本地创建一个文件：

+ (NSString *)messageData
{
    NSString *name = [NSString stringWithFormat:@"messageData.plist"];
    
    NSArray * pathArray = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString * path = [pathArray objectAtIndex:0];
    NSString *fullPathToFile = [path stringByAppendingPathComponent:@"caseNo"];
    NSFileManager *fileManager=[NSFileManager defaultManager];
    if (![fileManager fileExistsAtPath:fullPathToFile]) {
        [fileManager createDirectoryAtPath:fullPathToFile withIntermediateDirectories:YES attributes:nil error:nil];
    }
    NSString *plistPath = [fullPathToFile stringByAppendingPathComponent:name];


    return plistPath;
    
}