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Beginner's Guide to Delphi

February 7, 2025 · 16 min read

Introduction to Delphi #

What is Delphi? #

Delphi is a powerful, object-oriented programming language and integrated development environment (IDE) primarily used for creating visually appealing and robust applications for Windows, macOS, Android, iOS, and Linux. It’s based on the Pascal programming language and utilizes a visual component-based approach, allowing developers to rapidly build applications by dragging and dropping components onto a form and setting their properties. Delphi’s strength lies in its ease of use for creating database applications, desktop software, and mobile apps, often with significantly less code compared to other languages. It compiles directly to native code, resulting in high-performance applications.

Why learn Delphi? #

Learning Delphi offers several advantages:

Rapid Application Development (RAD): Delphi’s visual component library and intuitive IDE enable rapid prototyping and development, significantly reducing development time.
Native Code Compilation: Applications compiled with Delphi perform exceptionally well and require minimal system resources compared to interpreted languages.
Cross-Platform Development: Modern Delphi versions allow you to target multiple platforms (Windows, macOS, Android, iOS, Linux) from a single codebase, saving time and effort.
Large and Active Community: A vibrant community supports Delphi, providing readily available resources, libraries, and assistance.
Strong Database Connectivity: Delphi excels at creating database applications, offering seamless integration with various database systems.
High Demand: Despite being a mature language, Delphi remains in demand for specific application types, providing excellent job opportunities for skilled developers.

Delphi’s history and evolution #

Delphi originated from Pascal and Borland’s Turbo Pascal. It was first released in 1995 as Borland Delphi 1, quickly gaining popularity for its RAD capabilities. Over the years, it has undergone significant evolution, incorporating new features, improved performance, and support for newer technologies. Ownership has transitioned from Borland to CodeGear and finally to Embarcadero Technologies. Modern Delphi versions offer enhanced support for object-oriented programming, cross-platform development, and integration with various libraries and frameworks. The language itself has also evolved to incorporate modern programming paradigms and best practices.

Setting up your Delphi environment #

Setting up your Delphi development environment is relatively straightforward:

Download and Installation: Download the latest version of Delphi from the Embarcadero website. Choose the edition that best suits your needs and follow the installation instructions. You will need a valid license.
System Requirements: Ensure your system meets the minimum system requirements specified by Embarcadero. This typically includes sufficient RAM, hard drive space, and a compatible operating system.
IDE Configuration (Optional): After installation, you might want to customize your IDE settings, such as font size, color schemes, and keyboard shortcuts, to enhance your productivity. The IDE’s options allow for extensive personalization.
Trial Version (If Applicable): Embarcadero offers trial versions allowing you to evaluate Delphi before purchasing a license. Note that limitations apply to trial versions.

Understanding the IDE #

The Delphi IDE is a sophisticated yet user-friendly environment designed to facilitate efficient application development. Key components include:

Form Designer: A visual interface for designing the user interface (UI) of your applications by dragging and dropping components.
Code Editor: A powerful code editor with features like syntax highlighting, code completion, and debugging tools.
Project Manager: Manages your project files, allowing you to add, remove, and organize different parts of your application.
Object Inspector: Allows you to inspect and modify the properties and events of the components on your forms.
Debugger: A powerful debugging tool to help you identify and fix errors in your code. This includes setting breakpoints, stepping through code, and inspecting variables.
Tool Palette: Contains a range of visual components ready for use in your application.

Familiarizing yourself with these core components is crucial for effective Delphi development. The IDE offers extensive help documentation and tutorials to aid in learning its features.

Building Your First Delphi Application #

Creating a new project #

To create a new Delphi project, follow these steps:

Launch the IDE: Start the Delphi IDE.
New Project: Select “File” -> “New” -> “VCL Forms Application - Delphi” (or the equivalent for your target platform, e.g., “FireMonkey Application”). This creates a basic project template.
Save the Project: Before proceeding, save your project. Choose a project name (e.g., “HelloWorld”) and a location to store your project files. Delphi will create a folder for your project, containing various files associated with your application. It’s good practice to save your project frequently throughout the development process.
The Main Form: You’ll see a main form in the Form Designer. This is where you’ll design the user interface of your application.

Understanding the Form Designer #

The Form Designer is a visual interface where you design the user interface (UI) of your application. It’s a WYSIWYG (What You See Is What You Get) editor, meaning the form’s appearance in the designer closely resembles its appearance at runtime. Key features include:

Form: The main window of your application. You can resize and reposition it.
Components: These are pre-built, reusable elements like buttons, labels, text boxes, and more. You add them to your form from the Tool Palette.
Properties: Each component has properties (like text, color, size, etc.) that you can modify using the Object Inspector.
Events: Components respond to events (like button clicks, mouse movements, etc.). You write code to handle these events.

