I'm developing an iOS 4 application.
I have this ViewController:
#interface BlogViewController : UIViewController
{
...
UIView* tabBar;
}
#property (nonatomic, retain) IBOutlet UIView* tabBar;
And its implementation:
And its implementation:
#implementation BlogViewController
#synthesize tabBar;
- (void) dealloc
{
...
[super dealloc];
}
- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
self.tabBar = nil;
}
My question if I have a IBOutlet property, is it necessary to declare the UIView like this?
#interface BlogViewController : UIViewController
{
...
UIView* tabBar;
}
If I do it, Do I need to release it on dealloc?
- (void) dealloc
{
...
[tabBar release];
[super dealloc];
}
In order: no you don't need to declare the instance variable, yes you do need to release the object. You may consider using Automatic Reference Counting to get the memory management aspect correct for you.
Yes, you do need to release an IBOutlet, if you retained it.
However, IBOutlets are owned by their nib file, so the usual practice is to use an assign or weak #property instead of retain or strong. In which case you don't need to release it.
If you are using xcode 4+ then while creating the outlet it itself makes a release for the same in dealloc and viewDidUnload so no need to do it again.
Related
Manual memory management is used. The following code runs well and no crash occurs. But there is no -(void)dealloc method. Is this code wrong? Should I add -(void)dealloc?
MyClass.h
#import <UIKit/UIKit.h>
#interface MyClass : NSObject {
#private
BOOL flag;
UIView *view;
UILabel *label;
UIButton *button;
UITabBar *tabBar;
UIWebView *webView;
UIImageView *imageView;
}
#property (nonatomic, retain) UIView *view;
#property (nonatomic, retain) UILabel *label;
#property (nonatomic, retain) UIButton *button;
#property (nonatomic, retain) UITabBar *tabBar;
#property (nonatomic, retain) UIWebView *webView;
#end
MyClass.m
#import "MyClass.h"
#implementation MyClass
#synthesize view;
#synthesize label;
#synthesize button;
#synthesize tabBar;
#synthesize webView;
- (id)init {
self = [super init];
if (self) {
// Initialization code
// Among other code,
imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
}
return self;
}
// Other methods here.
// But -(void)dealloc is not overridden here in the MyClass.m
#end
If we must add -(void)dealloc for the above code, should it be like this:
Overridden -(void)dealloc
-(void)dealloc {
[view release];
[label release];
[button release];
[tabBar release];
[webView release];
[super dealloc];
}
Update 1
#synthesize added, see above.
Update 2
Didn't put this into another post because this seems rather related issue:
See the above MyClass.m/.h, there is a private ivar (not sure it should be called ivar or field here) UIImageView *imageView;, it has no property for it, no #synthesize, initialization given there, how can we dealloc it? Also [imageView release]; in -(void)dealloc?
Update 3
Do we have to check availability before releasing ivars? That is, instead of [view release];, use this:
if (nil != view) {
[view release];
}
Yes. You need to implement dealloc.
You dealloc will look like :
-(void)dealloc {
[_view release];
[_label release];
[_button release];
[_tabBar release];
[_webView release];
[super dealloc];
}
Any retained/copy property should be released on dealloc.
Your iVar have no meaning. They do not have the same information as the properties, so you can remove your iVars.
If you want your properties to be backed up by your iVars you should #synthesize them like:
#synthesize view = view;
#synthesize label = label;
#synthesize button = button;
#synthesize tabBar = tabBar;
#synthesize webView = webView;
As you are not using ARC, your code (including the dealloc method) is correct, however you are missing the #synthesize statement in the implementation for the properties to work:
#implementation MyClass
// this will synthesize the getters and setters
#synthesize view, label, button, tabBar, webView;
- (id)init {
self = [super init];
if (self) {
// Initialization code
}
return self;
}
// Other methods here.
-(void)dealloc {
[view release];
[label release];
[button release];
[tabBar release];
[webView release];
[super dealloc];
}
#end
While Daniel's answer is correct in addressing your question, it does not cover what you should do.
This is how your code would be written in a modern world:
turn on ARC. Especially if you are learning or this is your first project. There is no reason to not use ARC. Learning manual-retain-release is valuable, but not critical at this time as the tools do a very good job of providing analysis of when ARC based patterns are leaking memory (either the analyzer or using Instruments, both of which you would need to use under MRR and neither of which work as well under MRR).
Don't use #synthesize and don't declare iVars (and certainly don't declare iVars in your .h file). Let the compiler autho-synthesize the _ prefixed ivars automatically. The _ prefix has the added advantage of disallowing you from accidentally directly accessing an ivar in code. I.e. self.foo vs. foo; the second won't compile.
