Delphi FMX TListview - DynamicAppearance mode - Access Violation problem - delphi

Question

Setup TListview, ItemAppearance = DynamicAppearance
in the OnClickItemEX, let's say there's 2 Textobjects. click on both TextObjects - OK. Click on the space between 2 of them - Access Violation.
if click anywhere not covered by an item will result in an Access Violation for the simplest setup.
If I use OnButtonClick only without using OnClickItemEX, no such AV.
How can I resolve this? see below for a Minimal Working Example. (I'm not sure if it's correct to attach it this way as I don't see an Attachment option to upload a zip file of this mini project).
unit bug_main;
interface
type
TForm1 = class(TForm)
ListView1: TListView;
Button1: TButton;
FDMemTable1: TFDMemTable;
BindSourceDB1: TBindSourceDB;
FDMemTable1CustomerID: TIntegerField;
FDMemTable1CustomerName: TStringField;
BindSourceDB2: TBindSourceDB;
BindingsList1: TBindingsList;
procedure Button1Click(Sender: TObject);
procedure ListView1ItemClickEx(const Sender: TObject; ItemIndex: Integer;
const LocalClickPos: TPointF; const ItemObject: TListItemDrawable);
private
FLinkFillControlToField : TLinkFillControlToField;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.fmx}
procedure TForm1.Button1Click(Sender: TObject);
begin
with FDMemTable1 do
begin
Open;
Append;
FieldByName('CustomerID').AsInteger := 1;
FieldByName('CustomerName').AsString := 'ABC';
Post;
Append;
FieldByName('CustomerID').AsInteger := 2;
FieldByName('CustomerName').AsString := 'XYZ';
Post;
end;
if not Assigned(FLinkFillControlToField) then
begin
FLinkFillControlToField := TLinkFillControlToField.Create(BindingsList1);
FLinkFillControlToField.Control := listview1;
with FLinkFillControlToField do
begin
Category := 'Quick Bindings';
Track := False;
Direction := linkDataToControl;
AutoActivate := False;
AutoFill := True;
BindSourceDB1.DataSource.Enabled := True;
FillDataSource := BindSourceDB1;
end;
end;
with FLinkFillControlToField do
begin
with FillExpressions.AddExpression do
begin
SourceMemberName := 'CustomerID';
ControlMemberName := 'Text1';
end;
with FillExpressions.AddExpression do
begin
SourceMemberName := 'CustomerName';
ControlMemberName := 'Text2';
end;
end;
FLinkFillControlToField.Active := True;
end;
procedure TForm1.ListView1ItemClickEx(const Sender: TObject; ItemIndex: Integer;
const LocalClickPos: TPointF; const ItemObject: TListItemDrawable);
begin
if itemobject.Name = 'Text1' then
begin
showmessage('clicked on Text1');
end else if itemobject.Name = 'Text2' then
begin
showmessage('clicked on Text2');
end;
end;
end.
object Form1: TForm1
Left = 0
Top = 0
Caption = 'Form1'
ClientHeight = 404
ClientWidth = 763
FormFactor.Width = 320
FormFactor.Height = 480
FormFactor.Devices = [Desktop]
DesignerMasterStyle = 0
object ListView1: TListView
ItemAppearanceClassName = 'TDynamicAppearance'
ItemEditAppearanceClassName = 'TDynamicAppearance'
HeaderAppearanceClassName = 'TListHeaderObjects'
FooterAppearanceClassName = 'TListHeaderObjects'
Position.X = 16.000000000000000000
Position.Y = 24.000000000000000000
Size.Width = 561.000000000000000000
Size.Height = 353.000000000000000000
Size.PlatformDefault = False
ItemAppearanceObjects.ItemObjects.ObjectsCollection = <
item
AppearanceObjectName = 'Text1'
AppearanceClassName = 'TTextObjectAppearance'
Appearance.Width = 223.000000000000000000
Appearance.Height = 44.000000000000000000
end
item
AppearanceObjectName = 'Text2'
AppearanceClassName = 'TTextObjectAppearance'
Appearance.Width = 208.000000000000000000
Appearance.Height = 44.000000000000000000
Appearance.PlaceOffset.X = 326.000000000000000000
end>
ItemAppearanceObjects.ItemEditObjects.ObjectsCollection = <
item
AppearanceObjectName = 'Text1'
AppearanceClassName = 'TTextObjectAppearance'
end>
OnItemClickEx = ListView1ItemClickEx
end
object Button1: TButton
Position.X = 592.000000000000000000
Position.Y = 24.000000000000000000
Size.Width = 161.000000000000000000
Size.Height = 57.000000000000000000
Size.PlatformDefault = False
Text = 'Button1'
OnClick = Button1Click
end
object FDMemTable1: TFDMemTable
FetchOptions.AssignedValues = [evMode]
FetchOptions.Mode = fmAll
ResourceOptions.AssignedValues = [rvSilentMode]
ResourceOptions.SilentMode = True
UpdateOptions.AssignedValues = [uvCheckRequired, uvAutoCommitUpdates]
UpdateOptions.CheckRequired = False
UpdateOptions.AutoCommitUpdates = True
Left = 576
Top = 128
object FDMemTable1CustomerID: TIntegerField
FieldName = 'CustomerID'
end
object FDMemTable1CustomerName: TStringField
FieldName = 'CustomerName'
Size = 30
end
end
object BindSourceDB1: TBindSourceDB
DataSet = FDMemTable1
ScopeMappings = <>
Left = 576
Top = 192
end
object BindSourceDB2: TBindSourceDB
DataSet = FDMemTable1
ScopeMappings = <>
Left = 576
Top = 248
end
object BindingsList1: TBindingsList
Methods = <>
OutputConverters = <>
Left = 20
Top = 5
end
end

Answer 1

If you set a breakpoint on the first line of your ListView1ItemClickEx method and then run the app and click between two items, you'll see that there is no ItemObject because you're not clicking on an item (you're clicking between them). This results in ItemObject being nil, and you then try to read the Text value from that unassigned object, causing the AV.
You can correct this by checking to make sure that ItemObject is assigned a value before you use it.
procedure TForm1.ListView1ItemClickEx(const Sender: TObject; ItemIndex: Integer;
const LocalClickPos: TPointF; const ItemObject: TListItemDrawable);
begin
if ItemObject <> nil then
begin
if itemobject.Name = 'Text1' then
begin
ShowMessage('clicked on Text1');
end else if itemobject.Name = 'Text2' then
begin
ShowMessage('clicked on Text2');
end;
end else
ShowMessage('ItemObject is not assigned');
end;
Learning to use the debugger to step through the code will enable you to figure out this sort of simple issue yourself. There's no better tool to have in your programmers toolbox than a good debugger, and Delphi's debugger is quite good.