I have a class that instances some other classes. It's working to control their lifespan, or supposed to ;) A root class managing others which contain events and are subviews of the root view.
I have a lot of graphics involved per view and need to clear things out before loading the next.
Any idea how to unload the current subview and how to load the next subview, while maintaining a named reference to it to use in event handling, from a "touches ended" method?
Thanks
// :)
Assuming that you want to dump the old subview and hold a handle to the new one, this is actually pretty easy. You want something like this:
#interface YourView : UIView
{
// Create an ivar in your class
UIView *_subview;
}
// Propertize it as retain to take care of most of the heavy lifting
#property(nonatomic, retain) UIView *subview;
#end
#implementation YourView
// Map the ivar to the property
#synthesize subview = _subview;
// Call this to put in a new subview
-(void) switchToNewSubview:(UIView*)newSubview
{
// Remove the old subview, set the new one, and if the new one isn't nil
// add it as a subview
[self.subview removeFromSuperview];
self.subview = newSubview;
if(newSubview)
[self addSubview:self.subview];
}
// Don't forget to nil out the subview on dealloc to release it
-(void) dealloc
{
self.subview = nil;
[super dealloc];
}
#end
Related
How can I access the value from an inputField located in a second viewController?
The class name of the second view controller is SettingsViewController and the outlet name for the inputField is setRateInput.
I tried this but it didn't work…
double taxRateFromInput = [[self.settings.setRateInput text]doubleValue];
when I NSLog it comes out as The value is: (null)
Any idea what I'm doing wrong?
Here is the implementation file for the main viewController:
#import "SettingsViewController.h"
#interface ViewController ()
#property (strong, nonatomic) SettingsViewController * settings;
#end
#implementation ViewController
// lazy instantiation
-( SettingsViewController *) settings
{
if (_settings == nil) {
_settings = [[SettingsViewController alloc]init];
}
return _settings;
}
- (IBAction)calculatePrice:(id)sender {
double taxRateFromInput = [[self.settings.setRateInput text]doubleValue];
#end
In theory, you could create a global. Create a new class, call it something like taxRate (.h and .m)
In taxRate.h, add the following code:
#import <Foundation/Foundation.h>
#class MyTaxRate;
#interface TaxRate : NSObject {
}
#property (nonatomic, retain) double * taxRateFromInput;
+(TaxRate*)getInstance;
#end
Then, in your controller, put a "#import taxRate.h" in there. In your .m file, add the following:
#import "TaxRate.h"
#implementation TaxRate
#synthesize taxRateFromInput;
static TaxRate *instance =nil;
+(TaxRate *)getInstance
{
#synchronized(self)
{
if(instance==nil)
{
instance= [TaxRate new];
}
}
return instance;
}
#end
Note: This is extremely similar in structure to what I'm purposing.
if you have the reference from the object view controller you can just access by the property from your attribute.
You instantiated a new SettingsViewController, but you didn't do anything to instantiate its textfield setRateInput. You can do it when you instantiate it:
_settings = [[SettingsViewController alloc]init];
_settings.setRateInput = [UITextField alloc] initWithFrame:someFrame]];
or, as a beter solution, instantiate the text field in -init of SettingsViewController
- init {
if (self = [super init] {
self.setRateInput = [UITextField alloc] initWithFrame:someFrame]];
}
return self;
}
If you use nib files, this would be a lot easier.
Note: setRateInput is a bad name for a property. Consider rateTextField instead.
Edit I forgot to add that you have to add the text field as a subview to its parent view.
So it will be like,
_settings = [[SettingsViewController alloc]init];
_settings.setRateInput = [[UITextField alloc] initWithFrame:someFrame] autorelease];
[_settings.view addSubView:_settings.setRateInput];
In this case, the setRateInput is retained by its super view. You're not using ARC, so you can call autorelease on your text field.
The better solution: Use - (void) loadView; inside SettingsViewController. Loading the view is the responsibility of the correspondent view controller.
- (void) loadView {
self.setRateInput = [[UITextField alloc] initWithFrame:someFrame] autorelease];
[self.view addSubView:_settings.setRateInput];
}
Edit: xib files and storyboards can help you out. Give these tutorials a try.
You are on the right track, also well done with your lazy instantiation (as
a demonstration that you grasped the concept, I mean).
But note, that outlets don't get connected until viewDidLoad is called. So if you
just alloc/init your viewController (lazily), the outlet to your textfield is pointing to nil.
The outlet doesnt get connected until your controller's view property is accessed, ie the view is displayed.
What you could do is give the settings viewController a handle to your calculating viewController and let it set a public property on the calculating viewController that represents the rate.
This is a common pattern - delegation - where one viewController (settingsViewcontroller) calls a method on its delegate (calculating viewController).
You wouldn't need the settingsViewcontroller property in your calculating viewController then, but just instantiate a new settings viewController every time you want it to be brought up, giving it a reference to your calculating viewController.
