Android Notes (ListView Scroller)

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ListView使用技巧

  • 优化技巧
    • ViewHolder-ListView 视图缓存机制
    • 设置分割线divider=”@null”透明
    • 取消点击效果，listSelector
    • smoothScrollBy/ToPosition()
    • 处理空ListView,listView.setEmptyView(ImageView)
    • 滑动监听，onTouchListener,onScrollListener,GestureDetector手势识别,VelocityTracker滑动速度检测

  • 拓展

    • 滚动到顶部，底部时有个弹性距离可以继续滑动，松开后回弹

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      private void init(){
          mMaxOverDistance= (int) (getResources().getDisplayMetrics().density*mMaxOverDistance);
      }

      @Override
      protected boolean overScrollBy(int deltaX, int deltaY, int scrollX, int scrollY, int scrollRangeX, int scrollRangeY, int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {
          Log.e("overscroll","by "+mMaxOverDistance);
          return super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX, mMaxOverDistance, isTouchEvent);
      }

  • 聊天ListView

    • getItemViewType(position)-> mData.get(position).getType()
    • getViewTypeCount()->2
    • getView()区分type，实例化不同布局添加内容

  • listview选中未选中状态: 在getView()中判断，点击选中的item的position和当前position是否相同，添加不同的布局

Android Scroll

滑动效果是触摸事件不断改变View的坐标，移动位置，来达到滑动效果

  • 触摸事件类型
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 //单点触摸按下
 public static final int ACTION_DOWN= 0;
 //单点触摸离开
 public static final int ACTION_UP= 1;
 //触摸点移动
 public static final int ACTION_MOVE= 2;
 //触摸动作取消
 public static final int ACTION_CANCEL= 3;
 //触摸动作超出边界
 public static final int ACTION_OUTSIDE= 4;
 //多点触摸按下
 public static final int ACTION_POINTER_DOWN= 5;
 //多点触摸离开
 public static final int ACTION_POINTER_UP= 6;
 
int x = (int) event.getX();
int y = (int) event.getY();
switch (event.getAction()) {
  case MotionEvent.ACTION_DOWN:
  break;
  case MotionEvent.ACTION_UP:
  break;
  case MotionEvent.ACTION_MOVE:
  break;
}

  • 实项滑动的七种方法

    • layout()

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      相对于视图坐标系的获取坐标getX,getY,而lastX,lastY不需要重新设置坐标,因为相对于视图坐标，点击屏幕获取到的坐标会重新设置
      对于Android屏幕坐标系，getRawX,getRawY,lastRawX,lastRawY需要重新设置，获取准确的偏移量，第一次坐标位置getRawX,getRawY在(10,10),在移动到(20,20)，偏移量为10，此时不重新设置，下个点是(50,50),偏移量是50-10=40,而实际正确的偏移量为50-20=30
      @Override
          public boolean onTouchEvent(MotionEvent event) {
              int x = (int) event.getX();
              int y = (int) event.getY();
              int rx = (int) event.getRawX();
              int ry = (int) event.getRawY();
              switch (event.getAction()) {
                  case MotionEvent.ACTION_DOWN:
                      lastX = x;
                      lastY = y;
                      lastrX = rx;
                      lastrY = ry;
                      break;
                  case MotionEvent.ACTION_MOVE:
                      int dx = x - lastX;
                      int dy = y - lastY;
                      int rdx = rx - lastrX;
                      int rdy = ry - lastrY;
                      Log.e("drag", "x=" + x + " y=" + y
                              + " lastX=" + lastX + " lastY=" + lastY);
                      Log.e("drag", "rx=" + rx + " ry=" + ry
                              + " lastrX=" + lastrX + " lastrY=" + lastrY);
                      Log.e("drag", "dx=" + dx + " dy=" + dy
                              + " rdx=" + rdx + " rdy=" + rdy);
                      layout(getLeft() + dx, getTop() + dy,
                              getRight() + dx, getBottom() + dy);
      //                lastrX = x;
      //                lastrY = y;
                      break;
                  case MotionEvent.ACTION_UP:
                      break;
              }
              return true;
          }

    • offsetLeftAndrRight(),offsetTopAndBottom()

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      offsetLeftAndRight(dx);
      offsetTopAndBottom(dy);

    • LayoutParams(),ViewGroup.MarginLayoutParams

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      FrameLayout.LayoutParams layoutParams= (FrameLayout.LayoutParams) getLayoutParams();
      layoutParams.leftMargin=getLeft()+dx;
      layoutParams.topMargin=getTop()+dy;
      setLayoutParams(layoutParams);

      ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams) getLayoutParams();
      layoutParams.leftMargin = getLeft() + dx;
      layoutParams.topMargin = getTop() + dy;
      setLayoutParams(layoutParams);

    • ScrollTo(x,y)/ScrollBy(dx,dy)

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       ViewGroup 移动的是子View
       View移动的是内容
       
       //移动的是屏幕下方画布，会造成内容向相反方向移动
       //scrollBy(dx,dy);
       //所以移动父视图，并且值为负，相反方向scrollby才有正确的效果
      case MotionEvent.ACTION_DOWN:
          lastX = x;
          lastY = y;
          if (!isScroll) {
            lastrX = rx;
            lastrY = ry;
          }
          break;
      case MotionEvent.ACTION_MOVE:
          int dx = x - lastX;
          int dy = y - lastY;
        //移动的是屏幕下方画布，会造成内容向相反方向移动
        //  scrollBy(dx,dy);
        //((View) getParent()).scrollBy(-dx, -dy);
           ((View) getParent()).scrollTo(-(int) event.getRawX() + lastrX, -(int) event.getRawY() + lastrY);
          isScroll = true;
          break;

