此文章出自于：https://blog.csdn.net/qq_33339175/article/details/103025601

高德的效果

我的效果

image

所以，我准备自定义一个BottomSheetBehavior，再它的onSlide里返回剩下的高度，也就是leftHeight这个参数，不需要进行除法。

于是我套用的这位大佬的自定义BottomSheetBehavior：重写BottomSheetBehavior
他的BottomSheet实现的功能是，滑到哪就可以停在哪，当然我是不需要这个功能的，但是，大佬的类里，实现了：通过overScroller，根据当前的位置releasedChild.getTop()，以及速度yvel,来计算最终滚动到的位置overScroller.getFinalY()

也就是当你把BottomSheet往上或者往下一滑时，它会算出这个bottomsheet最终会滑到哪里，照着这个思路，我修改了一下BottomSheetBehavior，将这个最终位置命名为finalTop，并且将它传递了出来。

这样，根据finalTop这个参数，我把屏幕分成了几个部分：
整个屏幕的高度为 height
bottomsheet的peekheight为 minHeight
整个屏幕去掉minHeight，剩下的高度为 mHeight
然后将剩下的部分四等分，分别为：最上层、3/4层、1/2层和最底层
然后bottomsheet的最终滑动位置为 finalTop

这样，剩下的思路就出来了：
当你的finaltop在最底层的时候，也就是finalTop <= mHeight && finalTop > mHeight / 4 * 3，当finaltop在这个区间的时候，属于最底层，你需要的是将bottomsheet调用setState方法，让它进入默认的折叠状态–STATE_COLLAPSED

当你的finaltop在1/2层的时候，也就是finalTop <= mHeight / 4 * 3 && finalTop > mHeight / 2，当finaltop在这个区间的时候，属于1/2层，你需要的是将bottomsheet调用setState方法，让它滑动一半的距离–STATE_HALF_EXPANDED

当你的finaltop在3/4层的时候，也就是finalTop <= mHeight / 2 && finalTop > mHeight / 4，当你的finaltop在这个区间的时候，属于3/4层，你需要的是将bottomsheet调用setState方法，让它滑动一半的距离–STATE_HALF_EXPANDED

当你的finaltop在最上层的时候，也就是finalTop <= mHeight / 4，当你的finaltop在这个区间的时候，属于最上层，你需要的是将bottomsheet调用setState方法，让它进入完全展开状态–STATE_EXPANDED

这样，四种状态就出来了—这里说一下bottomsheet的6中状态：
1.STATE_DRAGGING：过渡状态此时用户正在向上或者向下拖动bottom sheet
2.STATE_SETTLING：视图从脱离手指自由滑动到最终停下的这一小段时间
3.STATE_EXPANDED：处于完全展开的状态
4.STATE_COLLAPSED：默认的折叠状态
5.STATE_HIDDEN：下滑到完全隐藏 bottom sheet
6.STATE_HALF_EXPANDED滑动到mHeight一半的距离

我看了好多篇介绍bottomsheet的文章，不知道为啥都没写STATE_HALF_EXPANDED这个状态。。。

那么，这时候，一开始的目的已经达到了：三段式
先上代码：
自定义BottomSheetBehavior

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package gxsh.xmlkd.tools;

import android.content.Context;
import android.content.res.TypedArray;
import android.os.Parcel;
import android.os.Parcelable;
import android.support.annotation.IntDef;
import android.support.annotation.NonNull;
import android.support.annotation.RestrictTo;
import android.support.annotation.VisibleForTesting;
import android.support.design.R;
import android.support.design.widget.CoordinatorLayout;
import android.support.v4.math.MathUtils;
import android.support.v4.view.AbsSavedState;
import android.support.v4.view.ViewCompat;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.widget.OverScroller;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.ref.WeakReference;

import static android.support.annotation.RestrictTo.Scope.LIBRARY_GROUP;


/**
 * An interaction behavior plugin for a child view of {@link CoordinatorLayout} to make it work as
 * a bottom sheet.
 */
public class MyBottomSheetBehavior<V extends View> extends CoordinatorLayout.Behavior<V>
{

    /**
     * Callback for monitoring events about bottom sheets.
     */
    public abstract static class BottomSheetCallback
    {

