(WebService_1AppDelegate*)[[UIApplication sharedApplication] delegate]
here - in above statement "WebService_1AppDelegate" is my application name.
But i don't understand what does this statement mean.
Please explain me - briefly this statement.
I will be thankful.
Thanks in advance for helping me.
An AppDelegate is a singleton that every iPhone program has. This class is responsible for receiving many system calls such as applicationDidFinishLaunching, applicationWillTerminate etc. It is the entry point for an iPhone app.
Each app defines their own AppDelegate and thus WebService_1AppDelegate is yours. You can define your own methods/properties there and when required cast the AppDelegate returned from [UIApplication sharedApplication] to access your methods/properties.
WebService_1AppDelegat *appDelegate = (WebService_1AppDelegate*)[[UIApplication sharedApplication] delegate];
[appDelegate yourCustomMethod];
That statement only make sense if you have a class named WebService_1AppDelegate. Then it's casting the return value of that method (which is the application delegate) to that type. If that is indeed the name of your application delegate class then that cast is superfulous,
Are you trying to figure out what "AppDelegate" is in an iPhone app? If so, AppDelegate acts as a central storage medium for your application that allows you to share data across all of your controllers seamlessly. If you're familiar with web development it is just like a Session variable.
Related
Due to a bug/problem with ZBar and iOS 7 we can not create, destroy and recreate a view controller that's used for scanning. So we need to keep an permanent and global instance of it to be accessed by several different views.
In the current solution the scanner view instance is a member of the app delegate and instanciated when the application starts. When it needs to be displayed it is accessed by [[UIApplication sharedApplication] delegate].
This is a forced solution but I still want it to be as descent as possible. Is there a better place to put the scanner view controller?
Make a Singleton class for your scanning
Better you put in .pch file,
#define MY_APP_DELEGATE ((AppDelegate *)[UIApplication sharedApplication].delegate)
I am currently developing an application for the iPhone. The appdelegate shows a splash-screen while I'm caching data (e.g. NSDictionary) for use in a certain view. What is the best way to call this data from the view I need it in? I don't think passing it along as a variable from view to view until it reaches the view is a correct way to do this.
App Delegate (with Splashscreen that should cache the data to NSDictionary)
|
View A
|
SubView
|
Final View (here I want to use the cached data)
Thanks :-)
If the NSDictionary that you're caching the data in is an ivar of your App Delegate you can access it from anywhere in your app using the following lines:
myAppDelegate *delegate = (myAppDelegate *)[[UIApplication sharedApplication] delegate];
NSDictionary *myData = [delegate cachedData];
Hope that answers your question.
If you have an object that will never be released throughout the entire life of the app, and really want it to be accessible from absolutely anywhere in the app (say, so that a simple debug NSLog from absolutely anywhere in the code can print it's state), then that's what global variables are for. Just assign a global variable with a reference to the object. If you don't mind generating nearly equivalent but microscopically slower and larger code, then assign it to an instance variable in the app delegate with a suitable getter.
Note that using global variables is a violation of encapsulation that won't be very scalable, maintainable or suitable for unit testing, but is perfectly suitable for a small app which is not much larger than most objects would encapsulate anyway.
Using the "Tab Bar" template in Xcode 4, each ViewController is created automatically, so I don't have the chance to set any properties on a ViewController as it's created. I want each ViewController to have access to an object (an instance of FMDB's FMDatabase).
There are a number of questions on StackOverflow relating to this already, but some are assuming that you are creating the VC's by hand, and others recommend using the AppDelegate as a mediator:
MyAppDelegateClass *appDelegate = [[UIApplication sharedApplicaton] delegate];
myLocalProperty = appDelegate.someDataModelProperty;
The above seems rather "hacky" to me. Is there a better way to access a single object from multiple ViewControllers?
Most probable implementation of FMDB's Data base would be to implement it as a Singleton and access it through out the application. Is there any reason for not doing so ?
This link should help you in doing so:
How do I make FMDB's database a singleton
To expand on KKK4SO's answer, you could implement the Database as a singleton. Then, have all of your UIViewControllers be a subclassed UIViewController that contains methods to access and modify the Database singleton.
MyAppDelegateClass *appDelegate = [[UIApplication sharedApplicaton] delegate];
myLocalProperty = appDelegate.someDataModelProperty;
There is a spelling error in this code 'sharedApplicaton' is incorrectly spelled it should be 'sharedApplication'.
Shame on me for copy and pasting! Anyway this will work for a quick and dirty way of passing data between ViewControllers etc.
I was reading a post on accessing the app delegate using shorthand with a macro here
Short hand for [[UIApplication sharedApplication] delegate]?.
The solution to the problem provided was to define the following macro in the app delegate header.
#define AppDelegate (YourAppDelegate *)[[UIApplication sharedApplication] delegate]
My question is how can I do this with a project that has multiple targets seeing as the appdelegate name would be different for each one?
T he #define macro is just a string substitution facility in the pre-processor, so I don't think there is much you can do short of defining another macro that has the name for each target's app delegate.
The savings in typing to abbreviate the app delegate is not going to be very much, and imo probably not worth the time to do it.
And I will editorialize further to say that if you're making enough references to your app delegate to justify abbreviating, I think you need to move some code out of the appDelegate into better factored (possibly singleton) classes. My 2 cents.
I have been making a few apps here and there, and I know my way around. What has always confused me is accessing global attributes, and where the best place to set them are. I have a few questions about accessing things and how to access them.
Do you have to include your application delegates header file into any other other file you want to access it in? Say I have a view controller, that I would like to use, do I need to include the .h inside my view controller's .h? Or can I set the:
#class AppDelegate;
Can you only access the delegate by typing out:
[UIApplication sharedApplication].delegate
EACH and every time? Is that something I just have to get used to? Or could I set the following in my implementation in each .h:
AppDelegate *delegate;
And inside the init function, put the singleton instance to that variable?
Sorry if this was off structure, but I think it's a logical question people have a problem encountering and solving.
Maybe you need to reconsider how you are using the App Delegate? It sounds to me like perhaps you are not making a very good class design.
Regardless, here's a way to make it easy. Don't put this in init just use it when you need it.
MyAppDelegate *delegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
Naturally, replace MyAppDelegate with the actual class name of your app delegate.
Another possibility is to add the code to use a properly casted app delegate reference as a #define in the app delegate header file, so after including it you can do something like:
MYAPPDELEGATE.customProperty = blah;
However I tend to favor just writing out the line that John presented, as use of #defines confuses code completion which I find more annoying than just typing the line.
As also mentioned, if you have a ton of references to the app delegate you may want to restructure to keep some of those references closer to home.