I am trying to call up a modal table view controller using presentModalViewController but I am not sure what to do about the delegate. The following code gives me an error:
MyRidesListView *controller = [[MyRidesListView alloc] init];
controller.delegate = self;
[self presentModalViewController:controller animated:YES];
[controller release];
Error:
Request for member 'delegate' is something not a structure or union
Now, I realized there is no delegate property in my MyRidesListView class. So, how would I add a reference to my delegate there? What am I missing here?
Generally delegates are properties defined as such:
id<NameOfDelegateProtocol> delegate;
And:
#property (nonatomic, assign) id<NameOfDelegateProtocol> delegate;
EDIT: You said your parent class is UITableViewController. You may have wanted to do this:
controller.tableView.delegate = self;
Why do you think you need a delegate? Why not just remove the "controller.delegate = self" line. Otherwise you need to implement a delegate system the way I outline below or else make MyRidesListView a subclass of a viewcontroller that implements delegates.
It looks like you cut and pasted some sample code that uses a delegate, then substituted your own viewcontroller that doesn't provide a delegate. If you don't know what the delegate is for, then just delete that line.
I'll cut and paste some actual code from one of my test programs to show you how it's done:
from the Interface file:
Add a delegate instance variable to your class and make it a property so you can use the "blah.delegate = foo" syntax to set it.
#interface BAPClient : NSObject {
CGSize imageSize;
id <BAPClientDelegate> delegate;
}
#property (nonatomic, readonly) CGSize imageSize;
#property (nonatomic, assign) id <BAPClientDelegate> delegate;
#end
// define the protocol spoken. (what the delegate must implement)
#protocol BAPClientDelegate
- (void)addTile:(BAPTile *)tile;
#end
in the implementation, you must call the delegate at the appropriate time:
- (void)deliverTile:(BAPTile *) tile {
NSLog(#"%s tile=%p",__FUNCTION__,tile);
if ([self delegate])
[[self delegate] addTile:tile];
[tile release];
}
Try to set the delegate object by the setter
[controller setDelegate:self];
This often works wonders.
Related
I'm hoping someone can shed some light on my question below.
I'm getting a property delegate not found on object of type viewcontroller error on when I declare the delegate in the parent view:
Here's the relevant code in the parent .h file:
#protocol ModalViewDelegate
- (void)didReceiveFrequencyMessage:(NSString *)message;
#end
#interface jhsManageRemindersViewController : UIViewController<UIAlertViewDelegate, UINavigationControllerDelegate, ModalViewDelegate>
and here's where I call the child view:
jhsScheduleViewController *jhsScheduleController = [[jhsScheduleViewController alloc]
initWithNibName:#"jhsScheduleViewControllerr" bundle:nil];
jhsScheduleController.delegate = self;
// Create the navigation controller and present it modally.
UINavigationController *navigationController = [[UINavigationController alloc]
initWithRootViewController:jhsScheduleController];
navigationController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentModalViewController:navigationController animated:YES];
and here's part of my child .h file
#protocol ModalViewDelegate ;
#interface jhsScheduleViewController : UIViewController {
//id<ModalViewDelegate> delegate;
// __unsafe_unretained id <ModalViewDelegate> _delegate;
__weak id <ModalViewDelegate> delegate;
NSMutableString *message;
}
#property ( weak) id<ModalViewDelegate> delegate;
//#property (nonatomic, weak) id<ModalViewDelegate> delegate;
#property (nonatomic, retain) NSMutableString *message;
and finally, here's my .m usage
#synthesize delegate;
//#synthesize delegate = _delegate;
I've viewed and tried various solutions based upon Stackoverflow questions and this recommended blogpost. I've included some of my attempted solutions in commented out code, just as an FYI.
I started with the code I had in an iOS4 app but that generates the error. As a footnote, this is an app with a TabBarController and a NavigationController
Can someone tell me how to fix this so the delegate error can be resolved?
Thank you for your help!
Well, I'm not sure what the problem was. But as a last resort, I saved every file, then tried to build it, with Xcode still reporting the error, which worked.