        /**
         * Called when the bottom sheet changes its state.
         *
         * @param bottomSheet The bottom sheet view.
         * @param newState    The new state. This will be one of {@link #STATE_DRAGGING},
         *                    {@link #STATE_SETTLING}, {@link #STATE_EXPANDED},
         *                    {@link #STATE_COLLAPSED}, or {@link #STATE_HIDDEN}.
         */
        public abstract void onStateChanged(@NonNull View bottomSheet, @State int newState, int finalTop);

        /**
         * Called when the bottom sheet is being dragged.
         *
         * @param bottomSheet The bottom sheet view.
         * @param slideOffset The new offset of this bottom sheet within [-1,1] range. Offset
         *                    increases as this bottom sheet is moving upward. From 0 to 1 the sheet
         *                    is between collapsed and expanded states and from -1 to 0 it is
         *                    between hidden and collapsed states.
         */
        public abstract void onSlide(@NonNull View bottomSheet, float slideOffset);
    }

    /**
     * The bottom sheet is dragging.
     */
    public static final int STATE_DRAGGING = 1;

    /**
     * The bottom sheet is settling.
     */
    public static final int STATE_SETTLING = 2;

    /**
     * The bottom sheet is expanded.
     */
    public static final int STATE_EXPANDED = 3;

    /**
     * The bottom sheet is collapsed.
     */
    public static final int STATE_COLLAPSED = 4;

    /**
     * The bottom sheet is hidden.
     */
    public static final int STATE_HIDDEN = 5;

    /**
     * 一半高度
     */
    public static final int STATE_HALF_EXPANDED = 6;

    private int finalTop = 0;

    /**
     * @hide
     */
    @RestrictTo(LIBRARY_GROUP)
    @IntDef({STATE_EXPANDED, STATE_COLLAPSED, STATE_DRAGGING, STATE_SETTLING, STATE_HIDDEN})
    @Retention(RetentionPolicy.SOURCE)
    public @interface State
    {
    }

    /**
     * Peek at the 16:9 ratio keyline of its parent.
     *
     * <p>This can be used as a parameter for {@link #setPeekHeight(int)}.
     * {@link #getPeekHeight()} will return this when the value is set.</p>
     */
    public static final int PEEK_HEIGHT_AUTO = -1;

    private static final float HIDE_THRESHOLD = 0.5f;

    private static final float HIDE_FRICTION = 0.1f;

    private float mMaximumVelocity;

    private int mPeekHeight;

    private boolean mPeekHeightAuto;

    private int mPeekHeightMin;

    int mMinOffset;

    int mMaxOffset;

    boolean mHideable;

    private boolean mSkipCollapsed;

    @State
    int mState = STATE_COLLAPSED;

    ViewDragHelper mViewDragHelper;

    private boolean mIgnoreEvents;

    private int mLastNestedScrollDy;

    private boolean mNestedScrolled;

    int mParentHeight;

    WeakReference<V> mViewRef;

    WeakReference<View> mNestedScrollingChildRef;

    private BottomSheetCallback mCallback;

    private VelocityTracker mVelocityTracker;

    int mActivePointerId;

    private int mInitialY;

    boolean mTouchingScrollingChild;

    /**
     * Default constructor for instantiating BottomSheetBehaviors.
     */
    public MyBottomSheetBehavior()
    {
    }

    private OverScroller overScroller;

    /**
     * Default constructor for inflating BottomSheetBehaviors from layout.
     *
     * @param context The {@link Context}.
     * @param attrs   The {@link AttributeSet}.
     */
    public MyBottomSheetBehavior(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        overScroller = new OverScroller(context);
        TypedArray a = context.obtainStyledAttributes(attrs,
                R.styleable.BottomSheetBehavior_Layout);
        TypedValue value = a.peekValue(R.styleable.BottomSheetBehavior_Layout_behavior_peekHeight);
        if (value != null && value.data == PEEK_HEIGHT_AUTO)
        {
            setPeekHeight(value.data);
        } else
        {
            setPeekHeight(a.getDimensionPixelSize(
                    R.styleable.BottomSheetBehavior_Layout_behavior_peekHeight, PEEK_HEIGHT_AUTO));
        }
        setHideable(a.getBoolean(R.styleable.BottomSheetBehavior_Layout_behavior_hideable, false));
        setSkipCollapsed(a.getBoolean(R.styleable.BottomSheetBehavior_Layout_behavior_skipCollapsed,
                false));
        a.recycle();
        ViewConfiguration configuration = ViewConfiguration.get(context);
        mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
    }

