How do I implement CompositeView so it displays the components correctly?

This is a classic issue in custom View implementations in Swing’s javax.swing.text framework. To fix this issue try to override layout(int width, int height) in MDListView If you don’t then the base CompositeView would not call your getChildAllocation() correctly.

@Override
protected void layout(int width, int height) {
    int n = getViewCount();
    if (n == 0) return;
    int y = 0;
    for (int i = 0; i < n; i++) {
        View v = getView(i);
        int h = (int) v.getPreferredSpan(YAXIS);
        v.setSize(width, h);
        // Store the offset in the child allocation manually if needed
        childAllocations[i] = new Rectangle(0, y, width, h); // Optional cache
        y += h;
    }
}

@Override
public Shape getChildAllocation(int index, Shape a) {
    if (a == null) return null;
    Rectangle alloc = a.getBounds();
    layout(alloc.width, alloc.height); // force layout
    int y = 0;
    for (int i = 0; i < index; i++) {
        y += (int) getView(i).getPreferredSpan(YAXIS);
    }
    int h = (int) getView(index).getPreferredSpan(Y_AXIS);
    return new Rectangle(alloc.x, alloc.y + y, alloc.width, h);
}

make sure setSize() is called on the root view

view.setSize(containerWidth, containerHeight);