这是我在这里工作的项目的延续: Circular reference issue with Classes which use each other
那里收到的建议修复了 ciruclar 参考问题(再次感谢您的帮助)。现在我正在与其他东西搏斗:TcmDataPanel.FObservingDataPanels 总是以 = nil 结束,显然是因为它永远不会被创建。(最初我遇到了访问冲突,但在进一步测试中发现 FObserver 始终为零)。
下面是相关代码(它是一个 TFrame 单元,TcmTPDataPanel 是 TFrame 的后代):
unit cmTPDataPanelFrame;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, cmTPBasePanelFrame, cmTPPanels, nxdb, nxllComponent;
type
TcmTPDataConnector = class;
TcmTPDataPanel = class(TcmTPBasePanel)
Database: TnxDatabase;
Session: TnxSession;
private
FDataConnector: TcmTPDataConnector;
MyNxDataBase: TnxDatabase;
MyNxSession: TnxSession;
MyRefNxDataBase: TnxDatabase;
protected
procedure Disconnect; virtual; abstract;
procedure Refresh; virtual;
procedure Requery; virtual; abstract;
public
procedure Connect;
published
property DataConnector: TcmTPDataConnector read FDataConnector write
FDataConnector;
end;
TcmTPCustomDataConnector = class(TComponent)
private
FDatabase: TnxDatabase;
FObservingDataPanels: TList;
FTableForCategories: TnxTable;
FTableForItemCategoryLinks: TnxTable;
FTableForItems: TnxTable;
procedure SetTableForItemCategoryLinks(const Value: TnxTable);
protected
procedure IterateObservers;
public
constructor Create(AOwner: TComponent);
destructor Destroy; override;
procedure Register(Instance: TcmTPDataPanel);
procedure ReportObservers;
procedure Unregister(Instance: TcmTPDataPanel);
published
property Database: TnxDatabase read FDatabase write FDatabase;
property TableForCategories: TnxTable read FTableForCategories write
FTableForCategories;
property TableForItemCategoryLinks: TnxTable read
FTableForItemCategoryLinks write SetTableForItemCategoryLinks;
property TableForItems: TnxTable read FTableForItems write FTableForItems;
end;
TcmTPDataConnector = class(TcmTPCustomDataConnector)
end;
var
cmTPDataPanel: TcmTPDataPanel;
implementation
=== 和 ===
{
*************************** TcmTPCustomDataConnector ***************************
}
constructor TcmTPCustomDataConnector.Create(AOwner: TComponent);
begin
ShowMessage('TcmTPCustomDataConnector.Create entered.');
// inherited Create(AOwner); // TODO : check duplicate
FObservingDataPanels := TList.Create();
end;
destructor TcmTPCustomDataConnector.Destroy;
begin
FreeAndNil(FObservingDataPanels);
//inherited Destroy; // TODO : check duplicate
end;
我希望在 cmTPDataConnector.Create 上运行的 ShowMessage 行从未出现,这让我认为它没有从 TcmTPCUstomDataConnector 继承 Create 方法。不应该吗?
它“感觉”好像我缺少一些明显的东西,但我没有看到它。:-\
两个问题:
1) 为什么没有创建 FObservingDataPanels?
2)“//继承的Create(AOwner);// TODO:检查重复”和“//inherited Destroy;//TODO:检查重复”行是由ModelMaker在某个时候放入的。他们应该被取消注释吗?
PS显然,我还在学习组件创建和继承。欢迎任何其他意见和建议。
PPS 今天我有很多问题。如果我需要将它降低一个档次,请随时告诉我......(只是在这里有一个奖励很多问题的日子)。
提前感谢您的任何帮助!:)