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Build a Simple Android App with Kotlin

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Simple Refactoring: Creating a New Class

5:45 with Ben Deitch

There is a famous Boy Scout rule that states: "Always leave the campground cleaner than you found it." As software developers we want to adopt a similar rule, except we're dealing with code, not campgrounds. In programming, this process is known as "refactoring," and we'll refactor our code using some handy tools built into the IDE.

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    [MUSIC] 0:00
    Have you ever heard the old boy scout rule, 0:04
    always leave the campground cleaner than you found it? 0:06
    As software developers, we want to adopt a similar rule. 0:10
    Every time we make a change to our code or someone else's code, we want to try and 0:13
    clean it up or improve it in some way. 0:17
    We don't necessarily want to make any big changes, but 0:20
    if we see an opportunity to let say user valuable instead of a hard coded value, 0:23
    then we should make and test that change. 0:28
    The important thing to emphasize here is that, 0:31
    we don't want to change the behavior of the code, we're just looking for 0:33
    opportunities to make it a little cleaner and more efficient, or 0:37
    maybe more maintainable for someone else to work within the future. 0:41
    This process is known as refactoring. 0:44
    Let's see how we can do some refactoring with our FunFact code. 0:47
    Right now, we have all of our code in this FunFactsActivity class. 0:51
    And it works fine, but what if we wanted to add a new activity 0:56
    that also randomly selected one of our facts? 0:59
    We could copy all of these code and add it to the new activity. 1:02
    But then we would have the same code doing the same thing in two different places. 1:07
    Then if we change this code for some reason, 1:12
    we have to remember to make the same change to the code for the other activity. 1:15
    This violates a core principle of software development, 1:19
    the don't repeat yourself principle. 1:22
    A better solution is to move the code that is repeated to a reusable component. 1:25
    In this case, that could be a new object that could be used in multiple activities. 1:30
    We learned before that activities are used to control how things work on the screen. 1:34
    Our code does that, but 1:38
    it also controls how the effect is generated behind the scenes. 1:40
    Let's make a new object that separates out fact generation. 1:44
    Not only will it make our code a little cleaner, but 1:48
    it will also prevent us from repeating our ourselves in code. 1:51
    It's another good programming practice to give each class a single responsibility. 1:55
    So in that case, 1:59
    the FunFactsActivity class will handle only how the screen looks and works. 2:00
    And the new object, which we'll call factBook, will only 2:05
    handle things about the facts themselves, like how they're stored and selected. 2:08
    This is another programming principle known as the single 2:13
    responsibility principle. 2:16
    All right, let's create our new factBook object. 2:18
    There are a couple ways we can do this. 2:21
    We can go to File, New, and then pick Kotlin File or Class, 2:24
    or in the Project Pane we can right-click on our package and 2:29
    select New Kotlin File or Class. 2:34
    I'll choose this option. 2:37
    Then for the name let's type FactBook. 2:40
    And since we're making the class, let's change the kind to Class and then hit OK. 2:44
    And here's our new file. 2:51
    If we look over to the project pane, 2:53
    we can see that a new FactBook file has been added to our package. 2:55
    And our package now has two classes in it. 2:59
    Also, I already fixed it from a high version. 3:02
    But at the top of your class, Android Studio may have added a comment. 3:05
    I'm not a huge fan of the automatic comment, but 3:09
    luckily we can change our preference to make it not happen in the future. 3:12
    Follow along if you'd like. 3:16
    I'm going to click on Android Studio and then open the preferences window. 3:18
    Then I'll expand Editor and select File and Code Templates. 3:24
    And over on the Includes tab, I'll select File Header and 3:29
    then delete everything in the window on the right. 3:34
    Remember, mines empty cuz I've already done this, then click OK. 3:37
    You'll still need to delete any remaining comments by hand though. 3:43
    This class will be the blueprint for our FactBook object. 3:46
    Remember, that an object has two main components, Properties, 3:50
    which are characteristics of the object 3:55
    and Methods, which are actions the object can take. 4:02
    This object only needs to do one thing, get a random fact. 4:08
    Let's define a method for it. 4:13
    We'll call it getFact and 4:16
    it will return a string, which will be the randomly chosen fact. 4:17
    Inside the class, type fun getFact with open and closing parenthesis. 4:22
    Then let's make it return a string, colon string, and add the brackets. 4:28
    Now we just need to make this method return a random fact. 4:36
    Let's cut and paste some code from our activity class into our getFact method, 4:39
    this is the refactoring part. 4:44
    Over in FunFactsActivity, select everything in the OnClickListener 4:46
    except for the last two lines where we're actually setting the text. 4:52
    Then let's cut the text with command or Ctrl+X, and leave this error for 4:57
    now and go back to our FactBook class, and paste in the code. 5:01
    We didn't copy over any of our imports, so 5:07
    hit OK to let Android Studio automatically create the ones we need. 5:10
    GetFact now gets a random element from the facts array, but 5:14
    we still need to return which fact was selected. 5:18
    So instead of setting up a fact variable with a random fact, 5:22
    let's just return the fact variable. 5:26
    Nice, we've just made a new FactBook class and 5:33
    given it a method which will return a random fact. 5:36
    Let's take a short break and 5:39
    then we'll see how we can use your new method in FunFactsActivity. 5:41

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