I have some heavy processing tasks in my view controller, so I put them in a background thread using GCD. And the tasks are encapsulated in a class AsyncImageProcessor
#interface AsyncProcessor : NSObject
#property (weak, nonatomic) id<AsyncProcessorDelegate> delegate;
// ... other unrelated stuff
#end
#protocol AsyncProcessorDelegate <NSObject>
- (void) asyncProcessorEvent:(AsyncProcessorEventType) event;
#end
The problem is that the view controller implementing the delegate is dismissed right after the AsyncProsessor tasks dispatched. And by the time the processing is done, the view controller memory is released, delegate is nil. Then delegated event can't be passed back to the view controller.
One solution I can think of is to define the delegate "strong", and in the delegated method asyncProcessorEvent, set delegate to nil to break the memory circle after all the processing is done. But I feel this is a hack, and I was told everywhere the delegate should be defined as "weak".
Has someone had this issue before? Please give some suggestions.
Related
I was messing around in Xcode creating... something... when I needed to send a message to the MainViewController.m from the FlipsideViewController.m. Except, when I do, the ViewController I am sending the message from does not detect the method as existing, despite the fact that I put the method in MainViewController.h. This is the method:
- (void)setAutosave:(BOOL)boolee {
_autosave = boolee;
}
I have imported the MainViewController into the FlipsideViewController, but as I call it ([NSMainViewController setAutosave:_autosave];), it simply throws an error:
No known class method for selector 'setAutosave:'
I am doing this because FlipsideViewController has a segmented control in it, which tells autosave to be on or off, but it needs to send it's value to the other ViewController.
I really am stumped, help is appreciated.
MainViewController is a class, you can't access instance method from a class.
You can add a property to FlipsideViewController, for example:
#property (weak, nonatomic) MainViewController *mainViewController;
Assign your MainViewController instance to mainViewController (how to assign depends on the relationship between your two view controllers), then you can invoke that method by [self.mainViewController setAutosave:_autosave];.
I am having problems updating a view when a message from another class is sent to a ViewController.
Basically I have an application with a single window where different custom views will be swapped out for another. I have an AppController Class that manages this and works fine:
#interface AppController : NSObject
#property (weak) IBOutlet NSView *ourView;
#property (strong) NSViewController *ourViewController;
- (IBAction)changeView:(id)sender;
- (IBAction)start:(id)sender;
- (void)changeViewContoller:(NSInteger)tag;
#end
When a new view is swapped out for another, the ourViewController property will be updated to point to that view's controller class. Every view controller class will have a method all named the same thing, for example "action". This method is supposed to change something on a view.
So the "start" method in AppController class will then call the "action" method on the ourViewController property. To do this I used the objc_msgSend() method:
objc_msgSend(self.ourViewController, action);
Here's the View Controller class definition:
#interface CountdownViewController : NSViewController
#property (weak) IBOutlet NSTextField *label;
- (IBAction)changeLabel:(id)sender;
- (void)start;
#end
I placed an NSLog() in the "action" method for each ViewController, to see if it was working, and it does, however the "action" method is also supposed to change a label's string value, but it does not. If anyone knows why the view is not being updated, that would be extremely helpful. Thanks!
the view is held weak?
TRY making it strong if you need to retain that pointer in this class
btw: ..also why do you objc_msgsend.... use performSelector
I have subclassed a UIScrollView to customize it a bit. I am trying to create a delegate that will notify several other classes that a user has done a certain thing in the UIScrollView. In my UIScrollView class I have the code below. The problem I am running into is I am getting the warning
Property 'delegate' 'retain (or strong)' attribute does not match the
property inherited from 'UIScrollView'
I see that this is because my Class in inheriting from UIScrollView, but my delegate is conforming to the NSObject. This is the first time I tried creating my own delegate. What can I do to fix this?
My Code:
#import <UIKit/UIKit.h>
#protocol ChangeSpaceDelegate <NSObject>
- (void)changeSpace:(int)spaceId;
#end
#interface CustomUIScrollView : UIScrollView {
id<ChangeSpaceDelegate> delegate;
}
#property (retain, nonatomic)id delegate;
#end
To answer your question specifically, you are redefining the property attribute on the delegate property you get from UIScrollView. It should, like all delegates, be weak (or, pre-iOS 5, unsafe_unretained).
However, you shouldn't do it this way. UIScrollView already has a delegate, and if you expect to put your own delegate object implementing your new delegate methods into it, the inner workings of UIScrollView aren't going to be happy. Define a new protocol and a new delegate property for it.