    @Override
    public Parcelable onSaveInstanceState(CoordinatorLayout parent, V child)
    {
        return new SavedState(super.onSaveInstanceState(parent, child), mState);
    }

    @Override
    public void onRestoreInstanceState(CoordinatorLayout parent, V child, Parcelable state)
    {
        SavedState ss = (SavedState) state;
        super.onRestoreInstanceState(parent, child, ss.getSuperState());
        // Intermediate states are restored as collapsed state
        if (ss.state == STATE_DRAGGING || ss.state == STATE_SETTLING)
        {
            mState = STATE_COLLAPSED;
        } else
        {
            mState = ss.state;
        }
    }

    @Override
    public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection)
    {
        if (ViewCompat.getFitsSystemWindows(parent) && !ViewCompat.getFitsSystemWindows(child))
        {
            ViewCompat.setFitsSystemWindows(child, true);
        }
        int savedTop = child.getTop();
        // First let the parent lay it out
        parent.onLayoutChild(child, layoutDirection);
        // Offset the bottom sheet
        mParentHeight = parent.getHeight();
        int peekHeight;
        if (mPeekHeightAuto)
        {
            if (mPeekHeightMin == 0)
            {
                mPeekHeightMin = parent.getResources().getDimensionPixelSize(
                        R.dimen.design_bottom_sheet_peek_height_min);
            }
            peekHeight = Math.max(mPeekHeightMin, mParentHeight - parent.getWidth() * 9 / 16);
        } else
        {
            peekHeight = mPeekHeight;
        }
        mMinOffset = Math.max(0, mParentHeight - child.getHeight());
        mMaxOffset = Math.max(mParentHeight - peekHeight, mMinOffset);
        if (mState == STATE_EXPANDED)
        {
            ViewCompat.offsetTopAndBottom(child, mMinOffset);
        } else if (mHideable && mState == STATE_HIDDEN)
        {
            ViewCompat.offsetTopAndBottom(child, mParentHeight);
        } else if (mState == STATE_COLLAPSED)
        {
            ViewCompat.offsetTopAndBottom(child, mMaxOffset);
        } else if (mState == STATE_DRAGGING || mState == STATE_SETTLING)
        {
            ViewCompat.offsetTopAndBottom(child, savedTop - child.getTop());
        }
        if (mViewDragHelper == null)
        {
            mViewDragHelper = ViewDragHelper.create(parent, mDragCallback);
        }
        mViewRef = new WeakReference<>(child);
        mNestedScrollingChildRef = new WeakReference<>(findScrollingChild(child));
        return true;
    }

    @Override
    public boolean onInterceptTouchEvent(CoordinatorLayout parent, V child, MotionEvent event)
    {
        if (!child.isShown())
        {
            mIgnoreEvents = true;
            return false;
        }
        int action = event.getActionMasked();
        // Record the velocity
        if (action == MotionEvent.ACTION_DOWN)
        {
            reset();
        }
        if (mVelocityTracker == null)
        {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(event);
        switch (action)
        {
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                mTouchingScrollingChild = false;
                mActivePointerId = MotionEvent.INVALID_POINTER_ID;
                // Reset the ignore flag
                if (mIgnoreEvents)
                {
                    mIgnoreEvents = false;
                    return false;
                }
                break;
            case MotionEvent.ACTION_DOWN:
                int initialX = (int) event.getX();
                mInitialY = (int) event.getY();
                View scroll = mNestedScrollingChildRef != null
                        ? mNestedScrollingChildRef.get() : null;
                if (scroll != null && parent.isPointInChildBounds(scroll, initialX, mInitialY))
                {
                    mActivePointerId = event.getPointerId(event.getActionIndex());
                    mTouchingScrollingChild = true;
                }
                mIgnoreEvents = mActivePointerId == MotionEvent.INVALID_POINTER_ID &&
                        !parent.isPointInChildBounds(child, initialX, mInitialY);
                break;
        }
        if (!mIgnoreEvents && mViewDragHelper.shouldInterceptTouchEvent(event))
        {
            return true;
        }
        // We have to handle cases that the ViewDragHelper does not capture the bottom sheet because
        // it is not the top most view of its parent. This is not necessary when the touch event is
        // happening over the scrolling content as nested scrolling logic handles that case.
        View scroll = mNestedScrollingChildRef.get();
        return action == MotionEvent.ACTION_MOVE && scroll != null &&
                !mIgnoreEvents && mState != STATE_DRAGGING &&
                !parent.isPointInChildBounds(scroll, (int) event.getX(), (int) event.getY()) &&
                Math.abs(mInitialY - event.getY()) > mViewDragHelper.getTouchSlop();
    }

