自定义Attributes

Currently the best documentation is the source. You can take a look at ithere (attrs.xml).

You can define attributes in the top<resources>element or inside of a<declare-styleable>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<declare-styleable>element it can be used outside of it and you cannot create another attribute with the same name of a different type.

An<attr>element has two xml attributesnameandformat.namelets you call it something and this is how you end up referring to it in code, e.g.,R.attr.my_attribute. Theformatattribute can have different values depending on the 'type' of attribute you want.

reference - if it references another resource id (e.g, "@color/my_color", "@layout/my_layout")
color
boolean
dimension
float
integer
string
fraction
enum - normally implicitly defined
flag - normally implicitly defined

You can set the format to multiple types by using|, e.g.,format="reference|color".

enumattributes can be defined as follows:

<attr name="my_enum_attr">  <enum name="value1" value="1" />  <enum name="value2" value="2" /> </attr>

flagattributes are similar except the values need to be defined so they can be bit ored together:

<attr name="my_flag_attr">  <flag name="fuzzy" value="0x01" />  <flag name="cold" value="0x02" /> </attr>

In addition to attributes there is the<declare-styleable>element. This allows you to define attributes a custom view can use. You do this by specifying an<attr>element, if it was previously defined you do not specify theformat. If you wish to reuse an android attr, for example, android:gravity, then you can do that in thename, as follows.

An example of a custom view<declare-styleable>:

<declare-styleable name="MyCustomView">  <attr name="my_custom_attribute" />  <attr name="android:gravity" /> </declare-styleable>

When defining your custom attributes in XML on your custom view you need to do a few things. First, declare a namespace to find your attributes. You do this on the top layout element. Normally there is thexmlns:android="http://schemas.android.com/apk/res/android"well you must also doxmlns:whatever="http://schemas.android.com/apk/res/org.example.mypackage". Theorg.example.mypackageis the root package as it is defined in yourAndroidManifest.xml.

Example:

<?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/org.example.mypackage"  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>

Finally, to access that custom attribute you normally do so in the constructor of your custom view as follows.

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(); }

The end. :)

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