Adding components to the form #

Adding components to your form is simple:

Select a Component: In the Tool Palette (usually located on the left side of the IDE), find the component you need (e.g., a TButton for a button, a TLabel for text display).
Click and Drag: Click on the component in the Tool Palette and drag it onto your form. This places the component on the form.
Resize and Position: Use your mouse to resize and position the component to your liking.
Modify Properties: Select the component in the Form Designer. The Object Inspector (usually to the right of the IDE) will display its properties. Change the properties as needed. For example, for a TButton, you might change its Caption property to specify the text displayed on the button.

Writing your first code: Hello, World! #

Let’s write a simple “Hello, World!” program:

Add a Button: Add a TButton component to your form.
Modify Button Caption: In the Object Inspector, change the button’s Caption property to “Click Me”.
Double-Click the Button: Double-clicking the button in the Form Designer will open the code editor and create an event handler for the button’s OnClick event.
Write the Code: Inside the OnClick event handler, add the following code:

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage('Hello, World!');
end;

This code uses the ShowMessage function to display a message box with the text “Hello, World!” when the button is clicked.

Running and debugging your application #

Run: Click the “Run” button (usually a green arrow) in the IDE’s toolbar to compile and run your application.
Test: Click the “Click Me” button in your application. You should see the “Hello, World!” message box.
Debugging: If your application doesn’t work as expected, use the debugger. Set breakpoints in your code (click in the gutter next to the line numbers), then run the application. The debugger will pause execution at the breakpoint, allowing you to inspect variables and step through your code line by line. The IDE provides various debugging tools to help find and fix errors.

Delphi Fundamentals #

Variables and data types #

Variables are named storage locations that hold data. In Delphi, you must declare a variable before using it, specifying its name and data type. Data types determine the kind of data a variable can hold and how much memory it occupies. Here are some common Delphi data types:

Integer: Whole numbers (e.g., Integer, ShortInt, LongInt, Int64). Integer is the most commonly used.
Real: Floating-point numbers (e.g., Single, Double, Extended). Double provides good precision and is often preferred.
Boolean: True or False values (Boolean).
Char: A single character (Char).
String: A sequence of characters (String).

Example:

var
  Age: Integer;
  Name: String;
  IsAdult: Boolean;
  Height: Double;
begin
  Age := 30;
  Name := 'Alice';
  IsAdult := True;
  Height := 1.75;
end;

Operators and expressions #

Operators perform operations on variables and values. Delphi supports various operators:

Arithmetic Operators: +, -, *, /, div (integer division), mod (modulo).
Relational Operators: =, <> (not equal), >, <, >=, <=.
Logical Operators: and, or, not.
Assignment Operator: := (assigns a value to a variable).

Example:

var
  x, y: Integer;
begin
  x := 10;
  y := 5;
  ShowMessage(IntToStr(x + y)); // Displays 15
  ShowMessage(IntToStr(x div y)); // Displays 2 (integer division)
  ShowMessage(IntToStr(x mod y)); // Displays 0 (remainder)
  if x > y then ShowMessage('x is greater than y');
end;

Expressions combine operators and operands (variables or values) to produce a result.

Control structures (if-then-else, loops) #

Control structures dictate the flow of execution in your program.

if-then-else: Executes a block of code conditionally.

if Age >= 18 then
  ShowMessage('Adult')
else
  ShowMessage('Minor');

for loop: Repeats a block of code a specific number of times.

for i := 1 to 10 do
  ShowMessage(IntToStr(i));

while loop: Repeats a block of code as long as a condition is true.

i := 1;
while i <= 10 do
begin
  ShowMessage(IntToStr(i));
  i := i + 1;
end;

repeat-until loop: Repeats a block of code until a condition becomes true.

i := 1;
repeat
  ShowMessage(IntToStr(i));
  i := i + 1;
until i > 10;

Procedures and functions #

Procedures and functions are blocks of code that perform specific tasks. Procedures don’t return a value, while functions return a value.

Procedure:

procedure Greet(Name: String);
begin
  ShowMessage('Hello, ' + Name + '!');
end;

Function:

function Add(x, y: Integer): Integer;
begin
  Result := x + y;
end;

Both are called using their names: Greet('Bob'); and z := Add(5, 3);

Working with strings #

Delphi provides extensive support for string manipulation:

Concatenation: Joining strings using the + operator.
Length: Getting the length of a string using the Length function.
Substrings: Extracting substrings using the Copy function.
Searching: Finding substrings using functions like Pos.
Conversion: Converting numbers to strings using functions like IntToStr and FloatToStr.

Example:

var
  str1, str2: String;
begin
  str1 := 'Hello';
  str2 := ' World!';
  ShowMessage(str1 + str2); // Concatenation
  ShowMessage(IntToStr(Length(str1 + str2))); // Length
  ShowMessage(Copy(str1 + str2, 1, 5)); // Substring
end;

These fundamentals form the basis for more advanced Delphi programming. Understanding them thoroughly is crucial before tackling more complex concepts.

