How to use SaveToFile and LoadFromFile in Delphi XE2?

The data retrieved via an ADO dataset component can be saved to a file for later retrieval on the same or a different computer. Save the data to a file using the SaveToFile method. Retrieve the data from file using the LoadFromFile method. The data is saved in one of two proprietary formats: ADTG and XML. Indicate which of these two formats to use for the save file with one of the TPersistFormat constants pfADTG or pfXML in the Format parameter of the SaveToFile method.

procedure TForm1.SaveBtnClick(Sender: TObject);

begin

  if (FileExists('c:\SaveFile')) then begin

    DeleteFile('c:\SaveFile');

    StatusBar1.Panels[0].Text := 'Save file deleted!';

  end;

  ADODataSet1.SaveToFile('c:\SaveFile', pfADTG);

end;

procedure TForm1.LoadBtnClick(Sender: TObject);

begin

  if (FileExists('c:\SaveFile')) then

    ADODataSet2.LoadFromFile('c:\SaveFile')

  else

    StatusBar1.Panels[0].Text := 'Save file does not exist!';

end;

Explanation: In the example above, the first procedure saves the dataset retrieved by the TADODataSet component ADODataSet1 to a file. The target file is an ADTG file named SaveFile, saved to a local drive. The second procedure loads this saved file into the TADODataSet component ADODataSet2.

The saving and loading dataset components need not be on the same form as above, in the same application, or even on the same computer. This allows for the briefcase-style transfer of data from one computer to another.

On calling the LoadFromFile method, the dataset component is automatically activated.

If the file specified in the FileName parameter of the SaveToFile method already exists, an EOleException exception is raised. Similarly, if the file specified in the FileName parameter of LoadFromFile does not exist, an EOleException exception is raised.

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How to use TADODataset, TDatasource and TDBGrid in Delphi XE2?

Below is the code snippet in Delphi XE2 to demonstrate the use of TADODataset, TDatasource and TDBGrid. The code fetches the data in dataset and then assigns that dataset to datasource and further that datasource is assigned to datagrid.

procedure TClass.PopulateGrid(aField: integer);
begin
  try
    with dsMyADODataSet do
    begin
      Close;
      Connection := connMyADOConnection;
      CommandType := cmdText;
      CommandText := 'SELECT * FROM myTable WHERE fieldA = :fieldA ';
      Parameters.ParamByName('fieldA').Value := aField;
      Open;
      dsMyDataSource.DataSet :=  dsMyDataSet;
      dgrMyDBGrid.DataSource := dsMyDataSource;
    end;
  except
    on E : Exception do
    begin
      ShowMessage('Error occured in function PopulateGrid: ' + E.Message);
      exit;
    end;
  end;
end;

Explanation: ADOConnection is set to dsMyADODataset. Then CommandType and CommandText are assigned to the dataset. Then this dataset is assigned to the datasource and then that datasource is assigned to the datagrid.

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Embarcadero HTML5 Builder Features List

1. HTML5 Builder uses standard web technologies such as HTML5, CSS3, PHP and JavaScript.

2. With HTML5 Builder you can develop  your app once using a single HTML5, CSS3, JavaScript and  PHP codebase and target multiple mobile operating systems ( iOS, Android, BlackBerry and Windows Phone), devices and Web browsers using a single click.

3.  HTML5 Builder comes with hundreds of reusable drag-and-drop components that you can use as is or customize to help you build your applications, faster. So, you don't need to know how to use jQuery or mobile JavaScript libraries, just drag and drop the components.

4. HTML5 Builder includes a source code editor, integrating debugging, wizards and other tools for everything from creating a new application to mobile deployment.

5. HTML5 Builder offers an intuitive visual interface for creating CSS3 animations and generates CSS3 code that can be viewed and edited in the Code Editor.

6. The jQuery Mobile UI theming interface in HTML5 Builder allows you to easily create new color schemes for your mobile applications by dragging and dropping colors on to your UI controls. After you have created your new theme, a CSS file is automatically generated that can be used to style a control or entire mobile app to your liking.

7. HTML5 Builder includes HD and 3D dynamic drawing and rendering for enhanced UX.

8. HTML5 Builder makes your apps more interactive with Geolocation Component.

9. HTML5 Builder provides audio and video components which make it easy to embed media in your web applications without requiring the user to install plugins like Flash to view them. Videos and audio clips are rendered directly in the browser, displaying the bowser's native media controls. Use the audio and video components to play movies or audio tracks, develop your own advanced media player with customer skins.

