I have a custom view to which I need to add a couple of subviews programmatically. Which is the best place to create and add these subviews? Apple docs say:
If your view class manages one or more integral subviews, do the following: Create those subviews during your view’s initialization sequence.
This is a bit unclear to me. Should I handle that in initWithFrame, initWithCoder or somewhere else?
Note that I'm not talking about controllers here, this is a View that needs to initialize itself.
initWithFrame is the method you call to create a UIView programmatically, while initWithCoder is called when a UIView is instanciated from a XIB.
So it all depends on how you're going to create your containing view.
A way to cover all cases :
- (id) initWithFrame:(CGRect)frame
{
if ((self = [super initWithFrame:frame])){
[self setUpSubViews];
}
return self;
}
- (id) initWithCoder:(NSCoder*)aDecoder
{
if ((self = [super initWithCoder:aDecoder])){
[self setUpSubViews];//same setupv for both Methods
}
return self;
}
- (void) setUpSubViews
{
//here create your subviews hierarchy
}
Do the following: take the method whichever is the designated initializer for your view. That is, it's the most configureable (i. e. most arguments) init... method that every other initializer calls. For example, it can be -initWithFrame:, as most commonly. Then implement this method as follows:
- (id) initWithFrame:(CGRect)frame {
if ((self = [super initWithFrame:frame])) {
// add new views here, for example:
UIImageView *imageView = [[UIImageView alloc] initWithImage:anImage];
[self addSubview:imageView];
[imageView release];
}
return self;
}
Generally , you should create the view and [self addSubView] in viewdidload/viewwillappear of the parent view controller if you want to show the view all the time. You can also set it hidden if you wih. In some other scenario like you want to show a view on a button click or some other actions, you should add subviews accordingly.
By integral, they mean either important or massive. viewDidLoad works just fine, but for really big, or important stuff, initialization methods are the way to go.
Related
I want to add borders and corner radius to my UIButtons,UITextFields, etc
I think I could extend UIControl to add this functionality.
I would need to add some properties and draw in awakeFromNib or 'layoutSubviews'.
If I subclass UIControl, I can't make UIButton use that subclass.
If I subclass my UIControl subclass, I need to "recreate" UIButton, UITextField, etc.
I could subclass UIButton, UITextField and add this behaviour, but then I would have one subclass for each component to add the same functionality to them, ending with a lot of duplicated code.
I think I can not change/alter UIControl's methods in a category.
Is there a way to add this kind of functionality to UIControl and it's subclasses without reinventing the wheel, or ending up with a lot of duplicated code?
What HellBoy89 says seems the easiest route to go on. Categories can also override default implementation, which makes things practical here. Here's an example to do what you want and it's automatically applied to all UIControls and their subclasses being instantiated.
#implementation UIControl (Styling)
- (id) initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
[self applyDefaultControlStyle];
}
return self;
}
-(id)initWithCoder:(NSCoder *)aDecoder {
self = [super initWithCoder:aDecoder];
if (self) {
[self applyDefaultControlStyle];
}
return self;
}
-(void)applyDefaultControlStyle {
[[self layer] setCornerRadius:8];
[[self layer] setBorderColor: [[UIColor redColor] CGColor]];
[[self layer] setBorderWidth: 2];
}
#end
You can use categories to extend UIControl. You will not be able to add properties to UIControl, but you can add methods.
Please refer to this question, it may be helpful: Adding a property to all of my UIControls
#import "DotAnimation.h"
#implementation DotAnimation
DoodlePad* dp;
-(void)setupView {
Ball = CGRectMake(10, 10, 10, 10);
[NSTimer scheduledTimerWithTimeInterval:(1.0f / 30.0f) target:self selector:#selector(traceBall) userInfo:nil repeats:YES];
}
-(id)initWithCoder:(NSCoder *)aDecoder {
if (self == [super initWithCoder:aDecoder]){
[self setupView];
}
return self;
}
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
[self setupView];
}
return self;
}
/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.*/
- (void)drawRect:(CGRect)rect {
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [[UIColor yellowColor] CGColor]);
CGContextFillEllipseInRect(context, Ball);
}
-(void)traceBall{
vector<CGPoint>::iterator L = dp.doodlePoints->begin();
while(L != dp.doodlePoints->end()){
Ball.origin.x += (*L).x;
Ball.origin.y += (*L).y;
++L;
}
[self setNeedsDisplay];
}
- (void)dealloc
{
[super dealloc];
}
#end
I have this Animation I am trying to use in another file.
