How to define an array of integers in a declare-styleable?

Defining an Array of Integers in a Declare-styleable

Overview

The declare-styleable resource is a powerful mechanism in Android for customizing views and components. While it primarily handles individual attributes, we can cleverly leverage it to work with arrays of integers.

Defining the Array Attribute

<resources>
  <declare-styleable name="MyCustomView">
    <attr name="array_of_integers" format="integer-array" />
  </declare-styleable>
</resources>

• declare-styleable: Defines the custom attributes for a specific view.
• name: Specifies the name of the view (e.g., “MyCustomView”).
• attr: Defines a single attribute within the view’s styleable.
• name: The name of the attribute (e.g., “array_of_integers”).
• format="integer-array": This crucial part indicates that the attribute will store an array of integers.

Providing Values in XML

<com.example.myapp.MyCustomView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:array_of_integers="@array/my_integer_array" />

• The attribute is defined as app:array_of_integers because we’re using the “app” namespace.
• @array/my_integer_array: This points to a resource defined in your arrays.xml file.

Defining the Integer Array Resource

<resources>
  <integer-array name="my_integer_array">
    <item>1</item>
    <item>5</item>
    <item>10</item>
  </integer-array>
</resources>

• integer-array: This tag tells Android to interpret the content as an array of integers.
• item: Each individual integer value within the array is wrapped in an item tag.

Retrieving the Integer Array in Java

public class MyCustomView extends View {
  // ...

  @Override
  protected void onAttachedToWindow() {
    super.onAttachedToWindow();

    TypedArray typedArray = getContext().obtainStyledAttributes(
        attrs, R.styleable.MyCustomView);

    int[] integerArray = typedArray.getIntArray(
        R.styleable.MyCustomView_array_of_integers);

    // Use the integerArray as needed
    // ...

    typedArray.recycle();
  }
}

• obtainStyledAttributes(): Retrieve the custom attributes defined in your declare-styleable.
• getIntArray(): This specific method extracts the integer array value from the TypedArray.
• R.styleable.MyCustomView_array_of_integers: This refers to the identifier of the “array_of_integers” attribute you defined.

Example:

<resources>
  <declare-styleable name="MyView">
    <attr name="myArray" format="integer-array" />
  </declare-styleable>
  <integer-array name="my_array">
    <item>1</item>
    <item>2</item>
    <item>3</item>
  </integer-array>
</resources>

<com.example.myapp.MyView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:myArray="@array/my_array" />

public class MyView extends View {
  // ...

  @Override
  protected void onAttachedToWindow() {
    super.onAttachedToWindow();

    TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.MyView);
    int[] myArray = a.getIntArray(R.styleable.MyView_myArray, null);

    if (myArray != null) {
      for (int value : myArray) {
        Log.d("MyView", "Value: " + value);
      }
    }

    a.recycle();
  }
}

D/MyView: Value: 1
D/MyView: Value: 2
D/MyView: Value: 3

Conclusion

By skillfully using the integer-array format, you can effectively represent and retrieve multiple integer values through your declare-styleable, granting your views enhanced flexibility in handling structured data.