Re: How to move one element of Dynamic Array of Objects

TeChNoInSiDe wrote:
I read a topic about moving array indexes here:

http://groups.google.com.br/group/comp.lang.pascal.delphi.misc/browse_thread/thread/b2a8c7320a060999/8de55d44c9827f7d?hl=pt-BR&lnk=gst

How about here?

http://pages.cs.wisc.edu/~rkennedy/array-delete

I demonstrate two ways of removing something from an array.

The real problem is those methods aren´t working for array of objects.

For example:

===================================================

var

TestArray: Array of TAdvGlowButton;

begin

//Clone components

TestArray[0] := TAdvGlowButton component; //component cloned from
original button
TestArray[1] := TAdvGlowButton component; //component cloned from
original button
TestArray[2] := TAdvGlowButton component; //component cloned from
original button

//Delete component at index 1

FreeAndNil(TestArray[1]);

//Move component at index 2 to index 1

for i := 2 to High(TestArray) do
begin

System.Move(TestArray[i], TestArray[(i - 1)], SizeOf(TestArray) *
(Length(TestArray) - (i - 1) - 1));

end;

===================================================

The above code seems to be working correctly.

If that code seems to work correctly, you're not looking very carefully. Test it again, but this time, delete an element earlier than the second-to-last one.

That "SizeOf(TestArray)" term is wrong whether you're using a loop or not. I think you meant "SizeOf(TestArray[0])" instead. You're moving the things in the array, so the number of bytes should be based on the array's contents, not the size of the variable.

The problem is when I
try to make the same thing with multi-dimensional arrays like this:

var

TestArray : Array of Array of TPanel;

begin

//clone components

TestArray[0][0] := TPanel cloned component;
TestArray[0][1] := TPanel cloned component;
TestArray[0][2] := TPanel cloned component;
TestArray[1][0] := TPanel cloned component;
TestArray[1][1] := TPanel cloned component;
TestArray[1][2] := TPanel cloned component;
TestArray[1][3] := TPanel cloned component;
TestArray[1][4] := TPanel cloned component;
TestArray[2][0] := TPanel cloned component;

//Delete components from index 1

for i := 0 to High(TestArray[1]) do FreeAndNil(TestArray[1][i]);

//Copy all elements from index 2 to index 1

for i := 2 to High(TestArray) do
begin

//Reset and resize main index with size of next index

SetLength(TestArray[(i - 1)], 0);
SetLength(TestArray[(i - 1)], Length(TestArray[i]));

You don't really need the first SetLength.

//Move data

for j := Low(TestArray[i]) to High(TestArray[i]) do
begin

System.Move(TestArray[i][j], TestArray[(i - 1)][j], SizeOf(TestArray)
* (Length(TestArray) - (VIv_i - 1) - 1));

What is VIv_i?

Remember that you're not really doesn't anything to TestArray. You're updating just one of its elements, TestArray[i].

Parentheses aren't required in "TestArray[(i - 1)]."

Did you know that you can assign arrays to each other?

TestArray[i - 1] := TestArray[i];

That can be the entire contents of your loop.

Do *not* use "Move" to remove an element when the element type is "dynamic array," unless you use the full version of DeleteX from the page I cite above. The Initialize and Finalize calls are crucial.

end;

end;

This code will either generate delayed runtime access violations or
when the main application is closed it generates access violation
errors or invalid pointer operations.

Any tips?

Thank you in advance for any help.


--
Rob
.

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