android-notes / Auto Scroll Capture

跟miui一样的自动滚动截屏

很久之前写过一篇完全不同于其他长截屏方案的的博客，不过很仓促，现在重新整理一下 android长截屏beta1

miui自动滚动长截屏效果

画

• 给滚动控件外面嵌套一个FrameLayout（LinearLayout等也可以）
• 手动调用FrameLayout的draw方法把view画到bitmap上

Bitmap bitmap = Bitmap.createBitmap(container.getWidth(), container.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
container.draw(canvas);

具体参考 DrawScrollViewAct DrawListViewAct

滚

• 通过不断改变motionEvent的y值并手动调用view的dispatchTouchEvent方法实现view滚动

 private void autoScroll() {
        final int delay = 16;
        final MotionEvent motionEvent = MotionEvent.obtain(SystemClock.uptimeMillis()
                , SystemClock.uptimeMillis()
                , MotionEvent.ACTION_DOWN
                , listView.getWidth() / 2
                , listView.getHeight() / 2
                , 0);
        listView.dispatchTouchEvent(motionEvent);//先分发 MotionEvent.ACTION_DOWN 事件

        listView.postDelayed(new Runnable() {
            @Override
            public void run() {
                motionEvent.setAction(MotionEvent.ACTION_MOVE); //延时分发 MotionEvent.ACTION_MOVE 事件
                //改变y坐标，越大滚动越快，但太大可能会导致掉帧
                motionEvent.setLocation((int) motionEvent.getX(), (int) motionEvent.getY() - 10);
                listView.dispatchTouchEvent(motionEvent);
                listView.postDelayed(this, delay);
            }
        }, delay);
    }

参考 ScrollAct

自动滚动效果

截屏

• 每自动滚动完一屏幕调用view.draw()把view画到bitmap上，最后拼接bitmap

参考 AutoScreenShotsAct

为什么要嵌套一层view

listview不嵌套时，不管是否滚动，都能得到正确的结果

但scrollview滚动后即使顶部的已经看不到了，但调用scrollview的draw时还是会把scrollview不可见的地方画进去

为了通用起间，我们给view外面嵌套了一层view

代码实现

关键逻辑如下，但有些细节还需要具体对待

 private void autoScroll() {
       final int delay = 16;//延时16毫秒分发滑动事件
       final int step = 10;//每次滑动距离5像素，可以根据需要调整（若卡顿的话实际滚动距离可能小于5）
       final MotionEvent motionEvent = MotionEvent.obtain(SystemClock.uptimeMillis()
               , SystemClock.uptimeMillis()
               , MotionEvent.ACTION_DOWN
               , listView.getWidth() / 2
               , listView.getHeight() / 2
               , 0);
       //先分发 MotionEvent.ACTION_DOWN 事件，我们指定为按下位置是listview的中间位置，当然其他位置也可以
       listView.dispatchTouchEvent(motionEvent);
       /*
       注意：
       查看Listview源码可知 滑动距离大于ViewConfiguration.get(view.getContext()).getScaledTouchSlop()时listview才开始滚动
        private boolean startScrollIfNeeded(int x, int y, MotionEvent vtev) {
           // Check if we have moved far enough that it looks more like a
           // scroll than a tap
           final int deltaY = y - mMotionY;
           final int distance = Math.abs(deltaY);
           final boolean overscroll = mScrollY != 0;
           if ((overscroll || distance > mTouchSlop) && (getNestedScrollAxes() & SCROLL_AXIS_VERTICAL) == 0) {
               ...
               return true;
           }
           return false;
       }
        */
       motionEvent.setAction(MotionEvent.ACTION_MOVE);
       motionEvent.setLocation(motionEvent.getX(), motionEvent.getY() - (ViewConfiguration.get(listView.getContext()).getScaledTouchSlop()));
       listView.dispatchTouchEvent(motionEvent);

       final int startScrollY = (int) motionEvent.getY();

