content: package com.yongzheng.com.richwebproject.view;
  
  import android.annotation.SuppressLint;
  import android.os.Build;
  import android.support.v7.widget.LinearLayoutManager;
  import android.support.v7.widget.RecyclerView;
  import android.view.View;
  import android.webkit.WebView;
  import android.widget.AbsListView;
  import android.widget.AdapterView;
  import android.widget.ScrollView;
  
  /**
   * 判断滚动是否到达顶部工具类
   */
  public class HeaderScrollHelper {
  
      private int sysVersion;         //当前sdk版本，用于判断api版本
  
      //滑动的内容监听
      private ScrollableContainer mCurrentScrollableContainer;
  
      public HeaderScrollHelper() {
          sysVersion = Build.VERSION.SDK_INT;
      }
  
      /** 包含有 ScrollView ListView RecyclerView 的组件 */
      public interface ScrollableContainer {
  
          /** @return ScrollView ListView RecyclerView 或者其他的布局的实例 */
          View getScrollableView();
      }
  
      public void setCurrentScrollableContainer(ScrollableContainer scrollableContainer) {
          this.mCurrentScrollableContainer = scrollableContainer;
      }
  
      /**
       * 获取滑动的view
       * @return
       */
      private View getScrollableView() {
          if (mCurrentScrollableContainer == null) return null;
          return mCurrentScrollableContainer.getScrollableView();
      }
  
      /**
       * 是否设置滑动的view
       * @return
       */
      public boolean isSetScrollableView(){
          return getScrollableView()!=null;
      }
  
      /**
       * 判断是否滑动到顶部方法,ScrollAbleLayout根据此方法来做一些逻辑判断
       * 目前只实现了AdapterView,ScrollView,RecyclerView
       * 需要支持其他view可以自行补充实现
       */
      public boolean isTop() {
          View scrollableView = getScrollableView();
          if (scrollableView == null) {
              return false;
  //            throw new NullPointerException("You should call ScrollableHelper.setCurrentScrollableContainer() to set ScrollableContainer.");
          }
          if (scrollableView instanceof AdapterView) {
              return isAdapterViewTop((AdapterView) scrollableView);
          }
          if (scrollableView instanceof ScrollView) {
              return isScrollViewTop((ScrollView) scrollableView);
          }
          if (scrollableView instanceof RecyclerView) {
              return isRecyclerViewTop((RecyclerView) scrollableView);
          }
          if (scrollableView instanceof WebView) {
              return isWebViewTop((WebView) scrollableView);
          }
          throw new IllegalStateException("scrollableView must be a instance of AdapterView|ScrollView|RecyclerView");
      }
  
      private boolean isRecyclerViewTop(RecyclerView recyclerView) {
          if (recyclerView != null) {
              RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
              if (layoutManager instanceof LinearLayoutManager) {
                  int firstVisibleItemPosition = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
                  View childAt = recyclerView.getChildAt(0);
                  if (childAt == null || (firstVisibleItemPosition == 0 && childAt.getTop() == 0)) {
                      return true;
                  }
              }
          }
          return false;
      }
  
      private boolean isAdapterViewTop(AdapterView adapterView) {
          if (adapterView != null) {
              int firstVisiblePosition = adapterView.getFirstVisiblePosition();
              View childAt = adapterView.getChildAt(0);
              if (childAt == null || (firstVisiblePosition == 0 && childAt.getTop() == 0)) {
                  return true;
              }
          }
          return false;
      }
  
      private boolean isScrollViewTop(ScrollView scrollView) {
          if (scrollView != null) {
              int scrollViewY = scrollView.getScrollY();
              return scrollViewY <= 0;
          }
          return false;
      }
  
      private boolean isWebViewTop(WebView scrollView) {
          if (scrollView != null) {
              int scrollViewY = scrollView.getScrollY();
              return scrollViewY <= 0;
          }
          return false;
      }
  
      /**
       * 将特定的view按照初始条件滚动
       *
       * @param velocityY 初始滚动速度
       * @param distance  需要滚动的距离
       * @param duration  允许滚动的时间
       */
      @SuppressLint("NewApi")
      public void smoothScrollBy(int velocityY, int distance, int duration) {
          View scrollableView = getScrollableView();
          if (scrollableView instanceof AbsListView) {
              AbsListView absListView = (AbsListView) scrollableView;
              if (sysVersion >= 21) {
                  absListView.fling(velocityY);
              } else {
                  absListView.smoothScrollBy(distance, duration);
              }
          } else if (scrollableView instanceof ScrollView) {
              ((ScrollView) scrollableView).fling(velocityY);
          } else if (scrollableView instanceof RecyclerView) {
              ((RecyclerView) scrollableView).fling(0, velocityY);
          } else if (scrollableView instanceof WebView) {
              ((WebView) scrollableView).flingScroll(0, velocityY);
          }
      }
  }
  