I'm trying to add this to my code
#implementation UIWebView(CustomScroll)
- (void) scrollViewDidScroll:(UIScrollView *)scrollView{
[self.delegate scrollViewDidScroll: scrollView];
}
#end
But getting "No known instance method for selector 'scrollViewDidScroll:'"
What am I missing here?
The UIWebViewDelegate protocol does not declare a method scrollViewDidScroll:. Hence, this is why you're getting the bad access error.
I'd recommend that you subclass UIWebView instead of trying to creating a category on it (yes, the docs recommend against subclassing... just don't override any of the methods it has, and it's safe).
On your subclass, you can either create a new protocol or simply overwrite the delegate property to also require that it conforms to `UIScrollViewDelegate (the later is shown below):
In Example:
// MyWebView.h
#import <UIKit/UIKit.h>
#interface MyWebView : UIWebView
#property (nonatomic, assign) id<UIWebViewDelegate, UIScrollViewDelegate> delegate;
#end
// MyWebView.m
#import "MyWebView.h"
#implementation MyWebView
-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
/* As scrollViewDidScroll: is optional, you should check if the super class
responds to this method (it doesn't appear to now, but this may change in future) */
if ([[self superclass] instancesRespondToSelector:#selector(scrollViewDidScroll:)])
{
[super scrollViewDidScroll:scrollView];
}
/* Likewise, you should check if your own delegate responds to this selector */
if ([self.delegate respondsToSelector:#selector(scrollViewDidScroll:)])
{
[self.delegate scrollViewDidScroll:scrollView];
}
}
#end
Related
today, i saw code that UIView's category reload respondsToSelector and forwardInvocation. i donot understand why do this. this code intent to unite UITableview style in iOS6 and iOS7. i konw resolveInstanceMethod and forwardInvocation can work togather to change function in runtime.
How to explain respondsToSelector and forwardInvocation. When ios call respondsToSelector?
i make a simple test,but it donot call respondsToSelector, the test code as follow:
#protocol MyViewDelegate <NSObject>//why cannot be <UIView>?
#optional
- (void)myViewDelegateMethod;
#end
#interface MyView : UIView
#property (nonatomic,weak) id<MyViewDelegate>delegate;
- (void)test;
#end
#implementation MyView
- (void)test{
NSLog(#"%s",__func__);
if ([self.delegate respondsToSelector:#selector(myViewDelegateMethod)]) {
[self.delegate myViewDelegateMethod];
}
}
#end
#implementation UIView (FunctionChain)
- (BOOL)respondsToSelector:(SEL)aSelector{
//when i call [myview test],can't execute this
return [super respondsToSelector:aSelector];
}
#end
I've been following this example to help me build a delegate but unfortunately I've missed something so it is not working for me. How do I set up a simple delegate to communicate between two view controllers?
My code looks like this:
// HintsViewController.h
#import <UIKit/UIKit.h>
#protocol HintDelegateProtocol;
#interface HintsViewController : UIViewController
#property (weak, nonatomic) id<HintDelegateProtocol> hintDelegate;
-(IBAction)showFirstLetter:(id)sender
-(IBAction)showHint:(id)sender;
-(IBAction)showAnswer:(id)sender;
#end
#protocol HintDelegateProtocol <NSObject>
-(void)HintsViewController:(HintsViewController*)hintsViewController
showFirstLetter:(NSString*)firstLetter;
-(void)HintsViewController:(HintsViewController*)hintsViewController
showHint:(NSString*)hint;
-(void)HintsViewController:(HintsViewController*)hintsViewController
showAnswer:(NSString*)answer;
#end
//
// HintsViewController.m
#import "HintsViewController.h"
#implementation HintsViewController
#pragma mark -
#pragma mark IBActions
/* As per a suggestion below I changed the code here /*
- (IBAction)showHint:(id)sender
{
[self.hintDelegate HintsViewController:self showHint:#"Hint"];
}
- (IBAction)showFirstLetter:(id)sender
{
[self.hintDelegate HintsViewController:self showFirstLetter:#"FirstLetter"];
}
- (IBAction)showAnswer:(id)sender
{
[self.hintDelegate HintsViewController:self showAnswer:#"Answer"];
}
#end
And then in the a Controller class I have the following:
//
// GameLogicController.h
#import "HintsViewController.h"
#interface GameLogicController : NSObject < HintDelegateProtocol>
#end
And in the implementation I have the following:
// GameLogicController.m
-(void) nextRiddle
{
HintsViewController *hintsViewController = [[HintsViewController alloc] init];
hintsViewController.hintDelegate = self;
}
#pragma mark -
#pragma mark HintsFunctionality
-(void)HintsViewController:(HintsViewController*)hintsViewController
showFirstLetter:(NSString*)firstLetter
{
NSLog(#"Show First Letter called");
}
-(void)HintsViewController:(HintsViewController*)hintsViewController
showHint:(NSString*)hint
{
NSLog(#"show Hint called");
}
-(void)HintsViewController:(HintsViewController*)hintsViewController
showAnswer:(NSString*)answer
{
NSLog(#"Show answer called");
}
Using breakpoints I can see that the IBActions in the HintsViewController are being called, but putting a breakpoint in any of the delegate methods in the gameLogicController are never hit. So I have missed an important step in setting up the connection between the GameLogicController and the HintsViewController. Can anyone help me spot it?
