这个Android可绘制背景资源是什么？

Question

I have just started learning Android, currently going through the tutorials on the Google Android developer website, so far not that impressed as there are a lot of things that go unexplained.

On the tutorial "Styling the Action Bar", it has the following XML style resource:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <!-- the theme applied to the application or activity -->
    <style name="CustomActionBarTheme"
           parent="@style/Theme.AppCompat.Light.DarkActionBar">
        <item name="android:actionBarStyle">@style/MyActionBar</item>

        <!-- Support library compatibility -->
        <item name="actionBarStyle">@style/MyActionBar</item>
    </style>

    <!-- ActionBar styles -->
    <style name="MyActionBar"
           parent="@style/Widget.AppCompat.Light.ActionBar.Solid.Inverse">
        <item name="android:background">@drawable/actionbar_background</item>

        <!-- Support library compatibility -->
        <item name="background">@drawable/actionbar_background</item>
    </style>
</resources>

(Android 2.1+ support)

At no point does it mention what the @drawable/actionbar_background is meant to be? As it is @drawable is this an image? I wouldn't understand why it would be as it's meant to be colouring the action bar background.

Any help would be greatly appreciated!!!!!!! :)

Answer 1

The line

<item name="background">@drawable/actionbar_background</item>

translates to English like

Add to this style an item representing a property called "background". As the value of this property, set a resource of type "drawable" with name "actionbar_background".

In this case the script will look for an image in the resources folder "drawable" the name of which matches the given one. If the line was

<item name="text">@string/actionbar_title</item>

The script would look in res/values for a resource defined as <string> with "name" property "actionbar_title".

Answer 2

In the layout files for Android, the '@' symbol followed by a word like 'drawable' or 'style', refers to a path and file in the res or resource folder.

http://developer.android.com/guide/topics/resources/drawable-resource.html

Answer 3

<item name="android:background">@drawable/actionbar_background</item> sets your actionBar's background to drawable(image) resource which is located in your project -> drawable folders.

I guess you can also use color to set your background like this: <item name="android:background">@android:color/black</item>