对类精通的同志请看看,怎么出现这个奇怪的问题

Question

unit OperationClass;interface
uses
  Forms, Windows,SysUtils,DB, ADODB,DBTables;
type
  //对数据集的操作
  ToperateDataSet=Class
  private
    FSQL_Text:String;
    //判断对数据集操作是否符合条件
    function JudgeIF:Boolean;
  protected
    procedure ExecuteAppend;
    procedure ExecuteDelete;
    procedure ExecuteModified;
  public
    //constructor Create(ADOQuy:TADOQuery;BDEQuy:TQuery;SQLText:String);
    //Destructor  Destroy;Override;
    property SQL_Text:String read FSQL_Text write FSQL_Text;
    procedure Append;
    procedure Delete;
    procedure Modified;
  end;
implementation
var
  FADOQuy:TADOQuery;
  FBDEQuy:TQuery;
  FSQLText:String;Type
   Box_Flag=(mtInformation,mtError,mtWarning);
Type
   Flag=(btOK,btOKCancel);//*================================================================
//* 函数 名：ShowMessageBox
//* 参    数：Content:string;Box_Type:Box_Flag;Flag:Flag
//*           Box_Type 1:mtWarning 2:mtError 3:mtInformation
//*           Flag 1:mb_Yes,mb_cancle
//* 功能描述: 各种提示信息(信息提示,错误提示,警告提示)
//*
//* 返 回 值：
//*
//* 抛出异常：
//*
//* 作    者：谈广才 2003/5/23
//*================================================================
Function Func_ShowMessagebox(Content:string;Box_Type:Box_Flag;Flag:Flag):Integer;
Begin
Case Box_Type Of
  mtInformation:
  Begin
     IF Flag=btOK Then
        Result:=Application.MessageBox(Pchar(Content),'提示信息',
                                       MB_OK+MB_ICONINFORMATION)
     Else
        Result:=Application.MessageBox(PChar(Content),'提示信息',
                                       MB_OKCANCEL+MB_ICONINFORMATION);
  End;
  mtError:
  Begin
     IF Flag=btOK Then
        Result:=Application.MessageBox(PChar(Content),'错误提示',
                                       MB_OK+MB_ICONERROR);
  End;
  mtWarning:
  Begin
     IF Flag=btOK Then
        Result:=Application.MessageBox(PChar(Content),'请您注意',
                                       MB_OK+MB_ICONWARNING)
     Else
        Result:=Application.MessageBox(PChar(Content),'请您注意',
                                       MB_OKCANCEL+MB_ICONWARNING);
  End;
End;
End;
{ ToperateDataSet }procedure ToperateDataSet.Append;
begin
  ExecuteAppend;
end;{constructor ToperateDataSet.Create(ADOQuy: TADOQuery; BDEQuy: TQuery;
  SQLText: String);
begin
  FADOQuy:=ADOQuy;
  FBDEQuy:=BDEQuy;
  FSQLText:=SQLText;
end; }procedure ToperateDataSet.Delete;
begin
  ExecuteDelete;
end;{destructor ToperateDataSet.Destroy;
begin
  FADOQuy:=nil;
  FBDEQuy:=nil;
  FSQLText:='';
  inherited;
end;
       }
procedure ToperateDataSet.ExecuteAppend;
begin
  if JudgeIF then
  begin
    try
       if (FADOQuy<>nil) and (FSQLText<>'')  then
       begin
          if FADOQuy.State<>dsInsert then
          begin
             with FADOQuy do
             begin
                Close;
                SQL.Clear;
                SQL.Add(FSQLText);
                Open;
                Append;
             end;
          end;
       end
       else if (FBDEQuy<>nil ) and (FSQLText<>'') then
       begin
          if FBDEQuy.State<>dsInsert then
          begin
             with FBDEQuy do
             begin
                Close;
                SQL.Clear;
                SQL.Add(FSQLText);
                Open;
                Append;
             end;
          end;
       end;
    except
       on E:Exception do
       Func_ShowMessagebox('执行增加操作出错!  错误原因如下:'+Chr(10)+E.message,mtError,btOK);
    end;
  end;end;

