leftBarButtonItem设置左边距，rightBarButtonItem设置右边距
UIButton *backButton = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 30, 44)];
[backButton addTarget:self action:@selector(navigationBackButtonClicked) forControlEvents:UIControlEventTouchUpInside];
[backButton setBackgroundImage:[UIImage imageNamed:@"fanHuiC60.88"] forState:UIControlStateNormal];
UIBarButtonItem *backBtnI = [[UIBarButtonItem alloc] initWithCustomView:backButton];
UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc]
initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace
target:nil action:nil];
negativeSpacer.width = -17;
self.navigationItem.leftBarButtonItems = @[negativeSpacer,backBtnI];
