如何檢測ListView是否快速滾動

Question

有沒有辦法檢測ListView是否快速滾動？也就是說，我們可以以某種方式知道用戶何時按下並釋放FastScroller？

Answer 1

嘗試使用setOnScrollListener並實現onScrollStateChanged。滾動狀態可以是空閒，觸摸滾動或一甩

setOnScrollListener(new OnScrollListener(){ 
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { 
     // TODO Auto-generated method stub 
    } 
    public void onScrollStateChanged(AbsListView view, int scrollState) { 
     // TODO Auto-generated method stub 
     if(scrollState == 2) Log.i("a", "fast scroll"); 
    } 
    }); 
} 

Answer 2

反射允許你這樣做。通過查看AbsListView source code，有一個FastScroller對象，它表示圍繞快速滾動功能的包裝。 Its source code顯示了一個有趣的field：

/** 
* Current decoration state, one of: 
* <ul> 
* <li>{@link #STATE_NONE}, nothing visible 
* <li>{@link #STATE_VISIBLE}, showing track and thumb 
* <li>{@link #STATE_DRAGGING}, visible and showing preview 
* </ul> 
*/ 
private int mState; 

該字段包含FastScroller對象的狀態。解決方案包括通過反射讀取該字段的值，每次觸發onScroll()和onScrollStateChanged()方法。

此代碼實現上述解決方案：

private class CustomScrollListener implements OnScrollListener { 

    private ListView list; 
    private int mState = -1; 
    private Field stateField = null; 
    private Object mFastScroller; 
    private int STATE_DRAGGING; 

    public CustomScrollListener() { 
     super(); 

     String fastScrollFieldName = "mFastScroller"; 
     // this has changed on Lollipop 
     if (Build.VERSION.SDK_INT >= 21) { 
      fastScrollFieldName = "mFastScroll"; 
     } 

     try { 
      Field fastScrollerField = AbsListView.class.getDeclaredField(fastScrollFieldName); 
      fastScrollerField.setAccessible(true); 
      mFastScroller = fastScrollerField.get(list); 

      Field stateDraggingField = mFastScroller.getClass().getDeclaredField("STATE_DRAGGING"); 
      stateDraggingField.setAccessible(true); 
      STATE_DRAGGING = stateDraggingField.getInt(mFastScroller); 

      stateField = mFastScroller.getClass().getDeclaredField("mState"); 
      stateField.setAccessible(true); 
      mState = stateField.getInt(mFastScroller); 

     } catch (NoSuchFieldException e) { 
      e.printStackTrace(); 
     } catch (IllegalAccessException e) { 
      e.printStackTrace(); 
     } 
    } 

    @Override 
    public void onScrollStateChanged(AbsListView view, int scrollState) { 

     // update fast scroll state 
     try { 
      if (stateField != null) { 
       mState = stateField.getInt(mFastScroller); 
      } 
     } catch (IllegalAccessException e) { 
      e.printStackTrace(); 
     } 


     if (mState == STATE_DRAGGING)) { 
      // the user is fast scrolling through the list 
     } 
    } 

    @Override 
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { 

     // update fast scroll state 
     try { 
      if (stateField != null) { 
       mState = stateField.getInt(mFastScroller); 
      } 
     } catch (IllegalAccessException e) { 
      e.printStackTrace(); 
     } 

    } 
}