Or to translate into code:
#interface MyClass : NSObject
#property (nonatomic, retain) UIView *view;
#property (nonatomic, retain) UILabel *label;
#property (nonatomic, retain) UIButton *button;
#property (nonatomic, retain) UITabBar *tabBar;
#property (nonatomic, retain) UIWebView *webView;
#end
And:
#implementation MyClass
{
BOOL _flag;
UIImageView *_imageView;
}
- (id)init {
self = [super init];
if (self) {
_imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
}
return self;
}
// no -dealloc
#end
Note that I declared _imageView as an instance variable that will be compatible with the obvious imageView #property should you need to refactor your class later to make that externally available.
If you realy must use manual retain-release, then add a -dealloc method that calls -release on all the ivars. I.e.[_view release];, [_imageView release];, etc...
Don't get what you mean by "Note that I declared _imageView as an
instance variable that will be compatible with the obvious imageView
#property should you need to refactor your class later to make that
externally available."
If you were to decide that _imageView needs to be accessible to other objects, then you would delete the iVar declaration and add:
#property(nonatomic, retain) UIImageView *imageView;
The compilers automatic synthesis would create an instance variable named _imageView automatically and none of the rest of your code would have to change.
Do we have to make sure an ivar is not nil before releasing it in
dealloc method? (See Update 3 above.)
No. In Objective-C, nil eats messages. That is, [nil release]; is perfectly valid and does absolutely nothing at runtime.
In your code the BOOL flag; has disappeared. Do we have make a
property for BOOL flag;, that is, #property BOOL flag;? Or all we have
to do is just placing a private field in the MyClass.h as #private
BOOL flag; up there in my original question?
I forgot it. You could create a property for it. Or you could declare _flag as an iVar next to _imageView as I've done above.
Most importantly, there is no longer any reason (save for a very rare case that is generally too be avoided) to declare instance variables in your .h.
I have a Subclass of NSObject in which I want to call IMMEDIATELY (a sort of -(void)viewDidLoad) a method (in this case to load a MkMapView): what's the better way to do this? I think I cant use viewDidLoad, so can I use performSelector?
SubClass.h
#interface Mysubclass : NSObject <MKMapViewDelegate> {
}
SubClass.m (1st alternative)
-(id)init{
self = [super init];
if ( self != nil ) {
// THE CODE TO INITIALIZE MKMAPVIEW
}
return self
}
OR
SubClass.m (2nd alternative)
-(id)init{
[self performSelector:#selector(myMethod)];
return self;
}
-myMethod{
// THE CODE TO INITIALIZE MKMAPVIEW
}
What's the better (or correct) alternative? Its possible to avoid -(id)init? Or everytime I add a subclass, to call a method I have to write it into -(id)init? Thank you!
There is no reason to use -performSelector: in this context. If you want to add a method that initializes the MKMapView when your object is created, call the method from within the if (self) block:
- (id)init
{
self = [super init];
if (self) {
[self setupMapView];
}
return self;
}
- (void)setupMapView
{
// THE CODE TO INITIALIZE MKMAPVIEW
}
It is a matter of personal preference/style whether to have a second method -setupMapView or to simply leave the code for setting up the MKMapView in the if (self) block of the -init method or to break the code off into a second method -setupMapView called from -init.
That being said, it sounds like other things may be off with your setup. Your MKMapView should [most likely] be within a UIViewController subclass (which will probably have an associated XIB), so you will be have access to -viewDidLoad. Note that your UIViewController subclass will serve as the delegate to your MKMapView.
Update 1
In your UIViewController subclass instance (I'll assume you called it ViewController, you should have an IBOutlet to an MKMapView object. Do this in ViewController.h either by (1) adding an instance variable
#interface ViewController : UIViewController
{
IBOutlet MKMapView *myMap;
}
#end
or by (2) adding a property
#interface ViewController : UIViewController
#property (nonatomic, strong, readwrite) IBOutlet MKMapView *myMap;
#end
Now open ViewController.xib in Interface Builder. You should have an MKMapView inside the view. If you don't already, add one from the Object Library. Right click on File's Owner. Locate the row with the item myMap. Drag from the circle on the right end of the row to the MKMapView in the visible view.
Your ViewController class now has an outlet to the MKMapView. You will be able to send messages to the MKMapView subview of your view controllers view after it has been loaded.
