Question

我有一个Web服务来获取JSON表单中的数据。我每次启动应用程序时都会调用此服务（在appDidFinishLaunching方法内）并将其存储在本地文件中。我想仅在应用程序首次启动时调用该服务，并且从下次我只想使用我已存储JSON数据的文件。

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];

    //live json data url

    NSURL *url = [NSURL URLWithString:@"My Url"];
    NSData *urlData = [NSData dataWithContentsOfURL:url];

    //attempt to download live data
    if (urlData)
    {
        NSString *filePath = [NSString stringWithFormat:@"%@/%@", documentsDirectory,@"data.json"];
        [urlData writeToFile:filePath atomically:YES];

    }
    //copy data from initial package into the applications Documents folder
    else
    {
        //file to write to
        NSString *filePath = [NSString stringWithFormat:@"%@/%@", documentsDirectory,@"data.json"];

        //file to copy from
        NSString *json = [ [NSBundle mainBundle] pathForResource:@"data" ofType:@"json" inDirectory:@"html/data" ];
        NSData *jsonData = [NSData dataWithContentsOfFile:json options:kNilOptions error:nil];

        //write file to device
        [jsonData writeToFile:filePath atomically:YES];
    }

    NSError *jsonError = nil;

    NSString *jsonFilePath = [NSString stringWithFormat:@"%@/%@", documentsDirectory,@"data.json"];
    NSData *jsonData = [NSData dataWithContentsOfFile:jsonFilePath options:kNilOptions error:&jsonError ];
    NSMutableArray *jsonArray = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:&jsonError];
    self.serverResponseArray = jsonArray;
    NSLog(@"%@",self.serverResponseArray);

通过这段代码，我正在编写JSON响应本地文件并存储在一个数组中，以便在整个应用程序中使用它。

Answer 1

   static NSString * const someKey = @"haveChecked";
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{

    NSUserDefaults * stdUserDefaults = [NSUserDefaults standardUserDefaults];
    if(![[stdUserDefaults objectForKey:someKey] boolValue])
    {
        [self trySomething];
    }
}
-(void)gotJson
{
    //async callback
    NSUserDefaults * stdUserDefaults = [NSUserDefaults standardUserDefaults];
    [stdUserDefaults setBool:YES forKey:someKey];
    [stdUserDefaults synchronize];

}

听起来你需要学习处理文件，所以这里有一些堆栈溢出读取：

What is the documents directory (NSDocumentDirectory)?
Write a file on iOS

Answer 2

试试这个

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

            if ([self fetchFromNSUserDefaults:@"FirstTimeNO"]==nil || [FunctionManager fetchFromNSUserDefaults:@"FirstTimeNO"]==@"") {
                 [self YourFunctionThatCallFirstTime];
            }
        return YES;
    }

    -(id)fetchFromNSUserDefaults:(NSString *)strKey{
             NSUserDefaults *objUserDefaults = [NSUserDefaults standardUserDefaults];
              return [objUserDefaults objectForKey:strKey];
    }

    -(void)addToNSUserDefaults:(id)objValue forKey:(NSString *)strKey{
        NSUserDefaults *objUserDefaults = [NSUserDefaults standardUserDefaults];
        [objUserDefaults setObject:objValue forKey:strKey];
        [objUserDefaults synchronize];
    }

    -(void)YourFunctionThatCallFirstTime {
                 //Your Stuff

           [self addToNSUserDefaults:@"1" forKey:@"FirstTimeNO"];
     }

第一次启动应用程序时，如何只访问任何方法一次

2 个答案: