ANDROID 3.0 APPLICATION DEVELOPMENT COOKBOOK PDF
What is it in the nature of reality and of mind that makes self- esteem an urgent concern? This is where our inquiry be Sams Teach Yourself Android. Android™ Application development cookbook: 93 Recipes for Building Winning . With the Android SDK and the ADT Plugin , it is now much easier to . As a book written to help jump-start beginning Android developers, it covers the Chapter 3: Getting to Know the Android User Interface covers the various.
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Download as PDF, TXT or read online from Scribd. Flag for inappropriate . More information on Android Application Development Cookbook Second Edition Android added features to take advantage of the growing tablet market. This book is written to help jump-start beginning Android developers, Android Studio to develop Android applications, and then you see how to test them on You also find out about the specialized fragments available in Android The Android Developer's Cookbook — Building Applications with the Android Android — Application Development Cookbook ().pdf.
How it works Any activities or any other component for that matter that are not declared in the manifest will not be included in the application. Attempting to access or utilize an undeclared component will result in an exception being thrown at runtime.
In the preceding code, there is another attributeandroid: This attribute indicates the title shown on the screen as well as the icon label if this is the Launcher activity. For a complete list of available application attributes, take a look at this resource: Starting a new activity with an intent object The Android application model can be seen as a service-oriented one, with activities as components and intents as the messages sent between them.
Here, an intent is used to start an activity that displays the user's call log, but intents can be used to do many things and we will encounter them throughout this book.
Getting ready To keep things simple, we are going to use an intent object to start one of Android's built-in applications rather than create a new one.
This only requires a very basic application, so start a new Android project with Android Studio and call it ActivityStarter. Again, to keep the example simple so that we can focus on the task at hand, we will create a function to show an intent in action and call this function from a button on our activity. Once your new project is created in Android Studio, follow these steps: Open the MainActivity.
While you are typing this code, Android Studio will give this warning on View and intent: Cannot resolve symbol 'Intent'. This means that you need to add the library reference to the project. You can do this manually by entering the following code in the import section: View; import android.
Chapter 1 android: Now it's time to run the application and see the intent in action. When you press the Launch Browser button, you will see the default web browser open with the URL specified.
Though simple, this app demonstrates much of the power behind the Android OS.
The intent object is just a message object. Intents can be used to communicate across your application's components such as services and broadcast receivers as well as with other applications on the device as we did in this recipe. To test on a physical device, you may need to install drivers for your device the drivers are specific to the hardware manufacturer. You will also need to enable Developer Mode on your device. If you do not see the Developer Mode option in your device settings, open the About Phone option and begin tapping Build Number.
After three taps, you should see a Toast message telling you that you are on your way to be a developer. Four more taps will enable the option. You may have noticed that when you typed Intent and then the period, Android Studio provided a pop-up list of possibilities this is the autocomplete feature , like this:. In this example, our intent is just to view the URL, so we call the intent with just the startActivity method. There are other ways to call the intent depending on our needs.
In the Returning a result from an activity recipe, we will use the startActivityForResult method. There's more It's very common for Android users to download their favorite apps for web browsing, taking photos, text messaging, and so on. Using intents, you can let your app utilize your user's favorite apps instead of trying to reinvent all of this functionality.
See also To start an activity from a menu selection, refer to the Handling menu selections recipe in Chapter 4, Menus. Switching between activities Often we will want to activate one activity from within another activity.
Although this is not a difficult task, it will require a little more setting up to be done than the previous recipes as it requires two activities.
We will create two activity classes and declare them both in the manifest. We'll also create a button, as we did in the previous recipe, to switch to the activity.
Getting ready We'll create a new project in Android Studio, just as we did in the previous recipes, and call this one ActivitySwitcher. Android Studio will create the first activity, ActivityMain, and automatically declare it in the manifest.
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Since the Android Studio New Project wizard has already created the first activity, we just need to create the second activity. Activities 2. In the Customize the Activity dialog, you can leave the default Activity Name as it is, which is Main2Activity, or change it to SecondActivity, as shown here:. You can actually run the code at this point and see the second activity come up. We're going to go further and add a button to SecondActivity to close it, which will bring us back to the first activity.
Open the SecondActivity. Finally, add the Close button to the SecondActivity layout. The real work of this exercise is in the onClickSwitchActivity method from Step 3. This is where we declare the second activity for the intent using SecondActivity. We went one step further by adding the close button to the second activity to show a common real-world situationlaunching a new activity, then closing it, and returning to the original calling activity. This behavior is accomplished in the onClickClose function.
