| Description |
The GetRange method is awkwardly named. It is really a variation of the Clone method - a new ArrayList is built, and set from element values from the current ArrayList.
Count elements from StartIndex of the current ArrayList are copied to the new ArrayList.
Just like Clone, GetRange performs a shallow copy. When the current array holds reference (non primitive) data types, the target array element values still refer to the same objects that current array elements refer to. This is what is referred to as a shallow copy. A deep copy would create new versions of the referred objects.
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| Microsoft MSDN Links |
System.Collections
System.Collections.ArrayList
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| A simple example |
program Project1;
{$APPTYPE CONSOLE}
uses
System.Collections;
var
Source, Target : System.Collections.ArrayList;
i : Integer;
begin
// Create our array list object
Source := ArrayList.Create;
// Fill it
Source.Add('0.Zero');
Source.Add('1.One');
Source.Add('2.Two');
Source.Add('3.Three');
Source.Add('4.Four');
Source.Add('5.Five');
Source.Add('6.Six');
Source.Add('7.Seven');
Source.Add('8.Eight');
Source.Add('9.Nine');
// Create a new ArrayList with just the middle 4 elements
Console.WriteLine('Copying the middle 4 elements ');
Console.WriteLine('to a new ArrayList :');
Console.WriteLine;
Target := Source.GetRange(3, 4);
// Display the new array contents
for i := 0 to Target.Count-1 do
Console.WriteLine(Target[i].ToString);
Console.Readline;
end.
| | Show full unit code | Copying the middle 4 elements
to a new ArrayList :
3.Three
4.Four
5.Five
6.Six
| | | Illustrating the shallowness of the GetRange element copy | program Project1;
{$APPTYPE CONSOLE}
uses
System.Collections;
type
MyClass = Class
private
mcName : String;
published
Property Name : String
read mcName
write mcName;
Constructor Create(Name : String); overload;
Function ToString : String; overload;
end;
// MyClass methods
constructor MyClass.Create(Name : String);
begin
inherited Create;
mcName := Name;
end;
function MyClass.ToString : String;
begin
Result := Name;
end;
// Main code
var
myArray, cloneArray : System.Collections.ArrayList;
myObject : MyClass;
i : Integer;
begin
// Create a 3 element array of strings
myArray := ArrayList.Create;
myArray.Add(MyClass.Create('Hello'));
myArray.Add(MyClass.Create('sad'));
myArray.Add(MyClass.Create('World'));
// Clone the array - this carries out a shallow copy
cloneArray := myArray.GetRange(0, 3);
// Display both arrays
for i := 0 to myArray.Count-1 do
begin
myObject := MyClass(myArray.Item[i]);
Console.WriteLine('myArray[{0}] = {1}',
i.ToString, myObject.ToString);
end;
Console.WriteLine;
for i := 0 to cloneArray.Count-1 do
begin
myObject := MyClass(cloneArray.Item[i]);
Console.WriteLine('cloneArray[{0}] = {1}',
i.ToString, myObject.ToString);
end;
// Demonstrate the shallowness of the GetRange process
Console.WriteLine;
myObject := MyClass(cloneArray.Item[1]);
myObject.Name := 'wonderful'; // Was 'sad'
Console.WriteLine('After updating just the cloneArray :');
Console.WriteLine;
// Display both arrays again
for i := 0 to myArray.Count-1 do
begin
myObject := MyClass(myArray.Item[i]);
Console.WriteLine('myArray[{0}] = {1}',
i.ToString, myObject.ToString);
end;
Console.WriteLine;
for i := 0 to cloneArray.Count-1 do
begin
myObject := MyClass(cloneArray.Item[i]);
Console.WriteLine('cloneArray[{0}] = {1}',
i.ToString, myObject.ToString);
end;
Console.ReadLine;
end.
| | Show full unit code | myArray[0] = Hello
myArray[1] = sad
myArray[2] = World
cloneArray[0] = Hello
cloneArray[1] = sad
cloneArray[2] = World
After updating just the cloneArray :
myArray[0] = Hello
myArray[1] = wonderful
myArray[2] = World
cloneArray[0] = Hello
cloneArray[1] = wonderful
cloneArray[2] = World
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