问题描述：

RecyclerView自带快速滚动无法控制滚动条的长度唯一，也就是说随着item的增多，滚动条的长度会越变越小。

解决问题：

通过自定义RecyclerView来实现滚动条的长度不会因为item的增多而发生长度变化。

具体实现：

package com.emsm.app.widget;import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.MotionEvent;import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;import com.emsm.app.util.LogHelps;/*** @Author emsm* @Time 2022/9/5 19:08* @Description 参考；RecyclerView中的initFastScroller实现* <p>* 专注美妆(香水口红护肤)批发代发-供淘宝/天猫/京东/微商/代购/闲鱼等* 主做欧美大牌：迪奥/阿玛尼/祖马龙/香奈儿/古驰/TF/MAC/圣罗兰等等* 只做高品质产品！(送朋友亲人客户公司活动以及自用或泡妞等等)* ＋V：em-smart-99999*/
public class FastScrollerRecyclerView extends RecyclerView {private FastScroller mFastScroller;public FastScrollerRecyclerView(Context context) {super(context);}public FastScrollerRecyclerView(Context context, AttributeSet attrs) {super(context, attrs);init(context, attrs);}public FastScrollerRecyclerView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);init(context, attrs);}private void init(Context context, AttributeSet attrs) {mFastScroller = new FastScroller(context, attrs);}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {super.onMeasure(widthMeasureSpec, heightMeasureSpec);int mMeasureWidth = MeasureSpec.getSize(widthMeasureSpec);int mMeasureHeight = MeasureSpec.getSize(heightMeasureSpec);setMeasuredDimension(mMeasureWidth, mMeasureHeight);LogHelps.w("setMeasuredDimension ");if (mFastScroller != null) {mFastScroller.onMeasure(mMeasureWidth, mMeasureHeight);}}private class FastScroller extends RecyclerView.ItemDecoration implements RecyclerView.OnItemTouchListener {private ScrollerDraw mScrollerDraw;private ScrollerEvent mScrollerEvent;FastScroller(Context context, AttributeSet attrs) {init(context, attrs);}private void init(Context context, AttributeSet attrs) {mScrollerDraw = new ScrollerDraw();mScrollerDraw.init(context, attrs);mScrollerDraw.setView(FastScrollerRecyclerView.this);if (isEnabled()) {addItemDecoration(this);addOnItemTouchListener(this);mScrollerEvent = new ScrollerEvent();mScrollerEvent.attachRecyclerView(FastScrollerRecyclerView.this, ratio -> {setRatio(ratio);});}}private void onMeasure(int measureWidth, int measureHeight) {if (isEnabled()) {mScrollerDraw.onMeasure(measureWidth, measureHeight, measureWidth);}}private boolean isEnabled() {return (mScrollerDraw != null && mScrollerDraw.isEnabled());}@Overridepublic void onDrawOver(@NonNull Canvas canvas, @NonNull RecyclerView parent, @NonNull State state) {super.onDrawOver(canvas, parent, state);try {if (!ScrollerEvent.isRecyclerScrollable(FastScrollerRecyclerView.this)) {LogHelps.w("item数量不足一屏 不支持展示滚动条");return;}if (!isEnabled()) {return;}if (!mScrollerDraw.isAlwaysShow()) {mScrollerDraw.mH.removeMessages(1);if (mScrollerDraw.getAnimatorWhat() == 1) {mScrollerDraw.mH.sendEmptyMessage(1);mScrollerDraw.setAnimatorWhat(2);}}mScrollerDraw.onDraw(canvas);if (!mScrollerDraw.isAlwaysShow()) {mScrollerDraw.mH.removeMessages(2);if (mScrollerDraw.getAnimatorWhat() == 2) {mScrollerDraw.mH.sendEmptyMessageDelayed(2, 1000);}}} catch (Exception e) {LogHelps.e("Exception-IllegalArgumentException :" + e.getMessage());}}@Overridepublic boolean onInterceptTouchEvent(@NonNull RecyclerView recyclerView, @NonNull MotionEvent ev) {// 判断是不是在滚动条范围之内 在就拦截item滚动boolean insideVerticalThumb = isPointInsideVerticalThumb(ev.getX(), ev.getY());if (ev.getAction() == MotionEvent.ACTION_DOWN && (insideVerticalThumb)) {return true;}return false;}private boolean isPointInsideVerticalThumb(float x, float y) {if (!isEnabled()) {return false;}// SeekbarRecyclerViewCopy.this.getPaddingRight() 获取的值相当于布局文件中 android:paddingRight="30dp"// LogHelps.i(SeekbarRecyclerViewCopy.this.getPaddingRight() + " |getPaddingRight " + SizeUtil.px2dip(mContext, 30));return x > mScrollerDraw.getThumbBitmapC() - FastScrollerRecyclerView.this.getPaddingRight();}@Overridepublic void onTouchEvent(@NonNull RecyclerView rv, @NonNull MotionEvent event) {if (mScrollerEvent != null && isEnabled()) {mScrollerEvent.onTouchEvent(event, getHeight());}}@Overridepublic void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {}public void setRatio(float ratio) {if (isEnabled()) {mScrollerDraw.setAnimatorWhat(1);mScrollerDraw.setRatio(ratio);postInvalidate();}}}
}

