设置导航栏返回按钮的大小

[btn.widthAnchor constraintEqualToConstant:25].active = YES;

[btn.heightAnchor constraintEqualToConstant:25].active = YES;

UIBarButtonItem *item = [[UIBarButtonItem alloc] initWithCustomView:btn];

[items addObject:item]; 

self.navigationItem.leftBarButtonItems = items;

模态跳转

QDCAddressBookViewController *vcer = [[QDCAddressBookViewController alloc] init];    UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:vcer];    nav.modalPresentationStyle = UIModalPresentationFullScreen;

[selfpresentViewController:nav animated:YEScompletion:nil];