how to dynamically create a component in delphi su

问题:

Using Delphi 2010

SQLQuery1.First; // move to the first record
while(not SQLQuery1.EOF)do begin
   // do something with the current record
   // What's the code should i write in this part in order to create a TEdit
   // containing the user fullname the current item.
   ShowMessage(SQLQuery1['whom']);
   SQLQuery1.Next; // move to the next record
end;

回答1:

Well, to create a TEdit you need to do the following:

Create a variable to work with. Either a local variable or a class member.

Edit: TEdit;

Then you construct it.

Edit := TEdit.Create(Self);

The parameter to the constructor is the owner. This ensures that the control is destroyed when its owner is destroyed. My assumption is that Self is a form.

Now you need to give the control a parent.

Edit.Parent := Self;

Or perhaps it's on a panel.

Edit.Parent := StatusPanel;

Finally, you set the text.

Edit.Text := SQLQuery1['whom']);

With a label it's all very similar except that you use the Caption property rather than the Text property.

And you will surely want to set other properties but I guess you already know how to do that.

回答2:

Var
  AnEdit : TEdit;
Begin
  AnEdit := TEdit.Create(self);
  AnEdit.Parent := self; // or some suitable container compoent e.g GroupBox, Panel
  AnEdit.Top := ?;
  AnEdit.Left := ?
  // any other properties you weant to set.
End;

The bit that catches people out is setting parent.

回答3:

You can also design the components visually, use the GExperts Components to Code expert on them and then delete them from the form designer again. For a label/edit pair this gives something like

var
  Edit1: TEdit;
  Label1: TLabel;

  Edit1 := TEdit.Create(Self);
  Label1 := TLabel.Create(Self);

  Edit1.Name := 'Edit1';
  Edit1.Parent := Self;
  Edit1.Left := 344;
  Edit1.Top := 172;
  Edit1.Width := 121;
  Edit1.Height := 21;
  Edit1.TabOrder := 0;
  Edit1.Text := 'Edit1';
  Label1.Name := 'Label1';
  Label1.Parent := Self;
  Label1.Left := 296;
  Label1.Top := 176;
  Label1.Width := 65;
  Label1.Height := 17;
  Label1.Caption := 'Label1';
  Label1.FocusControl := Edit1;

Most of the times it needs some reworking (remove the TabOrder lines, replace the Left/Top/... stuff by SetBounds, Align or your own logic, ...) and for some properties/components it doesn't work at all. But you can save a lot of time that way.

回答4:

with TEdit.Create(self) do
begin
  Parent:= ... // The name of the panel or form, on which you would like to place TEdit
  Text:= 'your text'; 
  // And you could set its position by giving "Left" and/or "Width", so on..
end;