All it does is call finish , but that tells the system that we're done with the activity. Finish doesn't actually return us to the calling activity or any specific activity for that matter; it just closes the current activity and relies on the back stack. If we want a specific activity, we can again use the intent object we just change the class name while creating the intent.
This activity switching does not make a very exciting application. Our activity does nothing but demonstrate how to switch from one activity to another, which of course will form a fundamental aspect of almost any application that we develop.
Activities If we had manually created the activities, we would need to add them to the manifest.
To see what Android Studio did, open the AndroidManifest. SecondActivity" android: The main activity is generally the entry point when starting the application.
To learn more about embedding widgets such as the Button, visit Chapter 3, Views, Widgets, and Styles.
Passing data to another activity The intent object is defined as a messaging object. As a message object, its purpose is to communicate with other components of the application. In this recipe, we'll show you how to pass information with the intent and how to get it out again.
Getting ready This recipe will pick up from where the previous one ended. We will call this project SendData. Since this recipe is building on the previous recipe, most of the work is already done.
We'll add an EditText element to the main activity so that we have something to send to SecondActivity. We'll use the autogenerated TextView view to display the message. Here are the complete steps: Chapter 1 1. Now, open the MainActivity. The last change is to edit the second activity to look for this new data and display it on the screen. Open SecondActivity. Now run the project. Type some text on the main activity and press Launch Second Activity to see it send the data.
As expected, the intent object is doing all the work. We created an intent just as in the previous recipe and then added some extra data.
Did you notice the putExtra method call? In our example, we used the already defined Intent. That's why we used the same key identifier when we read the extra data with getStringExtra. The second activity was launched with the intent that we created, so it's simply a matter of getting the intent and checking for the data sent along with it.
We do this in onCreate: We aren't limited to just sending String data. The intent object is very flexible and already supports basic data types. Go back to Android Studio and click on the putExtra method. Then hit Ctrl and the Spacebar. Android Studio will bring up the autocomplete list so that you can see the different data types that you can store. Returning a result from an activity Being able to start one activity from another is all well and good, but we will often need to know how the called activity has fared in its task or even which activity has been called.
The startActivityForResult method provides the solution. Getting ready Returning a result from an activity is not very different from the way we just called the activity in the previous recipes. You can either use the project from the previous recipe, or start a new project and call it GettingResults.
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Either way, once you have a project with two activities and the code needed to call the second activity, you're ready to begin. There are only a few changes needed to get the results: First of all, open MainActivity.
Chapter 1 2. Next, change the way the intent is called by modifying the onClickSwitchActivity method to expect a result: Then, add this new method to receive the result: Finally, modify onClickClose in SecondActivity.
As you can see, getting the results back is relatively straightforward.
We just call the intent with startActivityForResult, so it knows that we want a result. We set up the onActivityResult callback handler to receive the results. Finally, we make sure that the second activity returns a result with setResult before closing the activity. In this example, we are just setting a result with a static value. We just display what we receive to demonstrate the concept.
Activities It's good practice to check the result code to make sure that the user didn't cancel the action. It's technically an integer, but the system uses it as a boolean value. In our example, the second activity doesn't have a cancel button, so why bother to check? What if the user hits the back button? We made use of the Toast object, which is a convenient pop-up message that can be used to unobtrusively notify the user. It also functions as a handy method for debugging as it doesn't need a special layout or screen space.
Besides the result code, onActivityResults also includes a Request Code. Are you wondering where that came from?
Android 3.0 Application Development Cookbook
It is simply the integer value that was passed with the startActivityForResult call, which takes this form: We didn't check the request code because we knew we had only one result to handlebut in trivial applications with several activities, this value can be used to identify where the request originated. If startActivityForResult is called with a negative request code, it will behave exactly as if it were a call to startActivity that is, it will not return a result.
To learn more about creating new activity classes, refer to the Switching between activities recipe.
Saving an activity's state The mobile environment is very dynamic, with users changing tasks much more often than on desktops. With generally fewer resources on a mobile device, it should be expected that your application will be interrupted at some point.
It's also very possible that the system will shut down your app completely to give additional resources to the task at hand. It's the nature of mobiles. Chapter 1 A user might start typing something in your app, be interrupted by a phone call, or switch over to another app to send a text message, and by the time they get back to your app, the system may have closed it down completely to free up the memory.
