Android ListView Adapter 中 item-id 的目的是什么? [英] What's the purpose of item-id's in Android ListView Adapter?

问题描述

(不是特定于 ListView，而是特定于 Adapter).

(Not specific to ListView, but to Adapter).

当我继承 BaseAdapter 时，我一直在实现它:

I keep implementing this when I subclass BaseAdapter:

    @Override
    public long getItemId(int position) {
        return position; 
    }

因为必须实现它.我没有看到它的任何用途，我只需要 getItem(position)，而不是 getItemId(position).

Because have to implement that. I don't see any use of it, I need getItem(position) only, not getItemId(position).

我想知道它是否有任何意义(对 Android SDK 或其他东西)?

I wonder if it has any significance (to Android SDK or something else)?

推荐答案

拥有 稳定 项目 ID 的原因可能有很多.无法给出默认实现，因为它取决于存储在适配器中的对象类型.

There are probably many reasons to have stable item IDs. A default implementation cannot be given since it depends on the type of Object being stored in the Adapter.

Android 有一项检查，以确保仅在稳定后才使用项目 ID，即子类已正确覆盖 getItemId；BaseAdapter.hasStableIds 必须被覆盖才能返回 true.

Android has a check to make sure that item IDs are used only when they are stabled, i.e. the subclass has properly overridden getItemId; BaseAdapter.hasStableIds must be overriden to return true.

我遇到的几个原因:

• AdapterView.OnItemClickListener 的方法 onItemClick(AdapterView parent, View view, int position, long id) 也发送long id

getCheckedItemIds 方法 结果只有有效，如果选择模式尚未设置为Choice_Mode_None，并且适配器具有稳定的ID.

回复因为必须实现那个":您不必必须如果您不使用这些功能，则没有必要.但是如果你这样做了，不要忘记覆盖 boolean hasStableIds() .

Reply to "Because have to implement that": you don't have to If you don't use the features, there's no need. But if you do, don't forget to override boolean hasStableIds() as well.

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