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Moving TListView items loses "checked" setting in other items

Posted on 2014-07-17
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Last Modified: 2014-07-20
Hello Experts... I'm working with a TListView that has checkboxes enabled and in "vsReport" style. My goal is to be able to double-click on any item and have that item "swap places" with whatever item is in the top of the ListView (ie. Item[0]). Googling around, I found some code on this website that I'm using:

http://stackoverflow.com/questions/6213945/delphi-listview-move-items-up-down-with-buttons

It outlines an "ExchangeItems" procedure that looked to be just what I needed. I added only a few lines to it for my specific needs . Normally it would swap Item(i) and Item[j]... I wanted it to swap  Item[0] and Item[j]. And also to correctly swap the value of the "checked" property too. Here's my code:

procedure TForm1.ExchangeItems(lv: TListView; const j: Integer);
var
  tempLI: TListItem;
  Item0CheckedState, ItemJCheckedState : Boolean;
begin
  lv.Items.BeginUpdate;
  try
    Item0CheckedState:= lv.Items.Item[0].Checked;
    ItemJCheckedState:= lv.Items.Item[j].Checked;
    tempLI := TListItem.Create(lv.Items);
    tempLI.Assign(lv.Items.Item[0]);
    lv.Items.Item[0].Assign(lv.Items.Item[j]);
    lv.Items.Item[0].Checked:= ItemJCheckedState;
    lv.Items.Item[j].Assign(tempLI);
    lv.Items.Item[j].Checked:= Item0CheckedState;
    tempLI.Free;
  finally
    lv.Items.EndUpdate
  end;
end;  // procedure ExchangeItems

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Simple enough i thought... and seemed logically sound. I tried a small test - I added only 3 items to my ListView: Thing0, Thing1, and Thing2. I put a checkmark in the middle item Thing1.  and left the other two unchecked. Then I double-clicked on the bottom Thing2 item. The procedure does indeed "swap" the two items and their corresponding "checked" values correctly, but it unexpectedly and unwantedly turns the Checked setting of item Thing1 (...which was TRUE) to FALSE.  I put tracing statements after every line of the code in that procedure to find out where this was occurring, and it appears the culprit is this line:

    tempLI.Assign(lv.Items.Item[0]);

Immediately after this line, the "checked" value of Thing1 got switched to FALSE, for some reason. This one is driving me bonkers trying to figure out. Does anyone have some insight please?

Thanks!
    Shawn
0
Comment
Question by:shawn857
  • 2
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4 Comments
 
LVL 25

Expert Comment

by:Sinisa Vuk
Comment Utility
no need to complicate.....just use insert at specific index and assigned values (checked is included):
procedure TForm1.ListView1DblClick(Sender: TObject);
var
  itm: TListItem;
begin
  itm := ListView1.Selected;
  if Assigned(itm) then
    ExchangeItems(ListView1, itm.Index);
end;

procedure TForm1.ExchangeItems(lv: TListView; const j: Integer);
var
  tempLI, newLI: TListItem;
begin
  if j =0 then Exit;

  lv.Items.BeginUpdate;
  try
    tempLI := lv.Items.Item[j];
    newLI := lv.Items.Insert(0);
    newLI.Assign(tempLI);
    tempLI.Free;
  finally
    lv.Items.EndUpdate
  end;
end;

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0
 

Author Comment

by:shawn857
Comment Utility
Thanks Sinisa! Your ListView1DblClick procedure works perfectly, but your suggested code for procedure ExchangeItems does not work right. For my example of 3 items:

Thing0
Thing1  (this one is checked)
Thing2

It will result in:

Thing2
Thing0
Thing1  (this one remains checked... correct)

Instead of Thing2 and Thing0 swapping places (as I would like), Thing2 appears to have just "bumped down" Thing0 one notch below.  Do you see?

Thanks!
   Shawn
0
 
LVL 25

Accepted Solution

by:
Sinisa Vuk earned 500 total points
Comment Utility
Sorry, I miss that swap....here is new procedure...plain old "swap buckets":

procedure TForm1.ExchangeItems(lv: TListView; const j: Integer);
var
  newLI: TListItem;
begin
  if j = 0 then Exit;

  lv.Items.BeginUpdate;
  try
    //temp item
    newLI := lv.Items.Add;
    //keep old j
    newLI.Assign(lv.Items.Item[j]);
    //new j
    lv.Items.Item[j].Assign(lv.Items.Item[0]);
    //new 0
    lv.Items.Item[0].Assign(newLI);
    //remove temp item
    newLI.Free;
  finally
    lv.Items.EndUpdate
  end;
end;

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0
 

Author Closing Comment

by:shawn857
Comment Utility
Success!! Thank you Sinisa!

Cheers
    Shawn
0

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