    @Override
    public boolean onTouchEvent(CoordinatorLayout parent, V child, MotionEvent event)
    {
        if (!child.isShown())
        {
            return false;
        }
        int action = event.getActionMasked();
        if (mState == STATE_DRAGGING && action == MotionEvent.ACTION_DOWN)
        {
            return true;
        }
        if (mViewDragHelper != null)
        {
            mViewDragHelper.processTouchEvent(event);
        }
        // Record the velocity
        if (action == MotionEvent.ACTION_DOWN)
        {
            reset();
        }
        if (mVelocityTracker == null)
        {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(event);
        // The ViewDragHelper tries to capture only the top-most View. We have to explicitly tell it
        // to capture the bottom sheet in case it is not captured and the touch slop is passed.
        if (action == MotionEvent.ACTION_MOVE && !mIgnoreEvents)
        {
            if (Math.abs(mInitialY - event.getY()) > mViewDragHelper.getTouchSlop())
            {
                mViewDragHelper.captureChildView(child, event.getPointerId(event.getActionIndex()));
            }
        }
        return !mIgnoreEvents;
    }

    @Override
    public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, V child,
                                       View directTargetChild, View target, int nestedScrollAxes)
    {
        mLastNestedScrollDy = 0;
        mNestedScrolled = false;
        return (nestedScrollAxes & ViewCompat.SCROLL_AXIS_VERTICAL) != 0;
    }

    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, V child, View target, int dx,
                                  int dy, int[] consumed)
    {
        View scrollingChild = mNestedScrollingChildRef.get();
        if (target != scrollingChild)
        {
            return;
        }
        int currentTop = child.getTop();
        int newTop = currentTop - dy;
        if (dy > 0)
        { // Upward
            if (newTop < mMinOffset)
            {
                consumed[1] = currentTop - mMinOffset;
                ViewCompat.offsetTopAndBottom(child, -consumed[1]);
                setStateInternal(STATE_EXPANDED);
            } else
            {
                consumed[1] = dy;
                ViewCompat.offsetTopAndBottom(child, -dy);
                setStateInternal(STATE_DRAGGING);
            }
        } else if (dy < 0)
        { // Downward
            if (!target.canScrollVertically(-1))
            {
                if (newTop <= mMaxOffset || mHideable)
                {
                    consumed[1] = dy;
                    ViewCompat.offsetTopAndBottom(child, -dy);
                    setStateInternal(STATE_DRAGGING);
                } else
                {
                    consumed[1] = currentTop - mMaxOffset;
                    ViewCompat.offsetTopAndBottom(child, -consumed[1]);
                    setStateInternal(STATE_COLLAPSED);
                }
            }
        }
        dispatchOnSlide(child.getTop());
        mLastNestedScrollDy = dy;
        mNestedScrolled = true;
    }

    @Override
    public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, V child, View target)
    {
        if (child.getTop() == mMinOffset)
        {
            setStateInternal(STATE_EXPANDED);
            return;
        }
        if (mNestedScrollingChildRef == null || target != mNestedScrollingChildRef.get()
                || !mNestedScrolled)
        {
            return;
        }
        int top;
        int targetState;
//        if (mLastNestedScrollDy > 0) {
//            top = mMinOffset;
//            targetState = STATE_EXPANDED;
//        } else if (mHideable && shouldHide(child, getYVelocity())) {
//            top = mParentHeight;
//            targetState = STATE_HIDDEN;
//        } else if (mLastNestedScrollDy == 0) {
//            int currentTop = child.getTop();
//            if (Math.abs(currentTop - mMinOffset) < Math.abs(currentTop - mMaxOffset)) {
//                top = mMinOffset;
//                targetState = STATE_EXPANDED;
//            } else {
//                top = mMaxOffset;
//                targetState = STATE_COLLAPSED;
//            }
//        } else {
//            top = mMaxOffset;
//            targetState = STATE_COLLAPSED;
//        }
        targetState = STATE_SETTLING;
        top = child.getTop() - mLastNestedScrollDy;
        if (mViewDragHelper.smoothSlideViewTo(child, child.getLeft(), top))
        {
            setStateInternal(STATE_SETTLING);
            ViewCompat.postOnAnimation(child, new SettleRunnable(child, targetState));
        } else
        {
            setStateInternal(targetState);
        }
        mNestedScrolled = false;
    }

