效果图：
前言：
看了网上很多惯性滚动方案，都是通过Scroller 配合 computeScroll实现的，但在实际开发中可能有一些场景不合适，比如协调布局，内部子View有特别复杂的联动效果，需要通过偏移来配合。我通过VelocityTracker（速度跟踪器）实现了相同的效果，感觉还行🤣，欢迎指正，虚拟机有延迟，真机效果更好。
1. 布局文件 activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".MainActivity"><com.example.flingscrollview.LinerScrollViewandroid:id="@+id/mScrollView"android:orientation="vertical"android:layout_height="match_parent"android:layout_width="match_parent"/></FrameLayout>2. 演示View
package com.example.flingscrollview;import android.content.Context;
import android.graphics.Color;
import android.os.Handler;
import android.os.Looper;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;import androidx.annotation.Nullable;public class LinerScrollView extends LinearLayout {final Handler mHandler;private final int mTouchSlop; // 移动的距离大于这个像素值的时候，会认为是在滑动private final int mMinimumVelocity; // 最小的速度private final int mMaximumVelocity; // 最大的速度private VelocityTracker mVelocityTracker; // 速度跟踪器private int mScrollPointerId; // 当前最新放在屏幕伤的手指private int mLastTouchX; // 上一次触摸的X坐标private int mLastTouchY; // 上一次触摸的Y坐标private int mInitialTouchX; // 初始化触摸的X坐标private int mInitialTouchY; // 初始化触摸的Y坐标public final int SCROLL_STATE_IDLE = -1; // 没有滚动public final int SCROLL_STATE_DRAGGING = 1; // 被手指拖动情况下滚动public final int SCROLL_STATE_SETTLING = 2; // 没有被手指拖动情况下，惯性滚动private int mScrollState = SCROLL_STATE_IDLE; // 滚动状态// 在测试过程中，通过速度正负值判断方向，方向有概率不准确// 所以我在onTouchEvent里自己处理private boolean direction = true; // true：向上 false：向下private FlingTask flingTask; // 惯性任务public LinerScrollView(Context context, @Nullable AttributeSet attrs) {super(context, attrs);mHandler = new Handler(Looper.getMainLooper());// 一些系统的预定义值:ViewConfiguration configuration = ViewConfiguration.get(getContext());mTouchSlop = configuration.getScaledTouchSlop();mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();initView();}/*** 初始化视图*/private void initView() {for (int i = 0; i < 50; i++) {TextView textView = new TextView(getContext());ViewGroup.LayoutParams params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, 350);textView.setLayoutParams(params);textView.setText("index：" + i);textView.setTextColor(Color.BLACK);textView.setTextSize(30);textView.setBackgroundColor(Color.CYAN);textView.setGravity(Gravity.CENTER_VERTICAL);addView(textView);}}boolean notUp = false; // 是否 不能再向上滑了boolean notDown = false; // 是否 不能再向下滑了int listMaxOffsetY = 0; // 列表最大滑动Y值/*** 滚动列表* @param offsetY 偏移Y值*/private void translationViewY(int offsetY) {if (listMaxOffsetY == 0) {listMaxOffsetY = (350 * 50) - getHeight();}if (mScrollState == SCROLL_STATE_DRAGGING) {if (direction) { // 向上滑动if (Math.abs(getChildAt((getChildCount() - 1)).getTranslationY()) < listMaxOffsetY) {notUp = false;}} else { // 向下滑动if (getChildAt(0).getTranslationY() < 0) {notDown = false;}}}for (int i = 0; i < getChildCount(); i++) {View childView = getChildAt(i);int yv = (int) (childView.getTranslationY() + offsetY);if (direction) { // 向上滑动notDown = false;if (!notUp) {if (Math.abs(yv) >= listMaxOffsetY) {notUp = true;}}if (!notUp) childView.setTranslationY(yv);} else { // 向下滑动notUp = false;if (!notDown) {if (yv >= 0) {notDown = true;}}if (!notDown) childView.setTranslationY(yv);}}}/*** 惯性任务* @param velocityX X轴速度* @param velocityY Y轴速度* @return*/private