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

We have in our project a keyboard with "Key" elements, this Key elements have 开发者_StackOverflowattributes 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.

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>

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);
}

You can create custom attributes for your own classes that extend View or a subclass. The process is documented in the "Creating a View Class" section of the Android Dev Guide under the heading "Define Custom Attributes":

https://developer.android.com/training/custom-views/create-view#customattr

android:keyLabel is one of many XML attribute used by the Keyboard.Key class for each key on your keyboard. android:keyLabel is what you want to label the key with (like a "w" as in above). The attributes are pre-defined for the class. The "w" isn't but android:keyLabel is. If you could create android:alternativeKeyLabel what would you expect the class to do with it? I think maybe you should try to explain further what you are trying to accomplish.