关于iCloud的注册，到代码的实现

iCloud需要xcode4.x IOS5 sdk 请先做好准备工作

1.需要传件一个新的app id，要是有了一个的话，保证着个app id 不是一个通配符的那种。

2.创建完成之后，你要做的是开启这项功能，就跟开发推送一样，然后在创建一个新的Provisional Profile

3.选择工程的summary，滚动到entitlement点击entitlements，xcode会自动的创建一个*.entitlements

4.点击创建的*.entitlements，分别把pist列表里的三个字段都添上内容，格式为（Team_ID.com.yourcompany.icloudtest）,不要把team_id 跟 app_id弄混了啊，team_id是你创建完Provisional的时候，在最前面显示的那10个字符。

5.然后就可以在delegate里面写下面的代码了

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  // Override point for customization after application launch.
  self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

  NSFileManager *fileManager = [NSFileManager defaultManager];
  // Team-ID + Bundle Identifier
  NSURL *iCloudURL = [fileManager URLForUbiquityContainerIdentifier:@"ZZZZ826ZZ2.com.yourcompany.icloudtest"];
  NSLog(@"%@", [iCloudURL absoluteString]);

  NSUbiquitousKeyValueStore *cloudStore = [NSUbiquitousKeyValueStore defaultStore];
  [cloudStore setString:[iCloudURL absoluteString] forKey:@"iCloudURL"];
  [cloudStore synchronize]; // Important as it stores the values you set before on iCloud

  UILabel *myLabel = [[UILabel alloc] initWithFrame:CGRectMake(0,round(self.window.bounds.size.height/4.0),self.window.bounds.size.width,round(self.window.bounds.size.height/8.0))];
  myLabel.font = [UIFont fontWithName:@"Marker Felt" size:round(self.window.bounds.size.width/20.0)];
  myLabel.numberOfLines = 4;
  myLabel.text =[ @"iCloudURL=" stringByAppendingFormat:@"%@", [cloudStore stringForKey:@"iCloudURL"]];
  myLabel.backgroundColor = [UIColor clearColor];
  myLabel.textColor = [UIColor whiteColor];
  myLabel.textAlignment = UITextAlignmentCenter;
  [self.window addSubview:myLabel];

  [self.window makeKeyAndVisible];
  return YES;
}

下面的代码，是参考的一个demo，没有试验过，不过应该是没问题的，仅供参考

- (void)viewDidLoad
{
// 文件名
NSString *fileName = @"data.txt";

// 得到文件管理器
NSFileManager *manager = [NSFileManager defaultManager];

// 验证iCloud是否激活
NSURL *url = [manager URLForUbiquityContainerIdentifier:nil];
if (url == nil)
{
NSLog(@"iCloud未激活");
return;
}

// 指定iCloud完整路径
self.icloudURL = [NSURL URLWithString:fileName relativeToURL:url];

// 得到本程序沙盒路径
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
self.filePath = [[paths objectAtIndex:0] stringByAppendingPathComponent:fileName];

[super viewDidLoad];
}

- (void)viewDidUnload
{
self.filePath = nil;
self.icloudURL = nil;
self.textView = nil;
self.label = nil;
[super viewDidUnload];
}

// 按下上传按钮
- (IBAction)uploadPressed:(id)sender
{
// 另起一个线程上传
[NSThread detachNewThreadSelector:@selector(uploadICloud) toTarget:self withObject:nil];
}

- (void)uploadICloud
{
// 调用主进程的方法更新界面,在主进程外更新界面常会引起错误
[self performSelectorOnMainThread:@selector(setString:)
withObject:@"开始上传"
waitUntilDone:NO];

NSFileManager *manager = [NSFileManager defaultManager];

NSArray *data = [[NSArray alloc] initWithObjects:self.textView.text, nil];

// 判断本地文件是否存在
if (![manager fileExistsAtPath:self.filePath]) {
// 不存在则创建
if (![data writeToFile:self.filePath atomically:YES])
{
[self performSelectorOnMainThread:@selector(setString:)
withObject:@"写本地文件失败"
waitUntilDone:NO];
}
}

// 判断iCloud里该文件是否存在
if ([manager isUbiquitousItemAtURL:self.icloudURL]) {
// 存在则修改
if (![data writeToURL:self.icloudURL atomically:YES])
{
[self performSelectorOnMainThread:@selector(setString:)
withObject:@"写iCloud文件失败"
waitUntilDone:NO];
}
[self performSelectorOnMainThread:@selector(setString:)
withObject:@"上传成功"
waitUntilDone:NO];
return;
}

// 上传至iCloud
// 指定本地文件完整路径
NSURL *url = [NSURL fileURLWithPath:self.filePath];
NSError *error;
// 官方文档建议本方法不要在主进程里执行
if (![manager setUbiquitous:YES itemAtURL:url destinationURL:self.icloudURL error:&error])
{
NSLog(@"setUbiquitous error %@,\n%@", error, [error userInfo]);
self.label.text = @"上传失败";
return;
}
self.label.text = @"上传成功";
}

// 按下下载按钮
- (IBAction)downloadPressed:(id)sender
{
self.label.text = @"开始下载";

// 下载icloud文件
if (![self downloadFileIfNotAvailable:self.icloudURL])
{
self.label.text = @"下载失败";
return;
}
// 更新界面
NSArray *array = [[NSArray alloc] initWithContentsOfURL:self.icloudURL];
self.textView.text = [array objectAtIndex:0];

self.label.text = @"下载成功";
}

// 此方法是官方文档提供,用来检查文件状态并下载
- (BOOL)downloadFileIfNotAvailable:(NSURL*)file {
NSNumber* isIniCloud = nil;

if ([file getResourceValue:&isIniCloud forKey:NSURLIsUbiquitousItemKey error:nil]) {
// If the item is in iCloud, see if it is downloaded.
if ([isIniCloud boolValue]) {
NSNumber* isDownloaded = nil;
if ([file getResourceValue:&isDownloaded forKey:NSURLUbiquitousItemIsDownloadedKey error:nil]) {
if ([isDownloaded boolValue])
return YES;

// Download the file.
NSFileManager* fm = [NSFileManager defaultManager];
if (![fm startDownloadingUbiquitousItemAtURL:file error:nil]) {
return NO;
}
return YES;
}
}
}

// Return YES as long as an explicit download was not started.
return YES;
}