NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,  NSUserDomainMask,YES);//使用C函数NSSearchPathForDirectoriesInDomains来获得沙盒中目录的全路径。

    

//  ***  NSString * documentsDirectoryPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];

    

    NSString *ourDocumentPath =[documentPaths objectAtIndex:0];

    NSString *sandboxPath = NSHomeDirectory();

//    NSString *documentPath = [sandboxPath  stringByAppendingPathComponent:@"Purchase.app"];//将Documents添加到sandbox路径上//stringByAppendingPathComponent

    NSString *FileName=[ourDocumentPath stringByAppendingPathComponent:_fileName];//fileName就是保存文件的文件名

    

    NSLog(FileName);

    NSFileManager *fileManager = [NSFileManager defaultManager];

    // Copy the database sql file from the resourcepath to the documentpath

    if ([fileManager fileExistsAtPath:FileName])

    {

        return FileName;

    }else

    {

        NSURL *url = [NSURL URLWithString:fileUrl];

        NSData *data = [NSData dataWithContentsOfURL:url];

        [data writeToFile:FileName atomically:YES];//将NSData类型对象data写入文件，文件名为FileName

    }

    return FileName;