Answer 1

procedure ToperateDataSet.ExecuteDelete;
begin
  if JudgeIF then
  begin
     try
        if (FADOQuy<>nil) and (FSQLText<>'')  then
        begin
           with FADOQuy do
           begin
              Close;
              SQL.Clear;
              SQL.Add(FSQLText);
              Open;
              IF Not IsEmpty Then
              begin
                 if Func_ShowMessagebox('你确定要删除当前记录吗?',mtInformation,btOKCancel)=1 then
                    Delete ;
              end
              else
                 Func_ShowMessagebox('没有你要删除的记录!',mtInformation,btOK);
           end;
        end
        else if (FBDEQuy<>nil ) and (FSQLText<>'') then
        begin
           with FBDEQuy do
           begin
              Close;
              SQL.Clear;
              SQL.Add(FSQLText);
              Open;
              IF Not IsEmpty Then
              begin
                 if Func_ShowMessagebox('你确定要删除当前记录吗?',mtInformation,btOKCancel)=1 then
                    Delete ;
              end
              else
                 Func_ShowMessagebox('没有你要删除的记录!',mtInformation,btOK);
           end;
        end;
     except
        on E:Exception do
        Func_ShowMessagebox('执行删除操作出错!  错误原因如下:'+Chr(10)+E.message,mtError,btOK);
     end;
  end;end;procedure ToperateDataSet.ExecuteModified;
begin
  if JudgeIF then
  begin
     try
        if (FADOQuy<>nil) and (FSQLText<>'')  then
        begin
           if FADOQuy.State<>dsEdit then
           begin
              with FADOQuy do
              begin
                 Close;
                 SQL.Clear;
                 SQL.Add(FSQLText);
                 Open;
                 IF Not IsEmpty Then
                    Edit
                 else
                    Func_ShowMessagebox('没有你要修改的记录!',mtInformation,btOK);
              end;
           end
           else
              Func_ShowMessagebox('数据集已经是修改状态!',mtInformation,btOK);
        end
        else if (FBDEQuy<>nil ) and (FSQLText<>'') then
        begin
           if FBDEQuy.State<>dsEdit then
           begin
              with FBDEQuy do
              begin
                 Close;
                 SQL.Clear;
                 SQL.Add(FSQLText);
                 Open;
                 IF Not IsEmpty Then
                    Edit
                 else
                    Func_ShowMessagebox('没有你要修改的记录!',mtInformation,btOK);
              end;
           end
           else
              Func_ShowMessagebox('数据集已经是修改状态!',mtInformation,btOK);
        end;
     except
        on E:Exception do
        Func_ShowMessagebox('执行修改操作出错!  错误原因如下:'+Chr(10)+E.message,mtError,btOK);
     end;
  end;end;function ToperateDataSet.JudgeIF: Boolean;
begin
  if (FADOQuy=nil) and (FBDEQuy=nil) then
  begin
     Func_ShowMessagebox('数据集为空,此操作无效!',mtError,btOK);
     Result:=False;
     Exit;
  end
  else if (FADOQuy<>nil) and (FBDEQuy<>nil)  then
  begin
     Func_ShowMessagebox('数据集太多,此操作无效!',mtError,btOK);
     Result:=False;
     Exit;
  end;  if FSQLText='' then
     FSQLText:=SQL_Text;  if FSQLText='' then
  begin
     Func_ShowMessagebox('没有SQL语句,此操作无效!',mtError,btOK);
     Result:=False;
     Exit;
  end;
  Result:=True;
end;procedure ToperateDataSet.Modified;
begin
  ExecuteModified;
end;end.
unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs,OperationClass, DB, ADODB, StdCtrls, Grids, DBGrids;type
  TForm1 = class(TForm)
    DBGrid1: TDBGrid;
    Button1: TButton;
    Button2: TButton;
    ADOQuery1: TADOQuery;
    DataSource1: TDataSource;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;
  AddData:ToperateDataSet;
implementation{$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);
begin
AddData.Create(ADOQuery1,nil,'');
AddData.SQL_Text:='Select * from Sheet where 1=2';
AddData.Append;
end;end.当我点Button1时出现错位:Access violation at address 00403AC1 in module 'Project1.exe'. Read of address 00000000

Answer 2

AddData :=ToperateDataSet.Create(ADOQuery1,nil,'');
AddData.SQL_Text:='Select * from Sheet where 1=2';
AddData.Append;
试试
另外
//constructor Create(ADOQuy:TADOQuery;BDEQuy:TQuery;SQLText:String); 类的Create你得重构一下,就是上面这个方法你得写

Answer 3

同意： IwantFlay(我很爱她!!!!!!!!!!) AddData :=ToperateDataSet.Create(ADOQuery1,nil,'');
try
  AddData.SQL_Text:='Select * from Sheet where 1=2';
  AddData.Append;
finally
  AddData.Free;
end;同时
constructor Create(ADOQuy:TADOQuery;BDEQuy:TQuery;SQLText:String); 
begin
  inherited;
  FADOQuy:=ADOQuy;
  FBDEQuy:=BDEQuy;
  FSQLText:=SQLText;
end;看这个类感觉很累：
1，与问题无关的showxxx占了太多的篇幅（在这里）
2，应作为私有成员的FADOQuy:TADOQuery;  FBDEQuy:TQuery;  FSQLText:String;却变成了单元内的公用变量，试问，先后创建两个对象，这三个变量该是哪一个对象所需要的内容？
----建议将其放在private部分
3，Function Func_ShowMessagebox为何没有返回值？
----不如将其定义为procedure。
4，function ToperateDataSet.JudgeIF: Boolean;既判断是否XX又显示判断结果，不太符合习惯
----将两个功能分开
5,
           with FADOQuy do
           begin
              Close;
              SQL.Clear;
              SQL.Add(FSQLText);
              Open; ----------此处是否应为ExecSQL(我不确定)6，ADO,BDE混杂，不妨定义为两个子类。