Start a New Activity in an Android App

[treehouse™ presents] 0:00 [Quick Tips: Starting a New Activity in an Android App with Ben Jakuben] 0:02 Hi, I'm Ben, and in this Treehouse Quick Tip, 0:06 we'll learn how to switch from one screen to another 0:08 in an Android app. 0:10 A screen, or page, of an Android App is called 0:12 an 'activity.' 0:14 When you create a new Android project, you start with 1 basic activity, 0:16 often known as your 'main' activity. 0:19 You can switch to a different activity 0:21 in a variety of ways, but let's take a look at how to make 0:23 the switch using a button on the main activity. 0:25 Let's start by adding a button to an activity. 0:28 I created a new project with the Blank Activity template, 0:30 but you can use any old activity you have lying around. 0:34 Add a button and change the label to 0:36 Go To Activity #2. 0:38 [typing] 0:41 Click Okay, and save your changes. 0:46 Now, let's create Activity #2. 0:49 Expand Source, right-click on the package, 0:51 select New, 0:53 Other, expand Android, 0:55 select Android Activity, and click Next. 0:58 Click Next for the Blank Activity template, 1:01 and let's name our second activity, 'Second Activity.' 1:03 Click Finish. 1:07 This creates 2 files for us, 1:10 the SecondActivity java file 1:12 and the activity_second XML file, 1:14 which is open here on the right. 1:18 Right-click on the hello_world text, and let's change it to 1:20 This is Activity #2. 1:22 [typing] 1:26 Click Okay, 1:28 and to really make it stand out, 1:31 let's change the background color, too. 1:33 Select the RelativeLayout parent in the outline, 1:35 then set the Background property to #00FF00. 1:37 Hit Enter, and this gives us a nice 1:43 bright-green background that we will definitely notice. 1:45 Okay, let's save our changes here. 1:48 Now, let's open up MainActivity.java. 1:51 Open up our package, 1:54 double-click on the file, 1:56 and we'll start by declaring a button. 1:58 Button switchButton = 2:01 I'm going cast us a button 2:04 from the findViewById method, 2:06 and then our ID is button1. 2:09 Okay. Organize my imports. 2:14 Now, let's add an onClick listener, which listens for a 2:16 click or tap and then runs some code for us. 2:18 Type: switchButton 2:21 setOnClickListener, 2:24 hit Enter, 2:26 and we want a new View.OnClickListener, 2:28 hit Enter, and it drops in the code. 2:31 I'm going to scroll down 2:33 and add a semicolon before I forget. 2:35 Now, let's add the code that we need 2:37 to switch activities inside the onClick method. 2:39 In Android, we switch activities 2:42 by using intents. 2:44 Intents are abstract descriptions 2:46 of operations to be performed. 2:48 We will use an explicit intent 2:51 which provides the exact class 2:54 to be run. 2:56 In this case, the class is our second activity. 2:58 So, back in Eclipse, 3:01 I'm going to delete this comment, 3:03 and add: Intent intent = 3:05 new Intent 3:08 and for the parameters, type: 3:11 MainActivity.this, 3:13 SecondActivity.class. 3:17 The first parameter is the current context, 3:21 but since we're inside the onClick listener, 3:23 which is known as an anonymous inner class, 3:26 we need to reference it by the full class name. 3:28 The second parameter is the name of our target class. 3:30 Okay, let's organize our imports, 3:35 and, now, on a new line, type: 3:38 startActivity, 3:40 and the parameter is the intent we just created. 3:43 That's it. 3:46 Save and Run. 3:48 Run it as an Android application, Click Okay. 3:51 Okay, let's tap on the button, and, 3:53 hurray, there's Activity #2, 3:56 and we can use the Back button to go back to the first activity. 3:59 As you can see, switching activities is pretty easy 4:04 once you have the activities created. 4:06 Intents like these are incredibly versatile 4:08 and powerful and can make use of so many 4:10 classes, apps, and services on your device. 4:12 Switching apps is just as easy as switching activities. 4:14 If you'd like to see more advanced videos and tutorials like this one, 4:18 go to TeamTreehouse.com and start learning for free. 4:22 [treehouse™] 4:26

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