将文件复制到应用程序文档目录，错误控制

Question

我看到这篇文章有助于复制我的应用程序中包含的 .db 文件并将其复制到适当的目录：Where would you place your SQLite database file in an iPhone app?

完成这项工作的方法是否提供任何类型的故障或错误处理？就像用户认为应用程序被卡在 b/c 传输时间太长并决定强制退出应用程序一样？

方法：

// Creates a writable copy of the bundled default database in the application Documents directory.
- (void)createEditableCopyOfDatabaseIfNeeded {
    // First, test for existence.
    BOOL success;
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSError *error;
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"bookdb.sql"];
    success = [fileManager fileExistsAtPath:writableDBPath];
    if (success)
        return;
    // The writable database does not exist, so copy the default to the appropriate location.
    NSString *defaultDBPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"bookdb.sql"];
    success = [fileManager copyItemAtPath:defaultDBPath toPath:writableDBPath error:&error];
    if (!success) {
        NSAssert1(0, @"Failed to create writable database file with message '%@'.", [error localizedDescription]);
    }
}

Answer 1

不，如果存在同名的现有文件，它不会做任何事情。

因此，如果复制在中间由于某种原因被中断，那么下次运行时它会认为文件已经存在。

您可能应该先使用临时文件进行复制，然后如果完成，请将其重命名为正确的名称。

BOOL success;
NSFileManager *fileManager = [NSFileManager defaultManager];
NSError *error;

// Getting the writable path of the file
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0]; 
NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"bookdb.sql"];

// Checking if the file exists at the writable path
success = [fileManager fileExistsAtPath:writableDBPath];
if (success)
    return;

// Incase the file does not exist
// Getting the temporary path of the file
NSString *tempDBPath = [documentsDirectory stringByAppendingPathComponent:@"bookdb_temp.sql"];

// Just making sure no temporary file exists from a previous operation
success = [fileManager fileExistsAtPath:tempDBPath];
if (success)
{
    success=[fileManager removeItemAtPath:tempDBPath error:&error];
    NSAssert1(success, @"Failed to delete temp database file with message '%@'.", [error localizedDescription]);
}

// Getting the default path of the file
NSString *defaultDBPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"bookdb.sql"];

// Copying the file from the default path to the temporary
NSLog(@"Starting to copy");
success = [fileManager copyItemAtPath:defaultDBPath toPath:tempDBPath error:&error];
NSAssert1(success, @"Failed to copy database file with message '%@'.", [error localizedDescription]);
NSLog(@"Finished copying");

// Renaming the temporary file which wouldn't take time but to ensure the copying has finished successfully
success= [fileManager moveItemAtPath:tempDBPath toPath:writableDBPath error:&error];
NSAssert1(success, @"Failed to rename temp database file with message '%@'.", [error localizedDescription]);