xcode performSegueWithIdentifier 和 prepareForSegue
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performSegueWithIdentifier and prepareForSegue
提问by MichelleJS
I have a UIViewController *vc1with 4 buttons. Each button causes a push segue to another UIViewController *vc2. vc2is shows some information based on which button was pushed. I pass the infomation from vc1to vc2in vc1's prepareForSegue(its just an int value). This all works fine. Now I need to make it so that the vc2will also be called if the iphone is both on vc1(vc1isVisible) and a vc1receives a UINotification(something happens with a bluetooth device). Here is my code:
我有一个UIViewController *vc1带 4 个按钮的。每个按钮都会导致一个 push segue 到另一个UIViewController *vc2。vc2是根据按下的按钮显示一些信息。我通过信息来源从vc1到vc2在vc1的prepareForSegue（它只是一个int值）。这一切正常。现在我需要这样做，以便vc2在 iphone 处于开启状态vc1（vc1isVisible）和vc1接收 a UINotification（蓝牙设备发生某些事情）时也会调用。这是我的代码：
-(void) eventDetected:(NSNotification *)notification{
if(self.isViewLoaded && self.view.window){
[self performSegueWithIdentifier:@"detected" sender:self];
}
}
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
VC2 *destination = [segue destinationViewController];
[destination setValue:value];
}
Right now if the proper event happens vc2loads twice, instead of once. And I get these error messages in the output logs:
现在，如果正确的事件发生vc2加载两次，而不是一次。我在输出日志中收到这些错误消息：
"Nested push animation can result in corrupted navigation bar" & "Unbalanced calls to begin/end appearance transitions for .corrupted. & "Finishing up a navigaion transition in an unexpected state. Navigation Bar subview tree might get corrupted.
“嵌套推送动画可能会导致导航栏损坏”和“对 .corrupted 的开始/结束外观转换的调用不平衡。”和“在意外状态下完成导航转换。导航栏子视图树可能会损坏。
These errors happen after I press the back button. I added NSLogstatements which is why I know that vc2's viewDidLoadis getting called twice every time.
我按下后退按钮后会发生这些错误。我添加了NSLog语句，这就是为什么我知道vc2'sviewDidLoad每次都会被调用两次。
I created the push segues for all 4 buttons using the storyboard. I have not labelled them. I created the event push segue through the storyboard as well and gave it the identifier "detected". I hope someone on here has some idea about what I am doing wrong. Would appreciate advice. Thanks.
我使用故事板为所有 4 个按钮创建了 push segues。我没有给它们贴上标签。我也通过情节提要创建了事件推送segue，并给了它 identifier "detected"。我希望这里有人对我做错了什么有一些想法。将不胜感激的建议。谢谢。
Here is the current code:
这是当前的代码：
-(void)viewDidAppear:(BOOL)animated
{
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(exerciseDetected:) name:@"ExerciseDetected" object:nil];
[[NSNotifcationCenter defaultCenter] addObserver:self selector:@selector(cancelExercise:) name@"cancelExercise" object:nil];
}
-(void)exerciseDetected:(NSNotification *)notification{
if(self.isViewLoaded && self.view.window){
if(self == self.navigationController.topViewController){
if(!timerRunning){
timerRunning =YES;
_exerciseTimer = (NSTimer scheduledTimerWithTimeInterval:EXERCISE_AUTOSTART_TIME target:self selector:@selector(startExercise:) userInfo:nil repeats:NO];
}
}
}
}
-(void)cancelExercise:(id)sender{
[_exerciseTimer invalidate];
timerRunning = NO;
}
-(void) startExercise: (id)sender{
timerRunning = NO;
[self performSegueWithIdentifier:@"detected" sender:self];
}
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
vc2 *destination = [segue destinationViewController];
[destination setSElectedExerciseIDFromMenu:_selectedExercise];
}
回答by GayleDDS
You should definitely only call performSegueWithIdentifier when self is the top view controller
当 self 是顶视图控制器时，你绝对应该只调用 performSegueWithIdentifier
if (self == self.navigationController.topViewController) {
...
}
If you need to be sure something is only called once you can do:
如果您需要确保某事只被调用一次，您可以执行以下操作：
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
[self foo];
});
If you need to run something in the next run loop execution you can do:
如果您需要在下一个运行循环执行中运行某些内容，您可以执行以下操作：
dispatch_async(dispatch_get_main_queue(), ^{
[self bar];
});
