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 = (TextView) 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

I had the same problem, because in my custom view I have overridden the constructor, but invoked the super constructor without the attrs parameter. (That was a copy/paste mistake.)

My previous constructor version:

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

Now I have:

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

And that works!