Handling Bad Array Indexes

How did it go with the second challenge? 0:00 Let's walk through my solution. 0:02 To encapsulate the array of media type items inside of a class, 0:04 I started with adding a file named MediaLibrary.cs. 0:08 Then, I added the namespace, Treehouse.MediaLibrary. 0:14 And stubbed out the class, MediaLibrary. 0:24 In the MediaLibrary class I defined 0:29 a private array field of type 0:34 MediaType named, _items;. 0:38 Remember the private keyword makes this field only visible or 0:43 accessible to code within the MediaLiibrary class. 0:47 The underscore here at the beginning of the field name isn't required for 0:51 private fields, but it's a common naming convention. 0:55 Following this convention will make it easier to spot private fields in our code. 0:59 I then added a public constructor. 1:04 That accepts an array of MediaType items. 1:10 And then I used the items parameter to initialize the _items private field. 1:14 I completed my MediaLibrary class by adding a method named GetItemAt. 1:21 The method should accept an index of type int. 1:28 So int index, and it should have a return type, of MediaType. 1:31 Then, I just needed to return the item from the underscore items' private field 1:41 at the provided index. 1:46 So return _items[index]. 1:48 Moving on to the program.cs file's main method. 1:55 I instantiated an instance of the MediaLibrary class, 2:01 var mediaLibrary = new MediaLibrary. 2:08 And I passed my existing collection 2:13 of items into the constructor, 2:18 new MediaType[ ] and { }. 2:22 Then I cut and pasted my items from here, into here. 2:30 Notice that I needed to add back the new keyword, and the array type in order for 2:37 my program to successfully compile. 2:42 This is necessary because the compiler can't infer what we're 2:44 trying to do here with our { } and MediaTypes of class instances. 2:49 Adding new MediaType[ ] makes it clear that we're initializing an array 2:54 of MediaType items. 2:59 Then, I updated the rest of my code to use the GetItemAt method 3:01 to retrieve items from the MediaLibrary. 3:06 So, DetectMediaType, so instead of items[0], 3:08 (mediaLibrary.GetItemAt). 3:14 We call it as a method because it is a method and pass in 0, the index for 3:19 the element we want to retrieve. 3:23 I'll copy this code to the clipboard and 3:25 paste it inside of these other method calls. 3:28 And change the indexes, 1, 2, 3, and 4. 3:37 Then do the same for the Display method calls. 3:43 And lastly, I saved the Program.cs file and compiled and ran my program. 3:53 And here, we can see the expected output in the console. 4:01 The addition of a MediaLibrary class fills a gap in our program 4:05 as we work towards a more functional version. 4:09 Let's look at an issue with our MediaLibrary GetItemAt method 4:12 implementation. 4:15 Let's make a call to the GetItemAt method and pass in an index for 4:17 an element that doesn't exist in our array of media type items. 4:21 I'll copy this line of code and paste it right below the other and 4:25 pass in five for the index. 4:29 Remember an index of 5 would map to the sixth element in our array. 4:33 Our array only contains five elements. 4:38 So if we compile and run our program, we'll receive a runtime exception. 4:40 Exception: Index was outside the bounds of the array. 4:47 And execution of our program stops without running the rest of our code in 4:51 the main method. 4:55 Okay, so for our third and last challenge in this practice session, 4:56 let's work to improve the situation. 4:59 In the MediaLibrary class, 5:05 update the GetItemAt() method to gracefully handle a bad index. 5:07 Use the array's linked property to determine if an index is available before 5:12 attempting to access it. 5:17 And return null if the provided index isn't available in the array of items. 5:18 And in the Program.cs file, update the Display and 5:24 DetectMediaType methods to handle when the item parameter has a null value. 5:28 And that's it for the third challenge. 5:33 We'll see you in a bit. 5:35