How to create a custom LayoutParams to be used on a custom layout?

Question

I'm fairly proficient at creating complex custom layouts based on ViewGroup. The only thing I'm missing is the ability to create my custom LayoutParams. I really need the ability to get the margins and why not create other extra params to pass in to the parent.

How can I go about creating a custom LayoutParam and using it via xml? I tried using a LinearLayout.LayoutParam but it's obviously crashing since the parent is not a LinearLayout. How can I work with LayoutParams on custom layouts?

Update:

As of now I'm sticking with using a FrameLayout and overriding the onMeasure and onLayout functions to do the layout myself. This does provide FrameLayout.LayoutParams. I'm guessing the childs would have to support the custom LayoutParam?

Answer 1

In your custom layout, create a nested class extending ViewGroup.LayoutParams. Then override some methods (all of the required ones are in my example). Here's a stripped-down version of one of my custom layouts:

public class MyLayout extends ViewGroup {

    public MyLayout(Context context) {

    }

    public MyLayout(Context context, AttributeSet attrs) {

    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {

    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

    }

    @Override
    protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
        return p instanceof LayoutParams;
    }

    @Override
    protected LayoutParams generateDefaultLayoutParams() {
        return new LayoutParams();
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new LayoutParams(getContext(), attrs);
    }

    @Override
    protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
        return generateDefaultLayoutParams(); // TODO Change this?
    }

    public static class LayoutParams extends ViewGroup.LayoutParams {

        public LayoutParams() {

        }

        public LayoutParams(int width, int height) {

        }

        public LayoutParams(Context context, AttributeSet attrs) {

        }

    }

}

Further explanation: How to create a FlowLayout (thanks for the link Luksprog!)