从大致上来说，触摸事件是系统服务将触摸的状态封装成android.view.MotionEvent,调用android.app.Activity#dispatchTouchEvent 方法传递到Activity中。

//android.app.Activity#dispatchTouchEvent

public boolean dispatchTouchEvent(MotionEvent ev) {
    if (ev.getAction() == MotionEvent.ACTION_DOWN) {
        //空方法，注释说明可以用来说明当前activity与用户开始进行交互以及更好的处理状态栏的通知事件。这里不做深入。
        onUserInteraction();
    }
    //这里判断调用的PhoneWindow#superDispatchTouchEvent方法，是最核心的方法。superDispatchTouchEvent方法传入了MotionEvent，将触摸事件传递到activity的布局中，当布局中的控件返回true，表示相关触摸事件被消费掉，直接返回true并结束dispatchTouchEvent。当布局中的控件都返回false，表明布局中的控件没有处理触摸事件，交由当前android.app.Activity#onTouchEvent方法进行处理。
    if (getWindow().superDispatchTouchEvent(ev)) {
        return true;
    }
    return onTouchEvent(ev);
}
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//PhoneWindow#superDispatchTouchEvent

// This is the top-level view of the window, containing the window decor.
//mDecor是应用window中的顶级view
private DecorView mDecor;
//这里直接调用的DecorView#superDispatchTouchEvent
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
    return mDecor.superDispatchTouchEvent(event);
}
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//DecorView#superDispatchTouchEvent

//DecorView调用的父类ViewGroup#dispatchTouchEvent
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
    return super.dispatchTouchEvent(event);
}
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通过上面三步，将触摸事件从Acivity传递到Activity的contentView中了。

//ViewGroup#dispatchTouchEvent

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        //对输入事件的完整性做一个检查，检查事件的ACTION_DOWN 和 ACTION_UP 是否一一配对。还会打印错误日志。
        if (mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
        }

        // If the event targets the accessibility focused view and this is it, start
        // normal event dispatch. Maybe a descendant is what will handle the click.
        // 无障碍服务相关处理。
        if (ev.isTargetAccessibilityFocus() && isAccessibilityFocusedViewOrHost()) {
            ev.setTargetAccessibilityFocus(false);
        }

        boolean handled = false;
        //事件安全性过滤，如果window被遮挡，丢弃此触摸事件。
        if (onFilterTouchEventForSecurity(ev)) {
            final int action = ev.getAction();
            final int actionMasked = action & MotionEvent.ACTION_MASK;

            // Handle an initial down.
            // 处理点击事件开始的DOWN事件。
            if (actionMasked == MotionEvent.ACTION_DOWN) {
                // Throw away all previous state when starting a new touch gesture.
                // The framework may have dropped the up or cancel event for the previous gesture
                // due to an app switch, ANR, or some other state change.
                // 清除子view的触摸状态，
                cancelAndClearTouchTargets(ev);
                // 重置当前的触摸状态。
                resetTouchState();
            }

            // Check for interception.
            // 检查子view的拦截。
            final boolean intercepted;
            // 触摸事件第一次到达这里时mFirstTouchTarget为null。
            if (actionMasked == MotionEvent.ACTION_DOWN
                    || mFirstTouchTarget != null) {
                // public void requestDisallowInterceptTouchEvent(boolean disallowIntercept)
                // 被调用用来设置是否禁止拦截，默认disallowIntercept为fale
                final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
                if (!disallowIntercept) {
                    // onInterceptTouchEvent用于我们viewGroup中拦截触摸事件，我们重写此方法，根据我们的需要拦截相关触摸事件。当他返回true时，后面一系列触摸事件都会传到此viewGroup的onTouchEvent中而不会再次传到onInterceptTouchEvent中，我们应该在onTouchEvent中返回true以表明触摸事件处理完成。
                    intercepted = onInterceptTouchEvent(ev);
                    ev.setAction(action); // restore action in case it was changed
                } else {
                    intercepted = false;
                }
            } else {
                // There are no touch targets and this action is not an initial down
                // so this view group continues to intercept touches.
                intercepted = true;
            }

            // If intercepted, start normal event dispatch. Also if there is already
            // a view that is handling the gesture, do normal event dispatch.
            //无障碍服务相关处理。
            if (intercepted || mFirstTouchTarget != null) {
                ev.setTargetAccessibilityFocus(false);
            }

            // Check for cancelation.
            final boolean canceled = resetCancelNextUpFlag(this)
                    || actionMasked == MotionEvent.ACTION_CANCEL;

            // Update list of touch targets for pointer down, if needed.
            final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
            //重置newTouchTaget
            TouchTarget newTouchTarget = null;
            boolean alreadyDispatchedToNewTouchTarget = false;
            //判断是否CANCEL事件以及是否被拦截。
            if (!canceled && !intercepted) {

                //无障碍服务相关处理。
                View childWithAccessibilityFocus = ev.isTargetAccessibilityFocus()
                        ? findChildWithAccessibilityFocus() : null;

                // MotionEvent.ACTION_HOVER_MOVE 指针相关的。
                // MotionEvent.ACTION_POINTER_DOWN 多指操作的除了第一个手指之外的DOWN
                // 处理Down事件
                if (actionMasked == MotionEvent.ACTION_DOWN
                        || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
                        || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                    //多指触摸的index
                    final int actionIndex = ev.getActionIndex(); // always 0 for down
                    final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
                            : TouchTarget.ALL_POINTER_IDS;