So i figure i do something like
trace = [[DotAnimation alloc]initWithCoder];
or
trace = [[DotAnimation alloc]initWithFrame];
I am unsure which one to use or if i am even writing this correctly.
I want to be able to use:
while(k != dp.doodlePoints->end()){
Ball.origin.x += (*k).x;
Ball.origin.y += (*k).y;
++k;
}
In another file but I don't know how to call Ball.origin from DotAnimation
Also it would be great if you could link me to good information on understanding this.
initWithCoder is called by the framework when you embed an object into a XIB. Like a ViewController for example. So you should not call it by yourself.
Calling initWithFrame could be a better solution if you want to set the frame (like that seems to be done here). But you may give a frame, and add a subview created by yourself.
if you don't want to create the subview by yourself, then it's initWithNibName:bundle: that you may call/override. Creating the XIB that contains the view. But you will still need to add that view as subview to the main view that is showing that animated view.
initWithCoder: is something you would call yourself when restoring from an archive; it isn't appropriate for something which appears to be a view object. As it is only used for simple setup code, you can remove it.
Also, animating by changing the "Ball" object from another object isn't really consistent with Cocoa view programming. You should take a look at "Introduction to View Programming Guide for Cocoa" in the documentation, and work from there.
I would like to build a custom init method for a UIViewController, but after digging around on the Internet and specifically in SO I am confused about designated initializers.
I have a subclass of an UIViewController with these two initializers:
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if ( self ) {
}
return self;
}
- (id) initWithFilename:(NSString *)aFilename {
self = [self initWithNibName:#"WallpaperDetailsViewController" bundle:nil];
if ( self ) {
self.filename = aFilename;
}
return self;
}
Then I have a viewDidLoad method that customizes the view according to the filename property:
- (void)viewDidLoad {
[super viewDidLoad];
// Create a UIImageView to display the wallpaper
self.wallpaper = [[UIImageView alloc] initWithImage:[UIImage imageNamed:self.filename]];
// ...
}
In another UIViewController I make the following call:
WallpaperDetailsViewController *detailsViewController = [[WallpaperDetailsViewController alloc] initWithFilename:#"foobar.png"];
[[self navigationController] pushViewController:detailsViewController animated:YES];
The result is that viewDidLoad is being called as a consequence of [self initWithNibName:], which does not initialize the UIImageView because self.filename is null.
According to other SO questions and answers, that should be the expected behavior. I am not sure about this because of my own experience in other projects prior to iOS 5. My question is:
How can I ensure that viewDidLoad: is call after initWithFilename: and not between initWithFilename: and initWithNibNameOrNil:bundle:?
If that's not possible, how can I implement an initializer method that receives custom data to create and customize the view?
Thanks!
I have found the problem.
WallpaperDetailsViewController does not inherit directly from UIViewController, but from another custom UIViewController I have implemented.
And what was the problem? That I have initialized a subview in the parent's initWithNibName method, instead of following the lazy-load technique and doing it in viewDidLoad. When WallpaperDetailsViewController was calling its parent initializer it got messy and cause viewDidLoad not to behave properly.
The solution? I moved every subview initialization in the parent class to its viewDidLoad method, and keep my original implementation of WallpaperDetailsViewController intact. Now everything is working as expected
Thanks to #Josh Caswell and #logancautrell
You don't need that empty implementation of initWithNibName:bundle:. Furthermore, it looks like your class here is establishing its designated initializer to be initWithFilename: If that's true, initWithFilename: should be calling the superclass's D.I.:
- (id) initWithFilename:(NSString *)aFilename {
// Call super's designated initializer
self = [super initWithNibName:#"WallpaperDetailsViewController"
bundle:nil];
if ( self ) {
self.filename = aFilename;
}
return self;
}
The rule is that all initializers within a class should call the class's D.I., and the D.I. should itself call the superclass's D.I.
