Android custom component doesn't display its children

Question

Hi guys I want to create a FieldSet component in Android. (similar to html) so something like that. So I want my custom component to have children

Answer 1

When extending ViewGroup directly, you need to handle measuring and laying out the child Views yourself, or they never get sized or positioned correctly. Oftentimes, it's simpler to extend a ViewGroup subclass that already handles that stuff. In this case, you might as well extend RelativeLayout, since that's what's actually holding the internal Views, and the ViewGroup wrapping it is rather unnecessary.

The parent RelativeLayout in the internal layout XML is then redundant, and can be replaced with <merge> tags, which will cause the child Views to be added directly to your RelativeLayout subclass when inflated.

<merge xmlns:android="http://schemas.android.com/apk/res/android">

    <RelativeLayout
        android:id="@+id/field_set_content"
        ... />

    <TextView
        android:id="@+id/field_set_label"
        ... />

</merge>

We can further simplify things by setting up the internal structure in the constructor(s), and putting the child Views in the right place as they're added, rather than juggling all of that around in onFinishInflate(). For example:

public class FieldSet extends RelativeLayout {

    final ViewGroup vg;

    public FieldSet(Context context, AttributeSet attrs) {
        super(context, attrs);

        LayoutInflater.from(context).inflate(R.layout.field_set, this, true);
        vg = (ViewGroup) findViewById(R.id.field_set_content);
    }

    @Override
    public void addView(View child, int index, ViewGroup.LayoutParams params) {
        final int id = child.getId();
        if (id == R.id.field_set_content || id == R.id.field_set_label) {
            super.addView(child, index, params);
        }
        else {
            vg.addView(child, index, params);
        }
    }
}