RecyclerView使用notifyItemMoved()破坏视图 [英] RecyclerView corrupts view using notifyItemMoved()

问题描述

我在使用notifyItemMoved()方法时遇到问题.似乎错误地显示了未移动的视图.

I'm having a problem with using the notifyItemMoved() method. It seems to be incorrectly displaying unmoved views.

我的列表中有4个元素.我想做的是为第1项和第3项之间的交换设置动画效果.第1项和第3项可以正确交换，但是第2项显示第3项的内容！

My list has 4 element in it. What I want to do is animate a swap between item 1 and item 3. Items 1 and 3 swap correctly, but item 2 displays what was at item 3!

所以列表开始看起来像这样:

So the list starts off looking something like this:

Item 0
Item 1
Item 2
Item 3

并以此结尾:

Item 0
Item 3
Item 3 <!-- What the heck has this changed for?
Item 1

我的适配器由List mProductList支持.我调用以下代码:

My adapter is backed by a List mProductList. I call the following code:

public void sortBackingListUsingSortingList(List<ProductWrapper> newProductItems) {
    Log.e("", "Before:");
    for(ProductWrapper wrapper : mProductItems) wrapper.log();
    for(int i = 0; i < newProductItems.size(); i++) {
        ProductWrapper currentItem   = mProductItems.get(i);
        ProductWrapper correctItem   = newProductItems.get(i);

        if(!currentItem.equals(correctItem)) {
            // Item in wrong place
            int indexOfCorrectItem = getIndexOfItemInList(mProductItems, correctItem);
            Collections.swap(mProductItems, i, indexOfCorrectItem);
            notifyItemMoved(i, indexOfCorrectItem);
            Log.e("", "notifyItemMoved(" + i + ", " + indexOfCorrectItem+")");
            Log.e("", "After:");
            for(ProductWrapper wrapper : mProductItems) wrapper.log();
        }
    }
}

我还向onBindViewHolder添加了日志记录，以检查是否调用了我的视图逻辑:

I've also added logging to onBindViewHolder to check if my view logic is being called:

@Override
public void onBindViewHolder(HolderBasic holder, int position) {
    Log.e("", "onBindViewHolder(holder, " + position + ")");
    holder.fill(mProductItems.get(position));
}

我的日志如下:

09-02 14:39:17.853  ﹕ Before:
09-02 14:39:17.853  : Item 0
09-02 14:39:17.853  : Item 1
09-02 14:39:17.853  : Item 2
09-02 14:39:17.853  : Item 3

09-02 14:39:17.854  ﹕ notifyItemMoved(1, 3)

09-02 14:39:17.854  ﹕ After:
09-02 14:39:17.854  : Item 0
09-02 14:39:17.854  : Item 3
09-02 14:39:17.854  : Item 2
09-02 14:39:17.854  : Item 1

09-02 14:39:17.867  ﹕ onBindViewHolder(holder, 1)
09-02 14:39:17.874  ﹕ onBindViewHolder(holder, 3)

如您所见，项目2完全没有理由进行更改，但是确实如此.有人知道为什么吗?

As you can see, no reason for Item 2 to have change it's display at all - and yet, it does. Anybody know why?

编辑

我可以通过遍历整个适配器并在每个项目上调用notifyItemChanged()来解决上述问题.低效的解决方案不是很好的解决方案，但对用户而言是看不见的.

I can get around above by looping through the entire adapter and calling notifyItemChanged() on every item. Inefficient and not a good solution, but is invisible to the user.

推荐答案

感谢@ david.mihola指导我了解我在做错什么.

Thank you to @david.mihola for leading me to what I'm doing wrong.

花了很长时间才弄清楚症状没有使问题变得显而易见！

This took so long to figure out as the symptom didn't make the problem obvious!

我正在这样做:

Collections.swap(mProductItems, i, indexOfCorrectItem);
notifyItemMoved(i, indexOfCorrectItem)

但是，我显然没有想到notifyItemMoved()的实际作用.只是通知适配器项目i已移至indexOfCorrectItem ，而没有告诉适配器indexOfCorrectItem也已移至i .

But, I obviously didn't think through what notifyItemMoved() was actually doing. It is only notifying the adapter that item i has moved to indexOfCorrectItem it isn't telling the adapter that indexOfCorrectItem has also moved to i.

在幕后，它正在执行以下操作:

Under the covers it was doing the following:

1. 将项目1移至3
2. 将2处的位置移至1处以填补空白
3. 将3到2的位置移动以填补空白
4. notifyItemChanged(1);
5. notifyItemChanged(3);

1. Move item 1 to 3
2. Move what was at 2 to 1 to fill the gap
3. Move what was at 3 to 2 to fill the gap
4. notifyItemChanged(1);
5. notifyItemChanged(3);

以上内容当然会使第3项移至第2项，而没有刷新视图！是步骤4和5通过使item1和item3正确显示而使item2不正确隐藏了问题！

The above of course leaves item 3 moved down to item 2 without a refreshed view! It was steps 4 and 5 which were hiding the problem by making item1 and item3 display correctly and leaving item2 incorrect!

意识到这一点后，我尝试了以下代码:

As soon as I realised this I tried the following code:

notifyItemMoved(indexOfCorrectItem, i);
notifyItemMoved(i, indexOfCorrectItem);

这以正确的顺序离开了列表，但使动画短路了.

This left the list in the correct order, but it short circuited the animation.

因此，我完全放弃了交换:

So, instead, I dumped swapping altogether:

mProductItems.remove(indexOfCorrectItem);
mProductItems.add(i, correctItem);
notifyItemMoved(indexOfCorrectItem, i);

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