ListView源码阅读

1. ListView的继承关系

ListView

2.setViewTypeCount

在调用ListView的setAdapter方法时，会调用setViewTypeCount对缓存容器RecycleBin的数据结构进行初始化

frameworks\base\core\java\android\widget\ListView.java

(1)应用层调用setAdapter

public void setAdapter(ListAdapter adapter) {
  if (mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0) {
    mAdapter = wrapHeaderListAdapterInternal(mHeaderViewInfos, mFooterViewInfos, adapter);
  } else {
    mAdapter = adapter;
  }
  if (mAdapter != null) {
    mRecycler.setViewTypeCount(mAdapter.getViewTypeCount());
  }
}

(2)初始化RecycleBin的成员变量

public void setViewTypeCount(int viewTypeCount) {
  if (viewTypeCount < 1) {
    throw new IllegalArgumentException("Can't have a viewTypeCount < 1");
  }
  //noinspection unchecked
  ArrayList<View>[] scrapViews = new ArrayList[viewTypeCount];
  for (int i = 0; i < viewTypeCount; i++) {
    scrapViews[i] = new ArrayList<View>();  //mScrapViews 的数组大小跟view type count一致
  }
  mViewTypeCount = viewTypeCount;
  mCurrentScrap = scrapViews[0];
  mScrapViews = scrapViews;
}

3. layoutChildren

protected void layoutChildren() {
  if (dataChanged) { //如果数据改变
    for (int i = 0; i < childCount; i++) {
      recycleBin.addScrapView(getChildAt(i), firstPosition+i); //所有的view放入mScrapViews
    }
  } else { //没有改变，放入mActiveViews
    recycleBin.fillActiveViews(childCount, firstPosition);
  }
  detachAllViewsFromParent(); //清除所有子view
  
  fillFromTop(childrenTop);

  recycleBin.scrapActiveViews(); //存在于mActiveViews的view移动至mScrapViews
}

Adapter getView的调用堆栈

IconListAdapter[72]--> getView                                                        
| <-- ( android.widget.AbsListView[2490]--> obtainView )    
| <-- ( android.widget.ListView[2027]--> makeAndAddView )    
| <-- ( android.widget.ListView[750]--> fillDown )    
| <-- ( android.widget.ListView[815]--> fillFromTop )    
| <-- ( android.widget.ListView[1801]--> layoutChildren )    
| <-- ( android.widget.AbsListView[2278]--> onLayout ) 

4.fillFromTop

private View fillFromTop(int nextTop) {
  return fillDown(mFirstPosition, nextTop);
}

5.fillDown

private View fillDown(int pos, int nextTop) {
  while (nextTop < end && pos < mItemCount) {
    View child = makeAndAddView(pos, nextTop, true, mListPadding.left, selected);
  }
}

6.makeAndAddView

private View makeAndAddView(int position, int y, boolean flow, int childrenLeft,
            boolean selected) {
  if (!mDataChanged) {//数据未改变，从mActiveViews获得
    final View activeView = mRecycler.getActiveView(position);
    if (activeView != null) {
      setupChild(activeView, position, y, flow, childrenLeft, selected, true);
      return activeView;
    }
  }
  //数据改变，或者没有获取到，调用obtainView进行获取
  final View child = obtainView(position, mIsScrap);
  setupChild(child, position, y, flow, childrenLeft, selected, mIsScrap[0]);
  return child;
}

7.obtainView

View obtainView(int position, boolean[] outMetadata) {
  //1.从mTransientStateViews获取
  final View transientView = mRecycler.getTransientStateView(position);
  if (transientView != null) {
    return transientView;
  }
  //2.从mScrapViews处获取
  final View scrapView = mRecycler.getScrapView(position);
  //这里调用了mAdapter的getView，如果scrapView不为空，就不需要执行inflate方法来生成新view
  final View child = mAdapter.getView(position, scrapView, this);
  returrn child;
}

