UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];    negativeSpacer.width = -10;        UIButton *back2 = [UIButton buttonWithType:UIButtonTypeSystem];    [back2 setFrame:CGRectMake(0, 0, 100 * 0.5, 40 * 0.5)];    [back2 setBackgroundImage:[UIImage p_w_picpathNamed:@"back"] forState:UIControlStateNormal];    UIBarButtonItem *back = [[UIBarButtonItem alloc] initWithCustomView:back2];    self.navigationItem.leftBarButtonItems = @[negativeSpacer, back];