Resources
Android supports that resources, like images and
certain XML configuration files, can be keep separate from the source code.
These resources must be defined in the res directory
in a special folder dependent on their purpose. You can also append additional
qualifiers to the folder name to indicate that the related resources should be
used for special configurations, e.g. you can specify that a resource is only
valid for a certain screen size.
The following table give an overview of the
supported resources and their standard folder prefix.
|
Resource
|
Folder
|
Description
|
|
Simple Values
|
/res/values
|
Used to define strings, colors, dimensions, styles and static arrays
of strings or integers. By convention each type is stored in a separate file,
e.g. strings are defined in theres/values/strings.xml file.
|
|
Layouts
|
/res/values
|
XML file with layout description files used to define the user
interface for activities and Fragments.
|
|
Styles and Themes
|
/res/values
|
Files which define the appearance of your Android application.
|
|
Animations
|
/res/animator
|
Define animations in XML for the property animation API which allows
to animate arbitrary properties of objects over time.
|
|
Menus
|
/res/menu
|
Define the properties of entries for a menu.
|
The gen directory in an Android
project contains generated values. R.java is a generated class
which contains references to certain resources of the project.
If you create a new resource, the corresponding
reference is automatically created in R.java via the Eclipse
ADT tools. These references are static integer values and define IDs for the
resources.
The Android system provides methods to access the
corresponding resource via these IDs.
For example to access a String with the R.string.yourString ID,
you would use thegetString(R.string.yourString)) method.
R.java is
automatically created by the Eclipse development environment, manual changes
are not necessary and will be overridden by the tooling.
Assets
While the res directory contains
structured values which are known to the Android platform, the assets directory
can be used to store any kind of data. You access this data via the AssetsManager which
you can access the getAssets()method.
AssetsManager allows to read an assets
as InputStream with the open() method.
//
Get the AssetManager
AssetManager manager = getAssets();
//
Read a Bitmap from Assets
InputStream open = null;
try {
open = manager.open("logo.png");
Bitmap bitmap =
BitmapFactory.decodeStream(open);
//
Assign the bitmap to an ImageView in this layout
ImageView view = (ImageView)
findViewById(R.id.imageView1);
view.setImageBitmap(bitmap);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (open != null) {
try {
open.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
Defining IDs
Android allows that you define ID of user interface
components dynamically in the layout files, via the @+id/your_idnotation.
To control your IDs you can also create a file
called ids.xml in your /res/values folder and
define all IDs in this file.
<?xml
version="1.0" encoding="utf-8"?>
<resources>
<item name="button1" type="id"/>
</resources>
This allow you to use the ID directly in your
layout file.
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >
<Button
android:id="@id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:layout_marginRight="27dp"
android:text="Button" />
</RelativeLayout>
