How to force set layout params for custom view

Question

here is my code, I hope make view like html5 <hr/>

public class Hr extends View {

    public Hr(Context context) {
        super(context);
        ii();
    }

    public Hr(Context context, AttributeSet attrs) {
        super(context, attrs);
        ii();
    }

    void ii() {
        setBackgroundColor(col(this, R.color.gray));
        ViewGroup.MarginLayoutParams lp = new ViewGroup.MarginLayoutParams(MATCH_PARENT, 1);
        lp.topMargin = 5;
        lp.bottomMargin = 5;
        setLayoutParams(lp);
    }
}

but when i test it:

<ro.adr.Hr android:layout_width="match_parent" android:layout_height="match_parent"/>

the result is gray block, why lp doesn't work?

Answer 1

The issue is with the order of things that happen when a View is inflated from layout xml.

If you go through the code of the LayoutInflater class, you'll see that the order is:

1. Parsing xml as attrs (a particular part of the xml related to specific ViewGroup child)
2. Creating View
3. Setting LayoutParams created based on the previously obtained attrs

That means that the LayoutParams you create inside your constructor (lp) are being overwritten by the LayoutParams from the xml (in the 3. step).

What you can do to fix that is to move your ii() call to the onAttachedToWindow() method.

@Override
protected void onAttachedToWindow() {
    super.onAttachedToWindow();
    ii();
}

Answer 2

For custom views, you can override the onMeasure(), something like:

 @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        setMeasuredDimension(500,500);
    }

and setMeasuredDimension() can be used to set the desired dimensions.