怎样在对话框里选一个文件？(20分)

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procedure TfrmMain.btnFileClick(Sender: TObject);
begin
if Trim(edtFile.Text) = '' then
dlgOpen.InitialDir := ExtractFilePath(Application.ExeName)
else
dlgOpen.InitialDir := ExtractFilePath(edtFile.Text);
if dlgOpen.Execute then edtFile.Text := dlgOpen.FileName;
end;

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