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TListview.items.clear long execution time

Posted on 2003-11-16
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Last Modified: 2010-04-05
hi,

i am coding a simple app which contains a listview and records is inserted & deleted time by time.
Everytime records being refreshed, i call items.clear. i noticed there is quite a long execution time for items.clear. it's around 3 to 5 sec. During that time, i cannot move anything even the cursor, could anyone advise how to minimise the impact.

i am using D7 with win2000,clients machine is P4 with 256 Mb
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Question by:lamtl354
9 Comments
 
LVL 5

Expert Comment

by:Hypoviax
Comment Utility
If you have a lot of items and are calling items.clear regualrly this may take significant cpu time and thus result in the lag. To fix this problem try a linear deletion of the items:

For X:=0 to listview1.items.count-1 do
         begin
          listview1.items.item[x].delete
         end;

Hope this solves your problem

Hypoviax
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Expert Comment

by:13_th
Comment Utility
variant 1
// unhooking the renovation for time peelings - can enlarge speed

 ListView1.Items.BeginUpdate;
 ListView1.Items.clear;
 ListView1.Items.EndUpdate;

variant 2
//partial removing
 ListView1.Items.BeginUpdate;
For i:=0 to listview1.items.count-1 do
         begin
          listview1.items.item[0].delete;
          Application.ProcessMessages; //to did not hang
         end;
 ListView1.Items.EndUpdate;


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LVL 14

Accepted Solution

by:
DragonSlayer earned 50 total points
Comment Utility
or, alternatively:

ListView1.Items.BeginUpdate;
try
  ListView1.Items.Clear;
finally
  ListView1.Items.EndUpdate;
end;
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Expert Comment

by:13_th
Comment Utility
>try-finaly-end
IMHO, spare!

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Expert Comment

by:13_th
Comment Utility
>try-finaly-end
no need
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LVL 14

Expert Comment

by:DragonSlayer
Comment Utility
my friend, if you don't use the try-finally, and if something goes wrong while clearing the ListView (e.g. you added Objects to your ListView and something goes wrong while freeing them, etc), you will never be able to see refreshes/updates to the listview till you restart your application... better be safe than sorry.  :-)
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Expert Comment

by:13_th
Comment Utility
I agree . but when calling clear this unlikely.À at accompaniment in list or items[...].delete -  i agree :)
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LVL 14

Expert Comment

by:DragonSlayer
Comment Utility
actually, I didn't notice that we posted the Begin/End-Update thingy only 1 minute (or seconds apart!)... ehhehe... lamtl354, if it works, give the points to 13_th, not me, ok? :-)
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LVL 1

Expert Comment

by:hacibumbala
Comment Utility
Adding large number of items to a list view cripples, even crashes your application. I would recommend using Virtual ListView (normal ListView with OwnerData = True) instead. See "Virtual ListView" example under Demos folder of Delphi (i.e. C:\Program Files\Borland\Delphi7\Demos\Virtual Listview). Or, you may use a third-party component:

http://www.delphi-gems.com/VirtualTreeview/VT.php
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