delphi - Delphi TClientDataSet 定位问题

Question

我正在使用Delphi7,MS Vista和Devart's dbExpress驱动程序（4.70 版）。我放弃 a TSQLConnection， a TSQLTable( tabA)， a TDataSetProvider， a TClientDataSet( cdsA)， aDataSource和 a DBGrid。

我通过图形设计工具进行了所有设置。一切正常，当我打开cdsA时，我可以看到 Grid 中的所有数据。这是我的代码：

procedure TForm1.Button1Click(Sender: TObject);
var
  fields, values: string;
begin
  cdsA.Close;
  cdsA.Open;
  fields := 'fielda;fieldb';
  values := Edit1.Text+';'+Edit2.Text;
  cdsA.SetKey;
  cdsA.Locate(fields, values, [loCaseInsensitive]);
end;

fieldA并存fieldB在于表中，也定义于其中cdsA.Fields。当我执行此代码时，Locate指令会生成异常EVariantInvalidArgError ... Invalid argument。我想知道怎么了。TIA。

弗朗切斯科

Answer 1

Your code is wrong. :)

procedure TForm1.Button1Click(Sender: TObject);
var
  fields, values: string;
begin
  // Closing the CDS and opening it every time is foolish. Just
  // open it if it's not already open.
  if not cdsA.Active then
    cdsA.Open;

  // List of column names. Since column (field) names are always
  // strings, can just use semicolon-separated values
  fields := 'fielda;fieldb'; 

  // Values for columns. Since these could be any type, you can't
  // simply use semicolon-separated strings. You have to pass an
  // array of Variants. The easiest way is to just create it and
  // populate it, and let reference counting release it when it's
  // out of scope
  values := VarArrayOf([Edit1.Text, Edit2.Text]);  

  // No call to SetKey here. SetKey is used with FindKey, not Locate
  cdsA.Locate(fields, values, [loCaseInsensitive]);
end;