10. Your applications can either be completely self-contained client applications or you can power your apps with dynamic server based content and multi user capabilites then deploy the server component of your app to any PHP-support server in your enterprise, on the web or in the cloud.

11. HTML5 Builder provides Live Preview of your application before you go to production

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How to use FindComponent function in Delphi XE2?

Following is the code snippet which will show you how to use FindComponent in Delphi XE2?

procedure TClass1.UseFindComponent(FieldName : string);
var
  aComponent :TComponent;
begin
 try
   aComponent := Form1.FindComponent(FieldName);
   if aComponent <> nil then
   begin
     if (aComponent IS TEdit) then
     begin
        (aComponent AS TEdit).Clear;
        (aComponent AS TEdit).Enabled := false;
        (aComponent AS TEdit).Tag := 0;
     end;
   end;
 except
    on E : Exception do
    begin
      ShowMessage('Error occurred in function UseFindComponent: ' + E.Message);
      exit;
    end;
 end;
end;

Explanation: FindComponent function is used to find out the components present on a given form. In the above code, UseFindComponent function accepts the name of a component (it may be the name of textfield, button, dropdown etc.). Then it finds that component on Form1. If that component is a text field, it sets the properties (like Clear, Enabled, Tag) to that text field on runtime. Same you can do with buttons, labels or dropdowns.

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How to use TADOTable in Delphi XE2?

Following is the code snippet which will show you how to use TADOTable in Delphi XE2?

procedure TClass1.GetDataFromADOTable;
begin
  try
    if SetADOTable then
    begin
      if tADOTable.Locate('ColumnA;ColumnB', VarArrayOf([ValueA, ValueB]), [loPartialKey])  then
      begin
        VarX := tADOTable.FieldByName('ColumnX').AsInteger;
        VarY := tADOTable.FieldByName('ColumnY').AsInteger;
      end;
    end;
  except
    on E : Exception do
    begin
      ShowMessage('Error occured in function GetDataFromADOTable: ' + E.Message);
      exit;
    end;
  end;
end;

function TClass1.SetADOTable : boolean;
begin
  try
    tADOTable.Connection := ADOConnection;  //Connectin name
    tADOTable.TableName := 'myTableName';  //Table name
    tADOTable.Open;
    result := true;
  except
    on E : Exception do
    begin
      result := false;
      ShowMessage('Error occured in function SetADOTable: ' + E.Message);
      exit;
    end;
  end;
end;

Explanation: Lets discuss the SetADOTable function first. It assings TADOTable with connection name and table name and then it opens the table. Here all data is fetched in the ADOTable from myTableName table. Now come to the function GetDataFromADOTable. It checks if there is data in ADOTable, locates a pointer to a particular column/columns by using locate keyword. Then it fetches the values in VarX and VarY.

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How to use TADOQuery in Delphi XE2?

Following is the code snippet which will show you how to use ADOQuery in Delphi XE2?

function TClass1.UseADOQuery : integer;
begin
  try
    with qryADOQuery do
    begin
      Connection := ADOConnection; //Connection name
      Close;
      SQL.Clear;
      SQL.Text :=
        'SELECT ColumnX FROM TableA WHERE ' +
        'ColumnA = :ParameterA AND ' +
        'ColumnB = :ParameterB AND ' +
        'ColumnC = :ParameterC';

      Parameters.ParamByName('ColumnA').Value := ParameterA;
      Parameters.ParamByName('ColumnB').Value := ParameterB;
      Parameters.ParamByName('ColumnC').Value := ParameterC;
      Open;
      if (Recordcount = 0) then
        result := 0
      else
        result := Fields.FieldByName('ColumnX').Value; //Assume ColumnX value is an integer
      Close;
    end;
  except
    on E : Exception do
    begin
      result := 0;
      ShowMessage('Error occured in function UseADOQuery: ' + E.Message);
      exit;
    end;
  end;
end;

Explanation:First of all query has be be initialized with connection name. Now close it if already opened. For being on safer side, we should close it first before using it. Clear the SQL statement if any then write new SQL statement. Parameters to the query are passed by using colon (:) keyword. Recordcount keyword returns the number of rows affected.

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OnShortCut event of Delphi XE2 Forms

This article is about OnShortCut event of Delphi Forms. Lets discuss the requirement first.

Requirement: Assme that I have two Delphi forms in my project (MyForm1 and MyFrom2). Now my requirement is that, if I am on MyForm1 and press ESC, I should go to MyForm2 and vice versa.

Consider the code of MyForm1:

unit uf_MyUnit1;

interface

uses

  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes,   Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.Buttons, Vcl.Imaging.jpeg, Vcl.ExtCtrls, Vcl.ComCtrls;

type

  TfMyUnit1 = class(TForm)

    procedure FormShortCut(var Msg: TWMKey; var Handled: Boolean);  

  private

  

  public

  end;

var

  fMyForm1: TfMyUnit1;

implementation

uses uf_MyUnit2;

{$R *.dfm}

procedure TfMyUnit1.FormShortCut(var Msg: TWMKey; var Handled: Boolean);

begin

   case Msg.CharCode of

      27 : begin

             Handled := true;

             fMyForm2.Show;

             fMyForm1.Close;

           end;

   end;

end;

end.

Explanation: Remember to add FormShortCut function on the OnShortCut event of the form. By adding this function on the OnShortCut event of the form, this function will immediately gets fired when any key is pressed. '27' is the keycode for ESC key. So when ESC key is pressed fMyForm2 is displayed and current form is closed.

Similar is the code for MyForm2:

unit uf_MyUnit2;

interface

uses

  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.Buttons, Vcl.Imaging.jpeg, Vcl.ExtCtrls, Vcl.ComCtrls;

type

  TfMyUnit2 = class(TForm)

    procedure FormShortCut(var Msg: TWMKey; var Handled: Boolean);  

  private

  

  public

  end;

var

  fMyForm2: TfMyUnit2;

implementation

uses uf_MyUnit1;

{$R *.dfm}

procedure TfMyUnit2.FormShortCut(var Msg: TWMKey; var Handled: Boolean);

begin

   case Msg.CharCode of

      27 : begin

             Handled := true;

             fMyForm1.Show;

             fMyForm2.Close;

           end;

   end;

end;

end.

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Delphi 2010, Delphi XE and XE2: A comparison of features

Delphi 2010 vs older versions

Delphi 2010 Release Date: August 25, 2009

Delphi 2010 witnessed a lot of improvements and new features as compared to its older versions. Some of features are listed below:

 

1. Delphi 2010 included a new compiler run-time type information (RTTI) system
2. Support for Windows 7 direct 2D
3. Touch screen and gestures
4. Source code formatter
5. Debugger visualizers
6. Option to also have the old style component palette in the IDE

Note:  Because of the use of Unicode as the default string type, Windows 98, 95, and ME will not run applications produced with Delphi 2009 or later. These operating systems do not support Unicode strings, and Microsoft has dropped support for them. Applications built with Delphi XE2, XE, 2010 and 2009 and VCL will run on Windows 2000 or later.

Comparison between Delphi 2010 and Delphi XE

Delphi XE Release Date: August 30, 2010

Only few enhancements were done in Delphi XE as compared to Delphi 2010. Thats why Delphi XE did not gain much success. Some of the enhancements are listed below:

1. Some IDE fixes were done in Delphi XE which made the IDE faster
2. Some additional third party tools were added in Delphi XE to enhance the capabilities of Delphi
3. No support for Win64 platform in both of them
4. No Mac OSX support in both of them

Comparison between Delphi XE and Delphi XE2

Delphi XE2 Release Date: September 1, 2011

Very much successful release of Embarcadero. Delphi XE2 coexists nicely with earlier versions of RAD Studio, C++Builder and Delphi. A lot of industries and migrating to Delphi XE2 because of its exciting features:

1. Delphi XE2 supports Win64 native development which will make your application faster
2. Delphi XE2 supports Mac OSX native development
3. Delphi XE2 is supplied with both the VCL, and an alternative library called FireMonkey that supports Windows, Apple Mac OS X and the Apple iPhone, iPod Touch and iPad portable devices.
4. New naming scheme for the units
5. ODBC dbExpress driver support
6. Extensions to the REST support layer
7. Improved Cloud support
8. Improved RTTI (run-time type information)
9. Cross platform support
10. Little migration issues encountered
11. The DataSnap Mobile Connector feature: The DataSnap Mobile Connector feature generates connectivity code that you can incorporate into mobile applications for iOS, Android, Blackberry and Windows Phone 7. You develop your mobile applications using the standard development tools and languages for each platform such as Objective C with the Xcode IDE for iOS, Java for Android and Blackberry, or Silverlight for Windows Phone 7. You then use the DataSnap Mobile Connector code to provide connectivity to your native C++Builder or Delphi DataSnap server. You can create a single application and deploy to 32-bit Windows, 64-bit Windows and Mac OS X. To create an iOS application, you create a separate project type that is exported and built with Xcode.