Another possibility - maybe even better - is to define a model object that does calculation and takes care of the rate it needs to calculate. Then you could give your settingsViewcontroller a reference to that model object (probably instantiated in your
other viewController), so that it can change the rate on it.
PS: also re think how you instantiate viewControllers generally. The designated initialiser is -initWithNibName:bundle: - so usually, you wouldn't just alloc/ -init them.
If you use storyboards (you probably should!), use storyboard's -instantiateViewControllerWithIdentifier: or use the above mentioned designated initialiser.
I'm thinking of a way to have a UIView render itself onto another UIView as well as the first one. So I have my main UIView with it's bounds, and the UIView also renders itself in some other UIView.
Is this possible ? Does it require extensive layer operations?
Don't know whats your real intention is, but this will draw the view twice, userinteraction etc. will not work on the second view. Also this solution does not take care of different frame sizes.
Header of the View you want to clone
#interface SrcView : UIView
#property(nonatomic, readonly, strong) UIView *cloneView;
#end
#interface CloneView : UIView
#property(nonatomic, weak) UIView *srcView;
- (id)initWithView:(UIView *)src;
#end
implementation of the View you want to clone
#import "SrcView.h"
#import "CloneView.h"
#implementation SrcView
#synthesize cloneView;
- (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx{
[cloneView setNeedsDisplay];
}
- (UIView *)cloneView {
if (!cloneView) {
cloneView = [[CloneView alloc] initWithView:self];
}
return cloneView;
}
#end
#implementation CloneView
#synthesize srcView;
- (id)initWithView:(UIView *)src {
self = [super initWithFrame:src.frame];
if (self) {
srcView = src;
}
return self;
}
- (void)drawRect:(CGRect)rect
{
[srcView.layer renderInContext:UIGraphicsGetCurrentContext()];
}
#end
now you can just call cloneView and add it somewhere you want.
This seems to be an oft asked question here on StackOverflow. For example:
iphone, ipad Duplicate UIView - Cloned View
Copying the drawn contents of one UIView to another
UIView duplicate
Duplicate, clone or copy UIView
But if it were me doing this, my first approach would be to get a handle to the UIView I want to copy, then recursively iterate all the subviews of it and then copy & add them as subviews to the UIView I want to copy the main UIView into.
I can't imagine there's too much layer operations going on with this, but you would likely need to figure out how to programmatically re-establish outlets and/or actions.
There is no easy way to clone a view and then to update two views by one line of code. Because their underlying CALayers are different. But for duplicating a UIView, here is a new method you can use: Use UIView's method:
- (UIView *)snapshotViewAfterScreenUpdates:(BOOL)afterUpdates
This is the fastest way to draw a view. Available in iOS 7.
Create another instance of the UIView you wish to "clone" and add it as a subview to another view. You don't really clone a UIView object, you simply create another instance of it.
I have been working on an app, and the book I read said to put these statements into the viewDidUnload and dealloc methods. What other information should go here? I have buttons and labels in my program. Do I need to do anything for them?
I want an efficiently running application.
Here's my code:
- (void)viewDidUnload {
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
self.doublePicker = nil;
self.color = nil;
self.choice = nil;
[super viewDidUnload];
}
- (void)dealloc {
[doublePicker release];
[color release];
[choice release];
[super dealloc];
}
You should only release your IBOutlets and other UI elements in viewDidUnload. All the other data that you allocated in your view controller (as well as the IBOutlets) should be released in the dealloc method. That's because the view can be loaded and unloaded multiple times during the lifetime of a view controller. For example, a view can be unloaded if it is not visible, but the data behind it (in the view controller) still needs to be kept in memory. When both the view and its controller are no longer needed, the dealloc method is called.
The code you posted is correct, but you should also create properties for your outlets, like so:
in your .h file:
#property (nonatomic, retain) UIPickerView *doublePicker;
#property (nonatomic, retain) UIPickerView *color;
// ...etc
in your .m file:
#synthesize doublePicker;
#synthesize color;
// ...etc
There is some debate about this technique (explicitly retaining your outlets and releasing them like this), but it is the technique that Apple recommends:
http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmNibObjects.html#//apple_ref/doc/uid/TP40004998-SW2
The general rule is that you want to call release on anything that you alloc or init. Components that you create in xib's do not need to be released.
OK I'm pulling my hair on on this, it makes no sense so it must either be a bug, or some extremely stupid mistake I'm making.
Here's the situation: I have a UIViewController with a xib file. It has a UIView hooked up to the view property, a UIImageView hooked up to a property called imageView, and a UISegmentedControl hooked up to segmentControl.
Yet in my code, I'm unable to assign an image to the image view. When I NSLog the object, I'm getting the address of 0x0, so it's not associating at all. I have the bindings set up in Interface builder, I've restarted XCode and clean and built the project. Nothing is working and I've wasted a stupid amount of time trying to figure this out at this point. I've also NSLoged the segmentControl object and am getting 0x0 as well. So nothing from the XIB is hooking up with the code, but the XIB itself is loading because the objects are displayed on the screen.
