How can I create my custom properties on xml for Android?

Question

We have in our project a keyboard with "Key" elements, this Key elements have attributes such as android:codes="119", android:keyLabel="w" and so on.

My question is how can I include an custom attribute like a "android:alternativeKeyLabel" to do something else.

Answer 1

This link gives a superficial explanation: http://developer.android.com/guide/topics/ui/custom-components.html

Considering you have a CustomKeyboard that inherits from KeyboardView/View:

1. Create your custom properties in res/values/attrs.xml file (create the file if it does not exist):

<?xml version="1.0" encoding="utf-8"?> <resources>    <declare-styleable name="custom_keyboard">         <attr name="alternative_key_label" format="string" />     </declare-styleable>  </resources> 

1. Create a constructor in your custom component overriding default constructor that receives the attribute set because this one will be called when the layout is loaded.

   public CustomKeyboard(Context context, AttributeSet set) {     super(context, set);     TypedArray a = context.obtainStyledAttributes(set,R.styleable.custom_keyboard);     CharSequence s = a.getString(R.styleable.custom_keyboard_alternative_key_label);     if (s != null) {         this.setAlternativeKeyLabel(s.toString());     }     a.recycle(); } 

2. In your layout file, add your custom component and the link to your resources.

 <Layout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:app="http://schemas.android.com/apk/res/your.package.ProjectName"     .../>     ...     <your.package.projectname.CustomKeyboard         android:id="@+id/my_keyboard"         ...         app:alternative_key_label="F">     </your.package.projectname.CustomKeyboard> </Layout> 

Answer 2

For any other purpose, declaring a custom property in the XML file can be retrieve with attrs constructor parameter.

In my case I reuse a preference custom dialog, and set things like that:

<?xml version="1.0" encoding="utf-8"?> <!-- something here --> <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" >     <your.package.projectname.CustomView         foo="bar"     /> </PreferenceScreen> 

Then in my class contructor:

public CustomView(Context context, AttributeSet attrs) {     String bar = attrs.getAttributeValue(null, "foo");     Log.d("CustomView", "foo=" + bar); }