iOS UIView inheritance bad performance - ios

I just wanted to do performances test on iOS on my project, and I am a little bit surprised of this behaviour :
In a simple SingleView Application, if I add 1000 UITextField on rect (20, 20, 200, 200) from the viewDidLoad: main controller method, it works great. It's stupid, but it works.
Now i create my class "MyTextField" inherited from UITextField and that implements drawRect: . The drawRect: implementation does nothing and i'm not overriding any other methods of UITextField. I replace my 1000 UITextField with MyTextField class, and surprise : it crashes. Worse, my iPhone reboots !
I don't understand why. According to the Apple documentation, my drawRect does not need to call super. I also try to call super drawRect: but the result is the same. Reboot due to "Receive memory warning".
Is there an explanation to this please ?
EDIT : to be clear :
It crashed (and my iPhone reboots) :
#implementation MyTextField
-(void)drawRect:(CGRect)rect {
[super drawRect:rect];
}
#end
It crashed too (and my iPhone reboots) :
#implementation MyTextField
-(void)drawRect:(CGRect)rect {
// or does nothing
}
#end
It works :
#implementation MyTextField
#end
Here is my ViewController :
- (void)viewDidLoad {
[super viewDidLoad];
NSLog(#"######### START ###########");
for (int i = 0 ; i < 1000 ; i++) {
MyTextField *tf = [[MyTextField alloc] initWithFrame:CGRectMake(20, 20, 200, 200)];
[self.view addSubview:tf];
}
NSLog(#"######### END ###########");
}
It does nothing else

They are warning you that blank implementation of drawRect affects performance
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.

I think there's no guarantee that super has an implementation of drawRect.
So calling [super drawRect:rect] might cause a crash.
The reason why it affects the performance, is because the view normally doesn't use drawRect to draw itself.
If you implement drawRect, the GPU needs to offload this part to the CPU (called offscreen rendering).
I guess you think implementing drawRect overwrites the method in a superclass.
But you should think more about the superclass checking if drawRect exists (e.g. respondsToSelector) and calling it only in this case.

