Delegatlar, hodisalar va lyambda-ifodalar

2-Masala. Son, pul, o'nlik, harorat va o'n oltilik kabi har xil formatlarda butun sonlarni chiqaradigan quyidagi PrintHelper klassini ko'rib chiqing. U beforePrintEvent orqali raqamni chop etishdan oldin, BeforePrint hodisasi a’zosiga xabar bersin.

• public class PrintHelper {
• // declare delegate
• public delegate void BeforePrint();
• //declare event of type
• delegate public event BeforePrint beforePrintEvent;
• public PrintHelper()
• {
• }

public void PrintNumber(int num) {

• public void PrintNumber(int num) {
• //call delegate method before going to print
• if (beforePrintEvent != null) beforePrintEvent();
• Console.WriteLine("Number: {0,-12:N0}", num);
• }
• public void PrintDecimal(int dec) {
• if (beforePrintEvent != null) beforePrintEvent();
• Console.WriteLine("Decimal: {0:G}", dec);
• }
• public void PrintMoney(int money) {
• if (beforePrintEvent != null) beforePrintEvent();
• Console.WriteLine("Money: {0:C}", money);
• }

public void PrintTemperature(int num) {

• public void PrintTemperature(int num) {
• if (beforePrintEvent != null) beforePrintEvent(); Console.WriteLine("Temperature: {0,4:N1} F", num);
• }
• public void PrintHexadecimal(int dec) {
• if (beforePrintEvent != null) beforePrintEvent();
• Console.WriteLine("Hexadecimal: {0:X}", dec);
• }
• }

Dastur tahlili:

• PrintHelper beforePrint hodisasini nashr qiluvchi nashriyotchi klassdir. Shuni ta’kidlash joizki, har bir chiqaruvchi metod avvalo, beforePrintEvent nolga teng emasligini tekshiradi va shundan keyin beforePrintEvent() metodini chaqiradi. beforePrintEvent bu BeforePrint delegati tipidagi obyektdir. Shu bois, hech bir klass hodisaga a’zo bo’lmasa u nolga teng bo’lishi mumkin, shuning uchun ham delegat chaqirilishdan oldin u nolga teng emasligi tekshiriladi.

Lyambda ifodalar.

• Lyambda ifodalarni tushunishdan oldin anonim metodlar bilan tanishib olishingiz lozim bo’ladi. Keyingi darsimizda anonim metodlar bilan tanishtiraman va shundan keyin lyambda ifodalar bilan to’liq tanishib chiqamiz.