Creating Custom Components in C++ Builder

Custom components in C++ Builder allow developers to extend the functionality of the VCL (Visual Component Library) or FMX (FireMonkey) frameworks by creating reusable and specialized components tailored to specific needs. This guide covers the process of creating custom components, including the basics of component design, practical examples, and tips for best practices. By mastering custom component creation, you can build responsive user interface that enhances the overall user experience.

1. Understanding Custom Components

Custom components are user-defined classes derived from existing VCL or FMX components. They encapsulate functionality and user interface elements, enabling code reuse and modular design. Components can be visual (with a graphical user interface) or non-visual (performing background tasks or holding data). Additionally, custom components can integrate third-party libraries to extend their functionality and provide additional features.

1.1. Visual vs. Non-Visual Components

• Visual Components: Have a graphical representation and can be placed on forms or other containers. Examples include buttons, panels, and grids.
• Non-Visual Components: Do not have a graphical representation but provide functionality or manage data. Examples include timers, data sources, and custom data processors.

2. Creating a Custom Component

2.1. Setting Up a New Component

To create a custom component in C++ Builder:

1. Create a New Package:
   • Open C++ Builder.
   • Go to File > New > Package and create a new package for your custom components.
2. Add a New Component:
   • Right-click on the package and select Add > New Item.
   • Choose Component and name it accordingly.
3. Define the Component Class:
   • The component class should inherit from an existing VCL or FMX class. For visual components, inherit from TCustomControl or a similar base class. For non-visual components, inherit from TComponent.

Example of a Simple Visual Component:

#include <vcl.h>
#pragma hdrstop
#include “MyCustomComponent.h”
#pragma package(smart_init)
#pragma resource “*.dfm”

__fastcall TMyCustomComponent::TMyCustomComponent(TComponent* Owner)
    : TCustomControl(Owner)
{
    // Initialization code
}

void __fastcall TMyCustomComponent::Paint()
{
    // Custom painting code
    Canvas->Brush->Color = clRed;
    Canvas->FillRect(ClientRect);
}

Example of a Simple Non-Visual Component:

#include <System.Classes.hpp>
#pragma hdrstop
#include “MyNonVisualComponent.h”
#pragma package(smart_init)

__fastcall TMyNonVisualComponent::TMyNonVisualComponent(TComponent* Owner)
    : TComponent(Owner)
{
    // Initialization code
}

2.2. Adding Properties, Methods, and Events

Custom components can have properties, methods, and events that define their behavior and interaction.

• Properties: Define the attributes of the component.
• Methods: Implement the functionality of the component.
• Events: Allow other code to respond to component actions or state changes. Event-driven programming is crucial here, as it enables components to handle user actions or other events effectively.

Example of Adding a Property:

class TMyCustomComponent : public TCustomControl
{
private:
    int FMyProperty;
    void __fastcall SetMyProperty(int Value);

public:
    __property int MyProperty = {read=FMyProperty, write=SetMyProperty};
};

void __fastcall TMyCustomComponent::SetMyProperty(int Value)
{
    if (FMyProperty != Value)
    {
        FMyProperty = Value;
        Invalidate(); // Trigger repaint
    }
}

Example of Adding an Event:

class TMyCustomComponent : public TCustomControl
{
private:
    void __fastcall OnClick();

public:
    __property TNotifyEvent OnClick = {read=FOnClick, write=FOnClick};

protected:
    virtual void __fastcall Click();
};

void __fastcall TMyCustomComponent::Click()
{
    if (OnClick)
        OnClick(this);
}

3. Registering and Using Your Component

Once your component is developed, you need to register it with the IDE so it can be used on forms.

3.1. Register the Component

In the component’s header file, add a registration function:

void __fastcall Register()
{
    RegisterComponents(“MyComponents”, (TComponentClass[])
    {__classid(TMyCustomComponent)});
}

Include this function in your component source file and ensure it’s called during the package build process.

3.2. Compile and Install the Package

• Build the Package: Go to Project > Build All Projects to compile the package.
• Install the Package: Right-click the package in the Project Manager and select Install. The custom component should now appear in the Tool Palette.

Usage Example: Drag and drop your custom component from the Tool Palette onto a form, or create instances in code:

#include <vcl.h>
#include <MyCustomComponent.h>
#pragma hdrstop
#include “MainForm.h”
#pragma package(smart_init)
#pragma resource “*.dfm”

TForm1 *Form1;

__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
    TMyCustomComponent *myComp = new TMyCustomComponent(this);
    myComp->Parent = this;
    myComp->MyProperty = 10;
}

4. Best Practices for Custom Components

• Keep Components Simple: Focus on a single responsibility to ensure your components are easy to understand and maintain.
• Document Your Code: Provide clear documentation for properties, methods, and events to help users understand how to use your component.
• Test Thoroughly: Ensure your component works correctly in various scenarios and does not introduce unexpected issues.
• Follow Naming Conventions: Use consistent naming for properties, methods, and events to avoid confusion.

Conclusion

Creating custom components in C++ Builder involves defining new classes that extend existing VCL or FMX components, adding properties, methods, and events, and registering them with the IDE. By mastering this process, you can enhance the functionality of your applications with reusable and specialized components.