ios - 在 UICollectionView 中重新加载数据的正确方法是什么？

Question

如果我从用户 Assets 库中的相册中获取信息，并且他们在我的应用程序处于后台时添加图片或从中删除。什么是重新加载它们的最佳方法。

目前我有:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(assetsLibraryDidChange:) name:ALAssetsLibraryChangedNotification object:_photoListArray];

要获得初始通知，然后它会调用我的assetLibraryDidChange 方法:

看起来像这样:

- (void)assetsLibraryDidChange:(NSNotification *)note
{

    //dict nil reload
    if(note.userInfo==nil) {
        [self.CoverView reloadData];
        return;
    }

    //dict empty no reload
    if(note.userInfo.count == 0) {
        NSLog(@"empty");
        return;
    }

    else {
        [self.CoverView reloadData];
    }
}

尽管我正在考虑删除所有 if 和 else 并且每次都重新加载它。

我要做什么:

我的应用收到通知与实际更新之间似乎存在差距。 Apple 的默认照片应用程序似乎能够在大约 3-4 秒内完成，而我的需要将近 10 秒!有没有更有效的方法来做到这一点？

我继续在所有 if 之前放置一个 nslog，以查看该方法也被调用了多少次。

//Library Updated
- (void)assetsLibraryDidChange:(NSNotification *)note
{
    NSLog(@"photos updated");

    //dict nil reload
    if(note.userInfo==nil) {
        dispatch_async(dispatch_get_main_queue(), ^{
            [self.CoverView reloadData];
            NSLog(@"note: %@", note.userInfo);
            NSLog(@"array: %@", _photoListArray);
            return;
        });
    }

    //dict empty no reload
    if(note.userInfo.count == 0) {
        NSLog(@"empty");
        return;
    }

    else {
        dispatch_async(dispatch_get_main_queue(), ^{
            [self.CoverView reloadData];
            NSLog(@"note2: %@", note.userInfo);
            NSLog(@"array2: %@", _photoListArray);
        });
    }

}

结果如下:

2013-08-16 10:41:51.622 app[180:1803] photos updated
2013-08-16 10:41:51.635 app[180:60b] note2: {
    ALAssetLibraryUpdatedAssetsKey = "{(\n    assets-library://asset/asset.JPG?id=CCA17BE2-5633-4FFE-A113-F21E37B9882C&ext=JPG,\n    assets-library://asset/asset.JPG?id=7B05283E-87A5-4CFE-BDBE-7703E311E0DF&ext=JPG,\n    assets-library://asset/asset.JPG?id=5B1E736F-E21E-4400-9679-5DE8215AC09D&ext=JPG\n)}";
}
2013-08-16 10:41:51.638 app[180:60b] array2: (
    "<Media: 0x176b3410>",
    "<Media: 0x176b5b00>",
    "<Media: 0x176b5c90>",
    "<Media: 0x176b7590>",
    "<Media: 0x176b47c0>",
    "<Media: 0x176b7e10>",
    "<Media: 0x176b83b0>",
    "<Media: 0x176b8990>",
    "<Media: 0x176b8f40>",
    "<Media: 0x176b9530>",
    "<Media: 0x176ba160>",
    "<Media: 0x176ba960>",
    "<Media: 0x175794d0>",
    "<Media: 0x175503c0>",
    "<Media: 0x17571f80>",
    "<Media: 0x1756dc20>",
    "<Media: 0x17571060>",
    "<Media: 0x1757b0d0>",
    "<Media: 0x1757b8f0>",
    "<Media: 0x1757bee0>",
    "<Media: 0x1757bcf0>",
    "<Media: 0x1757ca80>",
    "<Media: 0x1757cbd0>"
)
2013-08-16 10:41:51.827 app[180:3e07] photos updated
2013-08-16 10:41:51.831 app[180:3e07] empty
2013-08-16 10:41:51.893 app[180:3e07] photos updated
2013-08-16 10:41:51.897 app[180:3e07] empty
2013-08-16 10:41:52.059 app[180:3e07] photos updated
2013-08-16 10:41:52.074 app[180:3e07] empty
2013-08-16 10:41:52.092 app[180:5117] photos updated
2013-08-16 10:41:52.095 app[180:5117] empty

Media 对象是一个类，我只是用来添加数据并将其与它们一起存储。姓名，分机。没有什么会改变实际图像。

没有调度:

2013-08-16 11:37:53.246 app[296:3d07] photos updated
2013-08-16 11:37:53.255 app[296:3d07] note2: {
    ALAssetLibraryUpdatedAssetsKey = "{(\n    assets-library://asset/asset.JPG?id=CCA17BE2-5633-4FFE-A113-F21E37B9882C&ext=JPG,\n    assets-library://asset/asset.PNG?id=D72A00CE-4198-45BE-BCC5-8DEB8419A5C8&ext=PNG,\n    assets-library://asset/asset.JPG?id=5B1E736F-E21E-4400-9679-5DE8215AC09D&ext=JPG\n)}";
}
2013-08-16 11:37:53.260 app[296:3d07] array2: (
    "<Media: 0x176271b0>",
    "<Media: 0x17577920>",
    "<Media: 0x17579c50>",
    "<Media: 0x17579eb0>",
    "<Media: 0x17579e00>",
    "<Media: 0x1757a9b0>",
    "<Media: 0x1757af50>",
    "<Media: 0x1757b540>",
    "<Media: 0x1757baf0>",
    "<Media: 0x1757c0e0>",
    "<Media: 0x17656510>",
    "<Media: 0x176570f0>",
    "<Media: 0x176572b0>",
    "<Media: 0x17657840>",
    "<Media: 0x17657e20>",
    "<Media: 0x17658400>",
    "<Media: 0x176589e0>",
    "<Media: 0x17659270>",
    "<Media: 0x17650470>",
    "<Media: 0x17659380>",
    "<Media: 0x176507a0>",
    "<Media: 0x17650ab0>",
    "<Media: 0x17659cb0>",
    "<Media: 0x1765a340>"
)
2013-08-16 11:37:53.404 app[296:4e17] photos updated
2013-08-16 11:37:53.408 app[296:4e17] empty
2013-08-16 11:37:53.450 app[296:3d07] photos updated
2013-08-16 11:37:53.458 app[296:3d07] empty
2013-08-16 11:37:53.466 app[296:4e17] photos updated
2013-08-16 11:37:53.470 app[296:4e17] empty

Answer 1

任何 UI 更改的东西都应该在主线程上完成.. 尝试:

- (void)assetsLibraryDidChange:(NSNotification *)note
{

    //dict nil reload
    if(note.userInfo==nil) {
        dispatch_async(dispatch_get_main_queue(), ^{
            [self.CoverView reloadData];
            return;
        }
    }

    //dict empty no reload
    if(note.userInfo.count == 0) {
        NSLog(@"empty");
        return;
    }

    else {
        dispatch_async(dispatch_get_main_queue(), ^{            
            [self.CoverView reloadData];
        }
    }
}