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本篇内容介绍了“Android 4.0 Launcher源码是什么”的有关知识,在实际案例的操作过程中,不少人都会遇到这样的困境,接下来就让小编带领大家学习一下如何处理这些情况吧!希望大家仔细阅读,能够学有所成!
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首先先画了个图来再来阐述一下WorkSpace的结构。如下图:
点击查看大图
桌面的左右滑动功能主要是在PagedView类中实现的,而WorkSpace是PagedView类的子类,所以会继承PagedView中的方法。当我们的手指点击WorkSpace时,首先就会触发PageView中的onInterceptTouchEvent()方法,会根据相应的条件来判断是否对Touch事件进行拦截,如果onInterceptTouchEvent()方法返回为true,则会对Touch事件进行拦截,PageView类的onTouch方法会进行响应从而得到调用。如果返回false,就分两钟情况:(1)我们是点击在它的子控键上进行滑动时,比如我们是点击在桌面的图标上进行左右滑动的,workspace则会把Touch事件分发给它的子控件。(2)而如果仅仅是点击到桌面的空白出Touch事件就不会发生响应。
在我们手指***次触摸到屏幕时,首先会对onInterceptTouchEvent中的事件进行判断,如果是按下事件(MotionEvent.ACTION_DOWN), 则会记录按下时的X坐标、Y坐标等等数据,同时改变现在Workspace的状态为滚动状态(OUCH_STATE_SCROLLING),这时会返回ture,把事件交给onTouchEvent函数来处理,onTouchEvent中同样会对事件类型进行判断,当事件方法为(otionEvent.ACTION_DOWN)的时候,就可以开始显示滚动的指示条了(就是Hotseat上显示第几屏的屏点)。当我们按着屏幕不放进行滑动的时候,又会在onInterceptTouchEvent进行事件拦截,但是现在的事件类型变为了 MotionEvent.ACTION_MOVE,因为是移动的操作,所以会在拦截的时候取消桌面长按的事件的响应,同时转到onTouchEvent中对ACTION_MOVE事件的响应中,判断我们移动了多少距离,使用scrollBy方法来对桌面进行移动,并刷新屏幕。***我们放开手后会触发onTouchEvent中的MotionEvent.ACTION_UP事件,这时会根据滑动的情况来判断是朝左滑动还是朝右滑动,如果手指只滑动了屏幕宽度的少一半距离,则会弹回原来的页面,滑动多于屏幕宽度的一半则会进行翻页。同时要注意无论在什么情况下触发了WorkSpace滑动的事件,则系统会不断调用computeScroll()方法,我们重写这个方法同时在这个方法中调用刷新界面等操作。
滑动过程中所要注意的主要方法如下,具体见代码注释。
//对Touch事件进行拦截 主要用于在拦截各种Touch事件时,设置mTouchState的各种状态 @Override public boolean onInterceptTouchEvent(MotionEvent ev) { /* * This method JUST determines whether we want to intercept the motion. * If we return true, onTouchEvent will be called and we do the actual * scrolling there. * 这个方法仅仅决定了我们是否愿意去对滑动事件进行拦截,如果返回为true,则会调用onTouchEvent我们将会在那里进行事件处理 */ //对滑动的速率进行跟踪。 acquireVelocityTrackerAndAddMovement(ev); // Skip touch handling if there are no pages to swipe // 如果没有页面,则跳过操作。 if (getChildCount() <= 0) return super.onInterceptTouchEvent(ev); /* * Shortcut the most recurring case: the user is in the dragging * state and he is moving his finger. We want to intercept this * motion. * shortcut最常见的情况是:用户处于拖动的状态下,同时在移动它的手指,这时候我们需要拦截这个动作。 * */ final int action = ev.getAction(); //如果是在MOVE的情况下,则进行Touch事件拦截 if ((action == MotionEvent.ACTION_MOVE) && (mTouchState == TOUCH_STATE_SCROLLING)) { return true; } switch (action & MotionEvent.ACTION_MASK) { case MotionEvent.ACTION_MOVE: { /* * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check * whether the user has moved far enough from his original down touch. * 如果mIsBeingDragged==false ,否则快捷方式应该捕获到该事件,检查一下用户从它点击的地方位移是否足够 */ if (mActivePointerId != INVALID_POINTER) { //根据移动的距离判断是翻页还是移动一段位移,同时设置lastMotionX或者mTouchState这些值。同时取消桌面长按事件。 determineScrollingStart(ev); break; } // if mActivePointerId is INVALID_POINTER, then we must have missed an ACTION_DOWN // event. in that case, treat the first occurence of a move event as a ACTION_DOWN // i.e. fall through to the next case (don't break) // (We sometimes miss ACTION_DOWN events in Workspace because it ignores all events // while it's small- this was causing a crash before we checked for INVALID_POINTER) // 如果mActivePointerId 是 INVALID_POINTER,这时候我们应该已经错过了ACTION_DOWN事件。