You should have a property or an instance variable for your SubClass instance so that it doesn't get destroyed as soon as -viewDidLoad returns. Do this again by either adding an instance variable to ViewController.h
#interface ViewController : UIViewController
{
IBOutlet MKMapView *myMap;
SubClass *istance;
}
#end
or by adding a property
#interface ViewController : UIViewController
#property (nonatomic, strong, readwrite) IBOutlet MKMapView *myMap;
#property (nonatomic, strong, readwrite) SubClass *istance;
#end
Now, in ViewController.m, you need to define -viewDidLoad so that self.istance is set as the delegate of self.myMap. In the comments, I had suggested creating your own initializer -initWithMapView:. If you plan on having SubClass do some extensive set-up of your MKMapView, that makes sense. If you just want SubClass to be the delegate of the MKMapView, there's no need for such a method.
Let's consider both cases:
(1) using a method -[SubClass initWithMapView:]:
In ViewController.m you'll have (within the #implementation of ViewController)
- (void)viewDidLoad
{
self.istance = [[SubClass alloc] initWithMapView:self.myMap];
}
In SubClass.h you'll have (within the #interface of SubClass)
- (id)initWithMapView:(MKMapView *)mapView;
#property (nonatomic, weak, readwrite) MKMapView *mapView;
In SubClass.m you'll have (within the #implementation of SubClass)
- (id)initWithMapView:(MKMapView *)mapView
{
self = [super init];
if (self) {
self.mapView = mapView;
self.mapView.delegate = self;
//more setup of mapView.
}
return self;
}
(2) using -[SubClass init]:
Instead, in ViewController.m you'll have
- (void)viewDidLoad
{
self.istance = [[SubClass alloc] init];
self.myMap.delegate = self.istance;
}
I have two classes:
A UIViewController and a class that's subclassing NSObject that acts as a downloading helper class called OfficesParser. OfficesParser is using ASIHTTPRequest and I set the delegate for the download requests to be my UIViewController.
EDIT: Interface for the UIViewController:
#interface OfficesViewController : UIViewController <UITableViewDelegate, UITableViewDataSource, ASIHTTPRequestDelegate> {
OfficesParser *officesParser;
}
#property (nonatomic, retain) OfficesParser *officesParser;
#end
In the UIViewController implementation I set up the OfficesParser like so:
- (void)viewDidLoad {
[super viewDidLoad];
self.officesParser = [[[OfficesParser alloc] init] autorelease]; // self.officesParser is retained
}
Then before the view appears I call my my OfficesParser object to download some data for me:
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
[self.officesParser doNetworkOperations];
}
Also in my UIViewController I have setup the appropriate delegate methods to deal with the data after it has been downloaded. In particular I'm interested in this delegate method that will run after all the data has been processed in my download queue. I can see that the delegate method is running from the log. But for some reason self.officesParser in here is nil.
- (void)queueFinished:(ASINetworkQueue *)queue {
DLog(#"queueFinished running");
[self.officesParser test]; // test will not get called because self.officesParser is nil
}
I know that if I retain an IBOutlet by using property then I have to set it to nil in viewDidUnload but what about others?
For example, i have three subviews view1, view2 and view3, that load from nib and that is the controller's header file
#interface MyViewController : UIViewController {
IBOutlet UIView *view1;
UIView *view2;
//no reference for view3
}
#property (nonatomic, retain) IBOutlet UIView *view2; //property view2 is an IBOutlet!!
#end
and method viewDidUnload
- (void)viewDidUnload {
self.view2 = nil;
//[view1 release];
//view1 = nil;
[super viewDidUnload];
}
do I have to release view1 and set it to nil? or UIViewController will set it to nil for me?
what about view3?
also do I have to release view1 in dealloc?
edit:
I think many people does not understand my question
Firstly, view1 is an IBOutlet which declared as an ivar and assign an ivar will not retain it. I know that UIViewController definitely will retain it but do i have to release it or UIViewController will release it for me? If UIViewController will release it then there is no point that i have to release it again.
Secondly, view2 is also an IBOutlet although it is declared as a property not ivar.
#property (nonatomic, retain) IBOutlet UIView *view2;
It is a retain property, therefore set it will retain it so I know that I have to set it to nil in order to release it. I have no problem about it.
For view3, there is no reference for it, therefore I am assuming I don't have to do anything about it. I also assuming there is no need to make a reference for every object in nib.
All outlets are retained by default even if they don't have a property declared for them. So you will need to release them. If you go on to declare an assigned property as an outlet, then you don't need to release but you can't rely on it either as you are not an owner.
So you need to release both view1 and view2 as they are declared as outlets. view3 is a variable that doesn't exist and hence needn't be worried about.
When a nib is loaded, all its objects are automatically instantiated and retained.
The file's owner of your nib file is then the owner of your UIView.
If you use UIView *view2 you can't connect them using interface builder.
So that doesn't make really sense to me.
You have to release in dealloc as well.