    @Override
    public boolean onNestedPreFling(CoordinatorLayout coordinatorLayout, V child, View target,
                                    float velocityX, float velocityY)
    {
        return target == mNestedScrollingChildRef.get() &&
                (mState != STATE_EXPANDED ||
                        super.onNestedPreFling(coordinatorLayout, child, target,
                                velocityX, velocityY));
    }

    /**
     * Sets the height of the bottom sheet when it is collapsed.
     *
     * @param peekHeight The height of the collapsed bottom sheet in pixels, or
     *                   {@link #PEEK_HEIGHT_AUTO} to configure the sheet to peek automatically
     *                   at 16:9 ratio keyline.
     * @attr ref android.support.design.R.styleable#BottomSheetBehavior_Layout_behavior_peekHeight
     */
    public final void setPeekHeight(int peekHeight)
    {
        boolean layout = false;
        if (peekHeight == PEEK_HEIGHT_AUTO)
        {
            if (!mPeekHeightAuto)
            {
                mPeekHeightAuto = true;
                layout = true;
            }
        } else if (mPeekHeightAuto || mPeekHeight != peekHeight)
        {
            mPeekHeightAuto = false;
            mPeekHeight = Math.max(0, peekHeight);
            mMaxOffset = mParentHeight - peekHeight;
            layout = true;
        }
        if (layout && mState == STATE_COLLAPSED && mViewRef != null)
        {
            V view = mViewRef.get();
            if (view != null)
            {
                view.requestLayout();
            }
        }
    }

    /**
     * Gets the height of the bottom sheet when it is collapsed.
     *
     * @return The height of the collapsed bottom sheet in pixels, or {@link #PEEK_HEIGHT_AUTO}
     * if the sheet is configured to peek automatically at 16:9 ratio keyline
     * @attr ref android.support.design.R.styleable#BottomSheetBehavior_Layout_behavior_peekHeight
     */
    public final int getPeekHeight()
    {
        return mPeekHeightAuto ? PEEK_HEIGHT_AUTO : mPeekHeight;
    }

    /**
     * Sets whether this bottom sheet can hide when it is swiped down.
     *
     * @param hideable {@code true} to make this bottom sheet hideable.
     * @attr ref android.support.design.R.styleable#BottomSheetBehavior_Layout_behavior_hideable
     */
    public void setHideable(boolean hideable)
    {
        mHideable = hideable;
    }

    /**
     * Gets whether this bottom sheet can hide when it is swiped down.
     *
     * @return {@code true} if this bottom sheet can hide.
     * @attr ref android.support.design.R.styleable#BottomSheetBehavior_Layout_behavior_hideable
     */
    public boolean isHideable()
    {
        return mHideable;
    }

    /**
     * Sets whether this bottom sheet should skip the collapsed state when it is being hidden
     * after it is expanded once. Setting this to true has no effect unless the sheet is hideable.
     *
     * @param skipCollapsed True if the bottom sheet should skip the collapsed state.
     * @attr ref android.support.design.R.styleable#BottomSheetBehavior_Layout_behavior_skipCollapsed
     */
    public void setSkipCollapsed(boolean skipCollapsed)
    {
        mSkipCollapsed = skipCollapsed;
    }

    /**
     * Sets whether this bottom sheet should skip the collapsed state when it is being hidden
     * after it is expanded once.
     *
     * @return Whether the bottom sheet should skip the collapsed state.
     * @attr ref android.support.design.R.styleable#BottomSheetBehavior_Layout_behavior_skipCollapsed
     */
    public boolean getSkipCollapsed()
    {
        return mSkipCollapsed;
    }

    /**
     * Sets a callback to be notified of bottom sheet events.
     *
     * @param callback The callback to notify when bottom sheet events occur.
     */
    public void setBottomSheetCallback(BottomSheetCallback callback)
    {
        mCallback = callback;
    }

