How to read custom dimension attribute from java code

For a little more context to the accepted answer:

attrs.xml

Set the custom attribute with the dimension format.

<resources>
    <declare-styleable name="CustomView">
        <attr name="valueTextSize" format="dimension" />
        <attr name="titleTextSize" format="dimension" />
        <attr name="unitsTextSize" format="dimension" />
    </declare-styleable>
</resources>

activity.xml

Reference your attributes with xmlns:app=... and set them in your xml with app:....

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                xmlns:app="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="match_parent">

    <com.example.myproject.CustomView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:valueTextSize="40sp"
        app:titleTextSize="20sp"
        app:unitsTextSize="24sp" /> 

</RelativeLayout>

CustomView.java

Obtain the values from the TypedArray using getDimensionPixelSize. Within your custom view just work with pixels. See this answer if you need to convert to a different dimension.

public class CustomView extends View {

    private float mValueTextSize; // pixels
    private float mTitleTextSize; // pixels
    private float mUnitsTextSize; // pixels

    public CustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray a = context.getTheme().obtainStyledAttributes(
                attrs, R.styleable.CustomView, 0, 0);
        try {
            mValueTextSize = a.getDimensionPixelSize(R.styleable.CustomView_valueTextSize, 0);
            mTitleTextSize = a.getDimensionPixelSize(R.styleable.CustomView_titleTextSize, 0);
            mUnitsTextSize = a.getDimensionPixelSize(R.styleable.CustomView_unitsTextSize, 0);
        } finally {
            a.recycle();
        }
    }

    // ...
}

A few things to say :

• first you need a xml name space declaration line at the top of your xml, exactly in the same way as you do with android xmlns : xmlns:foo="http://schemas.android.com/apk/res-auto"
• then you need to prefix valueTextSize with your xmlns : foo:valueTextSize="40sp"

After that, it's not a very good idea to get a string, android offers more powerfull solution to deal with dimensions :

int unitsTextSize = typedArray.getDimensionPixelSize(R.styleable.BasicGauge_unitsTextSize, textSize);

then there are some subtleties :

• for a Paint, or a TextPaint, you can this value as is : paint.setTextSize(unitTextSize):
• for a textview, the above approach would fail, and you have to use an overload of setText to get the correct result : textView.setTextSize(TypedValue.COMPLEX_UNIT_PX, unitTextSize);

The difference comes from what is called "raw pixels" (unscaled according to density, just raw) and "scaled pixels" (the opposite).