objective-c - copyItemAtPath -path 显示在后台线程中创建的 plist 为 null

Question

我有一个检查 plist 是否存在的函数，如果不存在，它将创建 plist。

此函数在后台调用，即[self performSelectorInBackground:@selector(CreatePlist:) withObject:xyz];

一切都很完美。

但是当我尝试从主线程的 plist 中获取数据时，即

NSString *path = [[NSBundle mainBundle] pathForResource:@"calendar" ofType:@"plist"];
NSLog(@"path is %@", path); // path comes null
fileName = [fileName stringByReplacingOccurrencesOfString:@"/" withString:@""];
NSLog(@"file name data contain %@",fileName);
NSFileManager *fileManager = [NSFileManager defaultManager];

//see if Data.plist exists in the Documents directory
if (![fileManager fileExistsAtPath:[self saveMyPath:fileName] ]) {
    [fileManager copyItemAtPath:path toPath:[self saveMyPath:@""] error:nil]; //at this point the app crashes saying path is null
}

当我将我的应用程序从后台移至主线程时，它运行良好。这里有什么问题？

Answer 1

看起来当主线程到达时后台线程还没有完成。

你可以尝试使用 grand central dispatch.. 例如

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
  [self CreatePlist:xyz];
  dispatch_async(dispatch_get_main_queue(), ^{
    NSString *path = [[NSBundle mainBundle] pathForResource:@"calendar" ofType:@"plist"];
    NSLog(@"path is %@", path); // path comes null
    fileName = [fileName stringByReplacingOccurrencesOfString:@"/" withString:@""];
    NSLog(@"file name data contain %@",fileName);
    NSFileManager *fileManager = [NSFileManager defaultManager];

    //see if Data.plist exists in the Documents directory
    if (![fileManager fileExistsAtPath:[self saveMyPath:fileName] ]) {
       [fileManager copyItemAtPath:path toPath:[self saveMyPath:@""] error:nil]; //at this point the app crashes saying path is null
  });
});