1
00:00:01,100 --> 00:00:07,130
‫Come back in this lecture, we will create our own delegates to filter a list of people, and this will

2
00:00:07,130 --> 00:00:11,080
‫give us a deeper understanding of how delegates work under the hood.

3
00:00:11,090 --> 00:00:14,960
‫So let's consider the following class that we have here.

4
00:00:14,960 --> 00:00:19,970
‫So it's a very simple class person with a name property as well as an age property.

5
00:00:19,970 --> 00:00:21,410
‫Just two properties here.

6
00:00:22,770 --> 00:00:27,990
‫So we want to create our own delegates to filter people based on the age.

7
00:00:28,350 --> 00:00:36,600
‫Our filter delegates will take a person as a parameter and we'll return a bool if the condition regarding

8
00:00:36,600 --> 00:00:37,680
‫the age is met.

9
00:00:38,010 --> 00:00:39,840
‫What is the condition exactly?

10
00:00:39,870 --> 00:00:46,560
‫Well, we don't care, since the code could be used to filter a list on a web page, for example, and

11
00:00:46,560 --> 00:00:49,210
‫the filtration feature might change rapidly.

12
00:00:49,230 --> 00:00:52,490
‫And, well, that's exactly the beauty of delegates.

13
00:00:52,500 --> 00:00:53,700
‫What a luxury.

14
00:00:54,000 --> 00:00:54,450
‫All right.

15
00:00:54,450 --> 00:00:56,880
‫So let's define our delegate type.

16
00:00:56,970 --> 00:01:04,840
‫And therefore, I'm going to just go ahead and say that this is going to be a delegate of type Boolean.

17
00:01:04,860 --> 00:01:06,900
‫I'm going to call it filter delegate.

18
00:01:06,900 --> 00:01:09,390
‫And it will require a person.

19
00:01:09,930 --> 00:01:12,210
‫So a person object called P.

20
00:01:13,950 --> 00:01:20,890
‫Now let's go ahead and just create a little list of people, of person objects, so to speak.

21
00:01:20,910 --> 00:01:23,790
‫Here we have four person objects.

22
00:01:24,330 --> 00:01:26,610
‫P one, p two, p three and P four.

23
00:01:26,610 --> 00:01:29,010
‫And then we add all of them to a list.

24
00:01:29,010 --> 00:01:32,280
‫So they have different names as well as different ages here.

25
00:01:34,150 --> 00:01:39,130
‫So now we want to actually filter those people based on their age.

26
00:01:39,130 --> 00:01:48,040
‫For example, display the adults only so age 18 and higher or the minors only so age below 18.

27
00:01:48,220 --> 00:01:54,160
‫Since we want to apply different filters, let's actually create a method called display people.

28
00:01:54,250 --> 00:02:01,000
‫This method will take the list of people and a filter as a delegate, and then it will filter the list

29
00:02:01,000 --> 00:02:02,950
‫of people based on that filter.

30
00:02:03,250 --> 00:02:11,690
‫So we also want to throw in a string called title to make things look more organized in the console.

31
00:02:11,710 --> 00:02:16,930
‫So first of all, let me set up the header of my method here.

32
00:02:17,500 --> 00:02:20,860
‫So here we have the display people method.

33
00:02:20,980 --> 00:02:27,160
‫It will require a string, the list of people and the filter delegate that I will call filter.

34
00:02:27,520 --> 00:02:30,160
‫Now, what is it that I want to do in here?

35
00:02:30,430 --> 00:02:34,000
‫Well, first of all, I'm just going to write the title.

36
00:02:35,890 --> 00:02:42,160
‫And then I'm going to go through all the people that are inside of my personal list here.

37
00:02:43,230 --> 00:02:47,940
‫And I'm going to check if the filter works with the person that we passed.

38
00:02:48,150 --> 00:02:53,730
‫So here we're just going to say the person's name as well as how old they are.

39
00:02:54,620 --> 00:03:00,080
‫And now we can go ahead and just define a couple of methods that we will use as filters.

40
00:03:00,830 --> 00:03:03,920
‫So one will be for the miners.

41
00:03:04,370 --> 00:03:06,320
‫So here is miner.

