解决ios7.0 以后自己定义导航栏左边button靠右的问题

1.自己定义button

//左button

        UIButton *leftBtn = [[UIButton alloc]initWithFrame:RectWithPara(-20, 0, 44, 44)];

        [leftBtn addTarget:self action:@selector(btnClicked:) forControlEvents:UIControlEventTouchUpInside];//设置button点击事件

       [leftBtn setBackgroundImage:ImageNamed(@"ic_fanhui_normal.png") forState:UIControlStateNormal ];//设置button正常状态图片

        [leftBtn setBackgroundImage:ImageNamed(@"ic_fanhui_pressed.png") forState:UIControlStateSelected];//设置button选中图片

2.初始化UIBarButtonItem

        UIBarButtonItem *leftBarButon = [[UIBarButtonItem alloc]initWithCustomView:leftBtn];

        // 调整 leftBarButtonItem 在 iOS7 以下的位置

        if(([[[UIDevice currentDevice] systemVersion] floatValue]>=7.0?20:0))

        {

            UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace

                target:nil action:nil];

              negativeSpacer.width = -20;//这个数值能够依据情况自由变化

            self.navigationItem.leftBarButtonItems = @[negativeSpacer, leftBarButon];

        }else

            self.navigationItem.leftBarButtonItem = leftBarButon;