write data to documents folder

ViewController.m

+ (void)writeDataToFile:(NSString *)fileName wirteData:(NSData*)data{
    NSString *filePath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject] stringByAppendingPathComponent:fileName];
    BOOL fileExists = [self fileExists:fileName];
    if(fileExists){
        NSFileHandle *fileHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];
        [fileHandle seekToEndOfFile];
        [fileHandle writeData:data];
        [fileHandle closeFile];
    }
    else{
        NSString *filePath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject] stringByAppendingPathComponent:fileName];
        BOOL writeSuccess = [data writeToFile:filePath atomically:YES];
    }
}

+ (BOOL)fileExists:(NSString *)fileName{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *path = [paths objectAtIndex:0];
    NSString *filePath = [path stringByAppendingPathComponent:fileName];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    BOOL result = [fileManager fileExistsAtPath:filePath];
    return result;
}