【Android 事件分发】事件分发源码分析 ( ViewGroup 事件传递机制 四 | View 事件传递机制 )

Android 事件分发 系列文章目录

【Android 事件分发】事件分发源码分析 ( 驱动层通过中断传递事件 | WindowManagerService 向 View 层传递事件 ) 【Android 事件分发】事件分发源码分析 ( Activity 中各层级的事件传递 | Activity -＞ PhoneWindow -＞ DecorView -＞ ViewGroup ) 【Android 事件分发】事件分发源码分析 ( ViewGroup 事件传递机制 一 ) 【Android 事件分发】事件分发源码分析 ( ViewGroup 事件传递机制 二 ) 【Android 事件分发】事件分发源码分析 ( ViewGroup 事件传递机制 三 ) 【Android 事件分发】事件分发源码分析 ( ViewGroup 事件传递机制 四 | View 事件传递机制 )

前言

接上一篇博客 【Android 事件分发】事件分发源码分析 ( ViewGroup 事件传递机制 三 ) , 继续分析 ViewGroup 的事件分发机制后续代码 ;

一、View 的事件传递机制 ( dispatchTouchEvent )

在上一篇博客 【Android 事件分发】事件分发源码分析 ( ViewGroup 事件传递机制 三 ) 二、当前遍历的子组件的事件分发 章节 , 分析到 ViewGroup 的 dispatchTouchEvent 方法中的最终事件分发 , 调用到了 View 的 dispatchTouchEvent 方法继续向子组件分发触摸事件 ;

View 组件设置 点击监听器 View.OnClickListener , 触摸监听器 View.OnTouchListener , 都设置在 View 的 View.ListenerInfo 类型成员中 ;

判断该组件是否被用户设置了 触摸监听器 OnTouchListener , 如果设置了 , 则执行被用户设置的 触摸监听器 OnTouchListener ; 如果用户设置的 触摸监听器 OnTouchListener 触摸方法返回 true , 此时该分发方法的返回值就是 true ;

public class View implements Drawable.Callback, KeyEvent.Callback,
        AccessibilityEventSource {
    public boolean dispatchTouchEvent(MotionEvent event) {
            //noinspection SimplifiableIfStatement
            // 设置的 触摸监听器 就是封装在该对象中 
            ListenerInfo li = mListenerInfo;
            // 判断该组件是否被用户设置了 触摸监听器 OnTouchListener
            if (li != null && li.mOnTouchListener != null
                    && (mViewFlags & ENABLED_MASK) == ENABLED
                    // 执行被用户设置的 触摸监听器 OnTouchListener
                    && li.mOnTouchListener.onTouch(this, event)) {
                // 如果用户设置的 触摸监听器 OnTouchListener 触摸方法返回 true
                // 此时该分发方法的返回值就是 true 
                result = true;
            }
	}
}

如果上述 li.mOnTouchListener.onTouch(this, event) 执行的触摸监听器触摸方法返回值为 true , 则不会调用 View 组件自己的 onTouchEvent 方法了 , 在 onTouchEvent 方法中会调用 点击监听器的方法 ; 如果用户的 触摸监听器 OnTouchListener 返回 true , 则 用户的 点击监听器 OnClickListener 会被屏蔽掉 ; 如果同时设置了 点击监听器 OnClickListener 和 触摸监听器 OnTouchListener , 此时需要做 触摸事件 与 点击事件的兼容处理 ;

public class View implements Drawable.Callback, KeyEvent.Callback,
        AccessibilityEventSource {
    public boolean dispatchTouchEvent(MotionEvent event) {
			// 如果上面为 true ( 触摸监听器的触摸事件处理返回 true ) , 就会阻断该分支的命中 , 该分支不执行了 
			// 也就不会调用 View 组件自己的 onTouchEvent 方法 
			// 因此 , 如果用户的 触摸监听器 OnTouchListener 返回 true 
			// 则 用户的 点击监听器 OnClickListener 会被屏蔽掉 
			// 如果同时设置了 点击监听器 OnClickListener 和 触摸监听器 OnTouchListener 
			// 触摸监听器 OnTouchListener 返回 false , 点击监听器 OnClickListener 才能被调用到 
            if (!result && onTouchEvent(event)) {
                result = true;
            }
	}
}

View 的 onTouchEvent 方法分析 :

Click 点击事件 , 是一次完整的按下 + 抬起操作 , 如果要判定点击 , 需要同时有 MotionEvent.ACTION_DOWN + MotionEvent.ACTION_UP 事件 , 因此这里在 MotionEvent.ACTION_UP 事件分支中查找点击事件 ;

最终找到了点击事件的调用方法 performClickInternal 方法 ;

public class View implements Drawable.Callback, KeyEvent.Callback,
        AccessibilityEventSource {
    public boolean onTouchEvent(MotionEvent event) {
        if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
            switch (action) {
                case MotionEvent.ACTION_UP:
                	// 点击事件 Click 是 按下 + 抬起 事件 
                	// 如果要判定点击 , 需要同时有 MotionEvent.ACTION_DOWN + MotionEvent.ACTION_UP 事件 
                
                        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) {
                                	// 此处创建点击对象 
                                    mPerformClick = new PerformClick();
                                }
                                // 调用点击事件 
                                if (!post(mPerformClick)) {
                                    performClickInternal();
                                }
                            }
                        }
	}
}

在 performClickInternal 方法中, 调用了 performClick 方法 ;

public class View implements Drawable.Callback, KeyEvent.Callback,
        AccessibilityEventSource {
    private boolean performClickInternal() {
        // Must notify autofill manager before performing the click actions to avoid scenarios where
        // the app has a click listener that changes the state of views the autofill service might
        // be interested on.
        notifyAutofillManagerOnClick();

        return performClick();
    }
}

在 performClick 方法中 , 调用了 li.mOnClickListener.onClick(this); , li.mOnClickListener 就是用户设置的点击事件监听器 ;

public class View implements Drawable.Callback, KeyEvent.Callback,
        AccessibilityEventSource {
    public boolean performClick() {
        // We still need to call this method to handle the cases where performClick() was called
        // externally, instead of through performClickInternal()
        notifyAutofillManagerOnClick();

        final boolean result;
        final ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnClickListener != null) {
            playSoundEffect(SoundEffectConstants.CLICK);

			// 此处直接执行了 点击监听器 的点击方法 
            li.mOnClickListener.onClick(this);
            result = true;
        } else {
            result = false;
        }

        sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);

        notifyEnterOrExitForAutoFillIfNeeded(true);

        return result;
    }
}

二、触摸事件 与 点击事件 冲突处理

通过分析上述 View 的 dispatchTouchEvent 方法的源码可知 ,

如果触摸事件 返回 true ,

public class View implements Drawable.Callback, KeyEvent.Callback,
        AccessibilityEventSource {
    public boolean dispatchTouchEvent(MotionEvent event) {
            //noinspection SimplifiableIfStatement
            // 设置的 触摸监听器 就是封装在该对象中 
            ListenerInfo li = mListenerInfo;
            // 判断该组件是否被用户设置了 触摸监听器 OnTouchListener
            if (li != null && li.mOnTouchListener != null
                    && (mViewFlags & ENABLED_MASK) == ENABLED
                    // 执行被用户设置的 触摸监听器 OnTouchListener
                    && li.mOnTouchListener.onTouch(this, event)) {
                // 如果用户设置的 触摸监听器 OnTouchListener 触摸方法返回 true
                // 此时该分发方法的返回值就是 true 
                result = true;
            }
	}
}

则点击事件就会被屏蔽 ;

public class View implements Drawable.Callback, KeyEvent.Callback,
        AccessibilityEventSource {
    public boolean dispatchTouchEvent(MotionEvent event) {
			// 如果上面为 true ( 触摸监听器的触摸事件处理返回 true ) , 就会阻断该分支的命中 , 该分支不执行了 
			// 也就不会调用 View 组件自己的 onTouchEvent 方法 
			// 因此 , 如果用户的 触摸监听器 OnTouchListener 返回 true 
			// 则 用户的 点击监听器 OnClickListener 会被屏蔽掉 
			// 如果同时设置了 点击监听器 OnClickListener 和 触摸监听器 OnTouchListener 
			// 触摸监听器 OnTouchListener 返回 false , 点击监听器 OnClickListener 才能被调用到 
            if (!result && onTouchEvent(event)) {
                result = true;
            }
	}
}

方法一 : 最简单的方法是 让 触摸事件 返回 false , 这样 点击和触摸 事件 都可以共存 ;

方法二 : 如果一定要让触摸事件返回 true , 则只能在触摸事件中 手动调用 View 的 performClick() 方法 , 但是要注意 控制 触摸的 按下 , 移动 , 抬起 事件 , 细粒度的分析与控制每个事件的关系 , 然后模拟出点击事件的调用逻辑 ;

三、View 事件分发相关源码

public class View implements Drawable.Callback, KeyEvent.Callback,
        AccessibilityEventSource {
    /**
     * 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) {
    	// 无障碍调用 , 辅助功能 
        // 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);
        }

		// 返回结果 
        boolean result = false;

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

		// 判定手指的动作 
        final int actionMasked = event.getActionMasked();
        if (actionMasked == MotionEvent.ACTION_DOWN) {
            // Defensive cleanup for new gesture
            stopNestedScroll();
        }

        if (onFilterTouchEventForSecurity(event)) {
            if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
                result = true;
            }
            //noinspection SimplifiableIfStatement
            // 设置的 触摸监听器 就是封装在该对象中 
            ListenerInfo li = mListenerInfo;
            // 判断该组件是否被用户设置了 触摸监听器 OnTouchListener
            if (li != null && li.mOnTouchListener != null
                    && (mViewFlags & ENABLED_MASK) == ENABLED
                    // 执行被用户设置的 触摸监听器 OnTouchListener
                    && li.mOnTouchListener.onTouch(this, event)) {
                // 如果用户设置的 触摸监听器 OnTouchListener 触摸方法返回 true
                // 此时该分发方法的返回值就是 true 
                result = true;
            }

