findViewById() returns null for custom component in layout XML, not for other components

Question

I have a res/layout/main.xml including these elements and others:

<some.package.MyCustomView android:id="@+id/foo" (some other params) />
<TextView android:id="@+id/boring" (some other params) />

In my Activity's onCreate, I do this:

setContentView(R.layout.main);
(TextView) boring = findViewById(R.id.boring);
// ...find other elements...
MyCustomView foo = (MyCustomView) findViewById(R.id.foo);
if (foo == null) { Log.d(TAG, "epic fail"); }

The other elements are found successfully, but foo comes back null. MyCustomView has a constructor MyCustomView(Context c, AttributeSet a) and a Log.d(...) at the end of that constructor appears successfully in logcat just before the "epic fail".

Why is foo null?

Answer 1

Because in the constructor, I had super(context) instead of super(context, attrs).

Makes sense, if you don't pass in the attributes, such as the id, then the view will have no id and therefore not be findable using that id. :-)

Answer 2

For me, the problem was solved when I added the res folder to the Source in Java Build Path in project Settings.