Android仿高德地图打车的三段式BottomSheet

首先声明:只是简单的实现了功能，但是实际与高德的还是有点区别

高德的效果：

我的效果：

Emmmm，感觉差不多吧。。。其他的还没弄呢，比如滑到最上面有阴影啊之类的。

首先说下思路，一开始，我是打算在滑动的时候，不停的监听onSlide里slideOffset这个参数，然后根据这个参数来动态设定bottomsheet的setPeekHeight，但是问题是，原生的BottomSheetBehavior里的返回参数slideOffset，是按当前高度除以从peekheight到屏幕顶部的距离来算的，也就是说，这个值是会根据peekheight的改变来改变的！

slideOffset = leftHeight / mHeight;
如果你的peekHeight改变了，那么mHeight这个参数也会改变，这就导致了slideOffset 参数的改变。

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;@Stateint 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();}@Overridepublic Parcelable onSaveInstanceState(CoordinatorLayout parent, V child){return new SavedState(super.onSaveInstanceState(parent, child), mState);}@Overridepublic void onRestoreInstanceState(CoordinatorLayout parent, V child, Parcelable state){SavedState ss = (SavedState) state;super.onRestoreInstanceState(parent, child, ss.getSuperState());// Intermediate states are restored as collapsed stateif (ss.state == STATE_DRAGGING || ss.state == STATE_SETTLING){mState = STATE_COLLAPSED;} else{mState = ss.state;}}@Overridepublic 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 outparent.onLayoutChild(child, layoutDirection);// Offset the bottom sheetmParentHeight = 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;}@Overridepublic boolean onInterceptTouchEvent(CoordinatorLayout parent, V child, MotionEvent event){if (!child.isShown()){mIgnoreEvents = true;return false;}int action = event.getActionMasked();// Record the velocityif (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 flagif (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();}@Overridepublic 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 velocityif (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;}@Overridepublic boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, V child,View directTargetChild, View target, int nestedScrollAxes){mLastNestedScrollDy = 0;mNestedScrolled = false;return (nestedScrollAxes & ViewCompat.SCROLL_AXIS_VERTICAL) != 0;}@Overridepublic 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){ // Upwardif (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){ // Downwardif (!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;}@Overridepublic 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;}@Overridepublic 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 laterif (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(){@Overridepublic 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}.*/@Statepublic 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;}@VisibleForTestingView 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(){@Overridepublic 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 upreturn false;}}return mViewRef != null && mViewRef.get() == child;}@Overridepublic void onViewPositionChanged(View changedView, int left, int top, int dx, int dy){dispatchOnSlide(top);}@Overridepublic void onViewDragStateChanged(int state){if (state == ViewDragHelper.STATE_DRAGGING){setStateInternal(STATE_DRAGGING);}}@Overridepublic 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);}}@Overridepublic int clampViewPositionVertical(View child, int top, int dy){return MathUtils.clamp(top, mMinOffset, mHideable ? mParentHeight : mMaxOffset);}@Overridepublic int clampViewPositionHorizontal(View child, int left, int dx){return child.getLeft();}@Overridepublic 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);}}@VisibleForTestingint getPeekHeightMin(){return mPeekHeightMin;}private class SettleRunnable implements Runnable{private final View mView;@Stateprivate final int mTargetState;SettleRunnable(View view, @State int targetState){mView = view;mTargetState = targetState;}@Overridepublic void run(){if (mViewDragHelper != null && mViewDragHelper.continueSettling(true)){ViewCompat.postOnAnimation(mView, this);} else{setStateInternal(mTargetState);}}}protected static class SavedState extends AbsSavedState{@Statefinal int state;public SavedState(Parcel source){this(source, null);}public SavedState(Parcel source, ClassLoader loader){super(source, loader);//noinspection ResourceTypestate = source.readInt();}public SavedState(Parcelable superState, @State int state){super(superState);this.state = state;}@Overridepublic void writeToParcel(Parcel out, int flags){super.writeToParcel(out, flags);out.writeInt(state);}public static final Creator<SavedState> CREATOR = new ClassLoaderCreator<SavedState>(){@Overridepublic SavedState createFromParcel(Parcel in, ClassLoader loader){return new SavedState(in, loader);}@Overridepublic SavedState createFromParcel(Parcel in){return new SavedState(in, null);}@Overridepublic 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;}}

在代码中，监听bottomsheet的滑动：

 LinearLayout bottom_sheet = findViewById(R.id.bottom_sheet); //bottomsheetLinearLayout layout_bottom_sheet = findViewById(R.id.layout_bottom_sheet); // bottomsheet里的布局MyBottomSheetBehavior<LinearLayout> behavior = MyBottomSheetBehavior.from(bottom_sheet);behavior.setBottomSheetCallback(new MyBottomSheetBehavior.BottomSheetCallback(){@SuppressLint("WrongConstant")@Overridepublic void onStateChanged(@NonNull View bottomSheet, int newState, int finalTop){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");behavior.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");behavior.setState(MyBottomSheetBehavior.STATE_HALF_EXPANDED);} else if (finalTop <= mHeight / 2 && finalTop > mHeight / 4){Log.e("3分之2层", "3分之2层");behavior.setState(MyBottomSheetBehavior.STATE_HALF_EXPANDED);} else if (finalTop <= mHeight / 4){Log.e("最上层", "最上层");behavior.setState(MyBottomSheetBehavior.STATE_EXPANDED);}}switch (newState){case 1://过渡状态此时用户正在向上或者向下拖动bottom sheetLog.e("state", "====用户正在向上或者向下拖动");break;case 2:// 视图从脱离手指自由滑动到最终停下的这一小段时间Log.e("state", "====视图从脱离手指自由滑动到最终停下的这一小段时间");break;case 3://处于完全展开的状态Log.e("state", "====处于完全展开的状态");break;case 4://默认的折叠状态Log.e("state", "====默认的折叠状态");break;case 5://下滑动完全隐藏 bottom sheetLog.e("state", "====下滑动完全隐藏");break;}}@Overridepublic void onSlide(@NonNull View bottomSheet, float slideOffset){Log.e("slideOffset", "===" + slideOffset);}});

再加上布局代码：

因为我这个布局CoordinatorLayout外面还有其他的布局，所以没有xmlns:tools啊之类的东西，能看懂就行，Framlayout里就是地图啊之类的布局了，这里主要看的还是bottomsheet的布局：

<LinearLayoutandroid:id="@+id/bottom_sheet"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical"android:visibility="gone"app2:behavior_hideable="false"app2:behavior_peekHeight="100dp"app2:layout_behavior="gxsh.xmlkd.tools.MyBottomSheetBehavior"tools:ignore="MissingPrefix"><LinearLayoutandroid:id="@+id/layout_bottom_sheet"android:layout_width="match_parent"android:layout_height="match_parent"android:layout_alignParentBottom="true"android:background="@color/main_color"android:orientation="vertical"></LinearLayout></LinearLayout>

注意，如果你使用了自定义的BottomSheetBehavior，那么app2:layout_behavior里一定要写上正确的路径，比如：gxsh.xmlkd.tools.MyBottomSheetBehavior，这是我自定义BottomSheetBehavior的路径。

此时，按照上面的代码一路走下来，直到运行，它展示的结果是这样的：

就是一个全屏的效果。

但是在高德地图里，它展示的最大展开是有一个阴影高度的，那么这个的实现就是在代码中修改bottomsheet的高度。

首先，把xml布局中，bottom_sheet和layout_bottom_sheet的layout_height，改成wrap_content：

<LinearLayoutandroid:id="@+id/bottom_sheet"android:layout_width="match_parent"android:layout_height="wrap_content"android:orientation="vertical"android:visibility="gone"app2:behavior_hideable="false"app2:behavior_peekHeight="100dp"app2:layout_behavior="gxsh.xmlkd.tools.MyBottomSheetBehavior"tools:ignore="MissingPrefix"><LinearLayoutandroid:id="@+id/layout_bottom_sheet"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_alignParentBottom="true"android:background="@color/main_color"android:orientation="vertical"></LinearLayout></LinearLayout>

然后在代码中，当你findviewbyid写出layout_bottom_sheet之后，你将它的高度修改一下：ViewGroup.LayoutParams layoutParams = layout_bottom_sheet.getLayoutParams(); layoutParams.height = minHeight + mHeight / 4 * 3; layoutParams.width = mWidth; layout_bottom_sheet.setLayoutParams(layoutParams);
然后再进行MyBottomSheetBehavior.from(bottom_sheet);的操作，得到MyBottomSheetBehavior，那么按照上面的计算结果，这个bottomsheet的最大高度为：minHeight(peekheight的高度)加上剩下屏幕高度mHeight的四分之三，这样的话，这个bottomsheet完全展开的时候，就不会全屏了，同样的，它的finaltop也不会到达最上层了！
那么这样的话，当你滑动到顶之后，它的finaltop还是只会在1/2层，结果只会变成完全折叠状态，这样就不是我们要的效果了。

我的处理方法是：去掉3/4层，和最上层，将原来的3/4层再平均分一下，分成A层和B层

这样，与上面同理，当finaltop在A层的时候，调用STATE_EXPANDED，当finaltop在B层的时候，则调用STATE_HALF_EXPANDED，其实理论上和上面一样，只是把最上层和3/4层改成了A层和B层，而它们的区间值也改了一下而已。

 behavior.setBottomSheetCallback(new MyBottomSheetBehavior.BottomSheetCallback(){@SuppressLint("WrongConstant")@Overridepublic void onStateChanged(@NonNull View bottomSheet, int newState, int finalTop){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");behavior.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");behavior.setState(MyBottomSheetBehavior.STATE_HALF_EXPANDED);} else if (finalTop <= mHeight / 2 && finalTop > mHeight / 4 + mHeight / 8){Log.e("B层", "B层");behavior.setState(MyBottomSheetBehavior.STATE_HALF_EXPANDED);} else if (finalTop <= mHeight / 4 + mHeight / 8){Log.e("A层", "A层");behavior.setState(MyBottomSheetBehavior.STATE_EXPANDED);}}}@Overridepublic void onSlide(@NonNull View bottomSheet, float slideOffset){Log.e("slideOffset", "===" + slideOffset);}});

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。

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