Delphin也不用眼红了,从D2005起,Delphi里面也有这个功能了.
首先我们要知道哪些类型可以用For In吧,下面就是:
- for Element in ArrayExpr do Stmt; 数组
- for Element in StringExpr do Stmt; 字符串
- for Element in SetExpr do Stmt; 集合
- for Element in CollectionExpr do Stmt; 集合
- for Element in Record do Stmt; 结构体
我们来看例子:
01 |
type |
02 |
THuangJacky = (hjA,hjB,hjC,hjD); |
03 |
TJackyHuang = record |
04 |
a,b,c:Integer; |
05 |
end; |
06 |
const |
07 |
stringExpr='HuangJacky'; |
08 |
arrayExpr:array[0..5] of Integer= (1,2,3,4,5,6); |
09 |
setExpr:set of THuangJacky = [hjA,hjB,hjD]; |
10 |
procedure TForm1.FormCreate(Sender: TObject); |
11 |
var |
12 |
I:Integer; |
13 |
C:Char; |
14 |
D:THuangJacky; |
15 |
F:TComponent; |
16 |
begin |
17 |
for c in stringExpr do |
18 |
ShowMessage(C); |
19 |
for i in arrayExpr do |
20 |
ShowMessage(IntToStr(i)); |
21 |
for d in setExpr do |
22 |
ShowMessage(IntToStr(Ord(d))); |
23 |
for F in Self do |
24 |
ShowMessage(f.Name); |
25 |
end; |
是不是很爽呀?哈哈,Delphi也与时俱进呀.
之前写了类助手文章中,老赵问是不是扩展方法,因为对C#没有了解到这么多,所以不知道.
那么我们在Java中要For In必须实现Iterator吧.
那么Delphi的会不会也要呢?
是的,如果我们要自己的类支持For In的话,就必须满足下面的条件:
1 必须有个公共方法GetEnumerator(),这个方法返回值是一个类,接口或者记录体.
2 上面返回的类,接口或者记录体中又必须有公共方法MoveNext(),这个方法的返回值是Boolean.
3 1中返回的类,接口或者记录体中必须有一个只读的属性Current,类型要和集合中的元素一样.
说了这么多,看个例子:
01 |
type |
02 |
TMyIntArray = array of Integer; |
03 |
|
04 |
TMyEnumerator = class |
05 |
Values: TMyIntArray; |
06 |
Index: Integer; |
07 |
public |
08 |
constructor Create; |
09 |
function GetCurrent: Integer; |
10 |
function MoveNext: Boolean; |
11 |
property Current: Integer read GetCurrent; |
12 |
end; |
13 |
|
14 |
TMyContainer = class |
15 |
public |
16 |
function GetEnumerator: TMyEnumerator; |
17 |
end; |
18 |
|
19 |
constructor TMyEnumerator.Create; |
20 |
begin |
21 |
inherited Create; |
22 |
Values := TMyIntArray.Create(100, 200, 300); |
23 |
Index := -1; |
24 |
end; |
25 |
|
26 |
function TMyEnumerator.MoveNext: Boolean; |
27 |
begin |
28 |
if Index < High(Values) then |
29 |
begin |
30 |
Inc(Index); |
31 |
Result := True; |
32 |
end |
33 |
else |
34 |
Result := False; |
35 |
end; |
36 |
|
37 |
function TMyEnumerator.GetCurrent: Integer; |
38 |
begin |
39 |
Result := Values[Index]; |
40 |
end; |
41 |
|
42 |
function TMyContainer.GetEnumerator: TMyEnumerator; |
43 |
begin |
44 |
Result := TMyEnumerator.Create; |
45 |
end; |
46 |
|
47 |
var |
48 |
MyContainer: TMyContainer; |
49 |
I: Integer; |
50 |
|
51 |
Counter: Integer; |
52 |
|
53 |
begin |
54 |
MyContainer := TMyContainer.Create; |
55 |
|
56 |
Counter := 0; |
57 |
for I in MyContainer do |
58 |
Inc(Counter, I); |
59 |
|
60 |
WriteLn('Counter = ', Counter); |
61 |
end. |
