部分索引器获取位置的部分返回0 [英] section indexer get section for position returns 0

问题描述

在我的项目中，我有一个扩展 ArrayAdapter 并实现 SectionIndexer 的类.在实现方法 getPositionForSection 和 getSectionForPosition 时，我发现了一些奇怪的行为.

In my project I have class that extends ArrayAdapter<String> and implements SectionIndexer. When implementing methods getPositionForSection and getSectionForPosition I have found some strange behaviour.

当 getSectionForPosition 返回 0 时，为什么节索引器正常工作?

Why section indexer works properly when getSectionForPosition returns 0?

public int getSectionForPosition(int position) {
    return 0;
}

这个实现在很多教程中都有使用，例如:

this implementation is used in many tutorials, for example:

http://androidopentutorials.com/android-listview-fastscroll/

http://www.survivingwithandroid.com/2012/12/android-listview-sectionindexer-fastscroll.html

文档说

给定适配器内的位置，返回部分对象数组中的相应部分.

Given a position within the adapter, returns the index of the corresponding section within the array of section objects.

因此，如果我的列表中有 5 个以字母A"开头的项目和一些以字母B"开头的项目，那么 getSectionForPosition(5) 应该返回 1.

so if my list have 5 items starting with letter "A" and some items starting with letter "B", then getSectionForPosition(5) should return 1.

推荐答案

虽然 sectionIndexer 的基本功能(在拉动滚动条拇指时滚动浏览节索引)不受影响，但在方法 getSectionForPosition 可能会导致滑动列表时滚动条定位的错误行为(例如滚动条在 y 轴上移出窗口).

While the basic functionality of the sectionIndexer (scrolling through the section indices when pulling the scrollbar thumb) is unaffected, returning a constant in the method getSectionForPosition can lead to a misbehaviour of the scrollbar positioning when swiping through the list (e.g. the scrollbar moving out of the window on the y-axis).

显然，这种错误行为仅在列表或单个部分超过特定长度时发生，因此对于较短的列表，索引器似乎可以正常工作(但实际上并非如此).在上述方法中多次返回常量时，我​​在较大的列表中遇到了这种不当行为，并通过以正确的方式实现 getSectionForPosition 来修复它.

Apparently this misbehaviour only occurs when the list or single sections exceed a certain length, so for shorter lists the indexer might seem to work correctly (but in fact doesn't). I experienced this misbehaviour in larger lists when returning a constant in the above method several times and fixed it by implementing getSectionForPosition in a correct way.

但是，因为其他人可能会感兴趣，所以我可以提供该方法的示例实现.让 azIndexer 成为包含正确 部分的 HashMap ->我的索引和 listItems 的位置 映射是由适配器排列的项目.下面构建一个 position ->sectionIndex 映射存储在 positionIndexer 中.

However, since it might be interesting for others I can provide a sample implementation of that method. Let azIndexer be a HashMap containing a correct section -> position mapping of my indices and listItems be the items arranged by the adapter. The following builds a position -> sectionIndex mapping stored in positionIndexer.

List<Integer> values = new ArrayList();
for (int i : azIndexer.values()) {
    values.add(i);
}
values.add(listItems.size()-1);
Collections.sort(values);

int k = 0;
int z = 0;
for(int i = 0; i < values.size()-1; i++) {
    int temp = values.get(i+1);
    do {
        positionIndexer.put(k, z);
        k++;
    } while(k < temp);
    z++;
}

然后将在 getSectionForPosition 方法中使用:

which will then be used in the getSectionForPosition method:

@Override
public int getSectionForPosition(int position) {
    return positionIndexer.get(position);
}

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