Related

UIPicker View subclassed not working IOS

Being new to objective-C coding I started out writing a basic app, fully programmatically (not using storyboards or xib) in one file, my AppViewController h and m files.
Everything worked lovely.
So then I wanted to break up the mass of code by subclassing sections, and everything went well apart from the UIPickerView. In fact simply commenting out the [background addSubview:colorPicker]; seemed to totally fix the issue. I never found the answer online so I proceeded to make a new document to replicate said issue.
So here goes:
UIPickerViewController.h
#import <UIKit/UIKit.h>
#import "Picker.h"
#interface UIPickerViewController : UIViewController
#end
Simply imports my new class.
UIPickerViewController.m
#import "UIPickerViewController.h"
#interface UIPickerViewController ()
#end
#implementation UIPickerViewController
- (void)viewDidLoad
{
[super viewDidLoad];
UIView *superview = self.view;
int height = superview.bounds.size.height;
int width = superview.bounds.size.width;
CGRect popupRect = CGRectMake(0, 0, width, height);
UIView *popup = [[UIView alloc]initWithFrame:popupRect];
popup.tag = 8;
[superview addSubview:popup];
Picker *picker = [[Picker alloc]initWithFrame:popupRect];
[picker viewAddTypeScreenToView:superview];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
}
#end
Sets up a new view with a tag (so that i could reference it later with my new class)
Then actions a method from my new class to populate my new view.
Picker.h
#import <UIKit/UIKit.h>
#interface Picker : UIView
<UIPickerViewDataSource,UIPickerViewDelegate>
{
UIPickerView *colorPicker;
NSMutableArray *colorsArray;
}
#property (nonatomic, retain) UIPickerView *colorPicker;
#property (nonatomic, retain) NSMutableArray *colorsArray;
#property (strong,nonatomic) UILabel *myValue;
-(void)viewAddTypeScreenToView:(UIView*)superview;
#end
Setting up my variables and accessible method.
Picker.m
#import "Picker.h"
#implementation Picker
#synthesize colorsArray;
#synthesize colorPicker;
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
}
return self;
}
-(void)viewAddTypeScreenToView:(UIView*)superview
{
UIView *baseView =[superview viewWithTag:8];
int height = baseView.bounds.size.height;
int width = baseView.bounds.size.width;
CGRect fullScreen = CGRectMake(0, 0, width, height);
UIView *background = [[UIView alloc]initWithFrame:fullScreen];
background.backgroundColor = [UIColor blackColor];
colorsArray = [[NSMutableArray alloc] initWithObjects:#"Red",#"Blue",#"Yellow",#"Green",nil];
CGRect myPickerRect = CGRectMake(10, 70, (width/2)-40, 200);
colorPicker = [[UIPickerView alloc]initWithFrame:myPickerRect];
colorPicker.dataSource = self;
colorPicker.delegate = self;
colorPicker.showsSelectionIndicator = YES;
[colorPicker selectRow:2 inComponent:0 animated:YES];
CGRect labelFrame = CGRectMake(10, 10, 180, 50);
_myValue = [[UILabel alloc]initWithFrame:labelFrame];
_myValue.textColor = [UIColor redColor];
_myValue.text = #"select colour";
[background addSubview:_myValue];
[background addSubview:colorPicker];
[baseView addSubview:background];
}
-(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{
return 1;
}
-(NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component{
return colorsArray.count;;
}
-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
return colorsArray[row];
}
-(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component{
_myValue.text = [NSString stringWithString:colorsArray[row]];
}
#end
And finally the initiation called by the method in the picker class file.
This gives me an error along these lines
-[UITableViewCellContentView pickerView:titleForRow:forComponent:]: unrecognized selector sent to instance 0x8f2b000
2014-03-19 10:29:48.407 Briefcase[1800:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UITableViewCellContentView pickerView:titleForRow:forComponent:]: unrecognized selector sent to instance 0x8f2b000'
Which i've read is to do with either the datasource, or ARC systems, however none of the responses that I have found relate to or work with the type of set up that I have above. I'm sure it's something really simple but after a few days of failed searching, it's officially driving me crazy.
The problem is most likely that the instance of Picker that is being created in UIPickerViewController is never added to the view hierarchy and thus gets released prematurely (provided we're talking about a project using ARC here).
This leads to the pickerview's delegate and datasource becoming invalid and, basically, pointing at any random object. That's what is causing your crash: A message to your delegate cannot be delivered because the delegate is dead already. The picker still keeps a pointer which used to point at the delegate, but which has become invalid and points at a random object now, in this case a table view cell, which basically doesn't know what to do with this message and crashes.
The problem should go away if you add Picker *picker as an ivar or a retaining / strong property to UIPickerViewController.h - this will retain the picker beyond the scope of the viewDidLoad method and should keep it alive.
But that would be just a workaround, the real problem is your overall design. You said you're new to objective-c and indeed, it looks like you lack a basic understanding of iOS view and view controller hierarchies and, to some degree, the concept of object oriented programming. You might want to dig into something more basic before trying to fix your code because, quite frankly, it should be rather re-written than fixed.
I'd be happy to provide you with suggestions about how to structure your code, but please provide some information about what functionality you'd like to achieve first.
Edit (in response to your comment):
As a rule of thumb, do not spread functionality over several classes unless necessary. For objects, which serve a rather infrastructural purpose, like a specialized textfield or a pickerview, always ask yourself: "If I would like to reuse that object in another project, would that be as easy as using any other existing object, like, for example, UILabel?" If the answer is "No", then something is wrong. Ideally, interface objects are self-contained and to use them, you just invoke them, add them to a view and tell them, which text to display or which options to offer. If that information is subject to change or if the object needs to interact with other parts of your code, make use of delegation and protocols. Under no circumstances should the functionality of your object be tied to hard coded values or rely to some view to have a certain tag.
If you subclass UIView, the resulting object should behave like any other instance of UIView. It should be added to the view hierarchy by you or some object, but it shouldn't add or remove itself. If it works without being added to the view hierarchy at all, something is wrong. A view serves the purpose of being a part in your interface and all the logic it contains should work to that end, not more, not less.
Normally, interface objects should not interfere with one another. If something happens to one object (button pressed, option selected, text changed...) and another object is supposed to reflect that change, it is the view controllers responsibility to make that happen. The view controller is the place where the logic happens. If there is a task which requires a lot of complex logic, it might be a good idea to encapsule that logic into a purpose build class. One such example would be a class which manages network connections. This class should be again self contained: If the view controller needs some remote information, it asks your network class. Once your network class has that information (or failed to retrieve it), it reports back to your view controller. The view controller then updates the interface - under no circumstance should the networking class contain code which affects the interface.
It is important to understand that you could very well ignore these rules and still end up with a working app. And in some cases, the "direct" way may appear to be easier to implement and thus may look very tempting. But you'll pay the price later - once you start debugging your code. If your picker does not behave the way it should, you need to look into several places and wrap your mind around several objects, just to make one interface object behave right. And likely you will break one functionality while fixing the other.
So, try to make it right from the start, even though it requires more planning and learning. Trust me, it pays out, I started out just like you several years ago ;)

