public class CoordinatorLayout extends ViewGroup implements NestedScrollingParent2,
        NestedScrollingParent3

class DependentView @JvmOverloads constructor(
    val mContext: Context,
    val attributeSet: AttributeSet? = null,
    val flag: Int = 0
) : View(mContext, attributeSet, flag) {
    private var paint: Paint
    private var mStartX = 0
    private var mStartY = 0
    init {
        paint = Paint()
        paint.color = Color.parseColor("#000000")
        paint.style = Paint.Style.FILL
        isClickable = true
    }
    override fun onDraw(canvas: Canvas?) {
        super.onDraw(canvas)
        canvas?.let {
            it.drawRect(
                Rect().apply {
                    left = 200
                    top = 200
                    right = 400
                    bottom = 400
                },
                paint
            )
        }
    }
    override fun onTouchEvent(event: MotionEvent?): Boolean {
        when (event?.action) {
            MotionEvent.ACTION_DOWN -> {
                Log.e("TAG","ACTION_DOWN")
                mStartX = event.rawX.toInt()
                mStartY = event.rawY.toInt()
            }
            MotionEvent.ACTION_MOVE -> {
                Log.e("TAG","ACTION_MOVE")
                val endX = event.rawX.toInt()
                val endY = event.rawY.toInt()
                val dx = endX - mStartX
                val dy = endY - mStartY
                ViewCompat.offsetTopAndBottom(this, dy)
                ViewCompat.offsetLeftAndRight(this, dx)
                postInvalidate()
                mStartX = endX
                mStartY = endY
            }
        }
        return super.onTouchEvent(event)
    }
}

class DependBehavior @JvmOverloads constructor(context: Context, attributeSet: AttributeSet) :
    CoordinatorLayout.Behavior<View>(context, attributeSet) {
    override fun layoutDependsOn(
        parent: CoordinatorLayout,
        child: View,
        dependency: View
    ): Boolean {
        return dependency is DependentView
    }
    override fun onDependentViewChanged(
        parent: CoordinatorLayout,
        child: View,
        dependency: View
    ): Boolean {
        //獲取dependency的位置
        child.x = dependency.x
        child.y = dependency.bottom.toFloat()
        return true
    }
}

<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <com.lay.learn.asm.DependentView
        android:layout_width="200dp"
        android:layout_height="200dp"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="我是跟隨者"
        app:layout_behavior="com.lay.learn.asm.behavior.DependBehavior"
        android:textStyle="bold"
        android:textColor="#000000"/>
</androidx.coordinatorlayout.widget.CoordinatorLayout>

@Override
public void onAttachedToWindow() {
    super.onAttachedToWindow();
    resetTouchBehaviors(false);
    if (mNeedsPreDrawListener) {
        if (mOnPreDrawListener == null) {
            mOnPreDrawListener = new OnPreDrawListener();
        }
        final ViewTreeObserver vto = getViewTreeObserver();
        vto.addOnPreDrawListener(mOnPreDrawListener);
    }
    if (mLastInsets == null && ViewCompat.getFitsSystemWindows(this)) {
        // We're set to fitSystemWindows but we haven't had any insets yet...
        // We should request a new dispatch of window insets
        ViewCompat.requestApplyInsets(this);
    }
    mIsAttachedToWindow = true;
}

class OnPreDrawListener implements ViewTreeObserver.OnPreDrawListener {
    @Override
    public boolean onPreDraw() {
        onChildViewsChanged(EVENT_PRE_DRAW);
        return true;
    }
}

final void onChildViewsChanged(@DispatchChangeEvent final int type) {
    final int layoutDirection = ViewCompat.getLayoutDirection(this);
    final int childCount = mDependencySortedChildren.size();
    final Rect inset = acquireTempRect();
    final Rect drawRect = acquireTempRect();
    final Rect lastDrawRect = acquireTempRect();
    for (int i = 0; i < childCount; i++) {
        final View child = mDependencySortedChildren.get(i);
        final LayoutParams lp = (LayoutParams) child.getLayoutParams();
        if (type == EVENT_PRE_DRAW && child.getVisibility() == View.GONE) {
            // Do not try to update GONE child views in pre draw updates.
            continue;
        }
        // Update any behavior-dependent views for the change
        for (int j = i + 1; j < childCount; j++) {
            final View checkChild = mDependencySortedChildren.get(j);
            final LayoutParams checkLp = (LayoutParams) checkChild.getLayoutParams();
            final Behavior b = checkLp.getBehavior();
            if (b != null && b.layoutDependsOn(this, checkChild, child)) {
                if (type == EVENT_PRE_DRAW && checkLp.getChangedAfterNestedScroll()) {
                    // If this is from a pre-draw and we have already been changed
                    // from a nested scroll, skip the dispatch and reset the flag
                    checkLp.resetChangedAfterNestedScroll();
                    continue;
                }
                final boolean handled;
                switch (type) {
                    case EVENT_VIEW_REMOVED:
                        // EVENT_VIEW_REMOVED means that we need to dispatch
                        // onDependentViewRemoved() instead
                        b.onDependentViewRemoved(this, checkChild, child);
                        handled = true;
                        break;
                    default:
                        // Otherwise we dispatch onDependentViewChanged()
                        handled = b.onDependentViewChanged(this, checkChild, child);
                        break;
                }
                if (type == EVENT_NESTED_SCROLL) {
                    // If this is from a nested scroll, set the flag so that we may skip
                    // any resulting onPreDraw dispatch (if needed)
                    checkLp.setChangedAfterNestedScroll(handled);
                }
            }
        }
    }
    releaseTempRect(inset);
    releaseTempRect(drawRect);
    releaseTempRect(lastDrawRect);
}

for (int j = i + 1; j < childCount; j++) {
    final View checkChild = mDependencySortedChildren.get(j);
    final LayoutParams checkLp = (LayoutParams) checkChild.getLayoutParams();
    final Behavior b = checkLp.getBehavior();
    if (b != null && b.layoutDependsOn(this, checkChild, child)) {
        if (type == EVENT_PRE_DRAW && checkLp.getChangedAfterNestedScroll()) {
            // If this is from a pre-draw and we have already been changed
            // from a nested scroll, skip the dispatch and reset the flag
            checkLp.resetChangedAfterNestedScroll();
            continue;
        }
        final boolean handled;
        switch (type) {
            case EVENT_VIEW_REMOVED:
                // EVENT_VIEW_REMOVED means that we need to dispatch
                // onDependentViewRemoved() instead
                b.onDependentViewRemoved(this, checkChild, child);
                handled = true;
                break;
            default:
                // Otherwise we dispatch onDependentViewChanged()
                handled = b.onDependentViewChanged(this, checkChild, child);
                break;
        }
        if (type == EVENT_NESTED_SCROLL) {
            // If this is from a nested scroll, set the flag so that we may skip
            // any resulting onPreDraw dispatch (if needed)
            checkLp.setChangedAfterNestedScroll(handled);
        }
    }
}

if (mBehaviorResolved) {
    mBehavior = parseBehavior(context, attrs, a.getString(
            R.styleable.CoordinatorLayout_Layout_layout_behavior));
}

static Behavior parseBehavior(Context context, AttributeSet attrs, String name) {
    if (TextUtils.isEmpty(name)) {
        return null;
    }
    final String fullName;
    if (name.startsWith(".")) {
        // Relative to the app package. Prepend the app package name.
        fullName = context.getPackageName() + name;
    } else if (name.indexOf('.') >= 0) {
        // Fully qualified package name.
        fullName = name;
    } else {
        // Assume stock behavior in this package (if we have one)
        fullName = !TextUtils.isEmpty(WIDGET_PACKAGE_NAME)
                ? (WIDGET_PACKAGE_NAME + '.' + name)
                : name;
    }
    try {
        Map<String, Constructor<Behavior>> constructors = sConstructors.get();
        if (constructors == null) {
            constructors = new HashMap<>();
            sConstructors.set(constructors);
        }
        Constructor<Behavior> c = constructors.get(fullName);
        if (c == null) {
            final Class<Behavior> clazz =
                    (Class<Behavior>) Class.forName(fullName, false, context.getClassLoader());
            c = clazz.getConstructor(CONSTRUCTOR_PARAMS);
            c.setAccessible(true);
            constructors.put(fullName, c);
        }
        return c.newInstance(context, attrs);
    } catch (Exception e) {
        throw new RuntimeException("Could not inflate Behavior subclass " + fullName, e);
    }
}

static final Class<?>[] CONSTRUCTOR_PARAMS = new Class<?>[] {
        Context.class,
        AttributeSet.class
};

