问题
I am developing a Multi-Device Application in Firemonkey where Main class has a ListBox component with some items. Each of these items has the same custom style.
My problem is when I have so many items in the ListBox and I have to do scroll vertical to see the rest of items. In this case, the ListBox has a strange behaviour and when I do scroll up after doing scroll down the item's components (a button for example) have changed his background colour and the items have changed his order inside ListBox.
For example, if I had:
- Item 1
- Item 2
- Item 3
after I do scroll I have:
- Item 2
- Item 3
- Item 1
This change is random. Each time is different.
Real example (process steps):
- Load the Main class where is ListBox.
Do vertical scrolling down to see the rest of items.
Do vertical scrolling upward to return to the top of the list.
- The items have changed position in the ListBox and the button (component of each item) changes its background color.
Why I have this behaviour in the ListBox?? How I can solve it and the ListBox do not change items order neither background colour of his components?
I do not know if there is any property to block items inside ListBox or similar ...
EDIT
This is the code to create and initialize the ListBox items:
procedure TRooms_Form.FormCreate(Sender: TObject);
var
...
begin
i := 0;
while i < numItems do begin
//Create ListBox item
item := TListBoxItem.Create(nil);
item.Parent := myListBox;
item.StyleLookup := 'styleLBox';
//Number
itemNumber := item.FindStyleResource('btt_number') as TButton;
if Assigned(itemNumber) then begin
itemNumber.Text := jsonNumber;
case jsonColor of
0 : itemNumber.TintObject.TintColor := TAlphaColors.Chocolate;
1 : itemNumber.TintObject.TintColor := TAlphaColors.Gold;
2 : itemNumber.TintObject.TintColor := TAlphaColors.Darkgreen;
3 : itemNumber.TintObject.TintColor := TAlphaColors.Deeppink;
end;
end;
//Title
itemTitle := item.FindStyleResource('txtstyle_title') as TText;
if Assigned(itemTitle) then begin
itemTitle.Text := jsonTitle;
end;
//Occupation
itemOccup := item.FindStyleResource('txt_occupation') as TText;
if Assigned(itemOccup) then begin
itemOccup.Text := jsonOccup;
end;
//Dates
itemDay := item.FindStyleResource('txt_day') as TText;
if Assigned(itemDay) then itemDay.Text := displayDay;
itemDateStart := item.FindStyleResource('txt_start') as TText;
if Assigned(itemDateStart) then itemDateStart.Text := jsonTimeStart;
itemDateEnd := item.FindStyleResource('txt_end') as TText;
if Assigned(itemDateEnd) then itemDateEnd.Text := jsonTimeEnd;
//Item background
itemBackgr := item.FindStyleResource('background_item') as TRectangle;
if Assigned(itemBackgr) then begin
itemBackgr.Fill.Kind := TBrushKind.Solid;
case jsonStatus of
0 : itemBackgr.Fill.Color := TAlphaColors.White;
1 : itemBackgr.Fill.Color := TAlphaColors.Lightgreen;
2 : itemBackgr.Fill.Color := TAlphaColors.Palegoldenrod;
3 : itemBackgr.Fill.Color := TAlphaColors.Lightcoral;
4 : itemBackgr.Fill.Color := TAlphaColors.Lightseagreen;
5 : itemBackgr.Fill.Color := TAlphaColors.Lightblue;
6 : itemBackgr.Fill.Color := TAlphaColors.Lightgrey;
end;
end;
//Empty item
if (StrToInt(jsonEmpty) = 1) or (StrToInt(jsonNull) = 1) then begin
startDetail[i] := False;
if Assigned(itemNumber) then itemNumber.Visible := False;
if Assigned(itemOccup) then itemOccup.Visible := False;
end
else begin
startDetail[i] := True;
end;
Inc(i);
end;
Thanks so much for your attention.
回答1:
After some days and some tests, I have already found a solution to my problem.
I do not understand well why but there was some code lines that they were interfering with my custom style.
For example, when I put:
//Item background
itemBackgr := item.FindStyleResource('background_item') as TRectangle;
if Assigned(itemBackgr) then begin
**itemBackgr.Fill.Kind := TBrushKind.Solid;**
...
After scroll, items changed order position and their color background. I have applied this property directly in the 'TRectangle' component in the custom style.
Moreover, I changed the allocation of all elements to this way:
-Before I had:
itemTitle := item.FindStyleResource('txtstyle_title') as TText;
if Assigned(itemTitle) then begin
itemTitle.Text := jsonTitle;
end;
-Now, I have:
item.StylesData['txtstyle_title'] := jsonTitle;
With these changes I get items do not change their position in ListBox neither background color after scroll.
I had a problem yet, buttons do not show their background color and it was due to these lines:
//Empty item
if (StrToInt(jsonEmpty) = 1) or (StrToInt(jsonNull) = 1) then begin
startDetail[i] := False;
**if Assigned(itemNumber) then itemNumber.Visible := False;**
**if Assigned(itemOccup) then itemOccup.Visible := False;**
end
else begin
startDetail[i] := True;
end;
Apparently, you cannot change visible property from item in 'FormCreate' method because when you do scroll some items elements change their property without control. Therefore, I have done some modifications in my code instead of putting to false the visibility:
if (StrToInt(jsonEmpty) = 1) or (StrToInt(jsonNull) = 1) then begin
startDetail[i] := False;
item.StylesData['btt_number.Text'] := '';
item.StylesData['txt_occupation'] := '';
if (StrToInt(jsonEmpty) = 1) then item.StylesData['btt_number.TintObject.TintColor'] := TAlphaColors.White;
if (StrToInt(jsonNull) = 1) then item.StylesData['btt_number.TintObject.TintColor'] := TAlphaColors.Lightblue;
end
else begin
startDetail[i] := True;
item.StylesData['btt_number.Text'] := jsonNumber;
item.StylesData['txt_occupation'] := jsonOccup;
end;
At this form, I put the text ' ' (empty) and the background color at the same color that his item (TRectangle) in the elements who should to have the visible property to false.
After all these changes I get the result that I wanted, that is to say, my items ListBox do not change when I scroll. XD
来源：https://stackoverflow.com/questions/38219295/listbox-items-change-after-doing-scroll-in-firemonkey