Android使用ScrollView导致鼠标点击事件无效

平台

测试平台:

• RK3288 + Android8.1
• RK3588 + Android 12

问题

 首先, 这个问题的前提是, 使用的输入设备是**鼠标**, 普通的触摸屏并不会出现这个问题. 大致的流程是APP的UI布局中采用ScrollView作为根容器, 之后添加各类子控件, 在一起准备就绪后, 使用鼠标进行功能测试, 出现无法点击控件触发事件响应.

<ScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <LinearLayout
            style="@style/settingsItems">
            <TextView style="@style/TV"
                android:text="XXX"
                android:layout_weight="1"
                />
            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="BTN"/>
        LinearLayout>
        <LinearLayout
            style="@style/settingsItems">
            <TextView style="@style/TV"
                android:text="XXX"
                android:layout_weight="1"
                />
            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="BTN"/>
        LinearLayout>
				
    LinearLayout>
ScrollView>

分析

最先从onInterceptTouchEvent函数入手, 各个层级的LOG大致分析, 由下往上发现控件BUTTON中根本没有捕获到MotionEvent, 那原因只可能是父控件自己捕获了而不下发. 兜兜转转最终来到了ScrollView.

通过重写onInterceptHoverEvent 判断是否时间已被捕获

  @Override
	public boolean onInterceptHoverEvent(MotionEvent event) {
		boolean b = super.onInterceptHoverEvent(event);
		Logger.d(TAG, "onInterceptHoverEvent " + b);
		return b;
	}

从输出的LOG可以看出来, 当使用鼠标的时候, TRUE 和 FALSE 均有可能出现(在后面排查是才发现这和控件处的位置有关), 当TRUE是, 说明事件由ScrollView处理了, 子控件自然就接收不到事件下发.

顺着onInterceptHoverEvent往上查:

• frameworks/base/core/java/android/view/ViewGroup.java

      public boolean onInterceptHoverEvent(MotionEvent event) {
          if (event.isFromSource(InputDevice.SOURCE_MOUSE)) {
              final int action = event.getAction();
              final float x = event.getX();
              final float y = event.getY();
              if ((action == MotionEvent.ACTION_HOVER_MOVE
                      || action == MotionEvent.ACTION_HOVER_ENTER) && isOnScrollbar(x, y)) {
                  return true;
              }
          }
          return false;
      }
  

  从代码中可以看出, 基本的判断条件都是成立的, 鼠标输入 + MOVE/ENTER时间, 最后一个是isOnScrollbar, 顾名思义输入鼠标的位置在ScrollBar 上?

• frameworks/base/core/java/android/view/View.java

  
      boolean isOnScrollbar(float x, float y) {
          if (mScrollCache == null) {
              return false;
          }
          x += getScrollX();
          y += getScrollY();
          if (isVerticalScrollBarEnabled() && !isVerticalScrollBarHidden()) {
              final Rect touchBounds = mScrollCache.mScrollBarTouchBounds;
              getVerticalScrollBarBounds(null, touchBounds);
              if (touchBounds.contains((int) x, (int) y)) {
                  return true;
              }
          }
          if (isHorizontalScrollBarEnabled()) {
              final Rect touchBounds = mScrollCache.mScrollBarTouchBounds;
              getHorizontalScrollBarBounds(null, touchBounds);
              if (touchBounds.contains((int) x, (int) y)) {
                  return true;
              }
          }
          return false;
      }
  