Difference in Delphi XE2 Professional and Enterprise Edition:

Delphi XE2 Enterprise Edition contains some extra features which are not present in Delphi XE2 Professiona Edition like:

1. Datasnap
2. DBExpress Driver Support for OSX, Firebird, Oracle, MSSQL, Informix
3. Advanced UML and Code Analysis Tools
4. FinalBuilder

Limitations of Delphi XE2:

1. Applications for 64-bit platforms can be compiled, but not tested or run, on the 32-bit platform.
2. FireMonkey and VCL are not compatible, one or the other must be used, and older VCL applications cannot use Firemonkey unless user interfaces are recreated with FireMonkey forms and controls.
3. Applications built with Delphi XE2 and FireMonkey will run on Windows XP and later.
4. Delphi XE2 uses the MSBuild system for the build engine, and thus requires a new project file if you are upgrading from version 2007 or earlier. However, the IDE will seamlessly update your projects to the new format.

Waiting for Delphi XE3 which may out in a month or two......

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How to create Logfiles in Delphi?

Manytimes in your delphi project, you will require to print logfiles in order to track the flow of control. Here is a simple code snippet to print logfiles in delphi.

Code snippet

procedure TMyClass.CreateLogfile;
var
  aLine : string;
  aFileName : string;
  myFile : TextFile;
  aFilePath : string;
begin
  try
    aLine := 'The line which you want to print. You can change this line dynamically by passing   aLine as  parameter to CreateLogfile function';
    aFileName := 'MyLogfile_' + FormatDateTime('dd-mm-yyyy',Now)+'.log';
    aFilePath := 'C:\ProjectFolder\'+aFileName;
    AssignFile(myFile, aFilePath);
    if FileExists(aFilePath) then
      Append(myFile)
    else
      Rewrite(myFile);
    WriteLn(myFile, FormatDateTime('dd-mmm-yyyy hh:nn:ss.zzz',Now) + ': ' + ALine);
    Flush(myFile);
  finally
    CloseFile(myFile);
  end;
end;

Explanation: CreatLogfile function creates a logfile MyLogfile_TodaysDateTime.log at C:\ProjectFolder. If the logfile exists, it will append the line at the end otherwise it will create a new logfile and then writes to it. Logfile will be created new on everyday as the DateTime will get changed everyday. Thats why, DateTime is embedded with the name of logfiles. If you don't want to create a new logfile everyday, just remove the datetime field from the name of logfile and keep it simple like MyLogfile.log.

I think, you have understood my point. For any doubts, just inform me. I will be pleased to help you.

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13 Things to keep in mind before using DLL in Delphi

Keep in mind the following tips when writing your DLL:

1. Make sure you use the proper calling convention (C or stdcall).

2. Know the correct order of the arguments passed to the function.

3. NEVER resize arrays or concatenate strings using the arguments passed directly to a function.

4. Remember, the parameters you pass are LabVIEW data. Changing array or string sizes may result in a crash by overwriting other data stored in LabVIEW memory. You MAY resize arrays or concatenate strings if you pass a LabVIEW Array Handle or LabVIEW String Handle and are using the Visual C++ compiler or Symantec compiler to compile your DLL.

5. When passing strings to a function, remember to select the correct type of string to pass . C or Pascal or LabVIEW string Handle.

6. Remember, Pascal strings are limited to 255 characters in length.

7. Remember, C strings are NULL terminated. If your DLL function returns numeric data in a binary string format (for example, via GPIB or the serial port), it may return NULL values as part of the data string. In such cases, passing arrays of short (8-bit) integers is most reliable.

8. If you are working with arrays or strings of data, ALWAYS pass a buffer or array that is large enough to hold any results placed in the buffer by the function unless you are passing them as LabVIEW handles, in which case you can resize them using CIN functions under Visual C++ or Symantec compiler.

9. Remember to list DLL functions in the EXPORTS section of the module definition file if you are using _stdcall.

10. Remember to list DLL functions that other applications call in the module definition file EXPORTS section or to include the _declspec (dllexport) keyword in the function declaration.

