C++Builder programming - Windows Controls: The Timer

	Windows Controls: The Timer

Introduction to the Timer

Description

A timer is a non-spatial object that uses recurring lapses of time in a computer or in an application. To work, every lapse of period, the control sends a message to the operating system. The message is something to the effect of "I have counted the number of lapses you asked me to count".

As opposed to the time that controls your computer, a timer is partly but greatly under your control. Users do not see nor do they use a timer as a control. As a programmer, you decide if, why, when, and how to use this control.

Practical Learning: Introducing the Timer Control

Start Embarcadero RAD Studio
To create a new application, on the main menu, click File -> New -> VCL Forms Application - C++Builder
In the Object Inspector, change the properties of the form as follows:
Caption: Traffic Light
BorderStyle: bsToolWindow
Name: frmTraffic
To save the project, on the Standard toolbar, click the Save All button
Click the New Folder button
Type TrafficLight1 as the name of the folder and press Enter twice to display the contents of the folder
Change the name of the unit to Traffic and click Save
Change the name of the project to TrafficLight and click Save
Press F9 to test the application
Close the form and return to your programming environment
Copy the following pictures and paste them in the Debug sub-folder of the current project:

Design the form as follows:

Control		AutoSize	Name	Picture
TImage		True	imgLight	RedLight.bmp

Under the Code Editor, click Traffic.h

Create an enumeration named CurrentLight and declare a variable for it named Light:

//---------------------------------------------------------------------------

#ifndef TrafficH
#define TrafficH
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <ExtCtrls.hpp>
#include <Graphics.hpp>
//---------------------------------------------------------------------------
enum CurrentLight { Red, Orange, Green };
//---------------------------------------------------------------------------
class TfrmTraffic : public TForm
{
__published:	// IDE-managed Components
	TImage *imgLight;
private:	// User declarations
	CurrentLight Light;
public:		// User declarations
	__fastcall TfrmTraffic(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TfrmTraffic *frmTraffic;
//---------------------------------------------------------------------------
#endif

Press F12 to display the form
In the Structure window, click frmTraffic
In the Object Inspector, click Events
Double-click the right box of OnCreate

Implement the event as follows:

//---------------------------------------------------------------------------
void __fastcall TfrmTraffic::FormCreate(TObject *Sender)
{
	Light = CurrentLight::Green;
}
//---------------------------------------------------------------------------

Press F12 to display the form
In the Object Inspector, click Properties

Creating a Timer

The timer in VCL applications is made available through the TTimer class. The TTimer class is (directly) derived from TComponent:

TTimer Inheritance

To add it to your application at design time, from the System property page of the Tool Palette, click Timer and click on the form.

Creating a Timer

The timer in VCL applications is made available through the TTimer class. The TTimer class is (directly) derived from TComponent:

TTimer Inheritance

To add it to your application at design time, from the System property page of the Tool Palette, click Timer and click on the form.

Characteristics of a Timer

The Interval

A timer is an object used to count lapses of time and send a message when it has finished counting. The amount of time allocated for counting is called an interval. The Interval is probably the most important characteristic of the timer because it measures and controls the total time needed to perform a complete count. The Interval is measured in milliseconds. Like any counter, the lower the value, the faster the count will finish, and the higher the value, the longer the count (if you ask one kid to count from 1 to 10 and you ask another to count from 1 to 20 and shout when finished, the first kid would finish first and would shout first). The amount of interval you specify will depend on what you are trying to do.

Enabling a Timer

One of the ways you can use a timer is to decide when it should start counting. In some applications, you may want the control to work full-time while in some other applications, you may want the control to work only in response to an intermediate event. The ability to stop and start a timer is set using the Enabled Boolean property. When, or as soon as, this property is set to true, the control starts counting. If, when, or as soon as, the Enabled property is set to false, the control stops and resets its counter to 0.

Practical Learning: Using Timer Controls

On the Tool Palette, click System
Click TTimer
Click the form
On the form, double-click the TTimer1 control to access its OnTimer event

Change its code as follows:

//---------------------------------------------------------------------------
void __fastcall TfrmTraffic::Timer1Timer(TObject *Sender)
{
	// If the current color is red
	if( Light == CurrentLight::Red )
	{
		// Change the amount of time to 1500 seconds
		Timer1->Interval = 1500;
		// Change the color to orange
		imgLight->Picture->LoadFromFile(L"OrangeLight.bmp");
		// Update the light tag
		Light = CurrentLight::Orange;
	}
	// But if the color is orange
	else if( Light == CurrentLight::Orange )
	{
		// Change the amount of time
		Timer1->Interval = 7500;
		// Change the color to green
		imgLight->Picture->LoadFromFile(L"GreenLight.bmp");
		// Update the light sentinel
		Light = CurrentLight::Green;
	}
	// Otherwise, if the color is green
	else //  if( Light == CurrentLight::Green )
	{
		// Change the amount of time
		Timer1->Interval = 5000;
		// Change the color to red
		imgLight->Picture->LoadFromFile(L"RedLight.bmp");
		// Update the light tag
		Light = CurrentLight::Red;
	}
}
//---------------------------------------------------------------------------

Save all
Press F9 to test the program