Actually, there was an error in the initWithNibName but it ran fine until it got to that point, and correcting the typo fixed that. Again, I'm not sure what the problem was but I seem to be on my way.
I am working on a splitView application for my iPad. I have implemented a UIButton called as Upload. On clicking on it, a UITableView appears inside a UIPoverController. On clicking on any of the contents, I want to display some respective site in my UIwebView in UIDetailView. For this I have implemented a delegate method protocol. I have used the following lines of code in UploadTableViewController.h file::
#protocol UploadTableViewDelegate <NSObject>
#required
- (void)selected:(NSString *)his;
#end
#interface UploadSpaceTableViewController : UITableViewController{
id<UploadSpaceTableViewDelegate> delegate;
}
#property (retain) id delegate;
#end
In the corresponding .m file I have used the following lines of code ::
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
if (delegate != nil) {
NSString *hisSelected = [keys objectAtIndex:indexPath.row];
NSLog(#"%# lolwa", hisSelected);
[delegate selected:hisSelected];
}
}
in the .m file of class where I have implemented the function Selected, the code is ::
- (void)selected:(NSString *)Key {
NSLog(#"hello");
[self.UploadSpaceTableViewPopover dismissPopoverAnimated:YES];
}
-(IBAction)uploadpressed:(id)sender{
Upload.delegate = self;
self.Upload = [[UploadSpaceTableViewController alloc]
initWithStyle:UITableViewStylePlain];
self.UploadTableViewPopover = [[UIPopoverController alloc]
initWithContentViewController:UploadSpace];
[self.UploadTableViewPopover presentPopoverFromBarButtonItem:sender
permittedArrowDirections:UIPopoverArrowDirectionAny animated:YES];
}
However, I am unable to get hello (written in the function Selected) NSLogged in gdb. This is the first time that I am using this delegate method protocol. I am unable to sort this out. Can someone help me out ? Thanks and regards.
[delegate keySelected:hisKeySelected]; is your first problem. You don't declare a delegate method named -keySelected:, you declare a delegate method named -Selected:.
Your second problem is the fact that you are most definitely not the delegate of your table view. In order for a delegate method like -didSelectRowAtIndexPath: to be called, you must be the table's delegate.
PS, don't begin instances, or method names, with an uppercase letter. In ObjC, uppercase letters indicate a class.
EDIT: this is what your UploadSpaceTableViewController header should look like:
#protocol UploadTableViewDelegate <NSObject>
#required
- (void)selected:(NSString *)his;
#end
#interface UploadSpaceTableViewController : UITableViewController<UITableViewDataSource, UITableViewDelegate>
#property (nonatomic, assign) id <UploadSpaceTableViewDelegate>delegate; //delegates are weak!!!
#end
And the .m, I will skip a lot of the unnecessary stuff:
-(void)viewDidLoad {
[self.tableView setDelegate:self];
[self.tableView setDataSource:self];
}
//other code
Furthermore, your delegate is declared retain, which is an absolutel No-No in ObjC. Declare is weak if using ARC, or assign if not.
You are also producing a nil delegate in in your -uploadPressed: method by setting it before you explicitly own or initialize the object. Here's how it should look:
self.Upload = [[UploadSpaceTableViewController alloc]initWithStyle:UITableViewStylePlain];
Upload.delegate = self;
Delegation works like this
declare a protocol - you have done this
declare a delegate property - you have done this
In the class which you want to be the delegate say it conforms to the protocoll
#interface MyClass : MySuperClass <UploadTableViewDelegate>
set the delegate property so the delegate class can get the delegate messages
uploadSpaceTVC.delegate = self;
call the delegate methods in your non delegate class (UploadSpaceTableViewController)
[self.delegate selected:#"test"];
As a new iOS developer, I have finally stumbled across delegates. I'm trying to follow a tutorial: http://gabriel-tips.blogspot.com/2011/05/input-accessory-view-how-to-add-extra.html, But I'm having difficulty understanding where I am supposed to put the actual delegate methods.
Secondly, would anyone mind providing a dumbed down explanation of how a delegate method is invoked?
Thanks!