11. If you use a C++ compiler, remember to export functions with the extern .C.{} statement in your header file in order to prevent name mangling.

12. If you are writing your own DLL, you should not recompile a DLL while the DLL is loaded into memory by another application (for example, your VI). Before recompiling a DLL, make sure that all applications making use of the DLL are unloaded from memory. This ensures that the DLL itself is not loaded into memory. You may fail to rebuild correctly if you forget this and your compiler does not warn you.

13. Test your DLLs with another program to ensure that the function (and the DLL) behave correctly. Testing it with the debugger of your compiler or a simple C program in which you can call a function in a DLL will help you identify whether possible difficulties are inherent to the DLL or LabVIEW related.

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COM Family: COM+ and DCOM, Interop, RPC and TLB

Microsoft COM (Component Object Model) technology enables different software components to communicate. It was introduced by Microsoft in 1993. The family of COM technologies includes COM+, Distributed COM (DCOM) and ActiveX Controls.

COM provides interoperability. COM allows reuse of objects with no knowledge of their internal implementation.COM objects can be used with all .NET languages through .NET COM Interop.

COM interfaces have bindings in several languages, such as C, C++, Visual Basic, Delphi, and several of the scripting languages implemented on the Windows platform. All access to components is done through the methods of the interfaces.

Type Library in COM (.tlb file)

First, you must create a type library for the assembly. A type library is the COM equivalent of the metadata contained within a .NET assembly. Type libraries are generally contained in files with the extension .tlb. A type library contains the necessary information to allow a COM client to determine which classes are located in a particular server, as well as the methods, properties, and events supported by those classes. Each component or dll file must contain type library.

COM Interop

COM Interop is a technology included in the .NET CLR that enables COM objects to interact with .NET objects, and vice versa. COM Interop allows COM developers to access managed objects as easily as they access other COM objects.

The .NET Framework creates a type library and special registry entries when a component (compiled in the form of DLL) is registered. It provides a specialized utility that exports the managed types into a type library and registers the managed component as a traditional COM component. When the type is instantiated through COM, the .NET CLR is the actual COM object that executes and it merely marshals any method calls or property access to the type implementation.

Reference Counting, Pooling and Memory Management in COM:

The COM specifications require a technique called reference counting to ensure that individual objects remain alive as long as there are clients which have acquired access to one or more of its interfaces and, conversely, that the same object is properly disposed of when all code that used the object have finished with it and no longer require it. A COM object is responsible for freeing its own memory once its reference count drops to zero. Pooling for objects can also be set for different components.

RPC (Remote Procedure Call)

Microsoft Remote Procedure Call (RPC) is a powerful technology for creating distributed client/server programs. RPC is an interprocess communication technique that allows client and server software to communicate.

dcomcnfg:

To access settings on a computer running Windows 2000, Windows XP and earlier, click Start > Run, and type "dcomcnfg". (Click NO for any warning screens that appear.) To access DCOM settings on a computer running Windows Vista or later, click Start, type "dcomcnfg", right-click "dcomcnfg.exe" in the list, and click "Run as administrator".

COM is very similar to other component software interface technologies, such as CORBA and Java Beans, although each has its own strengths and weaknesses.

COM Family:

COM+: COM+ is the name of the COM-based services and technologies first released in Windows 2000. It provides  distributed transactions, resource pooling, disconnected applications, event publication and subscription, better memory and processor (thread) management.

DCOM: DCOM isDistributed COM. DCOM uses RPC mechanism for communication. It allows COM components to communicate across network boundaries.It provides load balancing.COM installation and execution is done in its clien machine where DCOM is intalled and run on selected server machine.

DCOM is generally equivalent to the Common Object Request Broker Architecture ( CORBA ) in terms of providing a set of distributed services. But unlike CORBA, which runs on many operating systems, DCOM is currently implemented only for Windows.

Migrate from COM application

Although calling a COM component from managed code is simple, you should not consider this a permanent solution for most applications. Over the long run, you'll want to migrate heavily used components to native .NET code. This will provide you with the full range of .NET capabilities, as well as make your code faster by eliminating the RCW layer.

Decline of COM

Several of the services that COM+ provides have been largely replaced by recent releases of .NET. For example, the System.Transactions namespace in .NET provides the TransactionScope class, which provides transaction management without resorting to COM+. Similarly, queued components can be replaced by Windows Communication Foundation with an MSMQ transport.

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