Android ListView 源码分析

ListView 的源码实在太多, 重点分析ListView的几个机制

ListView的继承关系

可以看出,ListView和GridView的有极大的相似性,对ListView进行缓存,布局等操作都是在AbsListView中完成的.

RecycleBin机制

RecycleBin中的关键字段

RecycleBin将View分为两级,ActiveView和ScrapView,如果当前的view处于可见状态,将它放在ActiveView的数组中,如果ActiveView不可见了,开始将它降级为ScrapView,等待回收.

private RecyclerListener mRecyclerListener;/** * The position of the first view stored in mActiveViews. */ // 第一个ActiveView的下标,通过这个计算数组中的索引private int mFirstActivePosition;/** * Views that were on screen at the start of layout. This array is populated at the start of * layout, and at the end of layout all view in mActiveViews are moved to mScrapViews. * Views in mActiveViews represent a contiguous range of Views, with position of the first * view store in mFirstActivePosition. */ // ActiveView数组private View[] mActiveViews = new View[0];/** * Unsorted views that can be used by the adapter as a convert view. */ // ScrapView数组,因为有可能多个ViewType,所以使用二维数组进行存储private ArrayList<View>[] mScrapViews;// ViewType的数量,通过这个创建ScrapHeapprivate int mViewTypeCount;private ArrayList<View> mCurrentScrap;private ArrayList<View> mSkippedScrap;private SparseArray<View> mTransientStateViews;private LongSparseArray<View> mTransientStateViewsById;

RecycleBin中的关键方法

fillActiveViews()

RecycleBin当中使用mActiveViews这个数组来存储View，调用这个方法后就会根据传入的参数来将ListView中的指定元素存储到mActiveViews数组当中。

/** * Fill ActiveViews with all of the children of the AbsListView. * * @param childCount The minimum number of views mActiveViews should hold * @param firstActivePosition The position of the first view that will be stored in *        mActiveViews */void fillActiveViews(int childCount, int firstActivePosition) {    //针对数据,调整数组大小    if (mActiveViews.length < childCount) {        mActiveViews = new View[childCount];    }    // 记录ActiveView的首位置    mFirstActivePosition = firstActivePosition;    //noinspection MismatchedReadAndWriteOfArray    final View[] activeViews = mActiveViews;    for (int i = 0; i < childCount; i++) {        View child = getChildAt(i);        // 调整LayoutParams        AbsListView.LayoutParams lp = (AbsListView.LayoutParams) child.getLayoutParams();        // Don't put header or footer views into the scrap heap        // 除Header,Footer之外其他View将添加到ActiveView数组中        if (lp != null && lp.viewType != ITEM_VIEW_TYPE_HEADER_OR_FOOTER) {            // Note:  We do place AdapterView.ITEM_VIEW_TYPE_IGNORE in active views.            //        However, we will NOT place them into scrap views.            activeViews[i] = child;            // Remember the position so that setupChild() doesn't reset state.            lp.scrappedFromPosition = firstActivePosition + i;        }    }}

未完 doing….