我正在为Delphi 2007编写这个问题,但我很确定这是所有语言中的常见问题.
所以,我有一个项目,我需要保存关于某些字段的旧值和新值的信息(在我正在使用的数据集的BeforePost事件中给出)并在AfterPost事件中使用它们.
目前,我一直在使用全局变量,但在项目中已经有很多这样的变量,在管理文档和/或注释时,这成为一个真正的问题.
基本上,我问是否有更好的方法(在Delphi 2007或一般情况下)保持数据集的BeforePost事件的信息并将它们返回到AfterPost事件中.
解决方法
首先创建一个新的自定义数据源
TDataRecord = array of record
FieldName: string;
FieldValue: Variant;
end;
TMyDataSource = class(TDataSource)
private
LastValues: TDataRecord;
procedure MyDataSourceBeforePost(DataSet: TDataSet);
procedure SetDataSet(const Value: TDataSet);
function GetDataSet: TDataSet;
public
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
function GetLastValue(FieldName: string): Variant;
property MyDataSet: TDataSet read GetDataSet write SetDataSet;
end;
{ TMyDataSource }
constructor TMyDataSource.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
end;
destructor TMyDataSource.Destroy;
begin
SetLength(LastValues,0);
inherited Destroy;
end;
function TMyDataSource.GetDataSet: TDataSet;
begin
Result := DataSet;
end;
procedure TMyDataSource.SetDataSet(const Value: TDataSet);
begin
DataSet := Value;
DataSet.BeforePost := MyDataSourceBeforePost;
end;
procedure TMyDataSource.MyDataSourceBeforePost(DataSet: TDataSet);
var
i: integer;
begin
SetLength(LastValues,DataSet.FieldCount);
for i:=0 to DataSet.FieldCount-1 do
begin
LastValues[i].FieldName := DataSet.Fields.Fields[i].FieldName;
LastValues[i].FieldValue := DataSet.Fields.Fields[i].OldValue;
end;
end;
function TMyDataSource.GetLastValue(FieldName: string): Variant;
var
i: integer;
begin
Result := Null;
for i:=0 to Length(LastValues)-1 do
if SameText(FieldName,LastValues[i].FieldName) then
begin
Result := LastValues[i].FieldValue;
break;
end;
end;
并覆盖应用程序数据源
TForm1 = class(TForm)
private
MyDataSource: TMyDataSource;
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
ADOQuery1.Active := true;
MyDataSource := TMyDataSource.Create(Self);
MyDataSource.MyDataSet := ADOQuery1;
DBGrid1.DataSource := MyDataSource;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
MyDataSource.Free;
end;
procedure TForm1.ADOQuery1AfterPost(DataSet: TDataSet);
var
AValue: Variant;
begin
AValue := MyDataSource.GetLastValue('cname');
if not VarIsNull(AValue) then;
end;