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?Android Software Improvement
Chapter four. Underneath the Covers: Startup Code and Resources around the MJAndroid Software
Chapter 3 introduced the major software we use on this book to illustrate simple Android concepts. That chapter explained which information make up the source code, nonetheless it didnât actually cover any source code during the software. Weâll start off shopping at source code during this chapter. And to allow for you to definitely get started developing an software soon, weâll begin with the earliest task every standalone software has to perform: initialization.
The events covered in this particular chapter occur involving your selecting âRun As Android Applicationâ from the Eclipse menu and seeing the map that MJAndroid displays at startup. This chapter shows how Android makes it very simple to produce relatively complex purposes. In just 80 lines of code and some associated XML resource information, MJAndroid manages to:
Display an interactive map
Track the existing location from the Android phone and update the map
Build a local databases of guidance and load consumer preferences into it
Give a dynamically changing menu
Display person interface features this kind of as labels, buttons, and spinners
Run a new Activity to display a supporting screen
The Java code in an Android software interacts tightly with XML resource information, so weâll bounce again and forth relating to them in this particular chapter. As we point out repeatedly, XML information are easier to tweak during progress and retain over the life of an software. The create of Android encourages you to definitely specify the seem and behavior belonging to the software inside resource data files.
Initialization Parameters in AndroidManifest.xml
As Chapter 3 explained, we told Android to launch Microjobs.java because the initially Activity for MJAndroid. We defined that over the Software tab for the AndroidManifest.xml editor. The initial part for the XML code that successes from that choice is demonstrated right here:
This section of your chapter focuses within the XML with this file. The MicroJobs Activity is identified inside the manifest for the beginning from the file. This part belonging to the file is normally created in Eclipse in case you to start with formulate the Challenge that you just use to write down your software .
Like all suitable XML information, line 1 has the standard declaration of your XML version and therefore the character encoding employed. Before we get into the Activities that make up the MJAndroid software, we define just a few parameters and declare needed permissions for your whole software:
This is just the package name we gave when we created the software in Eclipse. It is also the default package for all the modules around the software.
This is definitely an integer that should always increment with each and every new version within the software. Every software should include a version code, and it should always be a monotonically increasing integer from version to version. This allows other programs (this kind of as Android Market, installers, and launchers) easily figure out which is the latest version of an software. The filename of your .apk file should include this same version quantity, so it is obvious which version it consists of.
This version identifier can be described as string, and it is intended to be considerably more like the version quantities you usually see for purposes. The naming convention is up to you, but generally the idea is to employ a scheme like m.n.o (for as most quantities as you should use), to identify successive ranges of change to the software. The idea is the fact this is the version identifier that would be displayed to some person (either by your software or another software).
There are four of these in MJAndroid, and they declare that the software intends to make use of capabilities of Android that require explicit permission from the person within the cell machine jogging the software. The permission is requested once the software is installed, and from then on Android remembers that the consumer explained it was OK (or not) to run this software and entry the secure characteristics. There are a good number of permissions now defined in Android, all described within the Android documentation (search for android.Manifest.permission ). Youâre able to also define your private permissions and use them to restrict other applicationsâ accessibility to functions with your software, unless the person grants one other software that permission. The permissions requested below are:
ACCESS_FINE_LOCATION. which is required to obtain location detail from the GPS sensor.
ACCESS_LOCATION_EXTRA_COMMANDS. The Android documentation doesnât tell us which location commands are âextra,â so weâll ask for all of these.
CALL_PHONE. This lets MJAndroid to request that the Dialer spot a cellular phone call on its behalf.
ACCESS_MOCK_LOCATION. so we can get fake location specifics when weâre functioning beneath the emulator.
INTERNET. so we can retrieve map tiles over an Internet link.
This is the filename for a PNG file that accommodates the icon youâd like to utilize to your software. In such a case weâre telling the Android SDK to glimpse for your icon file inside the drawable subdirectory with the res (resources) directory below MJAndroid. Android will use this icon in your software from the Android Desktop.
Turning our attention to the definition to the first of all (and main) Activity, MicroJobs, we first of all define two or three attributes for that Activity:
The name on the Activity. The 100 % name with the Activity incorporates the package name (which in our software is âcom.microjobsinc.mjandroid.MicroJobsâ), but since this file is always chosen on the packageâs namespace, we really don't need to have to include the leading package names. The Android SDK strips the package name down to â.MicroJobsâ when it creates this part of AndroidManifest.xml . and even the leading period is optional.
The label that we plan to appear within the top of your Android screen once the Activity is over the screen. We saw this before in HelloWorld, where we changed the string in strings.xml to match our software.
We then declare an intent filter that tells Android when this Activity should be run. We talked briefly about Intents in Chapter 1. and now we see them in use. As youâll recall, when Android encounters an Intent to fulfill, it looks among the for sale Activities and Products and services to choose something that can provider the Intent. We established two attributes:
Right now Android is trying to launch this software, so it is wanting for an Activity that declares itself wanting to resolve the MAIN action. Any software that is certainly going to be launched by the Launcher needs to have exactly a single Activity or Program that makes this assertion.
The Intent resolver in Android employs this attribute to further qualify the Intent that it is hunting for. In such a case, the qualification is weâd like for this Activity to be displayed inside Consumer Menu so the person can select it to begin this software. Specifying the LAUNCHER category accomplishes this. You are able to have a perfectly valid software without this attribute-you just wonât be able to launch it from the Android consumer interface. Normally, again, youâll have exactly one particular LAUNCHER for each software, and it will appear on the same intent filter since the opening Activity of your software.
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