Question

< Edit >

1. A new observation – I’ve tried the same ViewPager as stand alone Activity and as an AppWidget configuration view – and it crashes often as configuration view, while consistently runs well as a simple activity.

2. Another observation – If the configuration layout is ViewPager as root, no crashes happened. if the ViewPager is embedded in FlowLayout or RelativeLayout – it crashes often.

< / Edit >

I’m using v4 ViewPager with PagerTabStrip in my AppWidget configuration xml, and it works perfectly most of the time.

However, I get this error (app crash) when some processing involved while loading the view:

 java.lang.IllegalStateException: Must measure with an exact width
    at android.support.v4.view.PagerTitleStrip.onMeasure(PagerTitleStrip.java:428)
    at android.view.View.measure(View.java:8335)
    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1350)
    at android.view.View.measure(View.java:8335)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017)
    ...etc...

A code snippet from android.support.v4.view.PagerTitleStrip.onMeasure() –

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
    //...

    if (widthMode != MeasureSpec.EXACTLY) {
        throw new IllegalStateException("Must measure with an exact width");
    }
    //...
}

How could I control the widthMode??

All the stack above is happening outside my code.

In my code I’ve tried to rule out many factors, and eventually I may have managed to isolate a root cause:

When I’m adding a mock “work” of 5 milis sleep per fragment (X30 fragments), I get the above error, and when removing it – the error seem gone.
Tried moving the work to onCreate() – didn’t make a difference

public static class TestFragment extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater,
            ViewGroup container, Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.splash, container, false);
        try {
            Thread.sleep(5); // << mock work causes quite consistent error
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        Log.i(TAG, "..onCreateView");

        return v;
    }
}

The actual work I’m doing on my real adapter’s fragment is minimal and can’t be avoided (setting the initial values which later populate the data in a background thread). So I don’t know how much more I can defer to a background thread.

Does anyone have experience with this?
Any idea why the above error occurs, and if it is possible to avoid it?

For reference (Not sure if it’s relevant):

<LinearLayout ...>
<android.support.v4.view.ViewPager
    android:layout_marginLeft="16dp"
    android:layout_marginRight="16dp"
    android:id="@+id/aw_pager"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1.0"
    android:background="@drawable/dialog_full_holo_dark"
    android:fadingEdge="horizontal"
    android:fadingEdgeLength="40dp" >

    <android.support.v4.view.PagerTabStrip
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="top" />
</android.support.v4.view.ViewPager>
</LinearLayout>

Answer 1

Solved at last! (2 days wasted on this):
it was this line:

  android:background="@drawable/dialog_full_holo_dark"

I replaced it with:

  android:background="@color/black"

and the problem is gone.
Nothing in the error has suggested that, and it wasn’t deterministic. Solved the hard way by elimination – add code > test > again…

It is most likely a bug in Android code, probably some race condition in View layout management.

Hope I saved 2 days for fellow devs bumping here.

[Update]

In another project I worked around this bug by wrapping the ViewPager with a FrameLayout. I set the background I needed to the FrameLayout, and set @color/transparent to the ViewPager.