在这种情况下,把 // ***次发生移动的事件当作ACTION——DOWN事件,直接进入下一个情况下。 // 我们有时候会错过workspace中的ACTION_DOWN事件,因为在workspace变小的时候会忽略掉所有的事件。 } case MotionEvent.ACTION_DOWN: { final float x = ev.getX(); final float y = ev.getY(); // Remember location of down touch // 记录按下的位置 mDownMotionX = x; mLastMotionX = x; mLastMotionY = y; mLastMotionXRemainder = 0; mTotalMotionX = 0; //Return the pointer identifier associated with a particular pointer data index is this event. //The identifier tells you the actual pointer number associated with the data, //accounting for individual pointers going up and down since the start of the current gesture. //返回和这个事件关联的触点数据id,计算单独点的id会上下浮动,因为手势的起始位置挥发声改变。 mActivePointerId = ev.getPointerId(0); mAllowLongPress = true; /* * If being flinged and user touches the screen, initiate drag; * otherwise don't. mScroller.isFinished should be false when * being flinged. * 如果被拖动同时用户触摸到了屏幕,就开始初始化拖动,否则便不会。 * 当拖动完成后mScroller.isFinished就应该设置为false. * */ final int xDist = Math.abs(mScroller.getFinalX() - mScroller.getCurrX()); final boolean finishedScrolling = (mScroller.isFinished() || xDist < mTouchSlop); if (finishedScrolling) { //标记为TOUCH_STATE_REST状态 mTouchState = TOUCH_STATE_REST; //取消滚动动画 mScroller.abortAnimation(); } else { //状态为TOUCH_STATE_SCROLLING mTouchState = TOUCH_STATE_SCROLLING; } // check if this can be the beginning of a tap on the side of the pages // to scroll the current page // 检测此事件是不是开始于点击页面的边缘来对当前页面进行滚动。 if (mTouchState != TOUCH_STATE_PREV_PAGE && mTouchState != TOUCH_STATE_NEXT_PAGE) { if (getChildCount() > 0) { //根据触点的点位来判断是否点击到上一页,从而更新相应的状态 if (hitsPreviousPage(x, y)) { mTouchState = TOUCH_STATE_PREV_PAGE; } else if (hitsNextPage(x, y)) { mTouchState = TOUCH_STATE_NEXT_PAGE; } } } break; } case MotionEvent.ACTION_UP: case MotionEvent.ACTION_CANCEL: //触点不被相应时,所做的动作 mTouchState = TOUCH_STATE_REST; mAllowLongPress = false; mActivePointerId = INVALID_POINTER; //释放速率跟踪 releaseVelocityTracker(); break; case MotionEvent.ACTION_POINTER_UP: onSecondaryPointerUp(ev); releaseVelocityTracker(); break; } /* * The only time we want to intercept motion events is if we are in the * drag mode. * 我们唯一会去对移动事件进行拦截的情况时我们在拖动模式下 */ if(DEBUG) Log.d(TAG, "onInterceptTouchEvent "+(mTouchState != TOUCH_STATE_REST)); //只要是mTouchState的状态不为TOUCH_STATE_REST,那么就进行事件拦截 return mTouchState != TOUCH_STATE_REST; }
onTouchEvent方法,详细见代码注释:
@Override public boolean onTouchEvent(MotionEvent ev) { // Skip touch handling if there are no pages to swipe // 如果没有子页面,就直接跳过 if (getChildCount() <= 0) return super.onTouchEvent(ev); acquireVelocityTrackerAndAddMovement(ev); final int action = ev.getAction(); switch (action & MotionEvent.ACTION_MASK) { case MotionEvent.ACTION_DOWN: /* * If being flinged and user touches, stop the fling. isFinished * will be false if being flinged. * 如果在滑动的过程中下用户又点击桌面,则取消滑动,从而响应当前的点击。 * 在滑动的isFinished将返回false. */ if (!mScroller.isFinished()) { mScroller.abortAnimation(); } // Remember where the motion event started mDownMotionX = mLastMotionX = ev.getX(); mLastMotionXRemainder = 0; mTotalMotionX = 0; mActivePointerId = ev.getPointerId(0); //主要用来显示滚动条,表明要开始滚动了,这里可以进行调整,滚动条时逐渐显示还是立刻显示。 