Question

我正在函数中创建一个Tdataset对象。请找到以下代码：

procedure CreateDataset;
var
  LDataset: TDataset;
begin
  LDataset := TDataset.create(nil);
  if LDataset = nil then
    Exit;
  with LDataset do
  begin
    FieldDefs.Clear;
    FieldDefs.Add('NAME', ftString, 50);
    FieldDefs.Add('Designation', ftString, 20);
    FieldDefs.Add('Address', ftString,100);
    FieldDefs.Add('ContactNum', ftString,12);
    Open; // giving exception as 'AbstractError' at this line
  end;
end;

打开数据集时，我收到异常抽象错误。如果我有任何错误，请纠正我。

Answer 1

好的，让我们看看：

procedure CreateDataset;
var
  LDataset: TDataset;
begin
  LDataset := TDataset.create(nil);
    // ERROR. TDataset is an abstract class, don't instantiate it.
    // Use a descendant class instead.
  if LDataset = nil then
    Exit;
    // NONSENSE. It would never work. Maybe you're afraid about
    // 'dataset not created'. If so, the constructor will raise an
    // exception.
  with LDataset do
  begin
    FieldDefs.Clear;
      // FOR WHAT? You create this dataset a millisecond ago.
      // It's empty. 
    FieldDefs.Add('NAME', ftString, 50);
      // BTW, you should not create and fill components without
      // reason. Try to use design-time abilities instead.
    FieldDefs.Add('Designation', ftString, 20);
    FieldDefs.Add('Address', ftString,100);
    FieldDefs.Add('ContactNum', ftString,12);
    Open;
       // ERROR. Even if correct dataset class used, it will not
       // open if it is not linked to some correct connection object.
  end;
  // LEAK. And now? You created the dataset. You opened it. You
  // stored it nowhere. You do not return it. At the moment
  // you'll leave the procedure, the opened dataset would be
  // lost. It would never close and never be disposed until
  // the end of program.
end;

打开数据集时的抽象错误

1 个答案: