Simple Android application from scratch in IntelliJ IDEA 10.5
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Contents |
Introduction
IntelliJ IDEA supports development of applications to be executed on mobile phones that run under the Android operating system. Besides general coding assistance, the IDE lets you test Android applications on user-configured emulators of physical devices.
IntelliJ IDEA helps:
- Create an Android application using the New Project Wizard.
- Explore an Android application as a tree-view of files and folders.
- Create elements of an Android application and manage static content resources, such as strings, colors, etc. via tight integration between resources and the R.java file.
- Run an application.
- Configure an emulator of a physical device to run Android applications on.
This tutorial will walk you step-by-step through developing and launching a simple Android application.
Prerequisites
- You are working with IntelliJ IDEA Ultimate edition version 10.5 or higher.
- Java SDK (JDK) and Android SDK are installed on your machine. This tutorial uses SDK 3.1.
Creating a New Project
Let’s start from the very beginning and create a project for our application.
Choose File | New Project on the main menu or click the Create New Project icon on the Welcome screen (Image 1).
On the first page of the New Project wizard (Image 2), make sure that the option Create project from scratch is selected.
On the second page of the wizard (Image 3), choose the parent folder (1) to create the project in and specify the name of the project (2). As you type the project name, IntelliJ IDEA updates the path to the location of the project files accordingly. Select the Create module check box (3) and choose Android Module (4) as the module type. By default, the module will have the same name (5) as the project. The name of our project and module will be android_hello_world.
On the third page of the wizard (Image 4), choose the Create source directory option (1) and accept the default name src (2) for it. IntelliJ IDEA displays the full path to the src folder (3) for your information.
Configuring Android SDK and Java SDK
On the fourth page of the wizard (Image 5), we’ll integrate IntelliJ IDEA with the Android SDK and specify the target Android platform for which the application is intended.
Previously, you could configure an Android SDK inside the Android module facet settings, while the JDK played the role of the main project/module SDK. IntelliJ IDEA 10.5 considers the Android platform itself as the project/module SDK.
Besides an Android SDK, you still need a JDK because IntelliJ IDEA uses it in compilation.
When you are creating a project for the first time after IntelliJ IDEA installation, no Android or Java SDKs are configured at the IDE level yet. This means that IntelliJ IDEA does not know the location of any Android SDK or Java SDK home directories, even if you have several of them on your computer.
To configure a Java SDK and an Android SDK at the IDE level, click the Browse button (1) next to the Android SDK drop-down list.
Click the Configure button and specify the location of the desired JDK in the Select Home Directory for JSDK dialog box that opens. When you click OK, you return to the wizard where the selected JDK is listed as the Project JDK. The specified JDK is now available at the IDE level. IntelliJ IDEA will treat this JDK as the default project JDK for any new project and will not bring you to this page anymore.
Configuring Java SDK
Let’s first configure a Java SDK. In the Configure SDK dialog box that opens (Image 6), click the Add toolbar button (1) and choose JSDK (2) from the list:
In the Select Home Directory for JSDK dialog box (Image 7), specify the folder where the relevant version of Java SDK is located (1):
Upon clicking OK (2), you return to the Configure SDK dialog box (Image 8), where the selected JDK is already on the list (1):
Configuring Android SDK
Click the Add toolbar button (1) again. This time, choose Android SDK (2) from the list (Image 9):
In the Select Home Directory for Android SDK dialog box (Image 10) that opens, specify the folder where the relevant version of Android SDK is located (1):
When you click OK (2), IntelliJ IDEA asks you to specify which version of Java SDK (JDK) configured at the IDE level you want to use in this project (Image 11):
We have just configured the first JDK after IntelliJ IDEA installation, so the list contains only one item (1). Just click OK.
In the dialog box that opens (Image 12), select the Android target platform. This is the Android platform for running on which your application will be intended. Choose Android 3.1 (1):
Upon clicking OK, you return to the Configure SDK dialog box (Image 13), where both new SDK configurations – the Java SDK (1) and the Android SDK (2) – are on the list:
Click OK (3). At last we are back to the fourth page of the wizard (Image 14). As you can see, IntelliJ IDEA has detected and recognized the newly configured Android SDK (1):
Completing Project Creation
Now let’s specify some additional set-up parameters for our project (Image 15).
- To have the data automatically arranged so the compiled application completely fits the selected platform, select the Create default Android application structure check box (1).
- Select the Application (2) project type. We are not going to share the module resources with other modules so there is no need to declare it as library project.
- Accept the suggested application name (3) and package (4).
- To have a sample application created, select the Create “Hello, World!” activity check box (5) and accept the suggested activity name MyActivity (6).
When you click Finish (7), IntelliJ IDEA creates a project and generates the skeleton of our application. First, let’s look deeper into its structure.
Note: If you still have not configured an Android SDK yet, you can do it right now. Choose File | Project Structure on the main menu, the click the SDKs node in the Project Structure dialog box, that opens, and configure the Android SDK as described above.
Exploring an Android Application
To explore our application, we’ll use the Project tool window (Image 16) that shows the following files and folders:
The .idea (1) folder contains a number of subfolders, mainly with internal IntelliJ IDEA information.
The src (2) folder contains the MyActivity.java (3) file source code that implements the functionality of your application. The file belongs to the com.example package.
The res (4) folder contains various visual resources.
- The layout/main.xml file (5) defines the appearance of the application constituted of resources of various types.
- The values folder (6) is intended for storing
.xmlfiles that describe resources of various types. Presently, the folder contains astrings.xmlfile withStringresources definitions. As you will see from the Adding a Color section, the layout folder can also contain, for example, a descriptor of colors.
- The drawable folders contain images (7).
The gen (8) folder contains the R.java (9) file that links the visual resources and the Java source code. As you will see from the sections below, IntelliJ IDEA supports tight integration between static resources and R.java. As soon as any resources are added or removed, the corresponding classes and class fields in R.java are automatically generated or removed accordingly. The R.java file also belongs to the com.example package.
Creating Elements of Your Application
To illustrate the mainstream Android development workflow in IntelliJ IDEA, let’s expand the stub “Hello world!” application with a piece of text to explain the main goals of the application. Let’s also define the color in which the explanation text will be displayed on the screen.
As you can see from Image 17, the source code of MyActivity.java (1) just references the layout/main.xml file (4) that defines the application appearance. To navigate to the referenced code, position the caret at the reference (2) and press Ctrl+B.
The main.xml file (4) opens.
As you can see, the text to be displayed is Hello World, MyActivity.
We need to add two things to the application layout: an explanation string and a color to display it.
Adding a String
In the main.xml file, place the following piece of code inside the <LinearLayout /> tag:
<TextView android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/explanation"
/>
As you can see (Image 18), IntelliJ IDEA reports an unresolved reference and highlights it red.
But IntelliJ IDEA also suggests a quick fix for the problem: just press Alt+Enter or click the red bulb (1), then choose Create resource explanation in strings.xml option (2) from the list (Image 19):
IntelliJ IDEA opens the strings.xml file where a new empty string definition is added to the list (Image 20).
Type the application description inside the <string /> tag, for example:
This simple Android application illustrates the mainstream Android development workflow in IntelliJ IDEA.
Image 21 illustrates the updated source code of the strings.xml file (1). If you click the Go to resource button 
(2) in the left gutter area, the R.java file (3) opens, with the new string added to the list of string resources (4) and the cursor positioned at this new resource:
Adding a Color
Now let’s define the color to display the explanation string, To do that, we will create a color resource file with a string_color definition (Image 22).
In the project tree, right click the values folder (1) and choose New (2) | Values resource file (3) on the context menu. In the New values resource file dialog that opens, specify color as the new file name (4).
When you click OK, IntelliJ IDEA displays the new file in the project tree (Image 23):
Now, let’s add a string_color resource definition. Open the color.xml file in the editor by double-clicking it in the Project tool window.
Inside the <resources /> tag, type the color definition in the form:
<color name="string_color">hexadecimal identifier of the desired color prepended with #</color>
In our example (Image 24), the hexadecimal identifier is #ff00ff77.
As you type the color definition (1), IntelliJ IDEA shows the preview of the specified color (2) in the left gutter area:
As you might have guessed, the new resource definition is automatically reflected in R.java (Image 25):
Now, let’s apply the new color to the explanation string. In the main.xml file, locate the following <TextView /> item:
<TextView android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/explanation"
/>
and add the following code inside it below android:text="@string/explanation":
android:textColor="@color/string_color"
That’s all with developing the sources of our application.
Running Android Application
During the project creation, IntelliJ IDEA has generated the default run configuration android_hello_world. To launch the application straight away, we only need to configure a virtual device to run it on. This device will emulate execution of the application on the target physical device.
Configuring a Virtual Android Device
From the Run/Debug Configuration (Image 26) drop-down list on the toolbar, choose Edit Configurations (1).
IntelliJ IDEA opens the Run/Debug Configurations dialog box (Image 27) that shows the details of the default android_hello_world run configuration (1).
As you can see, IntelliJ IDEA has already selected the module hello_world(2) to apply the configuration to and the activity to launch (3).
Make sure the Deploy application check box (4) is selected and the Choose target device manually check box (5) is cleared.
Click the Browse button next to the Prefer Android Virtual Device for Deployment drop-down list (6). In the Select Android Virtual Device dialog box (Image 28) that opens. click Create:
The Create Android Virtual Device dialog box (Image 20) opens. Accept the suggested device name MyAvd0 (1) and Android 3.1 as the target platform (2):
The target platform must be the one appointed during the module Android SDK configuration.
When you click OK, IntelliJ IDEA brings you to the Select Android Virtual Device dialog box (Image 30), where the virtual device you’ve defined is already added to the list and selected.
Click OK to save the settings and return to the Run/Debug Configurations dialog box (Image 31), where the Prefer Android Virtual Device for Deployment drop-down list (1) now shows the emulator you’ve defined.
Complete the configuration definition settings by clicking OK.
Fortunately, you need to configure a virtual device only once, during the first application start. IntelliJ IDEA will use it by default when you start your application with the android_hello_world run configuration. Moreover, IntelliJ IDEA remembers this virtual device at the IDE level so you can use it for running other applications.
Start Application
Now that we are through with all the preliminary steps, let’s launch our application.
On the toolbar (Image 32), click 
(2) next to the Run/Debug Configuration (1) drop-down list where the android_hello_world run configuration is already selected by default.
IntelliJ IDEA launches the configured emulator (Image 33) and deploys the Hello world application on it:
Click the lock symbol twice to have the application output displayed (Image 34):
Congratulations! You have developed and launched a simple Android application.
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