A delegate is simply a class that agrees to do work for another class. The delegate methods are invoked by the delegating class. The delegate must therefore, provide an implementation of the appropriate method. Let's make a simple view controller with a table view.
// MyViewController.h
#interface MyViewController : UIViewController <UITableViewDelegate>
#property (nonatomic, retain) UITableView *myTableView;
#end
Here in the MyViewController.h file I have declared my view controller to be a delegate of type UITableViewDelegate (it really means it implements the UITableViewDelegate protocol. More on this later). I have thus agreed to respond to requests to my view controller. The requests will come from the table view called myTableView. However, simply stating that I adhere to UITableViewDelegate does not make my view controller a delegate of anything. I must specify that directly:
// MyViewController.m
#import "MyViewController.h"
#implementation MyViewController
- (void)loadView
{
myTableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 0, 320, 460)];
myTableView.delegate = self;
self.view = myTableView;
}
#end
Here I specifically set MyViewController to be the delegate of myTableView. Now whenever the table view wants to ask its delegate to do something, it will send that message to my view controller. Thus, MyViewController MUST provide implementations of the appropriate delegate methods:
// MyViewController.m
#import "MyViewController.h"
#implementation MyViewController
- (void)loadView
{
myTableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 0, 320, 460)];
myTableView.delegate = self;
self.view = myTableView;
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
NSLog(#"Selected section:%i row:%i", indexPath.section, indexPath.row);
}
#end
Here I have provided an implementation for the delegate method tableView:didSelectRowAtIndexPath: which will be called by myTableView when it is appropriate (the user selects a row).
Here you can find all the delegate methods defined in UITableViewDelegate. Some are required and others are optional:
http://developer.apple.com/library/ios/#documentation/UIKit/Reference/UITableViewDelegate_Protocol/Reference/Reference.html
In order to be a delegate of a class you should know which methods you are required to provide implementations for.
If you wanted to create your own delegate definitions, you would create a new protocol. You do not retain your delegates (see the property declaration), as this creates a retain cycle:
// MyViewController.h
#class MyViewController;
#protocol MyViewControllerDelegate
- (void)viewController:(MyViewController *)viewController didChangeSelection:(NSIndexPath *)newIndexPath;
#end
#interface MyViewController : UIViewController <UITableViewDelegate>
#property (nonatomic, retain) UITableView *myTableView;
#property (nonatomic, assign) id<MyViewControllerDelegate> delegate;
#end
Here we have created a new protocol. Any class that wants to be respond to the viewController:didChangeSelection: message could now do so. Just like with the table view above it would set the delegate to itself and then implement the method. Now that you have a delegate, you can invoke the method at an appropriate time.
// MyViewController.m
#import "MyViewController.h"
#implementation MyViewController
- (void)loadView
{
myTableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 0, 320, 460)];
myTableView.delegate = self;
self.view = myTableView;
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
NSLog(#"Selected section:%i row:%i", indexPath.section, indexPath.row);
indexPath = [NSIndexPath indexPathForRow:1 inSection:0];
[self.delegate viewController:self didChangeSelection:indexPath];
}
#end
Now the delegate can receive the message and do what it wants knowing that my view controller changed the selection.
A delegate pattern is a convenient way to allow for the communication between independent controller that allows for loose coupling. So let's say you have a pattern like this:
A
/ \
B C
Where A instantiates B and C. Communicating between A to B and A to C are easy but how would you communicate between B and C? B to A? C to A? There are a couple different ways you could do so such as Key-Value Observing or Block Callbacks. Delegation, though, are still most frequently used although Blocks are coming on strong.