Where do you set a subview's layer properties? Why not in the initWithCoder

I created a custom UITableViewCell (for this example, let's just say the subclass is MyViewCell) which has an Nib file associated to it MyViewCell.xib. The nib contains a UITableViewCell with one subview UIView (named cardContainer) that's simply a rectangle with a blue background. I want to add a drop shadow around the UIView, so I added set the layer properties in the -initWithCoder call:
#implementation MyViewCell
- (id)initWithCoder:(NSCoder *)aDecoder
{
self = [super initWithCoder:aDecoder];
if (self) {
[self initView];
}
return self;
}
- (void) initView
{
UIBezier Path*shadowPath =[UIBezierPath bezierPathWithRect:view.bounds];
[self.cardContainer.layer setShadowColor: [UIColor blackColor].CGColor];
[self.cardContainer.layer setShadowOpacity: 0.8];
[self.cardContainer.layer setShadowRadius:3.0];
[self.cardContainer.layer setShadowOffset: CGSizeMake(2.0,2.0)];
view.layer.shadowPath = shadowPath.CGPath;
}
#end
The problem I'm having is that these layer properties aren't being drawn. If I call the -initView call within awakeFromNib or drawRect it's drawn as expected. My question: why doesn't my original code work? Where should I be calling initView? Is there some view lifecycle? I understand that the initWithCoder doesn't have the outlets connected, but it didn't crash at runtime.
I read through Apple documentation around Views and searched through the SO questions without finding an answer. I found this SO answer, but again doesn't explain.
Hey I found a better way to do this ,just add some runtime attributes for your subview cardContainer
like this
no more code in .m file anymore.
EDIT:
From:NSNibAwaking Protocol
Important: Because the order in which objects are instantiated from an archive is not guaranteed, your initialization methods should not send messages to other objects in the hierarchy. Messages to other objects can be sent safely from within awakeFromNib—by which time it’s assured that all the objects are unarchived and initialized (though not necessarily awakened, of course).
You need to add this,
self.cardContainer.layer.masksToBounds = NO;