#property (weak, nonatomic) id<ChangeSpaceDelegate> changeSpaceDelegate;
You don't have to create the delegate object in custom scrollview class since you are subclassing it from UIScrollView. You can directly use it as self.delegate in your custom scrollview class.
As mentioned by #Steve Madsen, I often add own delegate properties for subclasses. Like UITableView has separate DataSource and Delegate properties, and being assigned with the same object. In a long run, this will definitely pay off by not forcing you to repeat what have been already implemented in super class, and keeping your subclass implementations more manageable
I am trying to get some code in a view working. I have declared a delegate and it does not get instantiated, any Idea what I am missing?
I have tried to summarise how I have done this below. I think that the issue is that somewhere, my dataSource delegate needs to be instantiated.
I have a View called graph view and a delegate that is in the viewcontroller GraphViewController.
I know that the method in GraphView is doing something as it calls the AxisDrawing helper class and draws in Axes.
Here is the relevant code
In GraphView.h I set up the protocol and the dataSourceDelegate
#class GraphView;
#protocol GraphViewDataSourceDelegate
- (float)functionOfX:(float)xValue inGraphView:(GraphView *)sender;
#end
#interface GraphView : UIView
#property(nonatomic, weak) IBOutlet id <GraphViewDataSourceDelegate> dataSourceDelegate;
#end
Which I synthesize in GraphView.m
#import "GraphView.h"
#import "AxesDrawer.h"
#implementation GraphView
#synthesize dataSourceDelegate = _dataSourceDelegate;
Also in Graph View I try to use the delegate as follows (pixel is a CGPoint). This routine does run and I can draw to GraphView from here provided I do not try to use my protocol method. i.e. Some of my DrawRect stuff does get drawn which checks out the linking of the UIView to my custom View
pixel.y = [self.dataSourceDelegate functionOfX:pixel.x inGraphView:self];
++++Breakpoint put in here+++++
In GraphViewController I state that I implement the protocol and implement it as follows. The compiler warns me and spots when the implementation is done, turning of the warning. (I am only returning 3.0 at the moment as a test).
#interface
GraphViewController () <GraphViewDataSourceDelegate>
#property (nonatomic, weak) IBOutlet GraphView *graphView;
#end
...
-(float) functionOfX:(float)xValue inGraphView:(GraphView *)sender{
NSLog(#"fofx accessed");
return 3.0;
}
If I look at the GraphView* object just after a breakpoint, it seems to have no instance. What am I missing out.
This is from the trace at the breakpoint
_dataSourceDelegate struct objc_object * 0x0
EDIT: (In addition to #Clays answer below)
It turned out that my connection to the custom view was broke. This meant that the fault lay with the View not talking to the Custom ViewController. The link is made by ctrl dragging from the View Controller button in the Interface builder to the View within the ViewController.
This caused the ViewController to be instantiated and everything then worked fine.
To put it another way.
The link in question was the Outlet. This has to be declared in the ViewController as a property and then linked in IB using ctrl Drag from the ViewController Name-Bar to the View in the Controller.
Provided that you have added the Outlet property correctly, when you do the ctrl drag, your view will appear an option.
The context button popup information on the ViewController button in IB does give a clue.
If you have neglected to put the outlet property into the view controller, the link does appear in the context button popup but it is greyed out, and when you do the link your View is not named.
Once you put the outlet in, the name appears in the menu but not greyed out.
Make sure you've hooked everything up correctly: setting your GraphView's dataSourceDelegate, and your GraphViewController's graphView.
From the trace it looks like you haven't done that; or you lose the reference somewhere along the way because at some point nothing's holding on to it.
If I have a view (mainView) in which I have added subViews. How do I get to subviews instance to mainView ?
I have a button in those subviews which when pressed should call a method in mainView, so I tried:
[myButton addTarget:self.presentingViewController
action:#selector(myMethod:)
forControlerEvents:UIControletcetc];
and
[myButton addTarget:self.parentViewController action:#selector....];
I read that parentViewController now returns nil in iOS 5, but presentingViewController doesn't seem the way to do it because its not presented modally. Its just a subview. Any hints?
Your question doesn't make it quite clear whether you are talking about views or view controllers. Use the superview property to access a view's parent.
There is generally no way to get from a view to its view controller.
It feels to me that you're trying to let your views know about objects beyond their scope.
If you need to notify about an event to anyone that included your view, you could use a delegate to do that.
Say:
#protocol YourClassDelegate
#optional
- (void)instanceOfYourClass:(YourClass *)instance tappedButton:(UIButton *)button;
#end
and then
#interface YourClass
#property (nonatomic, assign) id<YourClassDelegate> delegate;
#end
I hope you can take it from here, by synthesizing the property, assigning the delegate and calling the method when you need to.