android – 使用NestedScrollView处理VerticalViewPager的滚动

背景：

我使用的是ViewPager的变体,它不是在水平方向上滚动,而是在垂直方向上滚动.

VerticalViewPager：
https://android.googlesource.com/platform/packages/apps/DeskClock/+/master/src/com/android/deskclock/VerticalViewPager.java

android.support.v4.app.FragmentStatePagerAdapter用于设置VerticalViewPager中的内容.

每次调用FragmentStatePagerAdapter的getItem()时,我都会从FragmentStatePagerAdapter创建并返回一个新的android.support.v4.app.Fragment实例,如下所示：

@Override
public Fragment getItem(int position) {
   return  PreviewFragment.getNewFragmentInstance(position);
}

PreviewFragment呈现可能不适合屏幕的内容.
为了显示不适合屏幕的所有内容,android.support.v4.widget.nestedScrollView用作PreviewFragment布局的父元素.

问题：

PreviewFragment的内容按预期滚动到位置0.
但是,为了切换到下一页,必须多次执行甩动或滑动操作,因此向位置1的页面滑动是非常困难的.

此外,投掷或滑回到位置0非常困难或几乎不可能.

需要：

Fling或滑动或切换到PreviewFragment的下一个实例应该是平滑的.
换句话说,滚动内容应该是平滑的,同时请记住,滑动到下一页也应该顺利工作.

Link to the sample project as mentioned above

解决方法

我查看了你的 Github代码.我让它适合你.我也发了拉请求.问题是onInterceptTouchEvent如果返回true则使ViewPager滚动,如果我们返回false,则禁用ViewPager touch并使nestedScrollView滚动.所以我在这里检查是否需要滚动nestedScrollView然后如果nestedScrollView位于顶部或底部我返回false,我将其返回true.我在这里发布代码.您可以修改它并使其更干净.

Github Link – https://github.com/karanatwal/vertical-viewpager-nestedscrollview

以下是VerticalViewPager代码 –

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    boolean toIntercept = super.onInterceptTouchEvent(flipXY(ev));
    // Return MotionEvent to normal


    float x = ev.getX();

    flipXY(ev);
    int direction=1;

    switch (ev.getAction()) {
        case MotionEvent.ACTION_DOWN:
            mStartDragX = x;
            break;

        case MotionEvent.ACTION_MOVE:
            if (mStartDragX < x ) {
                direction=-1;
            } else if (mStartDragX > x) {
                direction=1;
            }
            MainActivity.MyPagerAdapter adapter = (MainActivity.MyPagerAdapter)this.getAdapter();
            if (adapter.getCurrentFragment() instanceof FragmentViewPager){
                FragmentViewPager fragmentViewPager = (FragmentViewPager)adapter.getCurrentFragment();
                toIntercept = !fragmentViewPager.getnestedScrollView().canScrollVertically(direction);
                int range = fragmentViewPager.getnestedScrollView().computeVerticalScrollRange();
                int offset = fragmentViewPager.getnestedScrollView().computeVerticalScrollOffset();
                int extent = fragmentViewPager.getnestedScrollView().computeVerticalScrollExtent();
                int percentage = (int)(100.0 * offset / (float)(range - extent));

                System.out.println("  range: "+range);
                System.out.print("  offset: "+offset);
                System.out.print("  extent: "+extent);                  
                System.out.print("  percentage: "+percentage);
                System.out.print("  direction: "+direction);

                if (fragmentViewPager.getnestedScrollView().computeVerticalScrollOffset()==0 && direction==-1){
                    //top
                    return true;
                }
                else if (percentage>99 && direction==1){
                    //bottom
                    return true;
                }else {
                    //scroll nestedscrollview
                    return false;
                }

            }

            break;
    }


    return toIntercept;
}

你的MyPagerAdapter –

public class MyPagerAdapter extends FragmentStatePagerAdapter {

    public MyPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    private Fragment mCurrentFragment;

    public Fragment getCurrentFragment() {
        return mCurrentFragment;
    }
    //...
    @Override
    public void setPrimaryItem(ViewGroup container,int position,Object object) {
        if (getCurrentFragment() != object) {
            mCurrentFragment = ((Fragment) object);
        }
        super.setPrimaryItem(container,position,object);
    }

    @Override
    public android.support.v4.app.Fragment getItem(int pos) {
        switch (pos) {
            case 0:
                return FragmentViewPager.newInstance("Title Start",R.drawable.ic_launcher_background);
            case 1:
                return FragmentViewPager.newInstance("Rock",R.drawable.rock);
            case 2:
                return FragmentViewPager.newInstance("Paper",R.drawable.paper);
            case 3:
                return FragmentViewPager.newInstance("Scissors",R.drawable.scissors);
            case 4:
                return FragmentViewPager.newInstance("Title End",R.drawable.ic_launcher_background);
            default:
                return FragmentViewPager.newInstance("Default Title",R.drawable.rock);
        }
    }

    @Override
    public int getCount() {
        return 5;
    }
}

为了避免受限制的API方法 – 使用以下逻辑作为替代

//offset,range and extent
            int scrollY = scrollView.getScrollY();               
            int scrollContentHeight = scrollView.getChildAt(0).getHeight();
            int screenHeight = Utility.getScreenHeight(context); 
            int statusBarHeight = Utility.getStatusBarHeight(context);

            double percent = ((((float) scrollY) / ((float) (scrollContentHeight - screenHeight + statusBarHeight))));

您只需要滚动百分比和滑动方向.在SO上找到滚动百分比和滑动方向有很多问题,如this和this.你应该为它做一点R& D.