    /**
     * Sets the state of the bottom sheet. The bottom sheet will transition to that state with
     * animation.
     *
     * @param state One of {@link #STATE_COLLAPSED}, {@link #STATE_EXPANDED}, or
     *              {@link #STATE_HIDDEN}.
     */
    public final void setState(final @State int state)
    {
        if (state == mState)
        {
            return;
        }
        if (mViewRef == null)
        {
            // The view is not laid out yet; modify mState and let onLayoutChild handle it later
            if (state == STATE_COLLAPSED || state == STATE_EXPANDED ||
                    (mHideable && state == STATE_HIDDEN))
            {
                mState = state;
            }
            return;
        }
        final V child = mViewRef.get();
        if (child == null)
        {
            return;
        }
        // Start the animation; wait until a pending layout if there is one.
        ViewParent parent = child.getParent();
        if (parent != null && parent.isLayoutRequested() && ViewCompat.isAttachedToWindow(child))
        {
            child.post(new Runnable()
            {
                @Override
                public void run()
                {
                    startSettlingAnimation(child, state);
                }
            });
        } else
        {
            startSettlingAnimation(child, state);
        }
    }

    /**
     * Gets the current state of the bottom sheet.
     *
     * @return One of {@link #STATE_EXPANDED}, {@link #STATE_COLLAPSED}, {@link #STATE_DRAGGING},
     * {@link #STATE_SETTLING}, and {@link #STATE_HIDDEN}.
     */
    @State
    public final int getState()
    {
        return mState;
    }

    void setStateInternal(@State int state)
    {
        if (mState == state)
        {
            return;
        }
        mState = state;
        View bottomSheet = mViewRef.get();
        if (bottomSheet != null && mCallback != null)
        {
            mCallback.onStateChanged(bottomSheet, state, finalTop);
        }
    }

    private void reset()
    {
        mActivePointerId = ViewDragHelper.INVALID_POINTER;
        if (mVelocityTracker != null)
        {
            mVelocityTracker.recycle();
            mVelocityTracker = null;
        }
    }

    boolean shouldHide(View child, float yvel)
    {
        if (mSkipCollapsed)
        {
            return true;
        }
        if (child.getTop() < mMaxOffset)
        {
            // It should not hide, but collapse.
            return false;
        }
        final float newTop = child.getTop() + yvel * HIDE_FRICTION;
        return Math.abs(newTop - mMaxOffset) / (float) mPeekHeight > HIDE_THRESHOLD;
    }

    @VisibleForTesting
    View findScrollingChild(View view)
    {
        if (ViewCompat.isNestedScrollingEnabled(view))
        {
            return view;
        }
        if (view instanceof ViewGroup)
        {
            ViewGroup group = (ViewGroup) view;
            for (int i = 0, count = group.getChildCount(); i < count; i++)
            {
                View scrollingChild = findScrollingChild(group.getChildAt(i));
                if (scrollingChild != null)
                {
                    return scrollingChild;
                }
            }
        }
        return null;
    }

    private float getYVelocity()
    {
        mVelocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
        return mVelocityTracker.getYVelocity(mActivePointerId);
    }

    void startSettlingAnimation(View child, int state)
    {
        int top;
        if (state == STATE_COLLAPSED)
        {
            top = mMaxOffset;
        } else if (state == STATE_EXPANDED)
        {
            top = mMinOffset;
        } else if (state == STATE_HALF_EXPANDED)
        {
            top = mParentHeight / 2;
        } else if (mHideable && state == STATE_HIDDEN)
        {
            top = mParentHeight;
        } else
        {
            throw new IllegalArgumentException("Illegal state argument: " + state);
        }
        if (mViewDragHelper.smoothSlideViewTo(child, child.getLeft(), top))
        {
            setStateInternal(STATE_SETTLING);
            ViewCompat.postOnAnimation(child, new SettleRunnable(child, state));
        } else
        {
            setStateInternal(state);
        }
    }

    private final ViewDragHelper.Callback mDragCallback = new ViewDragHelper.Callback()
    {

        @Override
        public boolean tryCaptureView(View child, int pointerId)
        {
            if (mState == STATE_DRAGGING)
            {
                return false;
            }
            if (mTouchingScrollingChild)
            {
                return false;
            }
            if (mState == STATE_EXPANDED && mActivePointerId == pointerId)
            {
                View scroll = mNestedScrollingChildRef.get();
                if (scroll != null && scroll.canScrollVertically(-1))
                {
                    // Let the content scroll up
                    return false;
                }
            }
            return mViewRef != null && mViewRef.get() == child;
        }

        @Override
        public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy)
        {
            dispatchOnSlide(top);
        }