Say you have two files: one is your ViewController, and other is your ConnectionManager Class.
Declare protocol and its methods in your ConnectionManager class, and define your protocol methods in the ViewController class. By setting the delegate of your ConnectionManager class in ViewController Class, you can call your Protocol method.
#protocol ConnManagerDelegate<NSObject>
- (void)didReceiveData:(NSDictionary *)data;
- (void)didFailWithError:(NSError*)error;
#end
#interface ConnectionManager : NSObject<NSURLConnectionDelegate>
#property(nonatomic,assign)id< ConnManagerDelegate > delegate;
And elseswhere in the same file .m, when your response comes just call
[Self.delegate didReceiveData:mDict];
In the ViewController file after you alloc init ConnectionManager class, set its delegate to self and define the protocol methods. It is these methods you will have your response from ConnectionManager class.
This is all Protocol Delegation pattern
I want to develop Custom Connection Class by which I can make API calls using it. I do not want to use any third party apis like afhttprequest or asihttp.
I want to develop my self this type of delegate. I have searched much things but I do not have much idea in CustomDelegates.
I wrote one example of custom delegate.
From ViewController.m we call method with two number for addition of another class (Addition class)
Addition class will add these two number and call delegate method so we can get answer of that two number in ViewController using custom delegate.
Addition.h
#import <Foundation/Foundation.h>
// write protocal for this class
// you can give any name of that protocol
#protocol AdditionDelgate <NSObject>
// delegate method of this delegate
-(void)answerOfTwoNumberAddition:(int)ans;
#end
#interface Addition : NSObject
{
}
// set property of that protocol, so using that we can call that protocol methods (i.e. ansOfYourAns)
#property (nonatomic, weak) id <AdditionDelgate> delegate;
-(void) addThisNumber:(int) firstNumber withSecondNumber:(int)secondNumber;
#end
Addition.m
#import "Addition.h"
#implementation Addition
-(void)addThisNumber:(int)firstNumber withSecondNumber:(int)secondNumber
{
int ans = firstNumber + secondNumber;
// call delegate method of "AdditionDelgate" protocol
// we already set delegate of viewController to this protocol
// so it will call viewController class "answerOfTwoNumberAddition" method
[self.delegate answerOfTwoNumberAddition:ans];
}
#end
ViewController.h
#import <UIKit/UIKit.h>
// import addition class
#import "Addition.h"
// set AdditionDelgate to class
#interface ViewController : UIViewController <AdditionDelgate>
#end
ViewController.m
#import "ViewController.h"
#interface ViewController ()
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// creat object of class
Addition * additionObj = [[Addition alloc] init];
// set delegate as self to that so that methods delegate methods will call
additionObj.delegate = self;
// call method
[additionObj addThisNumber:2 withSecondNumber:3];
}
#pragma mark ----- Delegate method of Addition view ----
// this is delegate method of Addition class, it will call from "addThisNumber" method line of code
// ([self.delegate answerOfTwoNumberAddition:ans];)
-(void)answerOfTwoNumberAddition:(int)ans
{
NSLog(#"addition of two number is %d",ans);
}
#end
I hope it will help you
I have class ImageViewController. It has delegate:
#protocol ImageViewControllerDelegate
#optional
- (void)singleTapGestureRecognizer:(UITapGestureRecognizer *)gesture;
- (void)imageDidLoaded;
I also have class AttachmentViewController that subclass of ImageViewController. In that class I want to get event then image property in changed. So here is my code of it change:
- (void)setImage:(UIImage *)image
{
// * Assign image with animation
[UIView transitionWithView:self.imageView
duration:k_DURATION_imageAppearence
options:UIViewAnimationOptionTransitionCrossDissolve
animations: ^{
self.imageView.alpha = 1;
} completion:^(BOOL finished) {
if ([self respondsToSelector:#selector(imageDidLoaded)]) {
[self.delegate imageDidLoaded];
}
}];
But I can not use
if ([self.DELEGATE respondsToSelector:#selector(imageDidLoaded)])
Then I do it I have error:
No known instance method for selector 'respondsToSelector:'
Why? And how here I need to use this capabilities? Is my implementation ok? Or how can I get this notification?
