Question

我是delphi的新手，正在尝试启动OOP。但是，使用公共属性设置私有字段时出现访问冲突。

type
  User = class;
  TData = class
  private
    CurrUser: User;
    Connection: TFDConnection;
    Query: TFDQuery;

  procedure SetUser(newUser: User);
  procedure SetConnection(newConn: TFDConnection);
  procedure SetQuery(newQry: TFDQuery);
public
  property CUser: User read CurrUser write SetUser;
  property Conn: TFDConnection read Connection write SetConnection;
  property Qry: TFDQuery read Query write SetQuery;

  class procedure Login(uID: integer); static;
  class procedure Logout(uID: integer); static;
  class procedure ExitApp(); static;
end;
implementation

{$R *.fmx}

procedure TData.SetUser(newUser: User);
begin
  CurrUser := newUser;
end;

procedure TData.SetConnection(newConn: TFDConnection);
begin
  Connection := newConn;
end;

procedure TData.SetQuery(newQry: TFDQuery);
begin
  Query := newQry;
end;

我希望能够使用该属性来设置Connection，但是使用该属性write的任何代码都会给我带来访问冲突： TData.Conn.LoginPrompt：= False; TData.Conn.Connected：= True;

var
  TData: frmData.TData;
  LoginForm: TLoginForm;
  ErrorCount : integer;

implementation

{$R *.fmx}

procedure TLoginForm.ExitAppButtonClick(Sender: TObject);
begin
  TData.ExitApp;
end;

procedure TLoginForm.LoginButtonClick(Sender: TObject);
var
  companyPath : string;
  nurseID : integer;
begin
  if(UsernameInput.Text = '') or (PasswordInput.Text = '') or (PincodeInput.Text = '') then
  begin
    ShowMessage('Please enter your login details.');
    Exit;
  end;

  try
    TData.Conn := TFDConnection.Create(nil);
    TData.Conn.Params.DriverID := 'MSAcc';
    TData.Conn.Params.Database := 'D:\PulseDB\AlfaPersonnel\Pulse.mdb';
    TData.Conn.LoginPrompt := False;
    TData.Conn.Connected := True;
    if(TData.Conn.Connected <> True) then
    begin
      ShowMessage('Could not connect, try again');
      Exit;
    end
    else //When Connection
    begin
      TData.Qry := TFDQuery.Create(TData.Conn);
      try
        TData.Qry.Connection := TData.Conn;
        TData.Qry.SQL.Text := 'SELECT * FROM NurseLogin WHERE Username=:uname AND Password=:pword AND PinCode=:pin;';
        TData.Qry.Params.ParamByName('uname').AsString := UsernameInput.Text;
        TData.Qry.Params.ParamByName('pword').AsString := PasswordInput.Text;
        TData.Qry.Params.ParamByName('pin').AsString := PincodeInput.Text;
        TData.Qry.Active := True;

        if TData.Qry.RecordCount = 0 then ShowMessage('Details not recognised.')
        else if TData.Qry.RecordCount = 1 then
             begin
               if TData.Qry.FieldByName('IsActive').AsBoolean then //If the user is active
               begin
                 try
                   //Connect to the path
                   companyPath := TData.Qry.FieldByName('CompanyName').AsString;
                   TData.Conn.Params.Database := 'D\PulseDB\' + companyPath + '\Pulse.mdb';
                   TData.Conn.Connected := True;

                   ShowMessage('Connected to ' + companyPath);
                 finally

                 end;
               end;
             end;
      finally
      end;
    end;
  finally
  end;
end;

Answer 1

您永远不会创建TData类的实例。在某些时候，您需要编写：

TData := frmData.TData.Create;

实例化实例的方式。完成后还需要销毁它。像这样：

TData.Free;

您没有实例化实例是对访问冲突的解释。

其他一些问题：

对类型使用T前缀。您的变量应命名为Data，而不是TData。
尽可能不要使用全局变量。

如何在Delphi中修复地址访问冲突

1 个答案: