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[treehouse™ presents]

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[Quick Tips: Starting a New Activity in an Android App with Ben Jakuben]

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Hi, I'm Ben, and in this Treehouse Quick Tip, 

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we'll learn how to switch from one screen to another

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in an Android app. 

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A screen, or page, of an Android App is called

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an 'activity.' 

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When you create a new Android project, you start with 1 basic activity,

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often known as your 'main' activity. 

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You can switch to a different activity

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in a variety of ways, but let's take a look at how to make

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the switch using a button on the main activity. 

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Let's start by adding a button to an activity. 

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I created a new project with the Blank Activity template, 

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but you can use any old activity you have lying around. 

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Add a button and change the label to

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Go To Activity #2. 

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[typing]

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Click Okay, and save your changes. 

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Now, let's create Activity #2. 

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Expand Source, right-click on the package, 

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select New, 

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Other, expand Android, 

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select Android Activity, and click Next. 

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Click Next for the Blank Activity template,

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and let's name our second activity, 'Second Activity.' 

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Click Finish. 

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This creates 2 files for us, 

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the SecondActivity java file

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and the activity_second XML file,

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which is open here on the right. 

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Right-click on the hello_world text, and let's change it to

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This is Activity #2. 

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[typing]

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Click Okay,

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and to really make it stand out,

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let's change the background color, too. 

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Select the RelativeLayout parent in the outline, 

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then set the Background property to #00FF00. 

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Hit Enter, and this gives us a nice

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bright-green background that we will definitely notice. 

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Okay, let's save our changes here. 

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Now, let's open up MainActivity.java. 

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Open up our package, 

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double-click on the file,

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and we'll start by declaring a button. 

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Button switchButton =

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I'm going cast us a button

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from the findViewById method,

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and then our ID is button1.

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Okay. Organize my imports. 

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Now, let's add an onClick listener, which listens for a 

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click or tap and then runs some code for us. 

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Type: switchButton

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setOnClickListener,

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hit Enter,

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and we want a new View.OnClickListener, 

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hit Enter, and it drops in the code. 

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I'm going to scroll down

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and add a semicolon before I forget. 

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Now, let's add the code that we need

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to switch activities inside the onClick method. 

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In Android, we switch activities

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by using intents. 

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Intents are abstract descriptions

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of operations to be performed. 

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We will use an explicit intent

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which provides the exact class 

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to be run. 

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In this case, the class is our second activity. 

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So, back in Eclipse, 

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I'm going to delete this comment, 

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and add: Intent intent =

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new Intent 

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and for the parameters, type:

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MainActivity.this,

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SecondActivity.class.

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The first parameter is the current context,

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but since we're inside the onClick listener,

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which is known as an anonymous inner class, 

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we need to reference it by the full class name. 

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The second parameter is the name of our target class. 

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Okay, let's organize our imports,

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and, now, on a new line, type:

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startActivity,

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and the parameter is the intent we just created.

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That's it. 

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Save and Run. 

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Run it as an Android application, Click Okay. 

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Okay, let's tap on the button, and, 

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hurray, there's Activity #2,

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and we can use the Back button to go back to the first activity. 

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As you can see, switching activities is pretty easy

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once you have the activities created. 

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Intents like these are incredibly versatile

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and powerful and can make use of so many

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classes, apps, and services on your device. 

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Switching apps is just as easy as switching activities. 

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If you'd like to see more advanced videos and tutorials like this one, 

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go to TeamTreehouse.com and start learning for free. 

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[treehouse™]