boolean fling(int velocityX, int velocityY) {if (Math.abs(velocityY) > mMinimumVelocity) {flingTask = new FlingTask(Math.abs(velocityY), mHandler, new FlingTask.FlingTaskCallback() {@Overridepublic void executeTask(int dy) {if (direction) { // 向上滑动translationViewY(-dy);} else { // 向下滑动translationViewY(dy);}}@Overridepublic void stopTask() {setScrollState(SCROLL_STATE_IDLE);}});flingTask.run();setScrollState(SCROLL_STATE_SETTLING);return true;}return false;}/*** 停止惯性滚动任务*/private void stopFling() {if (mScrollState == SCROLL_STATE_SETTLING) {if (flingTask != null) {flingTask.stopTask();setScrollState(SCROLL_STATE_IDLE);}}}@Overridepublic boolean onTouchEvent(MotionEvent event) {super.onTouchEvent(event);boolean eventAddedToVelocityTracker = false;// 获取一个新的VelocityTracker对象来观察滑动的速度if (mVelocityTracker == null) {mVelocityTracker = VelocityTracker.obtain();}mVelocityTracker.addMovement(event);// 返回正在执行的操作，不包含触摸点索引信息。即事件类型，如MotionEvent.ACTION_DOWNfinal int action = event.getActionMasked();int actionIndex = event.getActionIndex();// Action的索引// 复制事件信息创建一个新的事件，防止被污染final MotionEvent copyEv = MotionEvent.obtain(event);switch (action) {case MotionEvent.ACTION_DOWN: { // 手指按下stopFling();// 特定触摸点相关联的触摸点id,获取第一个触摸点的idmScrollPointerId = event.getPointerId(0);// 记录down事件的X、Y坐标mInitialTouchX = mLastTouchX = (int) (event.getX() + 0.5f);mInitialTouchY = mLastTouchY = (int) (event.getY() + 0.5f);}break;case MotionEvent.ACTION_POINTER_DOWN: { // 多个手指按下// 更新mScrollPointerId,表示只会响应最近按下的手势事件mScrollPointerId = event.getPointerId(actionIndex);// 更新最近的手势坐标mInitialTouchX = mLastTouchX = (int) (event.getX() + 0.5f);mInitialTouchY = mLastTouchY = (int) (event.getY() + 0.5f);}break;case MotionEvent.ACTION_MOVE: { // 手指移动setScrollState(SCROLL_STATE_DRAGGING);// 根据mScrollPointerId获取触摸点下标final int index = event.findPointerIndex(mScrollPointerId);// 根据move事件产生的x，y来计算偏移量dx，dyfinal int x = (int) (event.getX() + 0.5f);final int y = (int) (event.getY() + 0.5f);int dx = Math.abs(mLastTouchX - x);int dy = Math.abs(mLastTouchY - y);// 在手指拖动状态下滑动if (mScrollState == SCROLL_STATE_DRAGGING) {if (mLastTouchY - y > 0.5f) {direction = true;// Log.d("TAG", "向上");translationViewY(-dy);} else if (y - mLastTouchY > 0.5f) {direction = false;// Log.d("TAG", "向下");translationViewY(dy);}}mLastTouchX = x;mLastTouchY = y;}break;case MotionEvent.ACTION_POINTER_UP: { // 多个手指离开// 选择一个新的触摸点来处理结局，重新处理坐标onPointerUp(event);}break;case MotionEvent.ACTION_UP: { // 手指离开，滑动事件结束mVelocityTracker.addMovement(copyEv);eventAddedToVelocityTracker = true;// 计算滑动速度// mVelocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);mVelocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);// 最后一次 X/Y 轴的滑动速度final float xVel = -mVelocityTracker.getXVelocity(mScrollPointerId);final float yVel = -mVelocityTracker.getYVelocity(mScrollPointerId);if (!((xVel != 0 || yVel != 0) && fling((int) xVel, (int) yVel))) {setScrollState(SCROLL_STATE_IDLE); // 设置滑动状态}resetScroll(); // 重置滑动}break;case MotionEvent.ACTION_CANCEL: { //手势取消，释放各种资源cancelScroll(); // 退出滑动}break;}if (!eventAddedToVelocityTracker) {// 回收滑动事件，方便重用，调用此方法你不能再接触事件mVelocityTracker.addMovement(copyEv);}// 回收滑动事件，方便重用copyEv.recycle();return true;}/*** 有新手指触摸屏幕，更新初始坐标* @param e*/private void onPointerUp(MotionEvent e) {final int actionIndex = e.getActionIndex();if (e.getPointerId(actionIndex) == mScrollPointerId) {// Pick a new pointer to pick up the slack.final int newIndex = actionIndex == 0 ? 