以编程方式将选择器添加到导航栏按钮
嘿，我正在尝试以编程方式向导航栏中的按钮添加选择器，但我似乎无法找出它根本不起作用的原因。这是我得到的代码：
[self.navigationController.navigationItem.rightBarButtonItem setAction:@selector(showWithLabel)];
我这样做是否正确？还有什么我应该做的吗？
编辑：我发现该按钮是nil，我不明白，因为它连接到rightBarButton插座。
编辑（再次）：我发现导航项为零，知道问题出在哪里吗？
Hey, I am trying to add a selector to a button in my navigationbar programmatically and I can't seem to find out why it doesn't work at all. Here is the code I got:
[self.navigationController.navigationItem.rightBarButtonItem setAction:@selector(showWithLabel)];
Am I doing this correctly and is there anything else I should do?
EDIT: I found out that the button was nil, I don't understand as it is connected to rightBarButton outlet.
EDIT(Again): I found out that the navigationitem is nil, any idea where is the problem then?
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我曾经这样做过并且工作正常
presetButton = [[UIButton alloc] initWithFrame:framePresetButton]; UIImage *presetBtnBG = [[[UIImage imageNamed:@"segment_tools.png"] stretchableImageWithLeftCapWidth:12.0 topCapHeight:0.0] retain]; [presetButton setImage:presetBtnBG forState:UIControlStateNormal]; presetButtonItem = [[UIBarButtonItem alloc] initWithCustomView:presetButton]; [presetButton addTarget:self action:@selector(loadPreset) forControlEvents:UIControlEventTouchUpInside]; self.navigationItem.rightBarButtonItem = presetButtonItem;I use to do that like this and works fine
presetButton = [[UIButton alloc] initWithFrame:framePresetButton]; UIImage *presetBtnBG = [[[UIImage imageNamed:@"segment_tools.png"] stretchableImageWithLeftCapWidth:12.0 topCapHeight:0.0] retain]; [presetButton setImage:presetBtnBG forState:UIControlStateNormal]; presetButtonItem = [[UIBarButtonItem alloc] initWithCustomView:presetButton]; [presetButton addTarget:self action:@selector(loadPreset) forControlEvents:UIControlEventTouchUpInside]; self.navigationItem.rightBarButtonItem = presetButtonItem;所以你说 self.navigationController.navigationItem.rightBarButtonItem 是 nil，但是 rightBarButtonItem 在 IB 中是连接的。
造成这种情况的原因有两个：
navigationItem、navigationController或self是nil。请记住，属性访问表达式实际上是消息表达式。例如，如果
self.navigationController为nil，则向其发送navigationItem消息将返回nil。不管怎样，如果self.navigationController.navigationItem为nil，那么向其询问rightBarButtonItem将返回nil< /代码>。检查每一个子表达式 -
self、self.navigationController和self.navigationController.navigationItem- 并查看哪一个是零。然后，修复那个。So you say
self.navigationController.navigationItem.rightBarButtonItemisnil, butrightBarButtonItemis hooked up in IB.There are two reasons why this could be:
navigationItem,navigationController, orselfisnil.Remember that property access expressions are really message expressions. If, say,
self.navigationControllerisnil, then sending it thenavigationItemmessage will returnnil. If, one way or the other,self.navigationController.navigationItemisnil, then asking it for itsrightBarButtonItemwill returnnil.Check every one of those sub-expressions—
self,self.navigationController, andself.navigationController.navigationItem—and see which one isnil. Then, fix that one.您还应该设置一个将接收操作的目标（我认为您将使用“self”）：
You should set also a target which will receive an action (I think you'll use 'self'):
只需尝试在 viewDidLoad 方法中以编程方式创建 rightBarButtonItem 即可：
Just try to create rightBarButtonItem programmatically in viewDidLoad method:
尝试在选择器名称后添加冒号，如下所示：
Try adding a colon after your selector name, like this: