安卓：垂直ViewPager

实际上Android源代码中已经有一个了。不过我对它进行了修改以使其更好地工作：

package com.crnlgcs.sdk.widgets;



import android.content.Context;
import android.support.v4.view.ViewConfigurationCompat;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewParent;

public class VerticalViewPager extends ViewPager {
    private static final String TAG = "VerticalViewPager";
    private static final boolean DEBUG = true;

    private float mLastMotionX;
    private float mLastMotionY;
    private float mTouchSlop;
    private boolean mVerticalDrag;
    private boolean mHorizontalDrag;

    // Vertical transit page transformer
    private final ViewPager.PageTransformer mPageTransformer = new ViewPager.PageTransformer() {
        @Override
        public void transformPage(View view, float position) {
            final int pageWidth = view.getWidth();
            final int pageHeight = view.getHeight();
            if (position < -1) {
                // This page is way off-screen to the left.
                view.setAlpha(0);
            } else if (position <= 1) {
                view.setAlpha(1);
                // Counteract the default slide transition
                view.setTranslationX(pageWidth * -position);
                // set Y position to swipe in from top
                float yPosition = position * pageHeight;
                view.setTranslationY(yPosition);
            } else {
                // This page is way off-screen to the right.
                view.setAlpha(0);
            }
        }
    };

    public VerticalViewPager(Context context) {
        super(context, null);
    }

    public VerticalViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
        final ViewConfiguration configuration = ViewConfiguration.get(context);
        mTouchSlop = ViewConfigurationCompat.getScaledPagingTouchSlop(configuration);
        init();
    }

    private void init() {
        // Make page transit vertical
        setPageTransformer(true, mPageTransformer);
        // Get rid of the overscroll drawing that happens on the left and right (the ripple)
        setOverScrollMode(View.OVER_SCROLL_NEVER);
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {

        final float x = ev.getX();
        final float y = ev.getY();

        if (DEBUG) Log.v(TAG, "onTouchEvent " + x + ", " + y);

        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN: {
                mLastMotionX = x;
                mLastMotionY = y;
                if (!super.onTouchEvent(ev))
                    return false;
                return verticalDrag(ev);
            }
            case MotionEvent.ACTION_MOVE: {
                final float xDiff = Math.abs(x - mLastMotionX);
                final float yDiff = Math.abs(y - mLastMotionY);
                if (!mHorizontalDrag && !mVerticalDrag) {
                    if (xDiff > mTouchSlop && xDiff > yDiff) { // Swiping left and right
                        mHorizontalDrag = true;
                    } else if (yDiff > mTouchSlop && yDiff > xDiff) { //Swiping up and down
                        mVerticalDrag = true;
                    }
                }
                if (mHorizontalDrag) {
                    return super.onTouchEvent(ev);
                } else if (mVerticalDrag) {
                    return verticalDrag(ev);
                }
            }
            case MotionEvent.ACTION_UP: {
                if (mHorizontalDrag) {
                    mHorizontalDrag = false;
                    return super.onTouchEvent(ev);
                }
                if (mVerticalDrag) {
                    mVerticalDrag = false;
                    return verticalDrag(ev);
                }
            }
        }
        // Set both flags to false in case user lifted finger in the parent view pager
        mHorizontalDrag = false;
        mVerticalDrag = false;

        return false;
    }


    private boolean verticalDrag(MotionEvent ev) {
        final float x = ev.getX();
        final float y = ev.getY();
        ev.setLocation(y, x);
        return super.onTouchEvent(ev);
    }
}

这是一个可垂直滚动的ViewPager实现。与RecyclerView和ListView配合良好。guochong/VerticalViewPager。

使用ViewPager.PageTransformer使ViewPager可以垂直滚动，并提供View.OnTouchListener处理滚动冲突。

/**
 * 1.dispatch ACTION_DOWN,ACTION_UP,ACTION_CANCEL to child<br>
 * 2.hack ACTION_MOVE
 *
 * @param v
 * @param e
 * @return
 */
@Override
public boolean onTouch(View v, MotionEvent e) {
    Log.i(TAG, "onTouchEvent " + ", action " + e.getAction() + ", e.rawY " + e.getRawY() + ",lastMotionY " + lastMotionY + ",downY " + downY);
    switch (e.getAction()) {
        case MotionEvent.ACTION_DOWN:
            downY = e.getRawY();
            break;
        case MotionEvent.ACTION_MOVE:

            if (downY == Float.MIN_VALUE && lastMotionY == Float.MIN_VALUE) {
                //not start from MOTION_DOWN, the child dispatch this first motion
                downY = e.getRawY();
                break;
            }

            float diff = e.getRawY() - (lastMotionY == Float.MIN_VALUE ? downY : lastMotionY);
            lastMotionY = e.getRawY();
            diff = diff / 2; //slow down viewpager scroll
            Log.e(TAG, "scrollX " + dummyViewPager.getScrollX() + ",basescrollX " + dummyViewPager.getBaseScrollX());

            if (dummyViewPager.getScrollX() != dummyViewPager.getBaseScrollX()) {
                if (fakeDragVp(v, e, diff)) return true;
            } else {
                if (ViewCompat.canScrollVertically(v, (-diff) > 0 ? 1 : -1)) {
                    Log.e(TAG, "scroll vertically  " + diff + ", move.lastMotionY " + e.getY());
                    break;
                } else {
                    dummyViewPager.beginFakeDrag();
                    fakeDragVp(v, e, diff);
                    adjustDownMotion(v, e);
                    return true;
                }
            }

            break;
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_CANCEL:
            if (dummyViewPager.isFakeDragging()) {
                try {
                    dummyViewPager.endFakeDrag();
                } catch (Exception e1) {
                    Log.e(TAG, "", e1);
                }
            }
            reset();
            break;
    }

    return false;
}

我曾经也遇到了同样的问题，想要通过交换X和Y来使ViewPager垂直化，但是效果并不流畅。

这是因为它只有在滑动角度小于7.125度=arctan(1/8)时才能正常工作，而拦截和触摸时的角度为14度=arctan(1/4)，而原始的ViewPager水平滑动时，滑动角度小于26.565度=arctan(1/2)时才能正常工作，而拦截和触摸时的角度为45度=arctan(1)。

这就是为什么我复制了Android support-core-ui的代码，并将值移动到变量中，然后使用反射进行乘法运算。

请在https://github.com/deepakmishra/verticalviewpager找到代码和自述文件，以及在https://github.com/deepakmishra/verticalviewpager/blob/master/app/src/main/java/com/viewpager/VerticalViewPager.java找到VerticalViewPager。

更好的方法是将ViewPager旋转90度，并使用ConstraintLayout来调整位置。

<androidx.viewpager2.widget.ViewPager2
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/pager"
    android:orientation="vertical" />