Making a Button Do Something

We started with our layout where we created our button. 0:00 Then we made a variable for it in our activity class, and 0:03 we set that variable in the last code challenge. 0:06 But there's still one more step to make our button work. 0:09 I'll start by adding the code from the code challenge. 0:12 I'll type showF and then hit enter or tab to auto complete. 0:17 Then I'll set it = findViewById(R.id.showFactButton) 0:22 hit ALT+Enter to add the cast and it looks like I need to move that around and 0:28 there we go, ALT+Enter to add the cast and finish with a semicolon. 0:34 Now, it's time to make our button do something. 0:40 On a new line, type showFactButton and 0:43 remember that we can use enter or tab to auto complete. 0:46 Now, if we type a dot, we get a new menu for auto complete suggestions. 0:50 These are all methods available to a button object. 0:55 As we start typing, methods that don't match will be filtered out. 1:00 Let's type setOn. 1:04 We see the setOn click listener method near the top of our list. 1:07 That's also the method we're looking for, so let's select it. 1:11 An OnClickListener is exactly what it sounds like. 1:17 It's something that listens for the button to be clicked, or tapped. 1:20 Clicked and tapped mean the same thing when we're talking about a touch screen. 1:24 When the listener detects a click, 1:28 it then runs some code that we've given it ahead of time. 1:30 A setOnClickListener method is expecting a parameter 1:33 that is another new data type on ClickListener. 1:37 That's what this call out is telling us. 1:41 if you lose this call out somehow, simply hover over that error and 1:43 we can see the inside of these parenthesis is supposed to be an on ClickListener. 1:49 The listener parameter we provide here will be connected to our showFact button. 1:53 It doesn't exist yet, so let's add a line above this one and 1:58 start typing OnClickListener with a capital O. 2:02 Notice that there's more than one type of OnClickListener. 2:07 This first one is for a view and the second one is for a dialogue interface. 2:10 But how do we know which one of these we should choose? 2:16 There's actually a couple different ways we can get more information about 2:19 objects and methods like this one. 2:22 One way is to Google the class name, button, and 2:24 then the method we're looking for, setOnClickListener. 2:28 This first link is to the official Android Documentation. 2:36 Let's open it, and then use Cmd or 2:40 Ctrl + F to find where it mentions setOnClickListener. 2:43 Right at the top, there's some sample code for a button, and 2:48 it looks like it's using the OnClickListener from the View class. 2:51 Back in Android Studio, 2:55 we can use a shortcut to get at the documentation as well. 2:56 Let's click on setOnClickListener, and then use F1 for 3:00 Mac, or Ctrl+Q for Windows. 3:05 This brings up the quick documentation dialogue, and 3:08 again, we can see that we're looking for the OnClickListener from the view class. 3:10 Now that we know which OnClickListener to use, let's go back up here and 3:16 keep typing to bring back auto-complete. 3:20 Then let's select the View.OnClickListener and 3:23 notice the Android studio makes it very clear which OnClickListener we chose. 3:27 This way we can avoid any confusion between the different 3:31 On Click Listener classes. 3:35 Next, we need to name our listener and then set it equal to something. 3:37 Let's name it something descriptive, like listener. 3:41 Then type space equals space, new, another space and 3:44 then type on click listener with a capital o and hit enter to auto complete. 3:49 Whoa, it just dropped in a lot of code for us. 3:55 This is all the code that's required to create an on click listener. 4:00 But we still need to end our statement with a semicolon, so 4:04 before we forget let's add a semicolon after this last bracket. 4:07 This may seem like a lot, but that's why we have auto complete. 4:11 It's a lot easier to use auto complete than it is to remember all of that. 4:15 Before we move on, let's quickly copy our listener variable and 4:20 paste it down here as the parameter for setOnClickListener. 4:25 And now that there's no error let's take a short break before we finish our listener. 4:31