To provide the best user experience, you need to expect such behavior and make it easier for your user to resume from where they left off. The good thing is that the Android OS makes this easier by providing callbacks to notify your app of state changes. Simply rotating your device will cause the OS to destroy and recreate your activity. This might seem a bit heavy-handed, but it's done for good reasonit's very common to have different layouts for portrait and landscape, so this ensures that your app is using the correct resources.
In this recipe, you'll see how to handle the onSaveInstanceState and onRestoreInstanceState callbacks to save your application's state. We will demonstrate this by creating a counter variable and increment it each time the Count button is pressed. We will also have an EditText and a TextView widget to see their default behavior.
We need only a single activity, so the autogenerated main activity is sufficient. Activities android: Perform the following set of steps: To keep track of the counter, we need to add a global variable to the project, along with a key for saving and restoring.
Add the following code to the MainActivity. Then add the code needed to handle the button press; it increments the counter and displays the result in the TextView widget: To receive notifications of application state change, we need to add the onSaveInstanceState and onRestoreInstanceState methods to our application.
Open MainActivity. All activities go through multiple states during their lifetime. By setting up callbacks to handle the events, we can have our code save important information before the activity is destroyed. Step 3 is where the actual saving and restoring occurs.
But wait! Did you try typing text in the EditText view before rotating the device? If so, you'd have noticed that the text was also restored, but we don't have any code to handle that view. By default, the system will automatically save the state, provided it has a unique ID not all views automatically have their state saved, such as the TextView, but we can manually save it if we want.
Note that if you want Android to automatically save and restore the state of a view, it must have a unique ID specified with the android: Beware; not all view types automatically save and restore the state of a view.
The onRestoreInstanceState callback is not the only place where the state can be restored. Look at the signature of onCreate: Both methods receive the same Bundle instance named savedInstanceState. You could move the restore code to the onCreate method and it would work the same. But one catch is that the savedInstanceState bundle will be null if there is no data, such as during the initial creation of the activity.
If you want to move the code from the onRestoreInstanceState callback, just check to make sure that the data is not null, as follows: Storing persistent activity data Being able to store information about our activities on a temporary basis is very useful, but more often than not, we will want our application to remember information across multiple sessions.
Android supports SQLite, but that could be a lot of overhead for simple data, such as the user's name or a high score. Fortunately, Android also provides a lightweight option for these scenarios, with SharedPreferences.
Getting ready You can either use the project from the previous recipe or start a new project and call it PersistentData in a real-world application, you'll likely be doing both anyway. In the previous recipe, we saved mCounter in the session state. In this recipe, we'll add a new method to handle onPause and save mCounter to SharedPreferences.
We'll restore the value in onCreate. We have only two changes to make, and both are in MainActivity. Add the following onPause method to save the data before the activity closes: Then add the following code at the end of onCreate to restore the counter: In , he left the corporate world to start his own consulting business, NightSky Development.
He now focuses exclusively on Android and provides consulting and development for start-ups and small businesses. Feel free to contact him through his page, www.
Kyle Mew has been programming since the early eighties and has written for several technology websites. He has also written three radio plays and two other books on Android development. Android was first released in after being acquired by Google, Inc. Initially, Android was primarily used on a handset. Android 3. In , Google announced that Android had over 1 billion active users! With over 1 million applications available on Google Play, there's never been a more exciting time to join the Android community!
As we begin , we have the recently released Android 6. Chapter 1, Activities, discusses Activities, which represent the fundamental building blocks for most applications. See examples of the most common tasks, such as creating an activity and passing control from one activity to another.
Android Application Development Cookbook - Second Edition - Sample Chapter
Chapter 2, Layouts, talks about Layout options; while Activities are fundamental to the UI, the layout actually defines what the user sees on the screen. Learn the main layout options available and best practices. Chapter 3, Views, Widgets, and Styles, explores the basic UI object, from which all layouts are built. Widgets include everything from buttons and textboxes to more complicated NumberPicker and Calendar dialogs. Chapter 4, Menus, teaches you how to use menus in Android.With activity design covered, the book continues to guide the reader through application logic development, exploring the latest APIs provided by the SDK.
Declaring an activity Activities and other application components, such as services, are declared in the AndroidManifest XML file. With this extensively updated cookbook, you'll find solutions for working with the user interfaces, multitouch gestures, location awareness, web services, and device features such as the phone, camera, and accelerometer.
Mar 20, See also To start an activity from a menu selection, refer to the Handling menu selections recipe in Chapter 4, Menus. If nothing happens, download Xcode and try again. In this example, we are just setting a result with a static value. When viewing this xml within Android Studio, you may notice that the label element shows the actual text as defined in the strings. Launching Visual Studio
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