In this example, object A instantiates object B to create an object and fill it with info. How would object B pass the new object back to A as you want to keep things loose? Well, with these 9 easy steps, you can do it too! It may not make sense but we'll start with ClassB…
// ClassB.h
#protocol ClassBDelegate; //(1)
#interface ClassB : NSObject
#property (nonatomic, weak) id<ClassBDelegate>bDelegate; //(2)
-(void)makeNewObjectAndSendBack;
#end
#protocol ClassBDelegate : NSObject //(3)
-(void) classB:(Class B *)theClassB finishedWithObject:(id)finishedObject; //(4)
#end
ClassB.m
#implementation
#synthesize bDelegate = _bDelegate; //(5)
-(void)makeNewObjectAndSendBack {
//something something something
[self.bDelegate classB:self finishedWithObject:newObject]; //(6)
}
#end
define the protocol that will be established later
set an instance of an object that will conform to that protocol
set up the protocol
set up the method call that you'll use to send the finishedObject back to A.
synthesize the delegate
after you do what you need to do, you send it back using the method
you defined in 4
// ClassA.h
#interface ClassA : NSObject <ClassBDelegate> //(7)
#property (nonatomic, strong) ClassB theClassB;
-(void)yourMethodToDoSomething;
#end
ClassA.m
#implementation
#synthesize theClassB = _theClassB;
-(void)randomMethod {
self.theClassB = [ClassB new];
self.theClassB.bDelegate = self; //(8)
[self.theClassB makeNewObjectAndSendBack];
}
-(void) classB:(Class B *)theClassB finishedWithObject:(id)finishedObject { //(9)
[self doSomethingWithFinishedObject:finishedObject]; //ta-da!
}
#end
7.Conform to the ClassBDelegate protocol. This basically says that you
will implement the methods defined in the protocol definition.
8.Set the classB object's delegate object as self! This is crucial and
often skipped.
9.Implement the delegate method for when you get the new object back.
So the process, in short is: A instanciate B. A sets B's delegate as self. A tells B to do something. B does something and sends object back via delegate method. A gets it back.
For more information, including what you can do with protocols, check out:
Big Nerd Ranch talk about Protocols
Part 1
Part 2
Part 3
Good luck!
It seems you might be a little confused as to what delegates are and how they are used. Here are two links to Apple documentation you might find useful: A conceptual overview and a more in depth explaination.
I am building a utility-based application, the data is stored in the MainViewController, and now I know how to pass data to the FlipsideViewController (many regards to this thread BTW, Sending data from Mainview to Flipside?). But I am getting the data onto an subview (subclass of UIView) that I have added to the flipside view. How can I pass data to this subview? I saw there is already a delegate and protocol set up in the FlipsideViewController.h, I am really new to the delegate sort of things. Any help would be greatly appreciated!
Updates:
On the main view, I have a couple of text fields for users to input to create an object. All the objects are stored in an array. Namely, my data is created and stored in the MainViewController. Now on the flip side, I have a custom UIView subclass which allows me to do my own drawing based on the data in that array. What I need to do here is pass the data that stored in MainViewController to this subview. Here is my relevant code:
In the MainViewController.m
- (IBAction)showInfo:(id)sender {
FlipsideViewController *controller = [[FlipsideViewController alloc] initWithNibName:#"FlipsideView" bundle:nil];
controller.delegate = self;
controller.receiver = data;//this is what I've done.
controller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
[self presentModalViewController:controller animated:YES];
[controller release];
}
In the FlipsideViewController.h
#protocol FlipsideViewControllerDelegate;
#interface FlipsideViewController : UIViewController {
id <FlipsideViewControllerDelegate> delegate;
DataModel *receiver; //create a property to receive the data transferred from main view
}
#property (nonatomic, assign) id <FlipsideViewControllerDelegate> delegate;
#property (nonatomic, retain) DataModel *receiver;
- (IBAction)done:(id)sender;
#end
#protocol FlipsideViewControllerDelegate
- (void)flipsideViewControllerDidFinish:(FlipsideViewController *)controller;
#end
In the above code, "data" is an DataModel object declared in the MainViewController.h file.
And I want to do my custom drawing in drawing class (subclass of UIView), how can I pass data from the FlipsideViewControllerto this subview? Do I need to make use of delegate declared in the FlipsideViewController.h file? Thanks in advance!
I have had a quick look at the template and think you are getting confused with what the delegate is being used for.
The delegate in this template is not transferring data. When you have clicked the done button it calls back to MainViewController and asks it to call the dismissModalViewControllerAnimated method so that it can remove the view controller. This seems a bit superflous as the documentation states
If you call this method on the modal view controller itself, however, the modal view controller automatically forwards the message to its parent view controller.
