PagerTabStrip position within ViewPager

Question

I have the following code:

 <android.support.v4.view.ViewPager
    android:id="@+id/main_pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <android.support.v4.view.PagerTabStrip
        android:id="@+id/pager_tab_strip"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
         />
</android.support.v4.view.ViewPager>

and everything gets layouted like it should.

What I want now is that the PagerTabStrip overlays the ViewPager.

It should be rendered on top without taking up any layouting space. Basically the fragments in the ViewPager should start at 0,0 like the PagerTabStrip is doing.

Any help appreciated. Thanks!

Answer 1

I finally found a way to do this.

In the onAttachedToWindow of the PagerTitleStrip, this checks for the parent to be a ViewPager:

final ViewParent parent = getParent();
 if (!(parent instanceof ViewPager)) {
  throw new IllegalStateException("PagerTitleStrip must be a direct child of a ViewPager.");
}   

Therefore this needs to go.

Solution:

I solved it now by creating my own custom PagerTitleStrip/PagerTabStrip. I removed the above behaviour and replaced it by a styleable attribute for my PagerTitleStrip which points to the ViewPager. This is defined in values/attrs.xml like this:

<declare-styleable name="PagerTitleStripCustom">
    <attr name="parentViewPager" format="reference" />
</declare-styleable>

And read in the PagerTitleStrip constructor like this:

TypedArray types = context.obtainStyledAttributes(attrs,R.styleable.PagerTitleStripCustom, 0, 0);   
pagerID = types.getResourceId(R.styleable.PagerTitleStripCustom_parentViewPager, 0);

In the onAttachedToWindow we can now check for the mViewPager variable being null and assign it to our pagerID like this:

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

    final ViewParent parent = getParent();

    ViewPager pager = null;

    if (pagerID != 0) {
        View test2 = ((View) parent).findViewById(pagerID);
        pager = (ViewPager) test2;
    } else if (pagerID == 0 && (parent instanceof ViewPager)) {
        pager = (ViewPager) parent;
    } else if (pagerID == 0 && !(parent instanceof ViewPager)) {
        throw new IllegalStateException("PagerTitleStrip is neither a direct child of a ViewPager nor did you assign the ID of the ViewPager.");
    } else {
        throw new IllegalStateException("PagerTitleStrip: Something went completely wrong.");
    }

    final PagerAdapter adapter = pager.getAdapter();

    pager.setInternalPageChangeListener(mPageListener);
    pager.setOnAdapterChangeListener(mPageListener);
    mPager = pager;
    updateAdapter(mWatchingAdapter != null ? mWatchingAdapter.get() : null, adapter);
}

Now the PagerTitleStrip/PagerTabStrip control can be freely positioned in the layout like this:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:custom="http://schemas.android.com/apk/res/com.YOUR.PATH"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

 <android.support.v4.view.ViewPager
     android:id="@+id/main_pager"
     android:layout_width="match_parent"
     android:layout_height="match_parent" />

 <android.support.v4.view.PagerTabStripCustom
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     custom:parentViewPager="@id/main_pager" />

</RelativeLayout>

This is just the quick and dirty proof of concept. Hope this helps someone.