数据懒加载

-(NSArray *)roles
{
    if (_roles == nil) {
　　　　　//获取数据文件
        NSString       *path         = [[NSBundle mainBundle]pathForResource:@"heros.plist" ofType:nil];
        NSArray        *array        = [NSArray arrayWithContentsOfFile:path];
        NSMutableArray *mutableArray = [NSMutableArray array];
        //取数据
        for (NSDictionary *dic in array) {
            RoleEntity * role = [RoleEntity roleWithDictionary:dic];
            [mutableArray addObject:role];
        }
        _roles = mutableArray;
    }
    return  _roles;
}