How can I load Field1 and Field2 from TADOQuery to TTreeView?

Question

I want information from TADOQuery to be loaded into a TTreeView. For example, I want it to be loaded as Field1->Add in Table1 and as Field2->AddChild with buttonClick. But when I run the code, I am getting an error:

Access violation at adress 0043616B in module "TRV2.exe"

I'm making a mistake or something is missing. Can you guide me?

procedure TForm1.AddButtonClick(Sender: TObject); 
var
  t: Integer;
  MyNode, Node : TTreeNode; 
begin 
  MyNode := Node;
  t := Node.AbsoluteIndex;
  TreeView1.Items.Add(MyNode, ADOQuery1.FieldByName('CODE_NAME').AsString);
end;

procedure TForm1.AddChildButtonClick(Sender: TObject); 
var
  t: Integer;
  MyNode, Node: TTreeNode; 
begin 
  MyNode := Node;
  t := Node.AbsoluteIndex;
  TreeView1.Items.Add(MyNode, ADOQuery1.FieldByName('CODE_CHILD').AsString);
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  t: Integer;
  MyNode, Node: TTreeNode;
begin
  MyNode := Node;
  t := Node.AbsoluteIndex;
  ADOQuery1.Open;
end;

UPDATE: I want to get the whole table and update the TTreeView when I add new Add and Child to the database. With these codes (AddButtonClick and AddChildButtonClick) I can only import the first values into the TTreeView. I wonder if a loop is needed?

`MyNode:=Node;` is problematic: Both are uninitialized local variables and their value is random. Accessing Node or MyNode is likely to generate an access violation. — fpiette, Dec 25 '21 at 21:59

Remy Lebeau · Answer 1 · 2021-12-26T22:42:18.873

MyNode and Node are both local variables that you are not initializing to anything. Your AV is because you are trying to access an object that doesn't exist.

Try using a class member instead, where you initialize it with one button click, and then use it with the other button click, eg:

private
  MyNode: TTreeNode;

...

procedure TForm1.AddButtonClick(Sender: TObject); 
begin 
  MyNode := TreeView1.Items.Add(nil, ADOQuery1.FieldByName('CODE_NAME').AsString);
end;

procedure TForm1.AddChildButtonClick(Sender: TObject); 
begin
  if MyNode <> nil then
    TreeView1.Items.AddChild(MyNode, ADOQuery1.FieldByName('CODE_CHILD').AsString);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  ADOQuery1.Open;
end;

UPDATE: to iterate through multiple records in the query result, you need to call TADOQuery.Next() in a loop until TADOQuery.Eof is true.

while not ADOQuery1.Eof do //This line does not run the post-compiler program. — sadimba, Dec 27 '21 at 19:32

sadimba · Answer 2 · 2021-12-28T21:39:48.117

The database was taken into treview with the following codes. There is something missing. Because Field1=Add and Field2=Child. Same Fields repeating.

procedure TForm1.AddButtonClick(Sender: TObject);
var
CurrentDeptID, RecordDeptID: Integer; RootNode, DeptNode: TTreeNode;
begin
CurrentDeptID := 0;
TreeView1.Items.Clear;
RootNode := TreeView1.Items.Add(DeptNode, 'CODE_NAME');
DeptNode := nil;
ADOQuery1.SQL.Text := 'Select * from Tablo1 where CODE_NAME= CODE_NAME';
ADOQuery1.Open;
try
ADOQuery1.First;
while not ADOQuery1.Eof do
begin
RecordDeptID := ADOQuery1.FieldByName('ID').AsInteger;
if ( DeptNode  = nil) or (RecordDeptID <> CurrentDeptID) then
begin
DeptNode := TreeView1.Items.AddChild(RootNode, 
ADOQuery1.FieldByName('CODE_NAME').AsString); //
CurrentDeptID := RecordDeptID;
end;
TreeView1.Items.AddChild(DeptNode, 
ADOQuery1.FieldByName('CODE_CHILD').AsString);
ADOQuery1.Next;
end;
finally
ADOQuery1.close;
end;
end;

[https://i.stack.imgur.com/kNojV.jpg]

Blockquote

How can I load Field1 and Field2 from TADOQuery to TTreeView?

2 Answers2