       listView.postDelayed(new Runnable() {
           @Override
           public void run() {
               if (isScreenShots == false) {//注意：我们无法通过滚动距离来判断是否滚动到了最后，所以需要通过其他方式停止滚动
                   drawRemainAndAssemble(startScrollY, (int) motionEvent.getY());
                   return;
               }
               //滚动刚好一整屏时画到bitmap上
               drawIfNeeded(startScrollY, (int) motionEvent.getY());

               motionEvent.setAction(MotionEvent.ACTION_MOVE); //延时分发 MotionEvent.ACTION_MOVE 事件
               /*
                 改变motionEvent的y坐标，nextStep越大滚动越快，但太大可能会导致掉帧，导致实际滚动距离小于我们滑动的距离

                 因为我们是根据(curScrollY - startScrollY) % container.getHeight() == 0来判定是否刚好滚动了一屏幕的，
                 所以快要滚动到刚好一屏幕位置时，修改nextStep的值，使下次滚动后刚好是一屏幕的距离。
                 当然nextStep也可以一直是1，这时就不需要凑整了，但这样会导致滚动的特别慢
                */
               int nextStep;
               int gap = (startScrollY - (int) motionEvent.getY() + step) % container.getHeight();
               if (gap > 0 && gap < step) {
                   nextStep = step - gap;
               } else {
                   nextStep = step;
               }

               motionEvent.setLocation((int) motionEvent.getX(), (int) motionEvent.getY() - nextStep);
               listView.dispatchTouchEvent(motionEvent);

               listView.postDelayed(this, delay);
           }
       }, delay);
   }

   private void drawRemainAndAssemble(int startScrollY, int curScrollY) {
       //最后的可能不足一屏幕，需要单独处理
       if ((curScrollY - startScrollY) % container.getHeight() != 0) {
           Bitmap film = Bitmap.createBitmap(container.getWidth(), container.getHeight(), Bitmap.Config.RGB_565);
           Canvas canvas = new Canvas();
           canvas.setBitmap(film);
           container.draw(canvas);

           int part = (startScrollY - curScrollY) / container.getHeight();
           int remainHeight = startScrollY - curScrollY - container.getHeight() * part;
           Bitmap remainBmp = Bitmap.createBitmap(film, 0, container.getHeight() - remainHeight, container.getWidth(), remainHeight);
           bitmaps.add(remainBmp);
       }

       assembleBmp();

   }

   private void assembleBmp() {
       int h = 0;
       for (Bitmap bitmap : bitmaps) {
           h += bitmap.getHeight();
       }
       //如果你需要透明度或者对图片质量要求很高的话请使用Config.ARGB_8888
       Bitmap bitmap = Bitmap.createBitmap(container.getWidth(), h, Bitmap.Config.RGB_565);
       Canvas canvas = new Canvas(bitmap);
       for (Bitmap b : bitmaps) {
           canvas.drawBitmap(b, 0, 0, null);
           canvas.translate(0, b.getHeight());
       }
       ViewGroup.LayoutParams params = img.getLayoutParams();
       params.width = bitmap.getWidth() * 2;
       params.height = bitmap.getHeight() * 2;
       img.requestLayout();
       img.setImageBitmap(bitmap);
   }

   private void drawIfNeeded(int startScrollY, int curScrollY) {

       if ((curScrollY - startScrollY) % container.getHeight() == 0) {
           //正好滚动满一屏

           //为了更通用，我们是把ListView的父布局（和ListView宽高相同）画到了bitmap上
           Bitmap film = Bitmap.createBitmap(container.getWidth(), container.getHeight(), Bitmap.Config.RGB_565);
           Canvas canvas = new Canvas();
           canvas.setBitmap(film);
           container.draw(canvas);
           bitmaps.add(film);
       }
   }

最终效果

左边是自动滚动的Listview，右边是停止截屏后的bitmap，可以看到完全没有拼接痕迹

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