        @Override
        public void onViewDragStateChanged(int state)
        {
            if (state == ViewDragHelper.STATE_DRAGGING)
            {
                setStateInternal(STATE_DRAGGING);
            }
        }

        @Override
        public void onViewReleased(View releasedChild, float xvel, float yvel)
        {
            int top;
            @State int targetState;
//            if (yvel < 0) { // Moving up
//                top = mMinOffset;
//                targetState = STATE_EXPANDED;
//            } else if (mHideable && shouldHide(releasedChild, yvel)) {
//                top = mParentHeight;
//                targetState = STATE_HIDDEN;
//            } else if (yvel == 0.f) {
//                int currentTop = releasedChild.getTop();
//                if (Math.abs(currentTop - mMinOffset) < Math.abs(currentTop - mMaxOffset)) {
//                    top = mMinOffset;
//                    targetState = STATE_EXPANDED;
//                } else {
//                    top = mMaxOffset;
//                    targetState = STATE_COLLAPSED;
//                }
//            } else {
//                top = mMaxOffset;
//                targetState = STATE_COLLAPSED;
//            }

            targetState = STATE_SETTLING;
            if (yvel != 0)
            {//重新处理
                overScroller.fling(releasedChild.getLeft(), releasedChild.getTop(), 0, (int) yvel, 0, 0, mMinOffset, mMaxOffset);
                top = overScroller.getFinalY();
                finalTop = top;
            } else
            {
                top = releasedChild.getTop();
                finalTop = top;
            }
            if (mViewDragHelper.settleCapturedViewAt(releasedChild.getLeft(), top))
            {
                setStateInternal(STATE_SETTLING);
                ViewCompat.postOnAnimation(releasedChild,
                        new SettleRunnable(releasedChild, targetState));
            } else
            {
                setStateInternal(targetState);
            }
        }

        @Override
        public int clampViewPositionVertical(View child, int top, int dy)
        {
            return MathUtils.clamp(top, mMinOffset, mHideable ? mParentHeight : mMaxOffset);
        }

        @Override
        public int clampViewPositionHorizontal(View child, int left, int dx)
        {
            return child.getLeft();
        }

        @Override
        public int getViewVerticalDragRange(View child)
        {
            if (mHideable)
            {
                return mParentHeight - mMinOffset;
            } else
            {
                return mMaxOffset - mMinOffset;
            }
        }
    };

    void dispatchOnSlide(int top)
    {
        View bottomSheet = mViewRef.get();
        if (bottomSheet != null && mCallback != null)
        {
            mCallback.onSlide(bottomSheet,
                    top);
        }
    }

    @VisibleForTesting
    int getPeekHeightMin()
    {
        return mPeekHeightMin;
    }

    private class SettleRunnable implements Runnable
    {

        private final View mView;

        @State
        private final int mTargetState;

        SettleRunnable(View view, @State int targetState)
        {
            mView = view;
            mTargetState = targetState;
        }

        @Override
        public void run()
        {
            if (mViewDragHelper != null && mViewDragHelper.continueSettling(true))
            {
                ViewCompat.postOnAnimation(mView, this);
            } else
            {
                setStateInternal(mTargetState);
            }
        }
    }

    protected static class SavedState extends AbsSavedState
    {
        @State
        final int state;

        public SavedState(Parcel source)
        {
            this(source, null);
        }

        public SavedState(Parcel source, ClassLoader loader)
        {
            super(source, loader);
            //noinspection ResourceType
            state = source.readInt();
        }

        public SavedState(Parcelable superState, @State int state)
        {
            super(superState);
            this.state = state;
        }

        @Override
        public void writeToParcel(Parcel out, int flags)
        {
            super.writeToParcel(out, flags);
            out.writeInt(state);
        }

        public static final Creator<SavedState> CREATOR = new ClassLoaderCreator<SavedState>()
        {
            @Override
            public SavedState createFromParcel(Parcel in, ClassLoader loader)
            {
                return new SavedState(in, loader);
            }

            @Override
            public SavedState createFromParcel(Parcel in)
            {
                return new SavedState(in, null);
            }

            @Override
            public SavedState[] newArray(int size)
            {
                return new SavedState[size];
            }
        };
    }