Therefore you don't really need to call the parent to do this.
In Interface builder you can see that the FlipsideView.xib has it's File's Owner set to FlipsideViewController.xib.
Now if you right click the File's Owner you will see that view is connected to View this basically means that view is the name of the property in FlipsideViewController and View is the element in Interface Builder.
Therefore we can access elements in the xib file from FlipsideViewController using outlets.
To say draw a label you will need to do a couple of things
First add a property in the .h and synthesize it in the .m like
// FlipsideViewController.h
#interface FlipsideViewController : UIViewController
#property (nonatomic, retain) IBOutlet UILabel *testLabel; // <----- Added this
#property (nonatomic, assign) id <FlipsideViewControllerDelegate> delegate;
- (IBAction)done:(id)sender;
#end
// FlipsideViewController.m
#implementation FlipsideViewController
#synthesize delegate = _delegate;
#synthesize testLabel = _testLabel; // <----- Added this
// More methods
- (void)dealloc
{
[_testLabel release]; // Always do you memory management
[super dealloc];
}
Then back in Interface Builder
Add a UILabel element to your view
ctrl + drag from File's Owner to the UILabel you added
Select the label in my example it is testLabel
Now these are hooked up correctly. The place where you want to be setting the value of the label is in viewDidLoad: which you can now do like this
- (void)viewDidLoad
{
[super viewDidLoad];
self.testLabel.text = #"It Works"; // You would use the data passed in from `MainViewController`
}
I find the easiest way to pass data from one view to another is by directly setting the data in the next view from the original view.
For example;
In your FlipsideViewController.h, declare a 'container' for the data you want to pass. It must be the same class on both sides to work properly, ie. NSArray to NSArray, NSMutableDictionary to NSMutableDictionary.
NSMutableArray *newData;
...
#property (nonatomic, retain) NSMutableArray *newData; // This allows you to access this object from outside this class.
and in FlipsideViewController.m
#synthesize newData;
...
[newData release];
Now we need to pass the data, so to speak. Let's say the data we want to 'send' is stored in a NSMutableArray called 'results'.
In our MainViewController.m, when we are instantiating our next view controller (in this case FlipsideViewController) we can directly reference the newData mutable array after we initalize the nib.
FlipsideViewController *controller = [[FlipsideViewController alloc] initWithNibName:#"FlipsideView" bundle:nil];
controller.newData = results;
controller.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
[self presentModalViewController:controller animated:YES];
[controller release];
Make sure you are importing your FlipsideViewController in your MainViewController.h file.
If the property is declared in your .h file, you can pretty much reference the contents of the object from anywhere within the view stack!
Hope that helps :D
I've looked all over, and found many people with similar problems, but I still can't get my delegates working. I want to make a model view controller pop up, then call a method in the view that made the model view asking it to dismiss it. So I have this line:
mergeConfig *view = [[mergeConfig alloc] initWithNibName:#"mergeConfig" bundle:nil];
and I'm trying [view setDelegate:self]; as said to on apple's developer pages, but expectably my model view doesn't have a setDelegate method.
So what I want to know is, how do I get it so that I can set a delegate? And then once I do, does it just automatically pass calls to methods to methods in the parent view with the same name? Apple's pages didn't say what code to put in the model view controller.
You need to define a delegate on your custom view controller, as such:
#interface mergeConfig {
id delegate;
}
#property (nonatomic, assign) id delegate;
#end
#implementation mergeConfig
#synthesize delegate;
#end
Then, elsewhere in the class for your view controller you can invoke whatever methods you need on your delegate.
Personally I like to improve the above by defining a protocol that my delegates comply to, as follows:
#protocol MyDelegateProtocol
- (void)delegateMethod;
#end
#interface mergeConfig {
id<MyDelegateProtocol> delegate;
}
#property (nonatomic, assign) id<MyDelegateProtocol> delegate;
#end
#implementation mergeConfig
#synthesize delegate;
#end
If you simply need to dismiss the modal view controller, just call [self.parentViewController dismissModalViewControllerAnimated:YES]; at the appropriate time. No need for delegates unless you need to pass information back up the chain.