执行函数以从另一个类调用performSegueWithIdentifier

Question

I've spent a few hours on this trying to work it out myself but I give up!

I have a master-detail arrangement where the user input screen needs to call a function on another class to post to a web service. Upon completion of the asynchronous call, the class will then call a specified function. In this case, I'm just testing and all I want to do is go back to the main screen after the user input is accepted by the web service.

When the uses taps a button on the input screen (SetLocationViewController), the asynchronous operation is called in the class APIPostClass. After it is complete, I want SetLocationViewController to segue back to MasterViewController.

In APIPostClass.m in (called after the asynchronous op finishes)

-(void)callWhenDone {
NSLog(@"callWhenDone loaded.");

SetLocationViewController *SLVClassInstance = [[SetLocationViewController alloc] init];
[SLVClassInstance doSegue];
}

In SetLocationViewController.m

-(void) doSegue {
NSLog(@"doSegue loaded");
[self performSegueWithIdentifier:@"SetLocationViewControllerManualUnwind" sender:self];
}

Calling doSegue from an action on SetLocationViewController.m does work so I know my segue is ok but the above doesn't work. I get the error reason: 'Receiver () has no segue with identifier 'SetLocationViewControllerManualUnwind''

I'm guessing the reason is because of the alloc init way of initialising of the VC, but I don't know any better. Thus, how can I call a function on another class as if it was being called by it's own class?

Answer 1

Create a delegate it would be much more reliable and fast than Notifications.

@protocol APIPostDelegate <NSObject>
@required
-(void)OnRequestSucess;
@end

In your APIPost add new property for delegate

@interface APIPost : NSObject

@property (weak) id<APIPostDelegate> delegate;

In SetLocationViewController implement APIPostDelegate

SetLocationViewController.h

SetLocationViewController :NSObject<APIPostDelegate>

SetLocationViewController.m

-(void)OnRequestSucess
{
   [self doSegue];
}

before you make call to method on APIPost, assign self to delegate property.

APIPost *apipost=[[APIPost alloc]init];
apipost.delegate=self;

[apipost <your api method>];

APIPost.m

[self.delegate OnRequestSucess];

Hope this helps.

Answer 2

There are a few methods to make it happens:-

1. Use Delegate
2. Use NSNotification .
3. The way described by Artur above (For SplitViewController Only - iPad)

You should use delegate whenever it is possible but it might not be too straight forward. NSNotification is more straight forward but it is not a good practice and not a good programming style.

I will only share the NSNotification method as it is easier to implement.

In SetLocationViewController.m

-(void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear:animated];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(doSegue) name:@"calldoSegue" object:nil];
}

-(void)viewWillDisappear:(BOOL)animated{
    [super viewWillDisappear:animated];
    [[NSNotificationCenter defaultCenter]removeObserver:self name:@"calldoSegue" object:nil];
}

-(void) doSegue {
    NSLog(@"doSegue loaded");
    [self performSegueWithIdentifier:@"SetLocationViewControllerManualUnwind" sender:self];
}

In APIPostClass.m

-(void)callWhenDone {
    NSLog(@"callWhenDone loaded.");
    [[NSNotificationCenter defaultCenter]postNotificationName:@"calldoSegue" object:nil];
}

The above code should work but again, this is not a good practice. You should try to learn the Delegate method.

Answer 3

The answer is here: Performing segue from another class

In my APIPostClass.h, I setup the view controller:

@interface APIPostClass : NSObject  {
    SetLocationViewController *setLocationViewController;
}

@property(nonatomic, strong) SetLocationViewController *setLocationViewController;

@end

In my APIPostClass.m, I synthesize it:

@synthesize setLocationViewController;

then, instead of this (as in my question):

-(void)callWhenDone {
NSLog(@"callWhenDone loaded.");

SetLocationViewController *SLVClassInstance = [[SetLocationViewController alloc] init];
[SLVClassInstance doSegue];
}

I have:

-(void)callWhenDone {
    NSLog(@"callWhenDone loaded");
    [self.setLocationViewController doSegue];
}

Over in SetLocationViewController.m, the segue method remains unchanged:

-(void) doSegue {
NSLog(@"doSegue loaded");
[self performSegueWithIdentifier:@"SetLocationViewControllerManualUnwind" sender:self];
}

But when I call my API, I need to "attach" (forgive my terminology) the view controller to it. This is what I had:

- (IBAction)btnTestAPICall:(id)sender {
    NSLog(@"User tapped API button");

    APIPostClass *APIPostClassInstance = [[APIPostClass alloc] init];
    [APIPostClassInstance APICall: ... ....
}

But this is what works after bringing all of the above:

- (IBAction)btnTestAPICall:(id)sender {
    NSLog(@"User tapped API button");

    APIPostClass *APIPostClassInstance= [[APIPostClass alloc] init];

    UIViewController *currentVC=self;
    APIPostClassInstance.setLocationViewController = currentVC;

    [APIPostClassInstance APICall: ... ...

I hope this will help someone else!