			// 如果上面为 true ( 触摸监听器的触摸事件处理返回 true ) , 就会阻断该分支的命中 , 该分支不执行了 
			// 也就不会调用 View 组件自己的 onTouchEvent 方法 
			// 因此 , 如果用户的 触摸监听器 OnTouchListener 返回 true 
			// 则 用户的 点击监听器 OnClickListener 会被屏蔽掉 
			// 如果同时设置了 点击监听器 OnClickListener 和 触摸监听器 OnTouchListener 
			// 触摸监听器 OnTouchListener 返回 false , 点击监听器 OnClickListener 才能被调用到 
            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;
    }

    /**
     * Implement this method to handle touch screen motion events.
     * 

     * 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:
     * 

     * 
obeying click sound preferences
     * 
dispatching OnClickListener calls
     * 
handling {@link AccessibilityNodeInfo#ACTION_CLICK ACTION_CLICK} when
     * accessibility features are enabled
     * 
     *
     * @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();

        final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
                || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
                || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;

        if ((viewFlags & ENABLED_MASK) == DISABLED) {
            if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) {
                setPressed(false);
            }
            mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
            // A disabled view that is clickable still consumes the touch
            // events, it just doesn't respond to them.
            return clickable;
        }
        if (mTouchDelegate != null) {
            if (mTouchDelegate.onTouchEvent(event)) {
                return true;
            }
        }

        if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
            switch (action) {
                case MotionEvent.ACTION_UP:
                	// 点击事件 Click 是 按下 + 抬起 事件 
                	// 如果要判定点击 , 需要同时有 MotionEvent.ACTION_DOWN + MotionEvent.ACTION_UP 事件 
                	
                    mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                    if ((viewFlags & TOOLTIP) == TOOLTIP) {
                        handleTooltipUp();
                    }
                    if (!clickable) {
                        removeTapCallback();
                        removeLongPressCallback();
                        mInContextButtonPress = false;
                        mHasPerformedLongPress = false;
                        mIgnoreNextUpEvent = false;
                        break;
                    }
                    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) {
                                	// 此处创建点击对象 
                                    mPerformClick = new PerformClick();
                                }
                                // 调用点击事件 
                                if (!post(mPerformClick)) {
                                    performClickInternal();
                                }
                            }
                        }

                        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:
                    if (event.getSource() == InputDevice.SOURCE_TOUCHSCREEN) {
                        mPrivateFlags3 |= PFLAG3_FINGER_DOWN;
                    }
                    mHasPerformedLongPress = false;

                    if (!clickable) {
                        checkForLongClick(0, x, y);
                        break;
                    }

                    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, x, y);
                    }
                    break;

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

                case MotionEvent.ACTION_MOVE:
                    if (clickable) {
                        drawableHotspotChanged(x, y);
                    }

                    // Be lenient about moving outside of buttons
                    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;
    }

    /**
     * Entry point for {@link #performClick()} - other methods on View should call it instead of
     * {@code performClick()} directly to make sure the autofill manager is notified when
     * necessary (as subclasses could extend {@code performClick()} without calling the parent's
     * method).
     */
    private boolean performClickInternal() {
        // Must notify autofill manager before performing the click actions to avoid scenarios where
        // the app has a click listener that changes the state of views the autofill service might
        // be interested on.
        notifyAutofillManagerOnClick();

        return performClick();
    }

    /**
     * Call this view's OnClickListener, if it is defined.  Performs all normal
     * actions associated with clicking: reporting accessibility event, playing
     * a sound, etc.
     *
     * @return True there was an assigned OnClickListener that was called, false
     *         otherwise is returned.
     */
    // NOTE: other methods on View should not call this method directly, but performClickInternal()
    // instead, to guarantee that the autofill manager is notified when necessary (as subclasses
    // could extend this method without calling super.performClick()).
    public boolean performClick() {
        // We still need to call this method to handle the cases where performClick() was called
        // externally, instead of through performClickInternal()
        notifyAutofillManagerOnClick();

        final boolean result;
        final ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnClickListener != null) {
            playSoundEffect(SoundEffectConstants.CLICK);

			// 此处直接执行了 点击监听器 的点击方法 
            li.mOnClickListener.onClick(this);
            result = true;
        } else {
            result = false;
        }

        sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);

        notifyEnterOrExitForAutoFillIfNeeded(true);

        return result;
    }

}

源码路径 : /frameworks/base/core/java/android/view/View.java