android: viewpager2嵌套时不能滑动的解决

一，代码:

给内部的viewpager2外面包上一层NestedScrollableHost

java代码:

package com.example.okdemo1.lib;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewTreeObserver;
import android.widget.FrameLayout;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.viewpager2.widget.ViewPager2;

public class NestedScrollableHost extends FrameLayout {

    private ViewPager2 parentViewPager;
    private int touchSlop = 0;
    private float initialX = 0f;
    private float initialY = 0f;

    public NestedScrollableHost(@NonNull Context context) {
        super(context);
        init(context);
    }

    public NestedScrollableHost(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public NestedScrollableHost(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    public NestedScrollableHost(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init(context);
    }

    private void init(Context context){
        touchSlop = ViewConfiguration.get(context).getScaledTouchSlop();


        getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
            @Override
            public boolean onPreDraw() {
                View v = (View) getParent();
                while (v!=null && !(v instanceof ViewPager2)){
                    v = (View) v.getParent();
                }
                parentViewPager = (ViewPager2) v;

                getViewTreeObserver().removeOnPreDrawListener(this);
                return false;
            }
        });
    }


    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        handleInterceptTouchEvent(ev);
        return super.onInterceptTouchEvent(ev);
    }


    private boolean canChildScroll(int orientation, float delta) {
        int direction = (int) -delta;
        View child = getChildAt(0);
        if (orientation == 0) {
            return child.canScrollHorizontally(direction);
        } else if (orientation == 1) {
            return child.canScrollVertically(direction);
        } else {
            throw new IllegalArgumentException();
        }
    }

    private void handleInterceptTouchEvent(MotionEvent e) {
        if (parentViewPager == null) return;
        int orientation = parentViewPager.getOrientation();

        // Early return if child can't scroll in same direction as parent
        if (!canChildScroll(orientation, -1f) && !canChildScroll(orientation, 1f)) {
            return;
        }


        if (e.getAction() == MotionEvent.ACTION_DOWN) {
            initialX = e.getX();
            initialY = e.getY();
            getParent().requestDisallowInterceptTouchEvent(true);
        } else if (e.getAction() == MotionEvent.ACTION_MOVE) {
            float dx = e.getX()- initialX;
            float dy = e.getY() - initialY;
            boolean isVpHorizontal = orientation == ViewPager2.ORIENTATION_HORIZONTAL;

            // assuming ViewPager2 touch-slop is 2x touch-slop of child
            float scaledDx = Math.abs(dx) * (isVpHorizontal ?  .5f : 1f);
            float scaledDy = Math.abs(dy) * (isVpHorizontal ? 1f : .5f);
            if (scaledDx > touchSlop || scaledDy > touchSlop) {
                if (isVpHorizontal == (scaledDy > scaledDx)) {
                    // Gesture is perpendicular, allow all parents to intercept
                    getParent().requestDisallowInterceptTouchEvent(false);
                } else {
                    // Gesture is parallel, query child if movement in that direction is possible
                    if (canChildScroll(orientation, isVpHorizontal ? dx : dy)) {
                        // Child can scroll, disallow all parents to intercept
                        getParent().requestDisallowInterceptTouchEvent(true);
                    } else {
                        // Child cannot scroll, allow all parents to intercept
                        getParent().requestDisallowInterceptTouchEvent(false);
                    }
                }
            }
        }
    }}

 

kotlin代码:

import android.content.Context
import android.util.AttributeSet
import android.view.MotionEvent
import android.view.View
import android.view.ViewConfiguration
import android.widget.FrameLayout
import androidx.viewpager2.widget.ViewPager2
import androidx.viewpager2.widget.ViewPager2.ORIENTATION_HORIZONTAL
import kotlin.math.absoluteValue
import kotlin.math.sign

/**
 * Layout to wrap a scrollable component inside a ViewPager2. Provided as a solution to the problem
 * where pages of ViewPager2 have nested scrollable elements that scroll in the same direction as
 * ViewPager2. The scrollable element needs to be the immediate and only child of this host layout.
 *
 * This solution has limitations when using multiple levels of nested scrollable elements
 * (e.g. a horizontal RecyclerView in a vertical RecyclerView in a horizontal ViewPager2).
 */
class NestedScrollableHost : FrameLayout {
    constructor(context: Context) : super(context)
    constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)

    private var touchSlop = 0
    private var initialX = 0f
    private var initialY = 0f
    private val parentViewPager: ViewPager2?
        get() {
            var v: View? = parent as? View
            while (v != null && v !is ViewPager2) {
                v = v.parent as? View
            }
            return v as? ViewPager2
        }

    private val child: View? get() = if (childCount > 0) getChildAt(0) else null

    init {
        touchSlop = ViewConfiguration.get(context).scaledTouchSlop
    }

    private fun canChildScroll(orientation: Int, delta: Float): Boolean {
        val direction = -delta.sign.toInt()
        return when (orientation) {
            0 -> child?.canScrollHorizontally(direction) ?: false
            1 -> child?.canScrollVertically(direction) ?: false
            else -> throw IllegalArgumentException()
        }
    }

    override fun onInterceptTouchEvent(e: MotionEvent): Boolean {
        handleInterceptTouchEvent(e)
        return super.onInterceptTouchEvent(e)
    }

    private fun handleInterceptTouchEvent(e: MotionEvent) {
        val orientation = parentViewPager?.orientation ?: return

        // Early return if child can't scroll in same direction as parent
        if (!canChildScroll(orientation, -1f) && !canChildScroll(orientation, 1f)) {
            return
        }

        if (e.action == MotionEvent.ACTION_DOWN) {
            initialX = e.x
            initialY = e.y
            parent.requestDisallowInterceptTouchEvent(true)
        } else if (e.action == MotionEvent.ACTION_MOVE) {
            val dx = e.x - initialX
            val dy = e.y - initialY
            val isVpHorizontal = orientation == ORIENTATION_HORIZONTAL

            // assuming ViewPager2 touch-slop is 2x touch-slop of child
            val scaledDx = dx.absoluteValue * if (isVpHorizontal) .5f else 1f
            val scaledDy = dy.absoluteValue * if (isVpHorizontal) 1f else .5f

            if (scaledDx > touchSlop || scaledDy > touchSlop) {
                if (isVpHorizontal == (scaledDy > scaledDx)) {
                    // Gesture is perpendicular, allow all parents to intercept
                    parent.requestDisallowInterceptTouchEvent(false)
                } else {
                    // Gesture is parallel, query child if movement in that direction is possible
                    if (canChildScroll(orientation, if (isVpHorizontal) dx else dy)) {
                        // Child can scroll, disallow all parents to intercept
                        parent.requestDisallowInterceptTouchEvent(true)
                    } else {
                        // Child cannot scroll, allow all parents to intercept
                        parent.requestDisallowInterceptTouchEvent(false)
                    }
                }
            }
        }
    }
}

xml：
viewpager2是内层的

        <com.example.okdemo1.lib.NestedScrollableHost
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            >
        <androidx.viewpager2.widget.ViewPager2
            xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/cateViewPager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            />
        </com.example.okdemo1.lib.NestedScrollableHost>

二，测试效果: