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

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?

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. :-)

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!

I had the same problem. My mistake was that: I wrote

        LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View layout=inflater.inflate(R.layout.dlg_show_info, null);
        alertDlgShowInfo.setView(layout);
        TableRow trowDesc=(TableRow)findViewById(R.id.trowDesc);

and as I used an inflater to "load" the view from an XML file, the last line was wrong. To solve it, I had to write:

TableRow trowDesc=(TableRow)layout.findViewById(R.id.trowDesc);

I wrote my solution, in case someone have the same problem.

Seems there is a variety of reasons. I just used "Clean..." in Eclipse to solve a similar problem. (FindViewByID had worked before and for some reason started to return null.)

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

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