Android: I am unable to have ViewPager WRAP_CONTENT

Overriding onMeasure of your ViewPager as follows will make it get the height of the biggest child it currently has.

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);

    int height = 0;
    int childWidthSpec = MeasureSpec.makeMeasureSpec(
        Math.max(0, MeasureSpec.getSize(widthMeasureSpec) -
            getPaddingLeft() - getPaddingRight()),
        MeasureSpec.getMode(widthMeasureSpec)
    );
    for (int i = 0; i < getChildCount(); i++) {
        View child = getChildAt(i);
        child.measure(childWidthSpec, MeasureSpec.UNSPECIFIED);
        int h = child.getMeasuredHeight();
        if (h > height) height = h;
    }
    
    if (height != 0) {
        heightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);
    }

    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}

Another more generic solution is to get wrap_content to just work.

I've extended ViewPager to override onMeasure(). The height is wraped around the first child view. This could lead to unexpected results if the child views are not exactly the same height. For that the class can be easily extended to let's say animate to the size of the current view/page. But I didn't need that.

You can use this ViewPager in yout XML layouts just like the original ViewPager:

<view
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    class="de.cybergen.ui.layout.WrapContentHeightViewPager"
    android:id="@+id/wrapContentHeightViewPager"
    android:layout_alignParentBottom="true"
    android:layout_alignParentLeft="true"/>

Advantage: This approach allows using the ViewPager in any layout including RelativeLayout to overlay other ui elements.

One drawback remains: If you want to use margins, you have to create two nested layouts and give the inner one the desired margins.

Here's the code:

public class WrapContentHeightViewPager extends ViewPager {

    /**
     * Constructor
     *
     * @param context the context
     */
    public WrapContentHeightViewPager(Context context) {
        super(context);
    }

    /**
     * Constructor
     *
     * @param context the context
     * @param attrs the attribute set
     */
    public WrapContentHeightViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        // find the first child view
        View view = getChildAt(0);
        if (view != null) {
            // measure the first child view with the specified measure spec
            view.measure(widthMeasureSpec, heightMeasureSpec);
        }

        setMeasuredDimension(getMeasuredWidth(), measureHeight(heightMeasureSpec, view));
    }

    /**
     * Determines the height of this view
     *
     * @param measureSpec A measureSpec packed into an int
     * @param view the base view with already measured height
     *
     * @return The height of the view, honoring constraints from measureSpec
     */
    private int measureHeight(int measureSpec, View view) {
        int result = 0;
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);

        if (specMode == MeasureSpec.EXACTLY) {
            result = specSize;
        } else {
            // set the height from the base view if available
            if (view != null) {
                result = view.getMeasuredHeight();
            }
            if (specMode == MeasureSpec.AT_MOST) {
                result = Math.min(result, specSize);
            }
        }
        return result;
    }

}