8.ListView滑动

将屏幕之外的view加至mScrapViews

boolean trackMotionScroll(int deltaY, int incrementalDeltaY) {
  if (down) {
    for (int i = 0; i < childCount; i++) {
      final View child = getChildAt(i);
      if (child.getBottom() >= top) {//view在可见范围
        break;
      } else {
        count++;
        int position = firstPosition + i;
        if (position >= headerViewsCount && position < footerViewsStart) {
          // The view will be rebound to new data, clear any
          // system-managed transient state.
          child.clearAccessibilityFocus();
          mRecycler.addScrapView(child, position); //滑出范围之外，添加到mScrapViews
        }
      }
    }
  } else {
    int bottom = getHeight() - incrementalDeltaY;
    if ((mGroupFlags & CLIP_TO_PADDING_MASK) == CLIP_TO_PADDING_MASK) {
      bottom -= listPadding.bottom;
    }
    for (int i = childCount - 1; i >= 0; i--) {
      final View child = getChildAt(i);
      if (child.getTop() <= bottom) {
        break;
      } else {
        start = i;
        count++;
        int position = firstPosition + i;
        if (position >= headerViewsCount && position < footerViewsStart) {
          // The view will be rebound to new data, clear any
          // system-managed transient state.
          child.clearAccessibilityFocus();
          mRecycler.addScrapView(child, position);//滑出范围之外，添加到mScrapViews
        }
      }
    }
  }
}

8.retrieveFromScrap

• id相同
• position相同
• 从尾部获取

private View retrieveFromScrap(ArrayList<View> scrapViews, int position) {
  final int size = scrapViews.size();
  if (size > 0) {
    // See if we still have a view for this position or ID.
    for (int i = 0; i < size; i++) {
      final View view = scrapViews.get(i);
      final AbsListView.LayoutParams params =  (AbsListView.LayoutParams) view.getLayoutParams();

      if (mAdapterHasStableIds) {
        final long id = mAdapter.getItemId(position); //id相同
        if (id == params.itemId) {
          return scrapViews.remove(i);
        }
      } else if (params.scrappedFromPosition == position) { //position相同
        final View scrap = scrapViews.remove(i);
        clearAccessibilityFromScrap(scrap);
        return scrap;
      }
    }
    final View scrap = scrapViews.remove(size - 1); //从尾部获取
    clearAccessibilityFromScrap(scrap);
    return scrap;
  } else {
    return null;
  }
}

9.clear

页面退出时，会执行clear方法，清除缓存的view

void clear() {
  if (mViewTypeCount == 1) {
    final ArrayList<View> scrap = mCurrentScrap;
    clearScrap(scrap);
  } else {
    final int typeCount = mViewTypeCount;
    for (int i = 0; i < typeCount; i++) {
      final ArrayList<View> scrap = mScrapViews[i];
      clearScrap(scrap);
    }
  }

  clearTransientStateViews();
}

clear的调用堆栈

ListView--> onDetachedFromWindow                                              
| <-- ( android.view.View[15673]--> dispatchDetachedFromWindow )    
| <-- ( android.view.ViewGroup[3187]--> dispatchDetachedFromWindow )    
| <-- ( android.view.ViewGroup[3179]--> dispatchDetachedFromWindow )    
| <-- ( android.view.ViewGroup[3179]--> dispatchDetachedFromWindow )    
| <-- ( android.view.ViewGroup[3179]--> dispatchDetachedFromWindow )    
| <-- ( android.view.ViewGroup[3179]--> dispatchDetachedFromWindow )    
| <-- ( android.view.ViewGroup[3179]--> dispatchDetachedFromWindow )    
| <-- ( android.view.ViewGroup[3179]--> dispatchDetachedFromWindow )    
| <-- ( android.view.ViewRootImpl[3296]--> dispatchDetachedFromWindow )    
| <-- ( android.view.ViewRootImpl[6062]--> doDie )    
| <-- ( android.view.ViewRootImpl[6039]--> die )    
| <-- ( android.view.WindowManagerGlobal[457]--> removeViewLocked )    
| <-- ( android.view.WindowManagerGlobal[395]--> removeView )    
| <-- ( android.view.WindowManagerImpl[126]--> removeViewImmediate )    
| <-- ( android.app.ActivityThread[4480]--> handleDestroyActivity )