Object-Oriented Programming (OOP) in Delphi #

Classes and objects #

Object-Oriented Programming (OOP) is a programming paradigm that organizes code around “objects” rather than “actions” and data rather than logic. In Delphi, a class is a blueprint for creating objects. A class defines the data (fields or properties) and the behavior (methods) of its objects. An object is an instance of a class; it’s a concrete realization of that blueprint.

Think of a class as a cookie cutter and objects as the cookies created using that cutter. All cookies have the same basic shape (defined by the class), but each cookie is a unique instance (an object).

Inheritance and polymorphism #

Inheritance: Inheritance allows you to create new classes (derived classes) based on existing classes (base classes). The derived class inherits the properties and methods of the base class and can add its own unique members or override existing ones. This promotes code reusability and reduces redundancy.
Polymorphism: Polymorphism means “many forms.” It allows objects of different classes to be treated as objects of a common type. This is particularly useful when working with inheritance. A method defined in a base class can be overridden in derived classes to provide different implementations, yet still be called through a common interface.

Encapsulation #

Encapsulation is the bundling of data (fields) and the methods (procedures and functions) that operate on that data within a class. It protects the internal state of an object from external access and modification, except through defined methods. This promotes data integrity and makes code more maintainable. Access modifiers like public, private, and protected control the visibility and accessibility of class members.

Creating and using classes in Delphi #

To create a class in Delphi:

type
  TPerson = class
  private
    FName: string;
    FAge: Integer;
  public
    constructor Create(const AName: string; AAge: Integer);
    procedure Introduce;
    property Name: string read FName write FName;
    property Age: Integer read FAge write FAge;
  end;

constructor TPerson.Create(const AName: string; AAge: Integer);
begin
  FName := AName;
  FAge := AAge;
end;

procedure TPerson.Introduce;
begin
  ShowMessage('Hello, my name is ' + FName + ' and I am ' + IntToStr(FAge) + ' years old.');
end;

This defines a TPerson class with Name and Age properties and an Introduce method. You create an object using the Create constructor and access its members using the dot operator (.):

var
  Person1: TPerson;
begin
  Person1 := TPerson.Create('Alice', 30);
  Person1.Introduce; // Calls the Introduce method
  Person1.Name := 'Bob'; // Modifies the Name property
  Person1.Introduce;
  Person1.Free; // Important: release the object's memory
end;

Understanding Interfaces #

An interface defines a contract specifying a set of methods that a class must implement. It doesn’t provide implementation details; it only declares the methods’ signatures. Interfaces are crucial for achieving polymorphism and loose coupling in your applications. A class can implement multiple interfaces, allowing it to exhibit diverse behaviors.

type
  IMyInterface = interface
    procedure MyMethod;
  end;

  TMyClass = class(TInterfacedObject, IMyInterface)
  public
    procedure MyMethod;
  end;

procedure TMyClass.MyMethod;
begin
  ShowMessage('MyMethod implemented');
end;

procedure TestInterface;
var
  obj: IMyInterface;
begin
  obj := TMyClass.Create;
  obj.MyMethod; // Calls the MyMethod implementation in TMyClass
  obj := nil; // Important to release interface references.
end;

This example shows an interface IMyInterface and a class TMyClass that implements it. The key is that obj can be treated as IMyInterface even though it is actually a TMyClass object at runtime; this is polymorphism in action. Note the use of TInterfacedObject which is the base class for interface implementation. Always ensure to release interface references using obj := nil; to free up memory.

Working with Databases in Delphi #

Connecting to databases #

Delphi offers robust support for database connectivity through various database access components. The most common approach uses FireDAC (Firebird Data Access Components), a powerful, high-performance database library. To connect to a database, you typically follow these steps:

Add a Connection Component: Place a TFDConnection component on your form from the Tool Palette.
Configure Connection Properties: In the Object Inspector, configure the connection properties, including the database type (e.g., MySQL, PostgreSQL, SQL Server, Oracle, InterBase, Firebird), the server name or file path, the database name, the username, and the password. FireDAC supports a wide variety of databases.
Test the Connection: Use the TestConnection method to verify that the connection parameters are correct. This usually involves clicking a button or calling the method programmatically. A successful connection confirms that Delphi can communicate with the database server.

Executing SQL queries #

Once connected, you can execute SQL queries using TFDQuery or TFDStoredProc components.

TFDQuery: Used for executing general SQL queries (SELECT, INSERT, UPDATE, DELETE).
TFDStoredProc: Used for executing stored procedures.