      private void getVerticalScrollBarBounds(@Nullable Rect bounds, @Nullable Rect touchBounds) {
          if (mRoundScrollbarRenderer == null) {
              getStraightVerticalScrollBarBounds(bounds, touchBounds);
          } else {
              getRoundVerticalScrollBarBounds(bounds != null ? bounds : touchBounds);
          }
      }
      private void getStraightVerticalScrollBarBounds(@Nullable Rect drawBounds,
              @Nullable Rect touchBounds) {
          final Rect bounds = drawBounds != null ? drawBounds : touchBounds;
          if (bounds == null) {
              return;
          }
          final int inside = (mViewFlags & SCROLLBARS_OUTSIDE_MASK) == 0 ? ~0 : 0;
          final int size = getVerticalScrollbarWidth();
          int verticalScrollbarPosition = mVerticalScrollbarPosition;
          if (verticalScrollbarPosition == SCROLLBAR_POSITION_DEFAULT) {
              verticalScrollbarPosition = isLayoutRtl() ?
                      SCROLLBAR_POSITION_LEFT : SCROLLBAR_POSITION_RIGHT;
          }
          final int width = mRight - mLeft;
          final int height = mBottom - mTop;
          switch (verticalScrollbarPosition) {
              default:
              case SCROLLBAR_POSITION_RIGHT:
                  bounds.left = mScrollX + width - size - (mUserPaddingRight & inside);
                  break;
              case SCROLLBAR_POSITION_LEFT:
                  bounds.left = mScrollX + (mUserPaddingLeft & inside);
                  break;
          }
          bounds.top = mScrollY + (mPaddingTop & inside);
          bounds.right = bounds.left + size;
          bounds.bottom = mScrollY + height - (mUserPaddingBottom & inside);
  
          if (touchBounds == null) {
              return;
          }
          if (touchBounds != bounds) {
              touchBounds.set(bounds);
          }
          final int minTouchTarget = mScrollCache.scrollBarMinTouchTarget;
          if (touchBounds.width() < minTouchTarget) {
              final int adjust = (minTouchTarget - touchBounds.width()) / 2;
              if (verticalScrollbarPosition == SCROLLBAR_POSITION_RIGHT) {
                  touchBounds.right = Math.min(touchBounds.right + adjust, mScrollX + width);
                  touchBounds.left = touchBounds.right - minTouchTarget;
              } else {
                  touchBounds.left = Math.max(touchBounds.left + adjust, mScrollX);
                  touchBounds.right = touchBounds.left + minTouchTarget;
              }
          }
          if (touchBounds.height() < minTouchTarget) {
              final int adjust = (minTouchTarget - touchBounds.height()) / 2;
              touchBounds.top -= adjust;
              touchBounds.bottom = touchBounds.top + minTouchTarget;
          }
      }
  
  /**
       * 
  ScrollabilityCache holds various fields used by a View when scrolling
       * is supported. This avoids keeping too many unused fields in most
       * instances of View.
       */
      private static class ScrollabilityCache implements Runnable {
  
          /**
           * Scrollbars are not visible
           */
          public static final int OFF = 0;
  
          /**
           * Scrollbars are visible
           */
          public static final int ON = 1;
  
          /**
           * Scrollbars are fading away
           */
          public static final int FADING = 2;
  
          public boolean fadeScrollBars;
  
          public int fadingEdgeLength;
          public int scrollBarDefaultDelayBeforeFade;
          public int scrollBarFadeDuration;
  
          public int scrollBarSize;
          public int scrollBarMinTouchTarget;
          public ScrollBarDrawable scrollBar;
          public float[] interpolatorValues;
          public View host;
  
          public final Paint paint;
          public final Matrix matrix;
          public Shader shader;
  
          public final Interpolator scrollBarInterpolator = new Interpolator(1, 2);
  
          private static final float[] OPAQUE = { 255 };
          private static final float[] TRANSPARENT = { 0.0f };
  
          /**
           * When fading should start. This time moves into the future every time
           * a new scroll happens. Measured based on SystemClock.uptimeMillis()
           */
          public long fadeStartTime;
  
          /**
           * The current state of the scrollbars: ON, OFF, or FADING
           */
          public int state = OFF;
  
          private int mLastColor;
  
          public final Rect mScrollBarBounds = new Rect();
          public final Rect mScrollBarTouchBounds = new Rect();
  
          public static final int NOT_DRAGGING = 0;
          public static final int DRAGGING_VERTICAL_SCROLL_BAR = 1;
          public static final int DRAGGING_HORIZONTAL_SCROLL_BAR = 2;
          public int mScrollBarDraggingState = NOT_DRAGGING;
  
          public float mScrollBarDraggingPos = 0;
  