package com.emsm.app.widget;import android.animation.ValueAnimator;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.drawable.BitmapDrawable;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.util.AttributeSet;
import android.view.View;import androidx.annotation.NonNull;import com.emsm.app.R;
import com.emsm.app.util.BitmapUtils;
import com.emsm.app.util.LogHelps;/*** @Author chentao 0000668668* @Time 2023/2/10* @Description*  * 专注美妆(香水口红护肤)批发代发-供淘宝/天猫/京东/微商/代购/闲鱼等*  * 主做欧美大牌：迪奥/阿玛尼/祖马龙/香奈儿/古驰/TF/MAC/圣罗兰等等*  * 只做高品质产品！(送朋友亲人客户公司活动以及自用或泡妞等等)*  * ＋V：em-smart-99999*/
public class ScrollerDraw {private Paint mPaint;private Matrix matrix;private Bitmap mBgBitmap;private Bitmap mPgBitmap;private Bitmap mThumbBitmap;private boolean mEnabled = true;// true  说明 一直显示 false 说明 滑动显示不滑动隐藏private boolean mAlwaysShow = false;// 滚动的比例值 0-1private float mRatio = 0;private int mDrawHeight;private int mThumbBitmapW, mThumbBitmapH, mThumbBitmapC;private int mBgBitmapW, mBgBitmapH, mBgBitmapC;private int mPgBitmapW, mPgBitmapH, mPgBitmapC;private final ValueAnimator mShowHideAnimator = ValueAnimator.ofFloat(0, 1);public boolean isAlwaysShow() {return mAlwaysShow;}public boolean isEnabled() {return mEnabled;}public void setRatio(float ratio) {this.mRatio = ratio;}public void init(Context context, AttributeSet attrs) {TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.ScrollBar);mEnabled = array.getBoolean(R.styleable.ScrollBar_ScrollBarEnabled, true);if (!mEnabled) {LogHelps.w(" init-快速滚动设置为不可用！！！");array.recycle();return;}mAlwaysShow = array.getBoolean(R.styleable.ScrollBar_ScrollBarAlwaysShow, false);BitmapDrawable drawableBg = (BitmapDrawable) array.getDrawable(R.styleable.ScrollBar_ScrollBarBackground);if (drawableBg != null) {mBgBitmap = drawableBg.getBitmap();}BitmapDrawable drawablePr = (BitmapDrawable) array.getDrawable(R.styleable.ScrollBar_ScrollBarProgress);if (drawablePr != null) {mPgBitmap = drawablePr.getBitmap();}BitmapDrawable drawableTb = (BitmapDrawable) array.getDrawable(R.styleable.ScrollBar_ScrollBarThumb);if (drawableTb != null) {mThumbBitmap = drawableTb.getBitmap();}mRatio = array.getInt(R.styleable.ScrollBar_ScrollBarCurrentProgress, 0);array.recycle();mPaint = new Paint();mPaint.setAntiAlias(true);if (!mAlwaysShow) {mShowHideAnimator.addUpdateListener(new AnimatorUpdater());mH.sendEmptyMessage(1);}}private int mAnimatorWhat = 2;private static final int SCROLLBAR_FULL_OPAQUE = 255;private View mView;public void setView(View view) {this.mView = view;}public int getAnimatorWhat() {return mAnimatorWhat;}public void setAnimatorWhat(int mAnimatorWhat) {this.mAnimatorWhat = mAnimatorWhat;}public final Handler mH = new Handler(Looper.getMainLooper()) {@Overridepublic void handleMessage(@NonNull Message msg) {super.handleMessage(msg);switch (msg.what) {case 1:  // 显示LogHelps.i(" handleMessage show");mPaint.setAlpha(225);if (false) {mShowHideAnimator.setFloatValues((float) mShowHideAnimator.getAnimatedValue(), 1);mShowHideAnimator.setDuration(100);//  mShowHideAnimator.setStartDelay(0);mShowHideAnimator.start();}break;case 2: // 隐藏LogHelps.i(" handleMessage hide");if (mShowHideAnimator.isRunning()) {mShowHideAnimator.cancel();}mShowHideAnimator.setFloatValues((float) mShowHideAnimator.getAnimatedValue(), 0);mShowHideAnimator.setDuration(100);mShowHideAnimator.start();break;}}};private class AnimatorUpdater implements ValueAnimator.AnimatorUpdateListener {AnimatorUpdater() {}@Overridepublic void onAnimationUpdate(ValueAnimator valueAnimator) {int alpha = (int) (SCROLLBAR_FULL_OPAQUE * ((float) valueAnimator.getAnimatedValue()));// 隐藏之后把数字修改未其他的值 避免再次执行 显示和隐藏的逻辑mAnimatorWhat = 3;mPaint.setAlpha(alpha);if (mView != null) {mView.postInvalidate();}}}public void onMeasure(int measureWidth, int measureHeight,int left) {if (!mEnabled) {return;}if (mBgBitmap != null) {mBgBitmap = BitmapUtils.alterBitmapSize(mBgBitmap, mBgBitmap.getWidth(), measureHeight);}if (mPgBitmap != null) {mPgBitmap = BitmapUtils.alterBitmapSize(mPgBitmap, mPgBitmap.getWidth(), measureHeight);}mThumbBitmapW = mThumbBitmap.getWidth();mThumbBitmapH = mThumbBitmap.getHeight();mBgBitmapW = mBgBitmap.getWidth();mBgBitmapH = mBgBitmap.getHeight();mPgBitmapW = mPgBitmap.getWidth();mPgBitmapH = mPgBitmap.getHeight();if (measureHeight > mPgBitmapH) {measureHeight = mPgBitmapH;}this.mDrawHeight = measureHeight - mThumbBitmapH;mThumbBitmapC = left - mThumbBitmapW / 2;mBgBitmapC = left - mBgBitmapW / 2;mPgBitmapC = left - mPgBitmapW / 2;}public int getThumbBitmapC() {return mThumbBitmapC;}public void onDraw(Canvas canvas) {if (!mEnabled) {return;}try {float thumbBitmapTop = 0;if (mRatio > 0) {thumbBitmapTop = mRatio * mDrawHeight;}if (mThumbBitmap != null && mThumbBitmapW > 0 && mThumbBitmapH > 0) {canvas.drawBitmap(mThumbBitmap, mThumbBitmapC, thumbBitmapTop, mPaint);}if (mBgBitmap != null && mBgBitmapW > 0 && mBgBitmapH > 0) {canvas.drawBitmap(mBgBitmap, mBgBitmapC, thumbBitmapTop + mThumbBitmapH, mPaint);}if (mPgBitmap != null && mPgBitmapW > 0 && mPgBitmapH > 0 && mDrawHeight > 0 && mRatio > 0) {matrix = new Matrix();matrix.setScale(1, mRatio);Bitmap bitmap = Bitmap.createBitmap(mPgBitmap, 0, 0, mPgBitmapW, mDrawHeight, matrix, true);canvas.drawBitmap(bitmap, mPgBitmapC, 0, mPaint);}} catch (Exception e) {LogHelps.e("Exception-IllegalArgumentException :" + e.getMessage());}}}

