Recycle

Attributes should be recycled.
At code:

  if(attrs!=null)
  {
        TypedArray a=getContext().obtainStyledAttributes( attrs, R.styleable.StaggeredGridView);
        mColCount = a.getInteger(R.styleable.StaggeredGridView_numColumns, 2);
        mDrawSelectorOnTop = a.getBoolean(R.styleable.StaggeredGridView_drawSelectorOnTop, false);
        mItemMargin = (int) a.getDimension(R.styleable.StaggeredGridView_itemMargin, 0);
    }

Add

a.recycle();

More over,

mVelocityTracker

is never recycled.

Add the method to your StaggeredGridView class:

@Override
protected void onDetachedFromWindow()
{
    if (mVelocityTracker != null) mVelocityTracker.recycle();
    super.onDetachedFromWindow();
}