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    final int action = ev.getActionMasked();
    // Make sure we reset in case we had missed a previous important event.
    if (action == MotionEvent.ACTION_DOWN) {
        resetTouchBehaviors(true);
    }
    final boolean intercepted = performIntercept(ev, TYPE_ON_INTERCEPT);
    if (action == MotionEvent.ACTION_UP || action == MotionEvent.ACTION_CANCEL) {
        resetTouchBehaviors(true);
    }
    return intercepted;
}

private boolean performIntercept(MotionEvent ev, final int type) {
    boolean intercepted = false;
    boolean newBlock = false;
    MotionEvent cancelEvent = null;
    final int action = ev.getActionMasked();
    final List<View> topmostChildList = mTempList1;
    getTopSortedChildren(topmostChildList);
    // Let topmost child views inspect first
    final int childCount = topmostChildList.size();
    for (int i = 0; i < childCount; i++) {
        final View child = topmostChildList.get(i);
        final LayoutParams lp = (LayoutParams) child.getLayoutParams();
        final Behavior b = lp.getBehavior();
        if ((intercepted || newBlock) && action != MotionEvent.ACTION_DOWN) {
            // Cancel all behaviors beneath the one that intercepted.
            // If the event is "down" then we don't have anything to cancel yet.
            if (b != null) {
                if (cancelEvent == null) {
                    final long now = SystemClock.uptimeMillis();
                    cancelEvent = MotionEvent.obtain(now, now,
                            MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
                }
                switch (type) {
                    case TYPE_ON_INTERCEPT:
                        b.onInterceptTouchEvent(this, child, cancelEvent);
                        break;
                    case TYPE_ON_TOUCH:
                        b.onTouchEvent(this, child, cancelEvent);
                        break;
                }
            }
            continue;
        }
        if (!intercepted && b != null) {
            switch (type) {
                case TYPE_ON_INTERCEPT:
                    intercepted = b.onInterceptTouchEvent(this, child, ev);
                    break;
                case TYPE_ON_TOUCH:
                    intercepted = b.onTouchEvent(this, child, ev);
                    break;
            }
            if (intercepted) {
                mBehaviorTouchView = child;
            }
        }
        // Don't keep going if we're not allowing interaction below this.
        // Setting newBlock will make sure we cancel the rest of the behaviors.
        final boolean wasBlocking = lp.didBlockInteraction();
        final boolean isBlocking = lp.isBlockingInteractionBelow(this, child);
        newBlock = isBlocking && !wasBlocking;
        if (isBlocking && !newBlock) {
            // Stop here since we don't have anything more to cancel - we already did
            // when the behavior first started blocking things below this point.
            break;
        }
    }
    topmostChildList.clear();
    return intercepted;
}

public void onNestedPreScroll(View target, int dx, int dy, int[] consumed, int  type) {
    int xConsumed = 0;
    int yConsumed = 0;
    boolean accepted = false;
    final int childCount = getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View view = getChildAt(i);
        if (view.getVisibility() == GONE) {
            // If the child is GONE, skip...
            continue;
        }
        final LayoutParams lp = (LayoutParams) view.getLayoutParams();
        if (!lp.isNestedScrollAccepted(type)) {
            continue;
        }
        final Behavior viewBehavior = lp.getBehavior();
        if (viewBehavior != null) {
            mBehaviorConsumed[0] = 0;
            mBehaviorConsumed[1] = 0;
            viewBehavior.onNestedPreScroll(this, view, target, dx, dy, mBehaviorConsumed, type);
            xConsumed = dx > 0 ? Math.max(xConsumed, mBehaviorConsumed[0])
                    : Math.min(xConsumed, mBehaviorConsumed[0]);
            yConsumed = dy > 0 ? Math.max(yConsumed, mBehaviorConsumed[1])
                    : Math.min(yConsumed, mBehaviorConsumed[1]);
            accepted = true;
        }
    }
    consumed[0] = xConsumed;
    consumed[1] = yConsumed;
    if (accepted) {
        onChildViewsChanged(EVENT_NESTED_SCROLL);
    }
}