package com.emsm.app.widget;import android.view.MotionEvent;import androidx.annotation.NonNull;
import androidx.core.view.ViewCompat;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import androidx.recyclerview.widget.StaggeredGridLayoutManager;import com.emsm.app.util.LogHelps;/*** @Author chentao 0000668668* @Time 2023/2/10* @Description*  * 专注美妆(香水口红护肤)批发代发-供淘宝/天猫/京东/微商/代购/闲鱼等*  * 主做欧美大牌：迪奥/阿玛尼/祖马龙/香奈儿/古驰/TF/MAC/圣罗兰等等*  * 只做高品质产品！(送朋友亲人客户公司活动以及自用或泡妞等等)*  * ＋V：em-smart-99999*/
public class ScrollerEvent {private RecyclerView mRecyclerView;private float mInitialBarHeight;private float mLastPressedYAdjustedToInitial;private int mLastAppBarLayoutOffset;public void attachRecyclerView(RecyclerView recyclerView, CallBack call) {this.mRecyclerView = recyclerView;this.mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {@Overridepublic void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {super.onScrollStateChanged(recyclerView, newState);LogHelps.i("");}@Overridepublic void onScrolled(@NonNull RecyclerView parent, int dx, int dy) {super.onScrolled(parent, dx, dy);if (call == null) {return;}// 滚动条拇指的垂直范围float extent = parent.computeVerticalScrollExtent();//  可滚动的区域大小float range = parent.computeVerticalScrollRange();// 当前偏移量（当前滚动的距离）float offset = parent.computeVerticalScrollOffset();// 最大偏移量（最大可滚动的距离）float maxOffset = range - extent;// 可以滑动时，在绘制if (maxOffset > 0) {// float offsetY = ratio * mMeasureHeight;float ratio = offset / maxOffset;LogHelps.i("dx:" + dx +" dy:" + dy +" extent:" + extent +" range:" + range +" offset:" + offset +" maxOffset:" + maxOffset +" ratio:" + ratio);call.onScrolled(ratio);}}});}public boolean onTouchEvent(MotionEvent event, int viewHeight) {if (mRecyclerView == null || event == null) {return true;}if (event.getActionMasked() == MotionEvent.ACTION_DOWN) {mRecyclerView.stopScroll();int nestedScrollAxis = ViewCompat.SCROLL_AXIS_NONE;nestedScrollAxis |= ViewCompat.SCROLL_AXIS_VERTICAL;mRecyclerView.startNestedScroll(nestedScrollAxis);mInitialBarHeight = viewHeight;mLastPressedYAdjustedToInitial = event.getY() + 0;} else if (event.getActionMasked() == MotionEvent.ACTION_MOVE) {float newHandlePressedY = event.getY() + 0;int barHeight = viewHeight;float newHandlePressedYAdjustedToInitial = newHandlePressedY + (mInitialBarHeight - barHeight);float deltaPressedYFromLastAdjustedToInitial = newHandlePressedYAdjustedToInitial - mLastPressedYAdjustedToInitial;int dY = (int) ((deltaPressedYFromLastAdjustedToInitial / mInitialBarHeight) * (mRecyclerView.computeVerticalScrollRange() + 0));updateRvScroll(dY + mLastAppBarLayoutOffset);mLastPressedYAdjustedToInitial = newHandlePressedYAdjustedToInitial;} else if (event.getActionMasked() == MotionEvent.ACTION_UP) {mLastPressedYAdjustedToInitial = -1;mRecyclerView.stopNestedScroll();}return true;}public void updateRvScroll(int dY) {if (mRecyclerView == null) {return;}try {mRecyclerView.scrollBy(0, dY);} catch (Exception t) {t.printStackTrace();}}interface CallBack {// 滚动的比例值 0-1void onScrolled(float ratio);}/*** 判断是否可以滚动* @param recyclerView* @return*/public static boolean isRecyclerScrollable(RecyclerView recyclerView) {if (recyclerView == null) {return false;}float range = recyclerView.computeVerticalScrollRange();float height = recyclerView.getHeight();// LogHelps.i("recyclerView的滚动范围 " + range + " | RecyclerView的高度 " + height);// 滚动范围大于RecyclerView的高度 说明是可以滚动的if (true) {return range > height;}boolean h = false;if (recyclerView.getLayoutManager() instanceof LinearLayoutManager) {LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();RecyclerView.Adapter adapter = recyclerView.getAdapter();if (layoutManager == null || adapter == null) {h = false;} else {h = layoutManager.findLastCompletelyVisibleItemPosition() < adapter.getItemCount() - 1;}} else if (recyclerView.getLayoutManager() instanceof GridLayoutManager) {GridLayoutManager layoutManager = (GridLayoutManager) recyclerView.getLayoutManager();RecyclerView.Adapter adapter = recyclerView.getAdapter();if (layoutManager == null || adapter == null) {h = false;} else {h = layoutManager.findLastCompletelyVisibleItemPosition() < adapter.getItemCount() - 1;}} else if (recyclerView.getLayoutManager() instanceof StaggeredGridLayoutManager) {StaggeredGridLayoutManager layoutManager = (StaggeredGridLayoutManager) recyclerView.getLayoutManager();RecyclerView.Adapter adapter = recyclerView.getAdapter();if (layoutManager == null || adapter == null) {h = false;} else {h = layoutManager.findLastCompletelyVisibleItemPositions(null)[(layoutManager.getSpanCount() - 1)] < adapter.getItemCount() - 1;}}return h;}}

    <com.emsm.app.widget.FastScrollerRecyclerViewandroid:id="@+id/recycler"android:layout_width="0dp"android:layout_height="match_parent"android:layout_marginRight="100dp"android:background="@color/E3E3E3E3"android:paddingRight="30dp"app:ScrollBarAlwaysShow="true"app:ScrollBarBackground="@mipmap/ad3_bt_contacts_slider_n"app:ScrollBarBottom="20dp"app:ScrollBarCurrentProgress="0"app:ScrollBarEnabled="true"app:ScrollBarProgress="@mipmap/ad3_bt_contacts_slider_n"app:ScrollBarThumb="@mipmap/ad3_bt_contacts_slider_d"app:ScrollBarTop="20dp"app:layout_constraintLeft_toLeftOf="parent"app:layout_constraintRight_toRightOf="parent"app:layout_constraintTop_toTopOf="parent" />

具体效果:

附带：使用到的图片