It's not completely clear from what you've posted why loadView: is being called before your initializer has completed. Logancautrell's comment suggesting setting breakpoints in the view loading methods is good.
Why don't you just use a custom setter for the filename property that initializes the UIImage every time the filename is set?
Or, alternately, set the UIImage from the filename property in viewWillAppear: instead of viewDidLoad.
First, it is not recommended that you use dot syntax within your initializer. See the following for some good discussion:
Objective-C Dot Syntax and Init
Second, what you could do is assign the image in your initializer as well. So you could do something along the lines of
- (id) initWithFilename:(NSString *)aFilename {
self = [self initWithNibName:#"WallpaperDetailsViewController" bundle:nil];
if ( self ) {
filename = [aFilename retain];
wallpaper = [[UIImageView alloc] initWithImage:[UIImage imageNamed:aFileName]];
}
return self;
}
This will allow you to get everything setup and in good shape before viewDidLoad is called.
Good Luck!
edit : ok, what i've learned is you might choose between initWithNibName or initWithCoder, depending if you use a .xib or not. And "init" is just not the constructor method for UIVIewController.
This might seem to be a fairly simple question, but I'm not sure about the answer : I've read that this method "is only used for programatically creating view controllers", and in the doc : "It is loaded the first time the view controller’s view is accessed"
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) {
// Custom initialization
}
return self;
}
Ok so to understand it a bit more :
What would you write as "custom initialization" into this method?
When should you implement this method, like that in the code, if you can just write it after allocating your viewController (example : MyVC *myvc = [[MyVC alloc] initWithNibName:...bundle...];)
Thanks for your answer
Usually I do this:
// Initialize controller in the code with simple init
MyVC *myVC = [[MyVC alloc] init];
Then do this in my init method:
- (id)init {
self = [super initWithNibName:#"MyVC" bundle:nil];
if (!self) return nil;
// here I initialize instance variables like strings, arrays or dictionaries.
return self;
}
If controller needs some parameters from the initializee, then I write custom initWithFoo:(Foo *)foo method:
- (id)initWithFoo:(Foo *)foo {
self = [super initWithNibName:#"MyVC" bundle:nil];
if (!self) return nil;
_foo = [foo retain];
return self;
}
This allows simplification of initialization as well as extra initializers for your view controller if it can be initialized from different locations with different parameters. Then in initWithFoo: and initWithBar you'd simply call init which calls super and initializes instance variables with default values.
It's an init method, so you initialize everything you need to be initialized when you begin your work in your view controller. Every object ivar will be automatically initialized to nil, but you can initialize a NSMutableArray to work with or an BOOL that you want to be a certain value.
You implement this method every time you have something to initialize, as stated previously. You generally don't initialized things after allocating your view controller, that way you don't need it to do it every time you use your view controller (as you may use it at different place in your application). It's also the best practice.
I usually put in there configuration stuff that I know it wont change.
For example, the ViewController's title:
self.title = #"MyTitle";
Or if this is one of the main ViewController in a TabBar application. That is, it owns one of the tabs, then I configure its TabBarItemlike this:
UITabBarItem *item = [[UITabBarItem alloc] initWithTitle:#"something"
image:[UIImage imageNamed:#"something.png"]
tag:0];
self.tabBarItem = item;
There is all sorts of things you can do there.
I'm trying to lay out some images in code using addSubview, and they are not showing up.
I created a class (myUIView) that subclasses UIView, and then changed the class of the nib file in IB to be myUIView.
Then I put in the following code, but am still getting a blank grey screen.
- (id)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
// Initialization code
[self setupSubviews];
}
return self;
}
- (void)setupSubviews
{
self.backgroundColor = [UIColor blackColor];
UIImageView *black = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"black.png"]];
black.center = self.center;
black.opaque = YES;
[self addSubview:black];
[black release];
}
yes, just implement initWithCoder.
initWithFrame is called when a UIView is created dynamically, from code.
a view that is loaded from a .nib file is always instantiated using initWithCoder, the coder takes care of reading the settings from the .nib file
i took the habit to do the initialization in a separate method, implementing both initWithCode and initWithFrame (and my own initialization methods when required)
try implementing initWithCoder: sometimes I've had trouble with IB and initWithFrame:
or at least add a logging call to see if your init method is executed