How is declare-stylable name linked to the view that uses its attributes?

Question

Usually al examples of custom attributes are of the form:

<declare-stylable name="MyView">
    <attr name="name" format="string"/>
</declare-styleable>  

and its usage:

<com.example.test.MyView
    customns:name="Hello"/>

So the custom view has the same name as the stylable attributes.

But in this example (click for full code) you see:

<declare-styleable name="Options">
    <attr name="titleText" format="string" localization="suggested" />
    <attr name="valueColor" format="color" />
</declare-styleable>

used by:

<com.vogella.android.view.compoundview.ColorOptionsView
    android:layout_width="match_parent"
    android:layout_height="?android:attr/listPreferredItemHeight"
    custom:titleText="Background color"
    custom:valueColor="@android:color/holo_green_light"
    />

It made me wonder, how is it that ColorOptionsView was linked to the attributes defined with name Options?

Answer 1

Those options are available as part of the declared namespace custom, which is included at the top of the XML file:

xmlns:custom="http://schemas.android.com/apk/res/com.vogella.android.view.compoundview"

NOTE

Simply adding this line will not provide support for auto-complete. If that is what your mean by your question, you need to add the schema to your workspace's XML Catalog. You can do this in Eclipse by going to Eclipse -> Preferences, then XML -> XML Catalog. Here, click the Add... button. Navigate to the XML Schema file, then select OK. If you close and re-open the the XML file, you will now have autocompletion.

---

Finally, when unpacking the attributes used in ColorOptionsView.java, the author can specifically look for attributes from this namespace. This is from the same source (commented by me):

//grab the declared-styleable resource entries
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.Options, 0, 0);
//get the "titleText" entry from this element's attributes
String titleText = a.getString(R.styleable.Options_titleText);
//get the "valueColor" attribute. If it does not exists, set the default to holo_blue_light
int valueColor = a.getColor(R.styleable.Options_valueColor,
    android.R.color.holo_blue_light);
a.recycle();