  • Scroller 实现平移滑动

    • 初始化Scroller

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      mScroller=new Scroller(context);

    • 重写computeScroll()模拟滑动

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       @Override
       public void computeScroll() {
          super.computeScroll();
          //判断Scroll是否执行完毕，true 没有执行完
          if(mScroller.computeScrollOffset()){
       ((View)getParent()).scrollTo(mScroller.getCurrX(),mScroller.getCurrY());
          //只能通过invalidate()—>draw()->computeScroll()间接调用computeScroll()，
          //结束后computeScrollOffset()返回false，中断循环
          postInvalidate();
          }
      }

    • startScroll 开始模拟滑动

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      @Override
       public boolean onTouchEvent(MotionEvent event) {
           int x = (int) event.getX();
           int y = (int) event.getY();
           int rx = (int) event.getRawX();
           int ry = (int) event.getRawY();
           switch (event.getAction()) {
               case MotionEvent.ACTION_DOWN:
                   lastX = x;
                   lastY = y;
                   lastRx = rx;
                   lastRy = ry;
                   break;
               case MotionEvent.ACTION_MOVE:
                   ((View) getParent()).scrollTo(-rx + lastRx, -ry + lastRy);
                   break;
               case MotionEvent.ACTION_UP:
                   View parent = (View) getParent();
                   //模拟滑动，起始坐标和偏移量，滑动偏移为滑动距离的负数，相反方向滑动
                   mScroller.startScroll(parent.getScrollX(), parent.getScrollY(),
                           -parent.getScrollX(), -parent.getScrollY());
                   //通知重绘
                   invalidate();
                   break;
           }
           return true;
       }

  • ViewDragHelper实项Drawlayout菜单侧滑 youtubelayout

    • 回调

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        private ViewDragHelper.Callback callback = new ViewDragHelper.Callback() {
               /**重写tryCaptureView,何时开始检测触摸事件，
               * 当前触摸的是MainView时开始检测*/
              @Override
              public boolean tryCaptureView(View child, int pointerId) {
                  return mMainView == child;
              }

              /**水平垂直方向上的滑动,默认返回0，不滑动*/
              @Override
              public int clampViewPositionHorizontal(View child, int left, int dx) {
      //            return super.clampViewPositionHorizontal(child, left, dx);
                  return left;
              }

              @Override
              public int clampViewPositionVertical(View child, int top, int dy) {
      //            return super.clampViewPositionVertical(child, top, dy);
                  return top;
              }

              /**拖动结束后调用，自动滑动打开或关闭菜单*/
              @Override
              public void onViewReleased(View releasedChild, float xvel, float yvel) {
                  super.onViewReleased(releasedChild, xvel, yvel);
                  if (mMainView.getTop() > mHeight / 2) {
                      mViewDragHelper.smoothSlideViewTo(mMainView, 0, (int) (mHeight * 1.2f));
                  } else {
                      if (mMainView.getLeft() < mWidth / 2) {
                          //关闭菜单
                          mViewDragHelper.smoothSlideViewTo(mMainView, 0, 0);
                      } else {
                          mViewDragHelper.smoothSlideViewTo(mMainView, (int) (mWidth * 1.2f), 0);
                      }
                  }
                  ViewCompat.postInvalidateOnAnimation(ViewDragHelperView.this);
              }

              /**更改scale进行缩放*/
              @Override
              public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
                  super.onViewPositionChanged(changedView, left, top, dx, dy);
              }

              /**状态改变*/
              @Override
              public void onViewDragStateChanged(int state) {
                  super.onViewDragStateChanged(state);
              }

              /**触摸后回调*/
              @Override
              public void onViewCaptured(View capturedChild, int activePointerId) {
                  super.onViewCaptured(capturedChild, activePointerId);
              }
          };

    • 获取宽度

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      @Override
         protected void onSizeChanged(int w, int h, int oldw, int oldh) {
             super.onSizeChanged(w, h, oldw, oldh);
             mWidth = mMenuView.getMeasuredWidth();
             mHeight = mMenuView.getMeasuredHeight();
         }

    • 获取MenuView,MainView

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      @Override
      protected void onFinishInflate() {
           super.onFinishInflate();
           mMenuView = getChildAt(0);
           mMainView = getChildAt(1);
      }

  • 触摸事件拦截，并传递给VieDragHelper

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    /**
     * 触摸事件传递给ViewDragHelper,必须写
     */
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        mViewDragHelper.processTouchEvent(event);
        return true;
    }

    /**
     * 重写事件拦截方法，把事件传递给ViewDragHelper
     */
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return mViewDragHelper.shouldInterceptTouchEvent(ev);
    }

  • 重写computeScroll()

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    /**
     * 平滑移动
     */
    @Override
    public void computeScroll() {
        super.computeScroll();
        if (mViewDragHelper.continueSettling(true)) {
            ViewCompat.postInvalidateOnAnimation(this);
        }
    }
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