Add a Query Component: Place a TFDQuery component on your form.
Set the Connection: Set the Connection property of the TFDQuery to your TFDConnection component.
Define the SQL: Set the SQL property of the TFDQuery to your SQL statement. For example: SELECT * FROM Customers;
Execute the Query: Call the Open method of the TFDQuery to execute the query. This retrieves data for SELECT statements. For other types of SQL statements, the ExecSQL method can be used.

Retrieving and displaying data #

After executing a SELECT query, you can retrieve data using various methods:

FieldByName: Access individual fields by name (e.g., FDQuery1.FieldByName('CustomerID').AsInteger).
Fields Property: Iterate through the fields collection.
RecordCount Property: Determine the number of records.
Data Controls: Use data-aware controls like TDBGrid or TDBEdit to easily display and edit data directly from the TFDQuery. This eliminates much of the manual data handling code.

Example with TDBGrid:

Place a TDBGrid on your form. Set its DataSource property to a TDataSource component. Then, set the TDataSource’s DataSet property to your TFDQuery. The grid will automatically display the query results.

Data binding #

Data binding connects components to data sources, enabling dynamic updates. This is usually done through TDataSource components acting as intermediaries between data-aware components (e.g. TDBGrid, TDBEdit) and the actual dataset (TFDQuery). Changes in the data source are reflected in the components, and vice versa. This simplifies the development of data-driven applications, greatly reducing the amount of code required to manage the interaction between the UI and the underlying data.

Introduction to FireDAC #

FireDAC (Firebird Data Access Components) is Embarcadero’s modern data access library. It provides a unified approach to database access across various database systems, offering high performance and a consistent API. Key advantages of FireDAC include:

Cross-database support: Works with numerous databases (MySQL, PostgreSQL, SQL Server, Oracle, InterBase, Firebird, and more) using a largely consistent interface.
High performance: Optimized for speed and efficiency.
Flexible architecture: Supports various connection methods and allows for customization.
Rich functionality: Provides features like stored procedure execution, batch updates, and more.

FireDAC is the recommended approach for database access in modern Delphi applications. It significantly simplifies database interaction and improves application performance.

Advanced Topics #

Working with threads and concurrency #

Modern applications often require performing multiple tasks concurrently to improve responsiveness and performance. Delphi provides tools for managing threads and concurrency using the TThread class and related mechanisms. Creating a new thread involves deriving a class from TThread and overriding the Execute method, which contains the code to be executed in the new thread.

type
  TMyThread = class(TThread)
  protected
    procedure Execute; override;
  end;

procedure TMyThread.Execute;
var
  i: Integer;
begin
  for i := 1 to 1000 do
  begin
    // Perform some time-consuming operation
    Sleep(10); // Simulate work
    // Update UI elements using Synchronization (see below)
  end;
end;

Synchronization: Directly accessing UI elements from a secondary thread is generally unsafe. Use synchronization mechanisms like Synchronize or TThread.Queue to safely update the UI from within the Execute method. These methods marshal the UI update back to the main thread.

Example using Synchronize:

procedure TMyThread.Execute;
begin
  // ... other code ...
  Synchronize(
    procedure
    begin
      MyLabel.Caption := 'Thread finished!';
    end
  );
end;

Exception handling #

Exceptions are runtime errors that disrupt the normal flow of your program. Delphi’s exception handling mechanism uses try...except...finally blocks to gracefully handle errors.

try
  // Code that might raise an exception
  // ...
except
  on E: Exception do
  begin
    // Handle the exception
    ShowMessage('Error: ' + E.Message);
    // Log the error, etc.
  end;
finally
  // Code that always executes, regardless of exceptions
  // ... Release resources ...
end;

Using external libraries and components #

Delphi allows you to integrate external libraries (DLLs) and components to extend its functionality. This can involve using components from third-party vendors or creating your own. The process generally involves adding the library to your project’s search path and declaring the functions or classes provided by the library. Component integration usually involves adding the component to your project’s palette and dragging and dropping it onto your form. Correctly handling library dependencies during deployment is essential.

Deployment and packaging your application #

Deploying a Delphi application involves distributing the executable file and any necessary supporting files (DLLs, databases, etc.). The Delphi IDE provides tools to create installers that handle this process. Deployment options include creating standalone executables or using an installer package. Consider the target environment (e.g. 32-bit vs 64-bit) and include all required dependencies. Properly handling application settings and configuration files during deployment is crucial.

Further learning resources #

Numerous resources are available for continued learning:

Embarcadero Documentation: The official Delphi documentation provides comprehensive information on all aspects of the language and IDE.
Online Communities: Forums and online communities provide support, tutorials, and answers to questions from experienced Delphi developers.
Books: Several books cover Delphi programming at various skill levels.
Online Courses: Numerous online learning platforms offer Delphi courses.
Sample Projects: Studying sample projects provides practical experience and insights into best practices.

Continuously exploring these resources will enhance your Delphi programming skills and keep you updated with the latest features and techniques.

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