Call super without "super" keyword

I want' to implement "Fix and continue functionality" that was in Xcode 3.
CONTEXT:
The main idea is:
When I need to "Fix something fast", I'm not re-compiling, project. I'm compiling small Attacker class with 'updated' method implementation, loading it into memory and replacing VictimClass's method which have incorrect implementation in runtime.
I think that this method will work faster that full project recompilation.
When i'm done with fixes i'm just copying source of Attacker class method to Victim class.
PROBLEM
At the moment, I don't know how correctly call [super ...] in Attacker class.
For example, i have VictimClass
#interface VictimClass : UIView #end
#implementation VictimClass
- (void)drawRect:(CGRect)rect {
[super drawRect:rect];
}
#end
#interface AttackerClass : NSObject #end
#implementation AttackerClass
- (void)drawRect:(CGRect)rect {
[super drawRect:rect];
[self setupPrettyBackground];
}
#end
....
// EXCHANGE IMPLEMENTATIONS
Method m = class_getInstanceMethod([AttackerClass class], #selector(drawRect:));
const char * types = method_getTypeEncoding(m);
IMP attackerImp = method_getImplementation(m);
class_replaceMethod([VictimClass class], #selector(drawRect:), attackerImp, types);
// Invoking drawRect on Victim
VictimClass * view = /* */;
[view setNeedsDisplay];
At this point , when drawRect: method will be called, this will lead to exception, since drawRect: will be called on NSObject class, but not on UIView class
So, my question is, how correctly call [super drawRect:] in AttackerClass, to have possibility to correctly exchange implementation in runtime?
Main idea is to provide a way to correctly replace any method in Victim class by Attacker's class method. Generally, you don't know, superclass of Victim class.
UPDATE: Replacing implementation code added.
You will have to
get the receivers class (e.g. with object_getClass(rcv))
then get the super class of it (with class_getSuperclass(class))
then get the implementation of it (with class_getMethodImplementation(superclass, sel))
then call the imp.
done
Stop at any step if you got nil or NULL.
Oh, and all this seems silly. But I assume that the question just lacks of context to see the motivation for such a hack.
[Update]
An explanation for future readers:
The super keyword is resolved at compile time. Therefore it does not the intended thing when changing methods at runtime. A method which is intended to be injected in some object (and its class hierarchy) at runtime has to do super calls via runtime as outlined above.
Assuming that the runtime changes you're making involve modifying the superclass, you'll have to do something like this:
#implementation AttackerClass
-(void) drawRect:(CGRect)rect
{
if( [super respondsToSelector:#selector(drawRect:)] )
{
[super drawRect:rect];
}
[self setupPrettyBackground];
}
#end
This will check if the superclass "knows about" drawRect:, and doesn't call it in the case that super has no drawRect: selector.
Hence, when the superclass is NSObject the drawRect: message will not be sent. When you change it to UIView at runtime (whatever your reason for that is), the message can safely be sent.
One approach is to use objc_msgSendSuper. Your method -[AttackerClass drawRect:] will have the following implementation:
- (void)drawRect:(CGRect)rect {
struct objc_super superTarget;
superTarget.receiver = self;
superTarget.class = object_getClass(self);
objc_msgSendSuper(&superTarget, #selector(drawRect:), rect);
[self setupPrettyBackground];
}
but why do you need to call draw rect method for superclass NSObject, when NSObject hasn't got that method? just don't do it... call it just in VictimClass drawrect

