使非窗口组件数据感知

Question

I have a non-windowed component with a date property. I would like to make this component data aware with read and write capabilities to a date field. (In other words, if I change the date at runtime, I would like to write the new date property value to the dataset.) I have googled for examples, but I haven't been able to find any. Found several read-only examples, eg, TDbLabel, but none that allow changes to be written to the dataset. If anyone can point me to an example, I would be grateful.

Answer 1

Here is a generic code approach to your question

unit Unit1;

interface

uses
   Classes
  ,DB
  ,DBCtrls
  ;
type
  TDataAwareComponent = class(TComponent)
  private
    { private declarations }
    FDataLink : TFieldDataLink;
    FFromDateChange : Boolean;
    function GetDataField: string;
    function GetDataSource: TDataSource;
    function GetField: TField;
    function GetReadOnly: Boolean;
    procedure SetDataField(const Value: string);
    procedure SetDataSource(const Value: TDataSource);
    procedure SetReadOnly(const Value: Boolean);
    function GetDateProperty: TDateTime;
    procedure SetDateProperty(const Value: TDateTime);
  protected
    { protected declarations }
    procedure DataChange(Sender : TObject);
  public
    { public declarations }
    constructor Create(AOwner : TComponent);override;
    destructor  Destroy;override;
  public
    property Field        : TField    read GetField;
    property DateProperty : TDateTime read GetDateProperty write SetDateProperty;
  published
    { published declarations }
   property DataSource   : TDataSource           read GetDataSource  write SetDataSource;
   property DataField    : string                read GetDataField   write SetDataField;
   property ReadOnly     : Boolean               read GetReadOnly    write SetReadOnly;
  end;

implementation

{ TDataAwareComponent }
{------------------------------------------------------------------------------}
constructor TDataAwareComponent.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FDataLink                 := TFieldDataLink.Create;
  FDataLink.Control         := Self;
  FDataLink.OnDataChange    := DataChange;
end;
{------------------------------------------------------------------------------}
destructor TDataAwareComponent.Destroy;
begin
  FDataLink.Free;
  FDataLink := nil;
  inherited;
end;
{------------------------------------------------------------------------------}
procedure TDataAwareComponent.DataChange(Sender: TObject);
begin
  // Here a visual object would display the underlying field value.
  // For example if this component was a TEdit
  // the code would be something like

{  if FDataLink.Active then
    Self.Text := Field.AsString;
    And on the exit event of the TEdit the code would be reversed
    so the field can take the value the user entered.

    Since you do not need any UI interaction propably this event
    is useless to you.
    }
    // Of course there are more issues you should cover to
    // have a complete working solution.
    // This is only demostration code.

end;
{------------------------------------------------------------------------------}
function TDataAwareComponent.GetDataField: string;
begin
  Result := FDataLink.FieldName
end;
{------------------------------------------------------------------------------}
function TDataAwareComponent.GetDataSource: TDataSource;
begin
  Result := FDataLink.DataSource;
end;
{------------------------------------------------------------------------------}
function TDataAwareComponent.GetDateProperty: TDateTime;
begin
  //You do not need a separate property since you can access directly the field value.
  Result := 0;
  if Assigned(Field) and (Field.DataType in [ftTime,ftDate,ftDateTime]   then
    Result := Field.AsDateTime;
end;
{------------------------------------------------------------------------------}
function TDataAwareComponent.GetField: TField;
begin
  Result : FDataLink.Field;
end;
{------------------------------------------------------------------------------}
function TDataAwareComponent.GetReadOnly: Boolean;
begin
  Result := FDataLink.ReadOnly;
end;
{------------------------------------------------------------------------------}
procedure TDataAwareComponent.SetDataField(const Value: string);
begin
  FDataLink.FieldName := Value;
end;
{------------------------------------------------------------------------------}
procedure TDataAwareComponent.SetDataSource(const Value: TDataSource);
begin
  FDataLink.DataSource := Value;
end;
{------------------------------------------------------------------------------}
procedure TDataAwareComponent.SetDateProperty(const Value: TDateTime);
begin
  if Assigned(Field)  then
  begin
    FFromDateChange := True;
    try
      Field.DataSet.Edit;
      Field.Value := Value;
    finally
      FFromDateChange := False;
    end;
  end;
end;
{------------------------------------------------------------------------------}
procedure TDataAwareComponent.SetReadOnly(const Value: Boolean);
begin
  FDataLink.ReadOnly := Value;
end;
{------------------------------------------------------------------------------}

end.

Answer 2

It'd be a bit of code, but if your component has events triggered when its value changes, then that could be used to send updated values to the dataset, if it's in the dsEdit state. You'd also need to handle the various TDataSource Events to know when the dataset is changing.