1 : 0;mScrollPointerId = e.getPointerId(newIndex);mInitialTouchX = mLastTouchX = (int) (e.getX(newIndex) + 0.5f);mInitialTouchY = mLastTouchY = (int) (e.getY(newIndex) + 0.5f);}}/*** 手指离开屏幕*/private void cancelScroll() {resetScroll();setScrollState(SCROLL_STATE_IDLE);}/*** 重置速度*/private void resetScroll() {if (mVelocityTracker != null) {mVelocityTracker.clear();}}/*** 更新 滚动状态* @param state*/private void setScrollState(int state) {if (state == mScrollState) {return;}mScrollState = state;}}
3. 惯性滚动任务类（核心类）
package com.example.flingscrollview;import android.os.Handler;
import android.util.Log;class FlingTask implements Runnable {private Handler mHandler;private int velocityY = 0;private int originalVelocityY = 0;private FlingTaskCallback flingTaskCallback;public FlingTask(int velocityY, Handler handler, FlingTaskCallback callback) {this.velocityY = velocityY;this.mHandler = handler;this.originalVelocityY = velocityY;this.flingTaskCallback = callback;}boolean initSlide = false; // 初始化滑动int average = 0; // 平均速度int tempAverage = 1;boolean startSmooth = false; // 开始递减速度平滑处理int sameCount = 0; // 值相同次数// 这里控制平均每段滑动的速度private int getAverageDistance(int velocityY) {int t = velocityY;if (t < 470) {t /= 21;}// divide by zeroif (t == 0) return 0;int v = Math.abs(velocityY / t);if (v < 21) {t /= 21;if (t > 20) {t /= 5;}}return t;}@Overridepublic void run() {// 速度完全消耗完才结束任务，和view滚动结束不冲突// 这个判断是为了扩展，将没消耗完的速度，转给指定的滚动view// if (velocityY > 0) {// 只要view滚动结束，立刻结束任务if (tempAverage > 0 && velocityY > 0) {if (!initSlide) {average = getAverageDistance(velocityY);initSlide = true;}float progress = (float) velocityY / originalVelocityY;float newProgress = 0f;if (average > 300) {newProgress = getInterpolation(progress);} else {newProgress = getInterpolation02(progress);}int prTemp = tempAverage;if (!startSmooth) tempAverage = (int) (average * newProgress);// 递减速度平滑处理if (prTemp == tempAverage) {sameCount++;if (sameCount > 1 && tempAverage > 0) { // 这个值越大，最后衰减停止时越生硬，0 - 30tempAverage--;sameCount = 0;startSmooth = true;}}flingTaskCallback.executeTask(tempAverage);velocityY -= tempAverage;// 这里这样写是为了扩展，将没消耗完的速度，转给其他滚动列表// 判断语句需要改成 if (velocityY > 0)if (tempAverage == 0) { // view滚动停止时// 如果速度没有消耗完，继续消耗velocityY -= average;}// Log.d("TAG", "tempAverage：" + tempAverage + " --- velocityY：" + velocityY + " --- originalVelocityY：" + originalVelocityY);mHandler.post(this);} else {flingTaskCallback.stopTask();stopTask();}}public void stopTask() {mHandler.removeCallbacks(this);initSlide = false;}// 从加速度到逐步衰减（AccelerateDecelerateInterpolator插值器 核心源码）public float getInterpolation(float input) {return (float) (Math.cos((input + 1) * Math.PI) / 2.0f) + 0.5f;}// 速度逐步衰减（DecelerateInterpolator插值器 核心源码）public float getInterpolation02(float input) {return (float) (1.0f - (1.0f - input) * (1.0f - input));}interface FlingTaskCallback {void executeTask(int dy);void stopTask();}
}
4. Activity
package com.example.flingscrollview;import androidx.appcompat.app.AppCompatActivity;import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);}}
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