Android onTouch事件传递机制解析

/**
 * Pass the touch screen motion event down to the target view, or this
 * view if it is the target.
 *
 * @param event The motion event to be dispatched.
 * @return True if the event was handled by the view, false otherwise.
 */
 public boolean dispatchTouchEvent(MotionEvent event) {
    // If the event should be handled by accessibility focus first.
    if (event.isTargetAccessibilityFocus()) {
        // We don't have focus or no virtual descendant has it, do not handle the event.
        if (!isAccessibilityFocusedViewOrHost()) {
            return false;
        }
        // We have focus and got the event, then use normal event dispatch.
        event.setTargetAccessibilityFocus(false);
    }

    boolean result = false;

    if (mInputEventConsistencyVerifier != null) {
        mInputEventConsistencyVerifier.onTouchEvent(event, 0);
    }

    final int actionMasked = event.getActionMasked();
    if (actionMasked == MotionEvent.ACTION_DOWN) {
        // Defensive cleanup for new gesture
        stopNestedScroll();
    }

    if (onFilterTouchEventForSecurity(event)) {
        //noinspection SimplifiableIfStatement
        ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnTouchListener != null
                && (mViewFlags & ENABLED_MASK) == ENABLED
                && li.mOnTouchListener.onTouch(this, event)) {
            result = true;
        }

        if (!result && onTouchEvent(event)) {
            result = true;
        }
    }

    if (!result && mInputEventConsistencyVerifier != null) {
        mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
    }

    // Clean up after nested scrolls if this is the end of a gesture;
    // also cancel it if we tried an ACTION_DOWN but we didn't want the rest
    // of the gesture.
    if (actionMasked == MotionEvent.ACTION_UP ||
            actionMasked == MotionEvent.ACTION_CANCEL ||
            (actionMasked == MotionEvent.ACTION_DOWN && !result)) {
        stopNestedScroll();
    }

    return result;
}

ListenerInfo getListenerInfo() {
    if (mListenerInfo != null) {
        return mListenerInfo;
    }
    mListenerInfo = new ListenerInfo();
    return mListenerInfo;
}

/**
 * Register a callback to be invoked when a touch event is sent to this view.
 * @param l the touch listener to attach to this view
 */
public void setOnTouchListener(OnTouchListener l) {
    getListenerInfo().mOnTouchListener = l;
}

/**
 * Implement this method to handle touch screen motion events.
 * <p>
 * If this method is used to detect click actions, it is recommended that
 * the actions be performed by implementing and calling
 * {@link #performClick()}. This will ensure consistent system behavior,
 * including:
 * <ul>
 * <li>obeying click sound preferences
 * <li>dispatching OnClickListener calls
 * <li>handling {@link AccessibilityNodeInfo#ACTION_CLICK ACTION_CLICK} when
 * accessibility features are enabled
 * </ul>
 *
 * @param event The motion event.
 * @return True if the event was handled, false otherwise.
 */
public boolean onTouchEvent(MotionEvent event) {
    final float x = event.getX();
    final float y = event.getY();
    final int viewFlags = mViewFlags;
    final int action = event.getAction();

    if ((viewFlags & ENABLED_MASK) == DISABLED) {
        if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
            setPressed(false);
        }
        // A disabled view that is clickable still consumes the touch
        // events, it just doesn't respond to them.
        return (((viewFlags & CLICKABLE) == CLICKABLE
                || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
                || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
    }

    if (mTouchDelegate != null) {
        if (mTouchDelegate.onTouchEvent(event)) {
            return true;
        }
    }

    if (((viewFlags & CLICKABLE) == CLICKABLE ||
            (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
            (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
        switch (action) {
            case MotionEvent.ACTION_UP:
                boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;
                if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
                    // take focus if we don't have it already and we should in
                    // touch mode.
                    boolean focusTaken = false;
                    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.
                        setPressed(true, x, y);
                   }

                    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)) {
                                performClick();
                            }
                        }
                    }

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

                    if (prepressed) {
                        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:
                mHasPerformedLongPress = false;

                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.
                if (isInScrollingContainer) {
                    mPrivateFlags |= PFLAG_PREPRESSED;
                    if (mPendingCheckForTap == null) {
                        mPendingCheckForTap = new CheckForTap();
                    }
                    mPendingCheckForTap.x = event.getX();
                    mPendingCheckForTap.y = event.getY();
                    postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
                } else {
                    // Not inside a scrolling container, so show the feedback right away
                    setPressed(true, x, y);
                    checkForLongClick(0);
                }
                break;

            case MotionEvent.ACTION_CANCEL:
                setPressed(false);
                removeTapCallback();
                removeLongPressCallback();
                mInContextButtonPress = false;
                mHasPerformedLongPress = false;
                mIgnoreNextUpEvent = false;
                break;

            case MotionEvent.ACTION_MOVE:
                drawableHotspotChanged(x, y);

                // Be lenient about moving outside of buttons
                if (!pointInView(x, y, mTouchSlop)) {
                    // Outside button
                    removeTapCallback();
                    if ((mPrivateFlags & PFLAG_PRESSED) != 0) {
                        // Remove any future long press/tap checks
                        removeLongPressCallback();

                        setPressed(false);
                    }
                }
                break;
        }

        return true;
    }

    return false;
}

public boolean performClick() {
    final boolean result;
    final ListenerInfo li = mListenerInfo;
    if (li != null && li.mOnClickListener != null) {
        playSoundEffect(SoundEffectConstants.CLICK);
        li.mOnClickListener.onClick(this);
        result = true;
    } else {
        result = false;
    }

    sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
    return result;
}

/**
 * Register a callback to be invoked when this view is clicked. If this view is not
 * clickable, it becomes clickable.
 *
 * @param l The callback that will run
 *
 * @see #setClickable(boolean)
 */
public void setOnClickListener(@Nullable OnClickListener l) {
    if (!isClickable()) {
        setClickable(true);
    }
    getListenerInfo().mOnClickListener = l;
}