iPhone(iOS): copying files from main bundle to documents folder causes crash

Question

我正在尝试设置我的应用程序，以便在首次启动时，位于主包中“Populator”文件夹中的一系列文件被复制到文档目录中。

我当前的实现如下:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

  NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
  NSString *sourcePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Populator"];
  NSString *folderPath = [documentsDirectory stringByAppendingPathComponent:@"Files"];
  NSLog(@"Source Path: %@\n Documents Path: %@ \n Folder Path: %@", sourcePath, documentsDirectory, folderPath);

  NSError *error;

  [[NSFileManager defaultManager] copyItemAtPath:sourcePath 
                                        toPath:folderPath
                                         error:&error];

  NSLog(@"Error description-%@ \n", [error localizedDescription]);
  NSLog(@"Error reason-%@", [error localizedFailureReason]);
  ....
  return YES;
}

但是，第一次运行时会崩溃，并显示以下控制台消息(但文件已复制)。下次打开应用程序时，它不会崩溃。

    2010-07-13 15:14:26.418 AppName[5201:207] Source Path: /Users/jack/Library/Application Support/iPhone Simulator/3.2/Applications/1076C1FA-60B0-4AC7-8CD4-74F81472DAE6/AppName.app/Populator
 Documents Path: /Users/jack/Library/Application Support/iPhone Simulator/3.2/Applications/1076C1FA-60B0-4AC7-8CD4-74F81472DAE6/Documents 
 Folder Path: /Users/jack/Library/Application Support/iPhone Simulator/3.2/Applications/1076C1FA-60B0-4AC7-8CD4-74F81472DAE6/Documents/Files
2010-07-13 15:14:26.466 AppName[5201:207] *** +[AppNameAppDelegate localizedDescription]: unrecognized selector sent to class 0xa79c
2010-07-13 15:14:26.475 AppName[5201:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** +[AppNameAppDelegate localizedDescription]: unrecognized selector sent to class 0xa79c'
2010-07-13 15:14:26.495 AppName[5201:207] Stack: (
    40911435,
    2569270537,
    41183227,
    40645910,
    40642578,
    9142,
    2815466,
    2819475,
    2844680,
    2826401,
    2858055,
    49271164,
    40452156,
    40448072,
    2817668,
    2850273,
    8776,
    8630
)

有人对出了什么问题有什么建议吗？我已经设置了一些代码来实现“仅在首次启动时”功能，但为了清楚起见，没有将其包含在此处。

谢谢

Answer 1

   NSError *error;

您正在声明一个局部变量而不对其进行初始化。因此，它会充满垃圾。

  [[NSFileManager defaultManager] copyItemAtPath:sourcePath 
                                        toPath:folderPath
                                         error:&error];

如果该行没有发生错误，则仍然保持error的垃圾状态。

  NSLog(@"Error description-%@ \n", [error localizedDescription]);

现在您将消息发送到某个随机的、未初始化的位置。这就是崩溃的根源。

<小时/>

为避免这种情况，请将 error 初始化为 nil。

NSError* error = nil;
//             ^^^^^

或者仅当 -copyItemAtPath:... 返回 NO 时才打印错误(其中正确填充了 error)。

if (![[NSFileManager defaultManager] copyItemAtPath:sourcePath ...]) {
  NSLog(...); 
}