检索按iOS上次播放时间排序的歌曲列表 [英] Retrieve list of songs ordered by last play time in iOS

问题描述

我需要按顺序从iOS设备获取最近播放过的 N 首歌曲的列表.

I need to obtain a list of the N most recently played songs from an iOS device, in order.

目前，我能想象的唯一方法是通过MPMediaQuery获取所有歌曲，然后按lastPlayedDate对其进行手动排序.

The only way I can imagine doing it, at the moment, is by getting all the songs through an MPMediaQuery and manually sort them by lastPlayedDate.

这是一个潜在的昂贵手术，我想知道是否有更好的方法.

This is a potentially expensive operation and I was wondering if there was a better approach.

经过一些测试，这是一个非常昂贵的操作.在包含2500首歌曲的测试库中，花了大约20秒的时间:

After some tests, this is a very expensive operation. On a test library of 2500 songs, it took around 20 seconds to:

1. 获取所有歌曲.
2. 为所有从未播放过的歌曲指定日期(1970年1月1日).
3. 按日期排序.
4. 获取前 N 个条目.

1. Get all the songs.
2. Assign a date to all songs that had never played (January 1 1970).
3. Order them by date.
4. Fetch the first N entries.

任何改进的建议都会受到赞赏.

Any suggestion of improvements would be appreciated.

现在已解决，但仅出于记录目的，这就是我在做什么.

Edit 2: Solved now, but just for the record here's what I was doing.

我正在按照此处所述使用块进行排序: https://stackoverflow.com/a/805589/112702 .只需将排序方法更改为Bryan的回答，就可以在iPod Touch 3上将速度提高近20倍.

I was sorting using a block as described here: https://stackoverflow.com/a/805589/112702. Simply changing the sorting method to what's in Bryan's answer improved my speed by nearly 20 times on an iPod Touch 3.

推荐答案

一种方法是获取从MPMediaQuery获得的MPMediaItem数组，并使用NSSortDescriptor通过MPMediaItemPropertyLastPlayedDate对其进行排序:

One way is to take the array of MPMediaItems you get from the MPMediaQuery and sort it by MPMediaItemPropertyLastPlayedDate using an NSSortDescriptor:

NSTimeInterval start  = [[NSDate date] timeIntervalSince1970];

MPMediaQuery *songsQuery = [MPMediaQuery songsQuery];
NSArray *songsArray = [songsQuery items];

NSSortDescriptor *sorter = [NSSortDescriptor sortDescriptorWithKey:MPMediaItemPropertyLastPlayedDate
                                                         ascending:NO];
NSArray *sortedSongsArray = [songsArray sortedArrayUsingDescriptors:@[sorter]];

NSTimeInterval finish = [[NSDate date] timeIntervalSince1970];
NSLog(@"Execution took %f seconds.", finish - start);

这将按照最近播放的新数组对新数组进行排序.我在iPhone 4S上用2000首歌曲对其进行了测试，它花了0.98秒.

This sorts the new array by most recently played first. I tested this on a iPhone 4S using 2000 songs and it took .98 seconds.

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