Book Image

Android Application Development Cookbook - Second Edition

By : Kyle Mew
Book Image

Android Application Development Cookbook - Second Edition

By: Kyle Mew

Overview of this book

The Android OS has the largest installation base of any operating system in the world; there has never been a better time to learn Android development to write your own applications, or to make your own contributions to the open source community! This “cookbook” will make it easy for you to jump to a topic of interest and get what you need to implement the feature in your own application. If you are new to Android and learn best by “doing,” then this book will provide many topics of interest. Starting with the basics of Android development, we move on to more advanced concepts, and we’ll guide you through common tasks developers struggle to solve. The first few chapters cover the basics including Activities, Layouts, Widgets, and the Menu. From there, we cover fragments and data storage (including SQLite), device sensors, the camera, and GPS. Then we move on more advanced topics such as graphics and animation (including OpenGL), multi-threading with AsyncTask, and Internet functionality with Volley. We’ll also demonstrate Google Maps and Google Cloud Messaging (also known as Push Notifications) using the Google API Library. Finally, we’ll take a look at several online services designed especially for Android development. Take your application big-time with full Internet web services without having to become a server admin by leveraging the power of Backend as a Service (BaaS) providers.
Table of Contents (23 chapters)
Android Application Development Cookbook Second Edition
Credits
Disclaimer
About the Authors
About the Reviewer
www.PacktPub.com
Preface
Index

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.

How to do it...

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:

  1. Open activity_main.xml, remove the existing <TextView> element, and add the following <EditText> element:

    <EditText
        android:id="@+id/editTextData"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

    The <Button> element that we created in the previous recipe doesn't change.

  2. Now, open the MainActivity.java file and change the onClickSwitchActivity() method as follows:

    public void onClickSwitchActivity(View view) {
        EditText editText = (EditText)findViewById(R.id.editTextData);
        String text = editText.getText().toString();
        Intent intent = new Intent(this, SecondActivity.class);
        intent.putExtra(Intent.EXTRA_TEXT,text);
        startActivity(intent);
    }
  3. Next, open the activity_second.xml file and modify the<TextView> element to include the ID attribute:

    <TextView
        android:id="@+id/textViewText"
        android:text="@string/hello_world"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
  4. The last change is to edit the second activity to look for this new data and display it on the screen. Open SecondActivity.java and edit onCreate() as follows:

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        TextView textView = (TextView)findViewById(R.id.textViewText);
        if (getIntent()!=null && getIntent().hasExtra(Intent.EXTRA_TEXT)) {
            textView.setText(getIntent().getStringExtra(Intent.EXTRA_TEXT));
        }
    }
  5. Now run the project. Type some text on the main activity and press Launch Second Activity to see it send the data.

How it works...

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.EXTRA_TEXT as the identifier, but we didn't have to. We can use any key we want (you've seen this concept before if you're familiar with name/value pairs).

The key point about using name/value pairs is that you have to use the same name to get the data back out. 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():

textView.setText(getIntent().getStringExtra(Intent.EXTRA_TEXT));

There's more...

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.