if (mTouchState == TOUCH_STATE_SCROLLING) { pageBeginMoving(); } break; case MotionEvent.ACTION_MOVE: if (mTouchState == TOUCH_STATE_SCROLLING) { // Scroll to follow the motion event final int pointerIndex = ev.findPointerIndex(mActivePointerId); final float x = ev.getX(pointerIndex); final float deltaX = mLastMotionX + mLastMotionXRemainder - x; //总共移动的距离 mTotalMotionX += Math.abs(deltaX); // Only scroll and update mLastMotionX if we have moved some discrete amount. We // keep the remainder because we are actually testing if we've moved from the last // scrolled position (which is discrete). // 如果我们移动了一小段距离,我们则移动和更新mLastMotionX 。我们保存Remainder变量是因为会检测我们 //是否是从***的滚动点位移动的。 if (Math.abs(deltaX) >= 1.0f) { mTouchX += deltaX; mSmoothingTime = System.nanoTime() / NANOTIME_DIV; if (!mDeferScrollUpdate) { scrollBy((int) deltaX, 0); if (DEBUG) Log.d(TAG, "onTouchEvent().Scrolling: " + deltaX); } else { invalidate(); } mLastMotionX = x; mLastMotionXRemainder = deltaX - (int) deltaX; } else { //Trigger the scrollbars to draw. When invoked this method starts an animation to fade the //scrollbars out after a default delay. If a subclass provides animated scrolling, //the start delay should equal the duration of the scrolling animation. //触发scrollbar进行绘制。 使用这个方法来启动一个动画来使scrollbars经过一段时间淡出。如果子类提供了滚动的动画,则 //延迟的时间等于动画滚动的时间。 awakenScrollBars(); } } else { determineScrollingStart(ev); } break; case MotionEvent.ACTION_UP: if (mTouchState == TOUCH_STATE_SCROLLING) { final int activePointerId = mActivePointerId; final int pointerIndex = ev.findPointerIndex(activePointerId); final float x = ev.getX(pointerIndex); final VelocityTracker velocityTracker = mVelocityTracker; velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity); int velocityX = (int) velocityTracker.getXVelocity(activePointerId); final int deltaX = (int) (x - mDownMotionX); final int pageWidth = getScaledMeasuredWidth(getPageAt(mCurrentPage)); // 屏幕的宽度*0.4f boolean isSignificantMove = Math.abs(deltaX) > pageWidth * SIGNIFICANT_MOVE_THRESHOLD; final int snapVelocity = mSnapVelocity; mTotalMotionX += Math.abs(mLastMotionX + mLastMotionXRemainder - x); boolean isFling = mTotalMotionX > MIN_LENGTH_FOR_FLING && Math.abs(velocityX) > snapVelocity; // In the case that the page is moved far to one direction and then is flung // in the opposite direction, we use a threshold to determine whether we should // just return to the starting page, or if we should skip one further. // 这钟情况是页面朝一个方向移动了一段距离,然后又弹回去了。我们使用一个阀值来判断是进行翻页还是返回到初始页面 boolean returnToOriginalPage = false; if (Math.abs(deltaX) > pageWidth * RETURN_TO_ORIGINAL_PAGE_THRESHOLD && Math.signum(velocityX) != Math.signum(deltaX) && isFling) { returnToOriginalPage = true; } int finalPage; // We give flings precedence over large moves, which is why we short-circuit our // test for a large move if a fling has been registered. That is, a large // move to the left and fling to the right will register as a