Question

Does ViewGroup.addView clones LayoutParams data into inside or links to it? May I reuse the same instance of LayoutParams with multiple calls to addView() with different views?

There is nothing about it in apidoc.

WOW

The answer is NO (checked experimentally):

public class SymbolPadActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    RelativeLayout.LayoutParams labelParams;

    /*
     * This block to reuse is not working
    labelParams = new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
    labelParams.addRule(RelativeLayout.ALIGN_PARENT_LEFT, RelativeLayout.TRUE);
    labelParams.addRule(RelativeLayout.ALIGN_PARENT_TOP, RelativeLayout.TRUE);
    */


    RelativeLayout mover = new RelativeLayout(this);

    TextView textView;
    for(int leftMargin = 0; leftMargin<3000; leftMargin += 100) {
        for(int topMargin=0; topMargin<800; topMargin += 40) {

            // I can't omit these 3 lines 
            labelParams = new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
            labelParams.addRule(RelativeLayout.ALIGN_PARENT_LEFT, RelativeLayout.TRUE);
            labelParams.addRule(RelativeLayout.ALIGN_PARENT_TOP, RelativeLayout.TRUE);

            labelParams.leftMargin = leftMargin;
            labelParams.topMargin = topMargin;

            textView = new TextView(this);
            textView.setText("(" + leftMargin + "," + topMargin + ")");
            mover.addView(textView, labelParams);

        }
    }




    RelativeLayout.LayoutParams moverParams = new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
    moverParams.addRule(RelativeLayout.ALIGN_PARENT_LEFT, RelativeLayout.TRUE);
    moverParams.addRule(RelativeLayout.ALIGN_PARENT_TOP, RelativeLayout.TRUE);
    moverParams.leftMargin = 0;
    moverParams.topMargin = 0;

    RelativeLayout stator = new RelativeLayout(this);
    stator.addView(mover, 0, moverParams);

    setContentView(stator);


}

}

Answer 1

There is nothing about it in apidoc.

This means you need to make the more conservative choice, no matter what the current implementation is, as the implementation could change.

Hence, you need to assume that it is not safe to reuse an instance of LayoutParams with different Views.

For what it’s worth, as far as I can tell, that is true anyway – ViewGroup doesn’t make a copy.