iOS系统导航栏item

好像很多时候又回到了原点，刚开始接触iOS的时候，就接触到了backBarItem和leftBarItem。

*很多时候需要自己设点返回按钮的标题，系统给的返回键的标题分为两种情况。

前一个页面有标题的情况,系统返回键的标题默认为<标题;

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前一个页面没有标题的情况，系统返回键默认为

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*自己设定系统导航栏返回键标题有两个办法。

    // 细节: 本界面上设置, 下个界面上显示
    // 方式一
    self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"返回" style:UIBarButtonItemStylePlain target:nil action:nil];
    //方式二
    UIBarButtonItem * backButtonItem = [[UIBarButtonItem alloc] init];
    backButtonItem.title = @"返回";
    self.navigationItem.backBarButtonItem = backButtonItem;

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*导航栏的item全部由自己设定。比如：

    UIButton *rightButton=[UIButton buttonWithType:UIButtonTypeCustom];
    [rightButton setFrame:CGRectMake(0, 0, 30, 32)];
    [rightButton setImage:[UIImage imageNamed:@"icon_back"] forState:UIControlStateNormal];
    [rightButton addTarget:self action:@selector(onNaviBack) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *backBar = [[UIBarButtonItem alloc]initWithCustomView:rightButton];

此时需要修改item与屏幕之间的边界:

• 考虑到CustomView一般为UIButton，如果该按钮上面是一个图片，仅为了显示效果，我们可以通过setImage: forState:方法设置button的背景图片（注意这里不是setBackgroundImage: forState:），然后通过setImageEdgeInsets:方法设置按钮图片和按钮各个边界的距离即可。按钮为文字的情况类似，对应的方法是setTitle: forState:和setTitleEdgeInsets:

        UIButton *closeUpItem = [UIButton buttonWithType:UIButtonTypeCustom];
        closeUpItem.frame = CGRectMake(0, 0, 44, 32);
        [closeUpItem setTitleEdgeInsets:UIEdgeInsetsMake(0, -20, 0, 0)];
        [closeUpItem setBackgroundColor:[UIColor redColor]];
        [closeUpItem setTitle:@"关闭" forState:UIControlStateNormal];
        [closeUpItem setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
        [closeUpItem addTarget:self action:@selector(closeUpClick) forControlEvents:UIControlEventTouchUpInside];
        UIBarButtonItem *closeUpBarItem = [[UIBarButtonItem alloc] initWithCustomView:closeUpItem];
    

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• 初始化一个用于控制间距的UIBarButtonItem实例negativeSpacer，并设置negativeSpacer的width属性的值，设为-5的时候，正好可以使按钮与屏幕边界值为0，以rightBarButtonItem情况为例

UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    /**
     *  设置frame只能控制按钮的大小
     */
    btn.frame= CGRectMake(0, 0, 40, 44);
    [btn addTarget:self action:@selector(buttonClicked) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *btn_right = [[UIBarButtonItem alloc] initWithCustomView:btn];
    UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc] 
                                       initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace 
                                       target:nil action:nil];
    /**
     *  width为负数时，相当于btn向右移动width数值个像素，由于按钮本身和边界间距为5pix，所以width设为-5时，间距正好调整
     *  为0；width为正数时，正好相反，相当于往左移动width数值个像素
     */
    negativeSpacer.width = -5; 
    self.navigationItem.rightBarButtonItems = [NSArray arrayWithObjects:negativeSpacer, btn_right, nil];

通过往中间插入spaceItem来控制间距。

 UIBarButtonItem *space = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
    space.width = -20;
    
    UIButton *closeUpItem = [UIButton buttonWithType:UIButtonTypeCustom];
    closeUpItem.frame = CGRectMake(0, 0, 44, 32);
    [closeUpItem setTitle:@"关闭" forState:UIControlStateNormal];
    [closeUpItem setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
    [closeUpItem addTarget:self action:@selector(closeUpClick) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *closeUpBarItem = [[UIBarButtonItem alloc] initWithCustomView:closeUpItem];
    
    self.navigationItem.leftBarButtonItems = [NSArray arrayWithObjects:space,closeUpBarItem,nil];
    self.navigationController.navigationItem.leftBarButtonItems = [NSArray arrayWithObjects:space,closeUpBarItem, nil];
    
    
    UIBarButtonItem *firstSpace = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
    firstSpace.width = -20;
    
    UIButton *rightItem = [UIButton buttonWithType:UIButtonTypeCustom];
    rightItem.frame = CGRectMake(0, 0, 44, 30);
    [rightItem setTitle:@"前进" forState:UIControlStateNormal];
    [rightItem setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
    [rightItem addTarget:self action:@selector(forwardClick) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *rightBarItem = [[UIBarButtonItem alloc] initWithCustomView:rightItem];
    self.navigationItem.rightBarButtonItems = [NSArray arrayWithObjects:firstSpace,rightBarItem,nil];
    self.navigationController.navigationItem.rightBarButtonItems = [NSArray arrayWithObjects:firstSpace,rightBarItem,nil];

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