I think that here will be ok to create clear methods in superclass and override it in subclass if it needs to implement is. Is it best way?
You should declare your protocol as #protocol ImageViewControllerDelegate <NSObject>
This says that any object that conforms to your protocol will also conform to the NSObject protocol that respondsToSelector: is declared in.
There's really not enough code here to understand what you're trying to do. Generally to setup a delegate you have a weak property on your class that represents the delegate, and a parent to that class's instance would set the delegate.
Here's some pseudo code:
#protocol SomeDelegateProtocol<NSObject>
- (void)someMethod:(id)someObject;
#end
#interface SomeClass:NSObject
#property (nonatomic, weak) id<SomeDelegateProtocol>delegate;
#end
#implementation SomeClass
- (void)someFunction {
if ([self.delegate respondsToSelector:#selector(someMethod:)]) {
// do code stuff
}
}
#end
///////////
#implementation SomeParentClass
- (void)someOtherFunction {
SomeClass *instance = [SomeClass new];
instance.delegate = self; // assuming self implements SomeDelegateProtocol, otherwise you get a warning
}
Hope this helps!
I'm working with a custom delegate and protocol functionality.
I implemented my class like follows:
#protocol MyDelegate <NSObject>
#required
- (void)update;
#end
#interface MyHandlerClass : NSObject
{
id <MyDelegate>delegate;
}
#property (nonatomic, weak) id <MyDelegate>delegate;
#end
My implementation class looks like:
#implementation MyHandlerClass
#synthesize delegate = _delegate;
- (void)updateRequired: (id)sender
{
if(delegate)
{
[delegate update];
}
}
#end
And from another class I'm setting it like:
[sharedManager setDelegate:self];
But when the updateRequired is triggered it is showing as nil.
Then I added a setter method like:
- (void)setDelegate:(id<MyDelegate>)aDelegate
{
delegate = aDelegate;
}
Everything works fine !!!
Then I changed the updateRequired method (without custom setter) like:
- (void)updateRequired: (id)sender
{
if(_delegate)
{
[_delegate update];
}
}
It is also working fine !!!
I couldn't find why it is not worked for the first case and why it is worked for the other two cases ?
Please help me to find the issue, Thanks in advance
When you use
if(delegate)
You are pointing to the instance variable "delegate".
However, when you use
[sharedManager setDelegate:self]
This is setting the instance variable "_delegate" to "self".
Try this:
if (self.delegate) {
[self.delegate update];
}
You have inadvertently declared one ivar called delegate
id <MyDelegate>delegate;
and another ivar called _delegate
#synthesize delegate = _delegate;
Some suggestions...
don't declare the iVar separately from your #property declaration
don't #synthesize, since XCode 4.4 you don't have to. The compiler will autosynthesize and autocreate an iVar with leading underscore
always refer to you ivar via it's property, inside and outside of your class. Only exceptions are in init, dealloc and inside custom setters and getters.
So this is how your code should look
#protocol MyDelegate <NSObject>
#required
- (void)update;
#end
#interface MyHandlerClass : NSObject
#property (nonatomic, weak) id <MyDelegate>delegate;
#end
#implementation MyHandlerClass
- (void)updateRequired: (id)sender
{
if(self.delegate)
{
[self.delegate update];
}
}
#end
To access your delegate property in the updateRequired method, you can do it by either using the private variable _delegate or by using self.delegate. Because when you synthesize using delegate = _delegate, setters and getters are automatically created.
This line tells the compiler to create a setter and getter for delegate, and that they should use the ivar called _delegate. Without the = _delegate part, the compiler would assume that the property and ivar have the same name.