Does anyone have any ideas offhand of what I could be missing? This is such a simple thing, it's incredibly frustrating that it's refusing to work all of a sudden.
Here's the code below, in this case I'm accessing the objects in the setter for projectId, but I also tried accessing the imageView from another class and it didn't work either (and yes I had a #property declaration and synthesize for imageView when I tried).
DiagramViewController.h:
#import <UIKit/UIKit.h>
#interface DiagramViewController : UIViewController
{
NSUInteger projectId;
IBOutlet UIImageView *imageView;
IBOutlet UISegmentedControl *segmentControl;
}
#property NSUInteger projectId;
#end
DiagramViewController.m:
#import "DiagramViewController.h"
#implementation DiagramViewController
#synthesize projectId;
-(void)setProjectId:(NSUInteger)projId
{
NSLog(#"imageView: %#", imageView);
NSLog(#"segmentControl: %#", segmentControl);
projectId = projId;
NSString *filePath = [[NSBundle mainBundle] pathForResource:[NSString stringWithFormat:#"%i_schem", projectId] ofType:#"png" inDirectory:#"project-details/images/diagrams"];
NSData *imageData = [NSData dataWithContentsOfFile:filePath];
imageView.image = [UIImage imageWithData:imageData];
}
- (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
And here's an image of the Interface Builder hookups:
You need to make sure you're doing this in the -viewDidLoad method, otherwise the nib file hasn't actually unarchived the objects and thus they will be set to nil. In particular, you can't access items from the nib within an -init method.
Without seeing your code however, it's hard to say if this is the case for you.
EDIT: Ok, thanks for posting code. When does -setProjectId: get invoked? Are you sure the nib has finished loading at this point? You have no viewDidLoad method in your view controller so it appears you never check for this at any time.
See: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIViewController_Class/Reference/Reference.html
viewDidLoad
Called after the controller’s view is loaded into memory.
(void)viewDidLoad
Discussion
This method is called after the view controller has loaded its associated views into memory. This method is called regardless of whether the views were stored in a nib file or created programmatically in the loadView method. This method is most commonly used to perform additional initialization steps on views that are loaded from nib files.
Sounds like something went wrong when you wired up the IBOutlets.
In IB right click on the UISegmentedControl and post a screenshot so that we can see what you have there. If you see anything 'yellow' then you may have found your problem.
I was just wondering if this approach looks like a good practice for apps with a lot of custom views, for nested PNG graphics and animations that may change based on user interaction. I created a BaseView class that extends UIView
#interface BaseView : UIView {
#protected
BaseViewController *controller;
}
#property (retain) BaseViewController *controller;
#end
and a corresponding controller class which is the primary location which I am putting code to manipulate the view
#interface BaseViewController : UIViewController {
#protected
CGRect drawArea;
}
- (void) drawArea:(CGRect) _drawArea;
- (CGRect) drawArea;
- (void) linkSubviewController: (BaseViewController *) _subviewController;
#end
where "drawArea" is the CGRect used to pass to the view as a frame.
"linkSubviewController" allows you to nest a controller and view as follows :
- (void) linkSubviewController: (BaseViewController *) _subviewController {
[self.view addSubview:[_subviewController view]];
}
In addition I layered another custom pair called "ImageView" and "ImageViewController" which extend BaseView but also store a UIImage and an x,y,w,h
In the "drawRect" drawing methods on views I can check to see if any vars in the self.controller vars have been changed, or assign images, for example :
UIImage *image = [(ImageViewController *)self.controller image];
CGContextDrawImage( ... ) etc
I write most of the loadView methods something like this
- (void)loadView {
ImageView *v = [[ImageView new] initWithFrame:drawArea];
v.controller = self;
self.view = v;
}
The base "initWithFrame" routine contains
self.backgroundColor = [UIColor clearColor];
self.opaque = NO;
So I can load a variety of images with transparent backgrounds without having to assign that each time.
I've been able to use this code throughout my app and it seems to make it easy to write a top level class which assembles the layout of custom items. For animations I've been putting them in the controllers and manipulating self.view.layer.
Basically I am looking for feedback, I am new with Objective-C and the IPhone SDK
There are several issues here:
Using [[Classname new] init...] is incorrect usage of new. Using new is short for [[Classname alloc] init] so you are effectively calling init twice.
Views shouldn't really need to know who is controlling them.
Your view is retaining the controller, and since UIViewController retains its view, you have a retain cycle and neither will ever be fully released.
If you want this type of behavior (whereby a view can delegate its drawing to a parent), try creating a DrawDelegate protocol, have your controllers implement that protocol, and in your view subclass have a non-retaining drawDelegate property:
#protocol DrawDelegate
- (void) drawArea:(CGRect)rect;
#end
#interface BaseView : UIView {
id<DrawDelegate> drawDelegate;
}
#property (assign) id<DrawDelegate> drawDelegate;
#end