          public ScrollabilityCache(ViewConfiguration configuration, View host) {
              fadingEdgeLength = configuration.getScaledFadingEdgeLength();
              scrollBarSize = configuration.getScaledScrollBarSize();
              scrollBarMinTouchTarget = configuration.getScaledMinScrollbarTouchTarget();
              scrollBarDefaultDelayBeforeFade = ViewConfiguration.getScrollDefaultDelay();
              scrollBarFadeDuration = ViewConfiguration.getScrollBarFadeDuration();
  
              paint = new Paint();
              matrix = new Matrix();
              // use use a height of 1, and then wack the matrix each time we
              // actually use it.
              shader = new LinearGradient(0, 0, 0, 1, 0xFF000000, 0, Shader.TileMode.CLAMP);
              paint.setShader(shader);
              paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
  
              this.host = host;
          }
  
          public void setFadeColor(int color) {
              if (color != mLastColor) {
                  mLastColor = color;
  
                  if (color != 0) {
                      shader = new LinearGradient(0, 0, 0, 1, color | 0xFF000000,
                              color & 0x00FFFFFF, Shader.TileMode.CLAMP);
                      paint.setShader(shader);
                      // Restore the default transfer mode (src_over)
                      paint.setXfermode(null);
                  } else {
                      shader = new LinearGradient(0, 0, 0, 1, 0xFF000000, 0, Shader.TileMode.CLAMP);
                      paint.setShader(shader);
                      paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
                  }
              }
          }
  
          public void run() {
              long now = AnimationUtils.currentAnimationTimeMillis();
              if (now >= fadeStartTime) {
  
                  // the animation fades the scrollbars out by changing
                  // the opacity (alpha) from fully opaque to fully
                  // transparent
                  int nextFrame = (int) now;
                  int framesCount = 0;
  
                  Interpolator interpolator = scrollBarInterpolator;
  
                  // Start opaque
                  interpolator.setKeyFrame(framesCount++, nextFrame, OPAQUE);
  
                  // End transparent
                  nextFrame += scrollBarFadeDuration;
                  interpolator.setKeyFrame(framesCount, nextFrame, TRANSPARENT);
  
                  state = FADING;
  
                  // Kick off the fade animation
                  host.invalidate(true);
              }
          }
      }
  
  

View中的代码有点多, 简单的来说, 就是isOnScrollbar 这个函数通过获取ScrollBar的位置大小信息判断输入的事件是否处于其捕获的范围.

通过反射调用getVerticalScrollBarBounds并输出读取的信息: touchRect=[1464,0][1512,674], 基本可以判定是滚动条的位置.

Rect touchRect = new Rect();
getVerticalScrollBarBoundsRe(null, touchRect);
Logger.d(TAG, "touchRect=" + touchRect.toShortString());

void getVerticalScrollBarBoundsRe(Rect r, Rect r2){
		try {
			@SuppressLint("SoonBlockedPrivateApi")
			Method getVerticalScrollBarBounds = View.class.getDeclaredMethod("getVerticalScrollBarBounds", Rect.class, Rect.class);
			getVerticalScrollBarBounds.setAccessible(true);
			getVerticalScrollBarBounds.invoke(this, r, r2);
		} catch (NoSuchMethodException e) {
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		}
	}

计算宽度1512 - 1464 = 48, 这个宽度默认在系统中又定义, 如果是自定义的ScrollBar则大小不一定是48, 根据configuration.getScaledMinScrollbarTouchTarget();查到源码的定义如下:

• frameworks/base/core/java/android/view/ViewConfiguration.java

  private static final int MIN_SCROLLBAR_TOUCH_TARGET = 48;
  
  /**
   * @return the minimum size of the scrollbar thumb's touch target in pixels
   * @hide
   */
  public int getScaledMinScrollbarTouchTarget() {
      return mMinScrollbarTouchTarget;
  }
  

问题的根源如下图所示, 红色滚动条的宽度为48:

PS: 上图中的滚动条默认情况下并没有显示出来.

解决方法

1. 修改XML中ScrollView的属性android:scrollbars="none”
2. 避免需要输入的控件显示在ScrollBar的下方, 考虑给子控件加个padding或margin
3. 自定义ScrollView, 优化onInterceptHoverEvent函数