42
00:03:06,320 --> 00:03:11,960
‫So we take in the person and we check their age against 18.

43
00:03:11,960 --> 00:03:15,590
‫And if it's lower, then we know that we need to return.

44
00:03:15,830 --> 00:03:18,500
‫True, which means the person is a miner.

45
00:03:18,740 --> 00:03:21,080
‫Otherwise we will return false.

46
00:03:22,010 --> 00:03:24,840
‫So that's going to be the one filter.

47
00:03:24,860 --> 00:03:29,270
‫Then let's create another filter for adults like so.

48
00:03:29,510 --> 00:03:35,660
‫And now another filter for seniors, let's say people above the age of 65.

49
00:03:36,480 --> 00:03:36,810
‫Like.

50
00:03:36,810 --> 00:03:43,350
‫So now on the main method, let's call the display people method a few times, the one that we just

51
00:03:43,350 --> 00:03:44,850
‫created this one here.

52
00:03:45,330 --> 00:03:48,600
‫So let's go ahead into our main method.

53
00:03:48,990 --> 00:03:55,380
‫And here I'm going to display people and here I'm just going to pass in the title.

54
00:03:55,380 --> 00:04:02,610
‫I'm just going to say kids, for example, I'm passing in the people list as well as my filter.

55
00:04:02,610 --> 00:04:08,430
‫So here my is minor filter and I call it is minor like so.

56
00:04:10,270 --> 00:04:12,850
‫And now let's check it out.

57
00:04:15,440 --> 00:04:18,520
‫Let's run this and see if it will display our kids.

58
00:04:18,530 --> 00:04:21,860
‫And it only displays Walter, who is 12 years old.

59
00:04:22,610 --> 00:04:24,170
‫Okay, so that filter worked.

60
00:04:24,260 --> 00:04:30,440
‫You see, we passed in a method we didn't have to pass in any parameters to this method because we passed

61
00:04:30,440 --> 00:04:32,780
‫it in the position of a delegate.

62
00:04:32,780 --> 00:04:38,000
‫So here, this filter delegate, let me scroll out a little so you can see it's a little better.

63
00:04:38,000 --> 00:04:43,490
‫So here we need to pass into filter delegate, which means we can pass in a method that just follows

64
00:04:43,490 --> 00:04:49,940
‫the filter delegates description, which means it just needs to pass an ebullient and it needs to have

65
00:04:49,940 --> 00:04:52,130
‫one parameter of type person.

66
00:04:52,670 --> 00:04:58,610
‫And that's exactly what our methods slash filters, how I call them here are doing.

67
00:04:58,610 --> 00:05:02,270
‫They return a boolean and they require person P.

68
00:05:02,360 --> 00:05:07,160
‫So if it's minor weren't following the structure, this wouldn't work.

69
00:05:07,160 --> 00:05:16,370
‫So if I were to get rid of this and return true here, for example, then this wouldn't work.

70
00:05:16,400 --> 00:05:22,880
‫You see here it says is minor well can convert method group to program dot filter delegate so it doesn't

71
00:05:22,880 --> 00:05:25,910
‫follow the instructions of our delegates.

72
00:05:27,970 --> 00:05:28,570
‫All right.

73
00:05:28,960 --> 00:05:35,490
‫So now let's do the same thing with our other type of filters.

74
00:05:35,500 --> 00:05:39,250
‫So first of all, with adults and then with seniors.

75
00:05:39,250 --> 00:05:40,690
‫So let's look at it.

76
00:05:41,020 --> 00:05:47,440
‫And we see kids, Walter, adults, Aiden and Anatoly, and then seniors only Siv.

77
00:05:47,440 --> 00:05:49,150
‫And he's 69 years old.

78
00:05:49,840 --> 00:05:52,330
‫So that's it for a little introduction for delegates.

79
00:05:52,330 --> 00:06:00,880
‫But you might notice a annoying pattern that we have here, and we are going to eliminate that in the

80
00:06:00,880 --> 00:06:05,050
‫next lecture, which is the anonymous methods pattern.

81
00:06:05,050 --> 00:06:06,400
‫So see you there.