    /**
     * A utility function to get the {@link MyBottomSheetBehavior} associated with the {@code view}.
     *
     * @param view The {@link View} with {@link MyBottomSheetBehavior}.
     * @return The {@link MyBottomSheetBehavior} associated with the {@code view}.
     */
    @SuppressWarnings("unchecked")
    public static <V extends View> MyBottomSheetBehavior<V> from(V view)
    {
        ViewGroup.LayoutParams params = view.getLayoutParams();
        if (!(params instanceof CoordinatorLayout.LayoutParams))
        {
            throw new IllegalArgumentException("The view is not a child of CoordinatorLayout");
        }
        CoordinatorLayout.Behavior behavior = ((CoordinatorLayout.LayoutParams) params)
                .getBehavior();
        if (!(behavior instanceof MyBottomSheetBehavior))
        {
            throw new IllegalArgumentException(
                    "The view is not associated with BottomSheetBehavior");
        }
        return (MyBottomSheetBehavior<V>) behavior;
    }

}

实现效果代码：

package com.example.myapplication;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;



public class MainActivity extends AppCompatActivity {

    private int mHeight;
    private int mWidth;
    private int minHeight = 1000;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        DisplayMetrics outMetrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(outMetrics);
        mWidth = outMetrics.widthPixels;
        mHeight = outMetrics.heightPixels;
        LinearLayout bottom_sheet = findViewById(R.id.bottom_sheet); //bottomsheet
        LinearLayout layout_bottom_sheet = findViewById(R.id.layout_bottom_sheet); //bottomsheet
        Log.i("TAG", "widthPixels = " + mWidth + ",heightPixels = " + mHeight);
        ViewGroup.LayoutParams layoutParams = layout_bottom_sheet.getLayoutParams();
        layoutParams.height =
                minHeight + mHeight / 4 * 3;
        layoutParams.width = mWidth;
        layout_bottom_sheet.setLayoutParams(layoutParams);


        final MyBottomSheetBehavior bottomSheetBehavior = MyBottomSheetBehavior.from(bottom_sheet);
        //设置监听事件
        bottomSheetBehavior.setBottomSheetCallback(new MyBottomSheetBehavior.BottomSheetCallback() {


            @Override
            public void onStateChanged(@NonNull View bottomSheet, int newState, int finalTop) {
                //拖动
                if (newState == 2) {
                    Log.e("finalTop", "===" + finalTop);
                    if (finalTop <= mHeight && finalTop > mHeight / 4 * 3) {
                        // 最底层
                        Log.e("最底层", "最底层");
                        bottomSheetBehavior.setState(MyBottomSheetBehavior.STATE_COLLAPSED);
                    } else if (finalTop <= mHeight / 4 * 3 && finalTop > mHeight / 2) {
                        Log.e("2分之1层", "2分之1层");
                        bottomSheetBehavior.setState(MyBottomSheetBehavior.STATE_HALF_EXPANDED);
                    } else if (finalTop <= mHeight / 2 && finalTop > mHeight / 4 + mHeight / 8) {
                        Log.e("B层", "B层");
                        bottomSheetBehavior.setState(MyBottomSheetBehavior.STATE_HALF_EXPANDED);
                    } else if (finalTop <= mHeight / 4 + mHeight / 8) {
                        Log.e("A层", "A层");//STATE_EXPANDED
                        bottomSheetBehavior.setState(MyBottomSheetBehavior.STATE_EXPANDED);
                    }
                }
            }

            @Override
            public void onSlide(@NonNull View bottomSheet, float slideOffset) {
                //状态变化
            }
        });

    }
}

再加上布局代码：

<?xml version="1.0" encoding="utf-8"?><!--    CoordinatorLayout-->
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app2="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="213213321321321"
            android:visibility="visible" />

    </FrameLayout>
    <!--    @string/bottom_sheet_behavior-->

    <LinearLayout
        android:layout_marginTop="100dp"
        android:id="@+id/bottom_sheet"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"

        app2:behavior_hideable="false"
        app2:behavior_peekHeight="300dp"
        app2:layout_behavior=".MyBottomSheetBehavior"
        tools:ignore="MissingPrefix">

        <LinearLayout
            android:id="@+id/layout_bottom_sheet"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:background="#000"
            android:orientation="vertical">


        </LinearLayout>
    </LinearLayout>

</androidx.coordinatorlayout.widget.CoordinatorLayout>

这样，就可以达到最上面第二张gif图的效果了，里面的细节等东西，可以自己去优化一下，然后参数也可以又自己去修改，达到自己要的效果。