问题描述
我要对许多位置（航路点）到当前位置的距离进行排序。
当然，当前位置是一个移动目标，因此对于每个位置更新，都需要重新计算每个位置的距离。
I want to sort lots of locations (waypoints) on their distance from the current location.The current location is, of course, a moving target, so for every location update, recomputing the distance for every location is necessary. But only recomputing for close-by locations would by enough.
我目前使用核心数据，并将到当前位置的距离作为一个属性存储在表中（但仅在更改时才进行更新），方法是在configurecell：atindexpath：方法中。
这种工作方式，但是当核心数据自动更新所有距离时，应用程序没有响应。这适用于250个位置，但有5000个会崩溃。
我需要它在10.000个位置工作，尽管我可能只需要1000个附近的位置。
I currently use core-data, and store the distance to the current location as an attribute in the table (but only update is when it is changed) from within the configurecell: atindexpath: method.That sort of works, but the application is not responding while core-data automagically is updating all distances. This works for 250 locations, but for 5000 it crashes.I need it to work for 10.000 locations, although I probably only need the 1000 closest locations or so.
我还没有尝试过的想法：
将所有距离存储在单独的内存数组中，仅记录id和距离。然后按距离对数组进行排序。问题是我不能使用FetchedResultsController，因为数据库中没有排序字段。
Ideas that I did not try yet:Store all distances in a separate in-memory array with nothing but record id and distance. Then sort the array on distance. Problem is that then I can not use a FetchedResultsController because there is no sort field in the database.
使用谓词根据纬度和经度过滤位置。然后只显示已过滤的位置。
Filter locations based on their latitude and longitude by using a predicate. Then only present the filtered locations.
在单独的线程中重新计算距离。
Do the recalculation of distances in a separate thread.
有人提出建议，有不同的想法，对我的想法有所变化吗？
Anybody with suggestions, different ideas, a variation on my ideas?
推荐答案
我的最终解决方案如下：
我选择了经度和纬度为1度以内的所有航路点（通常约为1000个航路点），然后计算并存储与当前距离在表格中的位置。然后，我可以对距离进行排序。最慢的是保存核心数据。但是在排序（并提取）之后，我只是取消了更改。节省的费用占整个事情的90％以上，因此效果很好。
My final solution is as follows:I select all waypoints within 1 degree latitude and longitude (about 1000 waypoints normally) and then compute and store the distance to the current position in the table. I can then sort on the distance. The slow thing would be the saving in Core Data. But after sorting (and fetching), I simply cancel the changes. The saving was taking more than 90 % of the whole thing, so this worked quite well.
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