如何显示NSMigrationManager在UILabel中的迁移进度？ [英] How to show migration progress of NSMigrationManager in a UILabel?

问题描述

我有很多二进制数据Core数据，我想删除和保存为文件，所以我设置代码，以便它将运行手动迁移。

I have a lot of binary data on Core Data which I would like to remove and save as files so I setup the code so that it would run a manual migration.

问题是，因为我必须从Core Data中提取二进制文件并将其保存到文件，迁移过程可能需要很长时间，具体取决于有多少数据。

The problem is that because I have to pull binary from Core Data and save them to files, the migration process could take a very long time depending on how much data there is.

我想显示一个简单的进度标签，以便用户不会认为应用程序已冻结。

I would like to show a simple progress label so that users wouldn't think that the app is frozen.

// app did launch
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    ...
    // add the progress label
    self.progressLabel = [[UILabel alloc] initWithFrame:CGRectMake(103, 36, 114, 21)];
    [self.progressLabel setText:@"0%"];
    [self.window addSubview:self.progressLabel];
    [self.window makeKeyAndVisible];
    ...
    // start migration
    [self progressivelyMigrateURL:storeURL];
    ...
}

// manually migrate store
- (BOOL)progressivelyMigrateURL:(NSURL*)sourceStoreURL
{
    NSLog(@"start progressivelyMigrateURL");
    ...
    // create the migration manager
    NSMigrationManager *manager = [[NSMigrationManager alloc] initWithSourceModel:sourceModel destinationModel:targetModel];
    ...
    // register for KVO of migration progress here
    [manager addObserver:self forKeyPath:@"migrationProgress" options:NSKeyValueObservingOptionNew context:NULL];

    // start the migration
    if (![manager migrateStoreFromURL:sourceStoreURL type:type options:nil withMappingModel:mappingModel toDestinationURL:destinationStoreURL destinationType:type destinationOptions:nil error:&error])
    {
        return NO;
    }
    ...
}

// handle KVO of migration process here
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if ([keyPath isEqual:@"migrationProgress"])
    {
        float migrationProgress = [[change objectForKey:NSKeyValueChangeNewKey] floatValue];
        int percent = migrationProgress * 100;
        [self.progressLabel setText:[NSString stringWithFormat:@"%d%", percent]];
        [self.progressLabel layoutIfNeeded];
        [self.progressLabel setNeedsDisplay];

        NSLog(@"migrationProgress: %d", percent);
        NSLog(@"self.testLabel text: %@", self.testLabel.text);
    }
}

迁移运行完美，我可以确认NSLog

The migration runs perfectly and I can confirm that the NSLog is returning incrementing values while the migration is taking place.

问题是self.progressLabel不会在每次进度更新时重绘，只是从0％跳到100 ％，而迁移正在进行。我知道我不能在单独的线程上运行迁移。

The problem is that self.progressLabel does not redraw every time the progress is updated and just skips from 0% to 100% while the migration is taking place. I know I can't run the migration on a separate thread. How can I make this work?

推荐答案

您确实需要在后台线程上执行迁移，

You precisely need to perform the migration on a background thread, and update the UI as you get progress notifications on the main thread.

- (void)startMigration {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
    NSMigrationManager  * manager = [[NSMigrationManager alloc] initWithSourceModel:sourceModel destinationModel:destinationModel];
    [manager addObserver:self forKeyPath:@"migrationProgress" options:0 context:NULL];
    BOOL success = [manager migrateStoreFromURL:sourceStoreURL type:type options:nil withMappingModel:mappingModel toDestinationURL:destinationStoreURL destinationType:type destinationOptions:nil error:&error];
    [manager removeObserver:self forKeyPath:@"migrationProgress"];
    if(success) {
        dispatch_async(dispatch_get_main_queue(), ^{
        // Go back to the main thread and continue…
        });
    }
}

接收通知时：

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    dispatch_sync(dispatch_get_main_queue(), ^{
        CGFloat progress = [(NSMigrationManager *)object migrationProgress];
        // Update UI progress indicator
    });
}

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