ViewDragHelper.java 文件源码

/**
 * Apps should use ViewDragHelper.create() to get a new instance.
 * This will allow VDH to use internal compatibility implementations for different
 * platform versions.
 *
 * @param context   Context to initialize config-dependent params from
 * @param forParent Parent view to monitor
 */
private ViewDragHelper(Context context, ViewGroup forParent, Callback cb) {
    if (forParent == null) {
        throw new IllegalArgumentException("Parent view may not be null");
    }
    if (cb == null) {
        throw new IllegalArgumentException("Callback may not be null");
    }

    mParentView = forParent;
    mCallback = cb;

    final ViewConfiguration vc = ViewConfiguration.get(context);
    final float density = context.getResources().getDisplayMetrics().density;
    mEdgeSize = (int) (EDGE_SIZE * density + 0.5f);

    mTouchSlop = vc.getScaledTouchSlop();
    mMaxVelocity = vc.getScaledMaximumFlingVelocity();
    mMinVelocity = vc.getScaledMinimumFlingVelocity();
    mScroller = ScrollerCompat.create(context, sInterpolator);
}