ios - iOS代码跳过dispatch_async

Question

我需要从URL下载数据(这会以JSON格式打印数据)，并将其存储在应用程序的AppDelegate.m文件中，用于应用程序的“配置”文件中。当我运行该应用程序时，由于某种原因，它只是跳过了dispatch_async代码。为什么会发生这种情况，我该如何解决？

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    //Download the config.json file
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
        NSString *configFileUrl = @"http://webserviceurl";
        //NSString *downloadToFile = @"Configuration.json";
        NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:configFileUrl]];
        [self performSelectorOnMainThread:@selector(writeDataToConfigurationJsonFile:) withObject:data waitUntilDone:YES];
    });

 //More code below

这是我将数据写入应用程序文档目录中的文件的地方:

-(void)writeDataToConfigurationJsonFile:(NSData*)jsonData{

    NSString *content = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];

    //get the documents directory:
    NSArray *paths = NSSearchPathForDirectoriesInDomains
    (NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];

    //make a file name to write the data to using the documents directory:
    NSString *fileName = [NSString stringWithFormat:@"%@/Configuration.json", documentsDirectory];

    //save content to the documents directory
    [content writeToFile:fileName
              atomically:YES
                encoding:NSUTF8StringEncoding
                   error:nil];
}

Answer 1

performSelectorOnMainThread是一个运行循环方法，您需要使用:

dispatch_async(dispatch_get_main_queue(), ^{/*code*/});