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copied!<p>Currently the best documentation is the source. You can take a look at it <a href="https://github.com/android/platform_frameworks_base/blob/master/core/res/res/values/attrs.xml" rel="noreferrer">here (attrs.xml)</a>. </p> <p>You can define attributes in the top <code><resources></code> element or inside of a <code><declare-styleable></code> element. If I'm going to use an attr in more than one place I put it in the root element. Note, all attributes share the same global namespace. That means that even if you create a new attribute inside of a <code><declare-styleable></code> element it can be used outside of it and you cannot create another attribute with the same name of a different type.</p> <p>An <code><attr></code> element has two xml attributes <code>name</code> and <code>format</code>. <code>name</code> lets you call it something and this is how you end up referring to it in code, e.g., <code>R.attr.my_attribute</code>. The <code>format</code> attribute can have different values depending on the 'type' of attribute you want. </p> <ul> <li>reference - if it references another resource id (e.g, "@color/my_color", "@layout/my_layout")</li> <li>color</li> <li>boolean</li> <li>dimension</li> <li>float</li> <li>integer</li> <li>string</li> <li>fraction</li> <li>enum - normally implicitly defined</li> <li>flag - normally implicitly defined</li> </ul> <p>You can set the format to multiple types by using <code>|</code>, e.g., <code>format="reference|color"</code>.</p> <p><code>enum</code> attributes can be defined as follows:</p> <pre><code><attr name="my_enum_attr"> <enum name="value1" value="1" /> <enum name="value2" value="2" /> </attr> </code></pre> <p><code>flag</code> attributes are similar except the values need to be defined so they can be bit ored together:</p> <pre><code><attr name="my_flag_attr"> <flag name="fuzzy" value="0x01" /> <flag name="cold" value="0x02" /> </attr> </code></pre> <p>In addition to attributes there is the <code><declare-styleable></code> element. This allows you to define attributes a custom view can use. You do this by specifying an <code><attr></code> element, if it was previously defined you do not specify the <code>format</code>. If you wish to reuse an android attr, for example, android:gravity, then you can do that in the <code>name</code>, as follows.</p> <p>An example of a custom view <code><declare-styleable></code>:</p> <pre><code><declare-styleable name="MyCustomView"> <attr name="my_custom_attribute" /> <attr name="android:gravity" /> </declare-styleable> </code></pre> <p>When defining your custom attributes in XML on your custom view you need to do a few things. First you must declare a namespace to find your attributes. You do this on the root layout element. Normally there is only <code>xmlns:android="http://schemas.android.com/apk/res/android"</code>. You must now also add <code>xmlns:whatever="http://schemas.android.com/apk/res-auto"</code>.</p> <p>Example:</p> <pre><code><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:whatever="http://schemas.android.com/apk/res-auto" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <org.example.mypackage.MyCustomView android:layout_width="fill_parent" android:layout_height="wrap_content" android:gravity="center" whatever:my_custom_attribute="Hello, world!" /> </LinearLayout> </code></pre> <p>Finally, to access that custom attribute you normally do so in the constructor of your custom view as follows.</p> <pre><code>public MyCustomView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.MyCustomView, defStyle, 0); String str = a.getString(R.styleable.MyCustomView_my_custom_attribute); //do something with str a.recycle(); } </code></pre> <p>The end. :)</p>

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