<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <TextView
        android:layout_width="match_parent"
        android:layout_height="80dp"
        android:background="#2196F3"
        android:text="這是頂部TextView"
        android:gravity="center"
        android:textColor="#FFFFFF"/>
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_child"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="80dp"/>
</androidx.coordinatorlayout.widget.CoordinatorLayout>

class ScrollBehavior @JvmOverloads constructor(
    val mContext: Context,
    val attributeSet: AttributeSet
) : CoordinatorLayout.Behavior<TextView>(mContext, attributeSet) {
    //相對(duì)于y軸滑動(dòng)的距離
    private var mScrollY = 0
    //總共滑動(dòng)的距離
    private var totalScroll = 0
    override fun onLayoutChild(
        parent: CoordinatorLayout,
        child: TextView,
        layoutDirection: Int
    ): Boolean {
        Log.e("TAG", "onLayoutChild----")
        //實(shí)時(shí)測(cè)量
        parent.onLayoutChild(child, layoutDirection)
        return true
    }
    override fun onStartNestedScroll(
        coordinatorLayout: CoordinatorLayout,
        child: TextView,
        directTargetChild: View,
        target: View,
        axes: Int,
        type: Int
    ): Boolean {
        //目的為了dispatch成功
        return true
    }
    override fun onNestedPreScroll(
        coordinatorLayout: CoordinatorLayout,
        child: TextView,
        target: View,
        dx: Int,
        dy: Int,
        consumed: IntArray,
        type: Int
    ) {
        //邊界處理
        var cosumedy = dy
        Log.e("TAG","onNestedPreScroll $totalScroll dy $dy")
        var scroll = totalScroll + dy
        if (abs(scroll) > getMaxScroll(child)) {
            cosumedy = getMaxScroll(child) - abs(totalScroll)
        } else if (scroll < 0) {
            cosumedy = 0
        }
        //在這里進(jìn)行事件消費(fèi)，我們只需要關(guān)心豎向滑動(dòng)
        ViewCompat.offsetTopAndBottom(child, -cosumedy)
        //重新賦值
        totalScroll += cosumedy
        consumed[1] = cosumedy
    }
    private fun getMaxScroll(child: TextView): Int {
        return child.height
    }
}

<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical">
    <TextView
        android:layout_width="match_parent"
        android:layout_height="80dp"
        android:background="#2196F3"
        android:text="這是頂部TextView"
        android:gravity="center"
        android:textColor="#FFFFFF"
        app:layout_behavior=".behavior.ScrollBehavior"/>
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_child"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="80dp"/>
</androidx.coordinatorlayout.widget.CoordinatorLayout>

class RecyclerViewBehavior @JvmOverloads constructor(
    val context: Context,
    val attributeSet: AttributeSet
) : CoordinatorLayout.Behavior<RecyclerView>(context, attributeSet) {
    override fun layoutDependsOn(
        parent: CoordinatorLayout,
        child: RecyclerView,
        dependency: View
    ): Boolean {
        return dependency is TextView
    }
    override fun onDependentViewChanged(
        parent: CoordinatorLayout,
        child: RecyclerView,
        dependency: View
    ): Boolean {
        Log.e("TAG","onDependentViewChanged ${dependency.bottom} ${child.top}")
        ViewCompat.offsetTopAndBottom(child,(dependency.bottom - child.top))
        return true
    }
}

<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical">
    <TextView
        android:layout_width="match_parent"
        android:layout_height="80dp"
        android:background="#2196F3"
        android:text="這是頂部TextView"
        android:gravity="center"
        android:textColor="#FFFFFF"
        app:layout_behavior=".behavior.ScrollBehavior"/>
    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_child"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="80dp"
        app:layout_behavior=".behavior.RecyclerViewBehavior"/>
</androidx.coordinatorlayout.widget.CoordinatorLayout>