onTouchEvent源码解析

源码解析
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
//View触摸不考虑多点触控
final int action = event.getAction();

    //可点击 || 长按 || （长按菜单&&鼠标右键）
    final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
            || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
            || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
    
    //View不可用，返回clickable
    if ((viewFlags & ENABLED_MASK) == DISABLED) {
        if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
            setPressed(false);
        }
        mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
        // 按钮本可点击但是被设置为禁用，仍然消耗掉事件, 只是不做出响应。
        return clickable;
    }
    //点击代理
    if (mTouchDelegate != null) {
        if (mTouchDelegate.onTouchEvent(event)) {
            return true;
        }
    }
    
    //可点击 || tooltip（长按提示，api28引入）
    if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
        switch (action) {
            case MotionEvent.ACTION_UP:
                mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                if ((viewFlags & TOOLTIP) == TOOLTIP) {
                    //松手后隐藏tooltip
                    handleTooltipUp();
                }
                if (!clickable) {
                    removeTapCallback();
                    removeLongPressCallback();
                    mInContextButtonPress = false;
                    mHasPerformedLongPress = false;
                    mIgnoreNextUpEvent = false;
                    break;
                }
                boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
                //按下状态 || 预按下状态
                if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
                    // take focus if we don't have it already and we should in
                    // touch mode.
                    boolean focusTaken = false;
                    //isFocusableInTouchMode()，实体按键，获取焦点
                    if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
                        focusTaken = requestFocus();
                    }

                    if (prepressed) {
                        // The button is being released before we actually
                        // showed it as pressed.  Make it show the pressed
                        // state now (before scheduling the click) to ensure
                        // the user sees it.
                        //预按下状态设置为按下
                        setPressed(true, x, y);
                    }

                    //处理点击
                    if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
                        // This is a tap, so remove the longpress check
                        removeLongPressCallback();

                        // Only perform take click actions if we were in the pressed state
                        if (!focusTaken) {
                            // Use a Runnable and post this rather than calling
                            // performClick directly. This lets other visual state
                            // of the view update before click actions start.
                            if (mPerformClick == null) {
                                mPerformClick = new PerformClick();
                            }
                            if (!post(mPerformClick)) {
                                performClickInternal();
                            }
                        }
                    }

                    if (mUnsetPressedState == null) {
                        mUnsetPressedState = new UnsetPressedState();
                    }

                    if (prepressed) {
                        //预按下，延时取消按下状态，
                        postDelayed(mUnsetPressedState,
                                ViewConfiguration.getPressedStateDuration());
                    } else if (!post(mUnsetPressedState)) {
                        // If the post failed, unpress right now
                        mUnsetPressedState.run();
                    }

                    removeTapCallback();
                }
                mIgnoreNextUpEvent = false;
                break;

            case MotionEvent.ACTION_DOWN:
                //DOWN事件是否是触摸产生，实体按键也可产生DOWN事件，          
                PFLAG3_FINGER_DOWN影响tooltip呼出位置
                if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
                    mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
                }
                mHasPerformedLongPress = false;

              //不可点击，设置长按监听（用于呼出tooltip）， 
               if (!clickable) {
                    checkForLongClick(0, x, y);
                    break;
                }

                //检测鼠标右键点击
                if (performButtonActionOnTouchDown(event)) {
                    break;
                }

                // Walk up the hierarchy to determine if we're inside a scrolling container.
                boolean isInScrollingContainer = isInScrollingContainer();

                // For views inside a scrolling container, delay the pressed feedback for
                // a short period in case this is a scroll.
                //在滑动控件中
                if (isInScrollingContainer) {
                    //设置为预按下状态
                    mPrivateFlags |= PFLAG_PREPRESSED;
                    if (mPendingCheckForTap == null) 
                        mPendingCheckForTap = new CheckForTap();
                    }
                    mPendingCheckForTap.x = event.getX();
                    mPendingCheckForTap.y = event.getY();
                    //延时设置按下状态
                    postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
                } 
                //不在滑动控件中
                else {
                    // Not inside a scrolling container, so show the feedback right away
                    //设置为按下状态
                    setPressed(true, x, y);
                    //设置长按检测监听
                    checkForLongClick(0, x, y);
                }
                break;

            case MotionEvent.ACTION_CANCEL:
                //重置
                if (clickable) {
                    setPressed(false);
                }
                removeTapCallback();
                removeLongPressCallback();
                mInContextButtonPress = false;
                mHasPerformedLongPress = false;
                mIgnoreNextUpEvent = false;
                mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                break;

            case MotionEvent.ACTION_MOVE:
                if (clickable) {
                    //5.0移动水波纹中心位置
                    drawableHotspotChanged(x, y);
                }

                // Be lenient about moving outside of buttons
                //是否在View范围内
                if (!pointInView(x, y, mTouchSlop)) {
                    // Outside button
                    // Remove any future long press/tap checks
                    removeTapCallback();
                    removeLongPressCallback();
                    if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
                        setPressed(false);
                    }
                    mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                }
                break;
        }

        return true;
    }

    return false;
}

1、返回值表示是否消耗当前事件组，标记事件的归属。
2、是否消费事件取决于 ACTION_DOWN 返回值 ，仅ACTION_DOWN返回值有效。
3、true,消耗ACTION_DOWN事件及后续事件，后续事件全部交由当前View处理。
4、false,放弃ACTION_DOWN事件及后续事件，后续事件不会再触发当前View的onTouchEvent方法。
5、ACTION_DOWN返回ture，ACTION_MOVE返回false，Activity onTouchEvent也会触发MOVE事件。
6、图1为手机横截面，黄色和蓝色同为灰色子控件，且黄色和蓝色有部分重叠，重叠区域黄色在上方。箭头为DOWN事件最远路径。