Scroll Inside Scroll

This project shows how to add a vertically scrollable view into another vertically scrollable view upto any level of depth.

Placing vertically scrollable view into another vertically scrollable view is a bit tedious in android. Here we show how to place, withour sacrificing the recycling feature of various AbsListViews, ScrollView inside ScrollView, ScrollView inside ListView, ListView inside GridView, etc. And even ListView indide ScrollView which in turn inside another ScrollView, etc.

Note Eventhough you can nest scroll views to any level, please consider the user experiance. This project contains a complicated xml layout file scroll_in_scroll.xml which has no good user experiance.

Step 1

Write a method which determines wheather a View can be scrolled vertically and place the method inside a common utility class as follows. This method is taken from ViewPager.java and modified to find whether a View can vertically scrollable.

public static boolean canScroll(View v, boolean checkV, int dy, int x, int y) {
	if (v instanceof ViewGroup) {
		final ViewGroup group = (ViewGroup) v;
		final int scrollX = v.getScrollX();
		final int scrollY = v.getScrollY();
		final int count = group.getChildCount();
		for (int i = count - 1; i >= 0; i--) {
			final View child = group.getChildAt(i);
			if (x + scrollX >= child.getLeft()
					&& x + scrollX < child.getRight()
					&& y + scrollY >= child.getTop()
					&& y + scrollY < child.getBottom()
					&& canScroll(child, true, dy,
							x + scrollX - child.getLeft(), y + scrollY
									- child.getTop())) {
				return true;
			}
		}
	}
	return checkV && ViewCompat.canScrollVertically(v, -dy);
}

Step 2

Subclass the enclosing vertically scrollable view, it may be ScrollView or ListView, or the like and override the onInterceptTouchEvent() method as follows.

public boolean onInterceptTouchEvent(MotionEvent event) {
  int action = event.getAction();
	float x = event.getX();
	float y = event.getY();
	float dy = y - mLastMotionY;
	switch (action) {
	case MotionEvent.ACTION_DOWN:
		mLastMotionY = y;
		break;
	case MotionEvent.ACTION_MOVE:
		if (Util.canScroll(this, false, (int) dy, (int) x, (int) y)) {
			mLastMotionY = y;
			return false;
		}
		break;
	}
	return super.onInterceptTouchEvent(event);
}

Step 3

Subclass the enclosed vertically scrollable view, it may be GridView or ListView or the like and override the onMeasure() method as follows. No need to override this method in ScrollView. Its default implementation behaves in the right way.

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	super.onMeasure(widthMeasureSpec, heightMeasureSpec);
	int mode = MeasureSpec.getMode(widthMeasureSpec);
	if (mode == MeasureSpec.UNSPECIFIED) {
		int height = getLayoutParams().height;
		if (height > 0)
			setMeasuredDimension(getMeasuredWidth(), height);
	}
}

Step 4

Finally create an xml layout file as given below and see how it works. We have to hard code the layout_height of CustomListView. If you create the view hierarchy programmatically, then set the height via LayoutParams.

<com.dass.scroll_inside_scroll.CustomScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent" >
        
        <!-- Other Children -->
        
        <com.dass.scroll_inside_scroll.CustomListView
            android:layout_width="match_parent"
            android:layout_height="300dp" >
        </com.dass.scroll_inside_scroll.CustomListView>
        
        <!-- Other Children -->
        
    </LinearLayout>
</com.dass.scroll_inside_scroll.CustomScrollView>

In this project the classes CustomListView, CustomExpandableListView, CustomGridView overrides the method onInterceptTouchEvent() in order to place other vertically scrollable views inside them. If we dont add vertically scrollable views inside any of these classes then no need to override onInterceptTouchEvent().

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