recyclerView adapter.notifyDataSetChanged()分析

最新推荐文章于 2022-03-12 10:19:08 发布

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最新推荐文章于 2022-03-12 10:19:08 发布 · 1.6k 阅读

3 ·

CC 4.0 BY-SA版权

本文深入探讨了RecyclerView的adapter.notifyDataSetChanged()方法，通过观察者模式触发RecyclerViewDataObserver的onChange()，进而执行LayoutManager的onLayoutChildren()进行重绘。文章详细分析了回收过程，包括废料缓存、mCachedViews及RecyclerView.RecycledViewPool的使用，以及如何填充视图和通过recycler.getViewForPosition(position)创建或获取缓存的视图。

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① 
mAdapter.notifyDataSetChanged();
跟进源码,发现是通过观察者模式进行分发的
RecyclerView.Adapter：
public final void notifyDataSetChanged() {
   
   
            this.mObservable.notifyChanged();
        }

②
 找到注册观察者的地方:应该就是设置设配器的地方
 RecycerView.setAdapter(adapter);
 跟进源码->
 public void setAdapter(@Nullable RecyclerView.Adapter adapter) {
   
   
        ...
        this.setAdapterInternal(adapter, false, true);
        ...
 }
 private void setAdapterInternal(@Nullable RecyclerView.Adapter adapter, boolean compatibleWithPrevious, boolean removeAndRecycleViews) {
   
   
		// 上一个 mAdapter的观察者取消注册
        if (this.mAdapter != null) {
   
   
            this.mAdapter.unregisterAdapterDataObserver(this.mObserver);
            this.mAdapter.onDetachedFromRecyclerView(this);
        }
		...
		// 更新 设配器
        this.mAdapter = adapter;
        if (adapter != null) {
   
   
        	// 当前adapter 注册观察者
            adapter.registerAdapterDataObserver(this.mObserver);
            adapter.onAttachedToRecyclerView(this);
        }
        ...
    }

③
 可以看到观察者对象是 RecyclerView.this.mObserver
   mObserver的初始化是在RecyclerView构造器里面
   public RecyclerView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyle) {
   
   
        super(context, attrs, defStyle);
        this.mObserver = new RecyclerView.RecyclerViewDataObserver();
        ...
      }

// 观察者 与 设配器刷新方法一一对应
private class RecyclerViewDataObserver extends RecyclerView.AdapterDataObserver {
   
   
        RecyclerViewDataObserver() {
   
   
        }
        /**
        * 对应 mAdapter.notifyDataSetChanged();
        */
        public void onChanged() {
   
   
            RecyclerView.this.assertNotInLayoutOrScroll((String)null);
            RecyclerView.this.mState.mStructureChanged = true;
            RecyclerView.this.processDataSetCompletelyChanged(true);
            if (!RecyclerView.this.mAdapterHelper.hasPendingUpdates()) {
   
   
                RecyclerView.this.requestLayout();
            }
        }

		/**
        * 对应 mAdapter.onItemRangeChanged();
        */
        public void onItemRangeChanged(int positionStart, int itemCount, Object payload) {
   
   
            RecyclerView.this.assertNotInLayoutOrScroll((String)null);
            if (RecyclerView.this.mAdapterHelper.onItemRangeChanged(positionStart, itemCount, payload)) {
   
   
                this.triggerUpdateProcessor();
            }
        }
		/**
        * 对应 mAdapter.onItemRangeInserted();
        */
        public void onItemRangeInserted(int positionStart, int itemCount) {
   
   
            RecyclerView.this.assertNotInLayoutOrScroll((String)null);
            if (RecyclerView.this.mAdapterHelper.onItemRangeInserted(positionStart, itemCount)) {
   
   
                this.triggerUpdateProcessor();
            }
        }
		/**
        * 对应 mAdapter.onItemRangeRemoved();
        */
        public void onItemRangeRemoved(int positionStart, int itemCount) {
   
   
            RecyclerView.this.assertNotInLayoutOrScroll((String)null);
            if (RecyclerView.this.mAdapterHelper.onItemRangeRemoved(positionStart, itemCount)) {
   
   
                this.triggerUpdateProcessor(