fling to the right. //朝右移动 if (((isSignificantMove && deltaX > 0 && !isFling) || (isFling && velocityX > 0)) && mCurrentPage > 0) { finalPage = returnToOriginalPage ? mCurrentPage : mCurrentPage - 1; snapToPageWithVelocity(finalPage, velocityX); //朝左移动 } else if (((isSignificantMove && deltaX < 0 && !isFling) || (isFling && velocityX < 0)) && mCurrentPage < getChildCount() - 1) { finalPage = returnToOriginalPage ? mCurrentPage : mCurrentPage + 1; snapToPageWithVelocity(finalPage, velocityX); //寻找离屏幕中心最近的页面移动 } else { snapToDestination(); } } //直接移动到前一页 else if (mTouchState == TOUCH_STATE_PREV_PAGE) { // at this point we have not moved beyond the touch slop // (otherwise mTouchState would be TOUCH_STATE_SCROLLING), so // we can just page int nextPage = Math.max(0, mCurrentPage - 1); if (nextPage != mCurrentPage) { snapToPage(nextPage); } else { snapToDestination(); } } //直接移动到下一页 else if (mTouchState == TOUCH_STATE_NEXT_PAGE) { // at this point we have not moved beyond the touch slop // (otherwise mTouchState would be TOUCH_STATE_SCROLLING), so // we can just page int nextPage = Math.min(getChildCount() - 1, mCurrentPage + 1); if (nextPage != mCurrentPage) { snapToPage(nextPage); } else { snapToDestination(); } } else { onUnhandledTap(ev); } mTouchState = TOUCH_STATE_REST; mActivePointerId = INVALID_POINTER; releaseVelocityTracker(); break; //对事件不响应 case MotionEvent.ACTION_CANCEL: if (mTouchState == TOUCH_STATE_SCROLLING) { snapToDestination(); } mTouchState = TOUCH_STATE_REST; mActivePointerId = INVALID_POINTER; releaseVelocityTracker(); break; case MotionEvent.ACTION_POINTER_UP: onSecondaryPointerUp(ev); break; } return true; }
***有个小知识点要搞清楚,不少网友都问到过我。就是scrollTo和scrollBy的区别。我们查看View类的源代码如下所示,mScrollX记录的是当前View针对屏幕坐标在水平方向上的偏移量,而mScrollY则是记录的时当前View针对屏幕在竖值方向上的偏移量。
从以下代码我们可以得知,scrollTo就是把View移动到屏幕的X和Y位置,也就是绝对位置。而scrollBy其实就是调用的 scrollTo,但是参数是当前mScrollX和mScrollY加上X和Y的位置,所以ScrollBy调用的是相对于mScrollX和mScrollY的位置。我们在上面的代码中可以看到当我们手指不放移动屏幕时,就会调用scrollBy来移动一段相对的距离。而当我们手指松开后,会调用 mScroller.startScroll(mUnboundedScrollX, 0, delta, 0, duration); 来产生一段动画来移动到相应的页面,在这个过程中系统回不断调用computeScroll(),我们再使用scrollTo来把View移动到当前Scroller所在的绝对位置。
/** * Set the scrolled position of your view. This will cause a call to * {@link #onScrollChanged(int, int, int, int)} and the view will be * invalidated. * @param x the x position to scroll to * @param y the y position to scroll to */ public void scrollTo(int x, int y) { if (mScrollX != x || mScrollY != y) { int oldX = mScrollX; int oldY = mScrollY; mScrollX = x; mScrollY = y; invalidateParentCaches(); onScrollChanged(mScrollX, mScrollY, oldX, oldY); if (!awakenScrollBars()) { invalidate(true); } } } /** * Move the scrolled position of your view. This will cause a call to * {@link #onScrollChanged(int, int, int, int)} and the view will be * invalidated. * @param x the amount of pixels to scroll by horizontally * @param y the amount of pixels to scroll by vertically */ public void scrollBy(int x, int y) { scrollTo(mScrollX + x, mScrollY + y); }
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