Leak detection issue in iOS with xCode 4.3

I have a very strange issue with the xCode 4.3 memory leak instruments... Basically it does not work in the following case...
Project is created without ARC support.
Create a simple class which inherits UIView
use a "button" to create instance of this class and "leak" it... the leak will not be catch by Leak Instruments
so here is the code of the PROBLEMATIC class
#interface LeakTestView : UIView
- (id)initWithFrame:(CGRect)frame;
#end
#implementation LeakTestView
- (id)initWithFrame:(CGRect)frame
{
NSLog(#"initWithFrame called");
self = [super initWithFrame:frame];
if (self) {
// Initialization code
}
return self;
}
#end
And now I create the leak...
- (IBAction)leak:(id)sender {
LeakTestView* leak=[[LeakTestView alloc]initWithFrame:CGRectMake(0, 0, 100, 100)];
NSLog(#"class is %#", [leak class]);
}
So the problem is that this leak will not be detected...
If I change the base class to NSObject and instead of initWithFrame override init (see bellow) then the leak will be detected....
so here is the code for leak that WILL be detected
#interface LeakTestView : NSObject
- (id) init;
#end
#implementation LeakTestView
- (id) init {
NSLog(#"init called");
self = [super init];
if (self) {
}
return self;
}
#end
If I create object now and leave it - the leak detection will trigger and the leak will be "seen" into the Instruments.
- (IBAction)leak:(id)sender {
LeakTestView* leak=[[LeakTestView alloc]init];
NSLog(#"class is %#", [leak class]);
}
Any ideas what is going on? Why the leak of the UIView subclass will not be detected but changing the base class to NSObject will "fix" the issue?
Oh and yes the leaked object can be seen using the "Mark heap" - one mark before the leak and one mark after I click the button and create the leak - the class will be seen into the heap delta...
EDIT: one more "funny" situation... If I remove the "init" stuff (only alloc the object)
LeakTestView* leak=[LeakTestView alloc];
then the leak will be detected no matter what is the base class... What the hell is going on here?
EDIT2: one more "funny" thing. The Leak detection issue can be observed only in Simulator (iOS 5.0, 9A334 is mine) but the leak will be detected always if using the iPad device...
Any comments? If you dont have the issue or consider that I speek "lies" just tell me I am wrong and the above case is working "just fine" - leaks I describe are detected by your xCode instruments!
Maybe it is not leaking?
You are calling a method that is a black box. How UIView initWithFrame is implemented is none of your business. It has a contract of sorts, but you have no right to demand this to leak anymore than you can assume the retain count is 1.
Leaks is a useful tool but it doesn't do what you think it does. It does not tell you when you have messed up. It tells you when you have unreachable allocations. This is not the same thing.
Or, it might be a bug.

Infinite loop when using loadView

Very interesting problem when using loadView in UIViewController.
Usually we used like this way
// Implement loadView to create a view hierarchy programmatically, without using a nib.
- (void)loadView {
NSLog(#"loadview");
[super loadView];
}
If remove
[super loadView];
We will get dead loop with this
- (void)loadView {
NSLog(#"loadview");
}
Why ?
Only one way to make infinite loop in this case - is getting view property until its not set. If you write next (for example):
- (void)loadView {
self.view = [[UIView alloc] initWithFrame:self.view.bounds];
}
You'll got infinite loop, but
- (void)loadView {
self.view = [[UIView alloc] initWithFrame:CGRectZero];
}
works OK.
So you can't to access view property until you didn't set it.
Since you are just INHERITING what's being implemented in super class(UIViewController), if you don't call super methods, then implementation that needs to be done is NOT done.
Almost all super methods do something critical and the local class inheriting super class implementations must either override them all together (unless you know everything about what super does by referring to the documentation, it's never a good idea), or just ADD local class implementation to the inherited super class implementations.
In conclusion, whenever you inherit a class, which is in most cases of software development, you should let the super class do its implementations unless it's safe to override them.
If I am correct, it seems like super loadView implements something very critical to avoid the loop.
ADDITIONAL NOTE:
However, based on the documentation, you should not call super method: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIViewController_Class/Reference/Reference.html
Probably, the reason for infinite loop is caused by not implementing view property appropriately.
If you override loadView, you are expected to provide a root view for the controller's view hierarchy. If you don't provide it loadView would get called every time the view is referenced, possibly leading to an infinite loop. From the docs:
If you specify the views manually, you must implement the loadView method and use it to assign a root view object to the view property.
Implementations that would cause an infinite loop:
- (void)loadView {
NSLog(#"loadview");
}
...self.view is nil after loadView
- (void)loadView {
self.view; // Or anything that references self.view
}
...referencing self.view causes loadView to be invoked, hence an infinite loop.
Correct:
- (void)loadView {
self.view = [[UIView alloc] init];
if (self.view == nil) {
[super loadView]; // Try to load from NIB and fail properly, also avoiding inf. loop.
}
}

Resources