- (void)viewDidUnload {
self.view1 = nil;
self.view2 = nil;
[super viewDidUnload];
}
- (void)dealloc {
[self.view1 release];
self.view1 = nil;
[self.view2 release];
self.view2 = nil;
}
Ok, so I'm a relative noob with Objective-C/iOS programming, so hopefully someone with more knowledge here can help me out.
I have an iPad application using the SplitViewController template (with Core Data). I created another UIViewController (with xib file) called PlayerViewController. This View has several UILabel components on it.
I have a list of players that show up in the RootViewController (UITableView) and when you select a player, I programmatically create a PlayerViewController (in DetailViewController), pass it the NSManagedObject that was passed to the DetailViewController, try to set the text of one of the labels on the PlayerViewController's view, and then add it as a subview to the DetailViewController.
All of this works great except for the setting the text of the label on the PlayerViewController's view. I'm not sure what I'm doing wrong. I have used NSLog to confirm that the NSManagedObject is not nil and that the NSManagedObject property I'm trying to use has the correct text.
I'm at a loss here. Any help would be greatly appreciated. (Code follows):
This method is in the DetailViewController.m file:
- (void)configureView {
// Update the user interface for the detail item.
PlayerViewController *player = [[PlayerViewController alloc] init];
player.player = detailItem;
[self.view addSubview:player.view];
}
This method is called when the user selects an item from the RootViewController (This functionality, calling of configureView, is setup by the template and I haven't changed it).
Setting the player property of the PlayerViewController to object detailItem is handled in the setPlayer method of that class.
- (void)setPlayer:(NSManagedObject *)managedObject {
if (player != managedObject) {
[player release];
player = [managedObject retain];
// Update the view.
[self configureView];
}
}
I then have a configureView method as well in PlayerViewController that sets the text of the label:
- (void)configureView {
nickName.text = [[player valueForKey:#"Nickname"] description];
NSLog(#"Nickname %#", [[player valueForKey:#"Nickname"] description]);
NSLog(#"Nickname %#", nickName.text);
}
Ok, so the first NSLog statement prints the desired value, but the text of the UILabel (called nickName) returns nil.
The following is the full PlayerViewController.h & .m files:
PlayerViewController.h:
#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>
#interface PlayerViewController : UIViewController {
NSManagedObject *player;
IBOutlet UILabel *nickName;
IBOutlet UILabel *goalCount;
IBOutlet UILabel *assistCount;
IBOutlet UILabel *timeInGame;
}
#property (nonatomic, retain) IBOutlet UILabel *nickName;
#property (nonatomic, retain) IBOutlet UILabel *goalCount;
#property (nonatomic, retain) IBOutlet UILabel *assistCount;
#property (nonatomic, retain) IBOutlet UILabel *timeInGame;
#property (nonatomic, retain) NSManagedObject *player;
#end
PlayerViewController.m:
#import "PlayerViewController.h"
#implementation PlayerViewController
#synthesize nickName, goalCount, assistCount, timeInGame, player;
#pragma mark -
#pragma mark Managing the detail item
/*
When setting the player item, update the view
*/
- (void)setPlayer:(NSManagedObject *)managedObject {
if (player != managedObject) {
[player release];
player = [managedObject retain];
// Update the view.
[self configureView];
}
}
- (void)configureView {
nickName.text = [[player valueForKey:#"Nickname"] description];
NSLog(#"Nickname %#", [[player valueForKey:#"Nickname"] description]);
NSLog(#"Nickname %#", nickName.text);
}
/*
// The designated initializer. Override if you create the controller programmatically and want to perform customization that is not appropriate for viewDidLoad.
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
if ((self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil])) {
// Custom initialization
}
return self;
}
*/
/*
// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
[super viewDidLoad];
}
*/
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {
// Overriden to allow any orientation.
return YES;
}
- (void)didReceiveMemoryWarning {
// Releases the view if it doesn't have a superview.
[super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}
- (void)viewDidUnload {
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
- (void)dealloc {
[super dealloc];
}
#end
I'm sure I'm just missing something trivial, but I can't figure it out, and haven't been able to find any answers searching the web.
Thanks for any help!
Ok, so after playing with this for a bit and searching and searching around, I have gotten the answer to my problem. It turns out all the code I had was fine except the location of one statement. My call to configureView in PlayerViewController.m needed to be in viewDidLoad() not in the setPlayer() method. It all works great now.
Change the configureView method to that :
- (void)configureView {
nickName.text = (NSString*)[player valueForKey:#"Nickname"];
}
Yes, better place to call method is
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[self configureView];
}
(void)setPlayer:(NSManagedObject *)managedObject called before your nib files loaded.