                    // Clean up earlier touch targets for this pointer id in case they
                    // have become out of sync.
                    // 清除其他手指的touchTarget，将touchTarget设置为当前手指
                    // TODO touchTarget是个链表，在多指触摸的时候，依照手指的顺序排序。
                    removePointersFromTouchTargets(idBitsToAssign);

                    final int childrenCount = mChildrenCount;
                    if (newTouchTarget == null && childrenCount != 0) {
                        final float x = ev.getX(actionIndex);
                        final float y = ev.getY(actionIndex);
                        // Find a child that can receive the event.
                        // Scan children from front to back.
                        final ArrayList<View> preorderedList = buildTouchDispatchChildList();
                        // 是否有自定义绘制顺序
                        final boolean customOrder = preorderedList == null
                                && isChildrenDrawingOrderEnabled();
                        final View[] children = mChildren;
                        for (int i = childrenCount - 1; i >= 0; i--) {
                            final int childIndex = getAndVerifyPreorderedIndex(
                                    childrenCount, i, customOrder);
                            final View child = getAndVerifyPreorderedView(
                                    preorderedList, children, childIndex);

                            //...省略无障碍相关代码

                            // 如果mFirstTouchTarget为null，返回null
                            // 如果mFirstTouchTarget的队列中含有此子view，返回此子view的touchTarget。
                            // 否则返回null。
                            newTouchTarget = getTouchTarget(child);
                            if (newTouchTarget != null) {
                                // Child is already receiving touch within its bounds.
                                // Give it the new pointer in addition to the ones it is handling.
                                newTouchTarget.pointerIdBits |= idBitsToAssign;
                                break;
                            }

                            // 重置cancel和up的标志？TODO
                            resetCancelNextUpFlag(child);
                            // event.getPointerIdBits(); 是否多指触摸手指的判断 TODO
                            // 调用子view的dispatchTouchEvent(transformedEvent);将触摸事件传到子view中。但当子view为null时，调用父view的dispatchTouchEvent(transformedEvent)。
                            if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
                                // Child wants to receive touch within its bounds.
                                mLastTouchDownTime = ev.getDownTime();
                                if (preorderedList != null) {
                                    // childIndex points into presorted list, find original index
                                    for (int j = 0; j < childrenCount; j++) {
                                        if (children[childIndex] == mChildren[j]) {
                                            mLastTouchDownIndex = j;
                                            break;
                                        }
                                    }
                                } else {
                                    mLastTouchDownIndex = childIndex;
                                }
                                mLastTouchDownX = ev.getX();
                                mLastTouchDownY = ev.getY();
                                //mFirstTouchTarget赋值 TODO
                                newTouchTarget = addTouchTarget(child, idBitsToAssign);
                                // 是否已经将触摸事件交给newTouchTarget处理。
                                alreadyDispatchedToNewTouchTarget = true;
                                break;
                            }

                            // The accessibility focus didn't handle the event, so clear
                            // the flag and do a normal dispatch to all children.
                            ev.setTargetAccessibilityFocus(false);
                        }
                        if (preorderedList != null) preorderedList.clear();
                    }

                    if (newTouchTarget == null && mFirstTouchTarget != null) {
                        // Did not find a child to receive the event.
                        // Assign the pointer to the least recently added target.
                        // 没有子view接收这个触摸事件，将newTouchTarget赋值为最近一次触摸事件的target。
                        newTouchTarget = mFirstTouchTarget;
                        while (newTouchTarget.next != null) {
                            newTouchTarget = newTouchTarget.next;
                        }
                        newTouchTarget.pointerIdBits |= idBitsToAssign;
                    }
                }
            }

            // Dispatch to touch targets.
            // 上面方法处理了
            if (mFirstTouchTarget == null) {
                // No touch targets so treat this as an ordinary view.
                // 没有子view，将自己当作是view处理触摸事件。
                handled = dispatchTransformedTouchEvent(ev, canceled, null,
                        TouchTarget.ALL_POINTER_IDS);
            } else {
                // Dispatch to touch targets, excluding the new touch target if we already
                // dispatched to it.  Cancel touch targets if necessary.
                TouchTarget predecessor = null;
                TouchTarget target = mFirstTouchTarget;
                // 将触摸事件分发给touchTarget，不包括已经分发了的newTouchTarget。
                // 如果需要给其他touchTarget分发取消事件。
                // 这里主要处理除了DOWN以外的事件分发，每次进来这个方法newTouchTarget都会被重置为NUll，
                // 触摸事件第一次进来传递DOWN事件，如果有子view处理了，newTouchTarget和mFirstTouchTarget会被赋值，
                // 后续move事件进来mFirstTouchTarget不为空，而newTouchTarget都会被重置为NUll，这时就会给处理了Down事件的子view去处理后续的事件。
                while (target != null) {
                    final TouchTarget next = target.next;
                    if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
                        handled = true;
                    } else {
                        final boolean cancelChild = resetCancelNextUpFlag(target.child)
                                || intercepted;
                        if (dispatchTransformedTouchEvent(ev, cancelChild,
                                target.child, target.pointerIdBits)) {
                            handled = true;
                        }
                        if (cancelChild) {
                            if (predecessor == null) {
                                mFirstTouchTarget = next;
                            } else {
                                predecessor.next = next;
                            }
                            target.recycle();
                            target = next;
                            continue;
                        }
                    }
                    predecessor = target;
                    target = next;
                }
            }

            // Update list of touch targets for pointer up or cancel, if needed.
            // 在cancel、up的状态下重置触摸状态。
            if (canceled
                    || actionMasked == MotionEvent.ACTION_UP
                    || actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
                resetTouchState();
            } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
                final int actionIndex = ev.getActionIndex();
                final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
                removePointersFromTouchTargets(idBitsToRemove);
            }
        }

        // 未处理事件
        if (!handled && mInputEventConsistencyVerifier != null) {
            mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
        }
        return handled;
    }
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