为何未调用通知方法RecyclerView仍自动更新？

Hey there, let's break down what's happening with your RecyclerView behavior—it's all tied to how RecyclerView handles layout triggers and when it reads your data source.

1. Why does data from addMoreData() show up without calling notifyDataSetChanged()? #

When you set the adapter in onCreate() and immediately call addMoreData() to update your mList, RecyclerView hasn't finished its first layout pass yet.

Once your Activity's view tree is fully initialized and attached to the window, RecyclerView automatically triggers an initial layout request. During this layout, it calls your adapter's getItemCount() and onBindViewHolder() methods. By this point, your mList already includes the 10 items added by addMoreData(), so RecyclerView renders all of them. This is just the default behavior of RecyclerView's first layout—no manual notify call is needed here.

2. Why does clicking the button show 3 items when only notifyItemInserted() is called once? #

Look at your button click logic:

mList.add("Button add " +0);
mAdapter.notifyItemInserted(mList.size()-1);
//Again it's showing but never notify
mList.add("Button add " +1);
mList.add("Button add " +2);

The key point here is: notifyItemInserted() doesn't update the UI immediately. It just tells RecyclerView that a change needs to happen, and RecyclerView queues this update for the next UI refresh cycle (like the next frame).

Between calling notifyItemInserted() and the actual UI update, you've already added two more items to mList. When RecyclerView finally runs the layout update, it checks the current state of mList—which now has 3 new items—and binds all visible positions. That's why all three items show up, even though you only notified for one insertion.

Fix if you want to only show the first inserted item #

If you intend to display only the first new item when clicking the button, don't modify the data source after calling the notify method. Or, if you want to add all three, pair each addition with its own notify call:

button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        mList.add("Button add " +0);
        mAdapter.notifyItemInserted(mList.size()-1);
        
        // Uncomment below if you want to add and notify the other two items
        // mList.add("Button add " +1);
        // mAdapter.notifyItemInserted(mList.size()-1);
        // mList.add("Button add " +2);
        // mAdapter.notifyItemInserted(mList.size()-1);
    }
});

内容的提问来源于stack exchange，提问作者aTo