I am using App Delegate object in different classes. I want access it in whole project. Am define this object in Prefix.pch file as
#define Appdelegate (AppDelegate *)[[UIApplication sharedApplication] delegate]
but problem is that Appdelegate variable does not access App delegate variable.
it Shows error.
but if am use this code works fine
AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
appDelegate.variablename;
Am I doing it correct or is there a way of doing what I do?
thanks in Advance.
Should be:
#define Appdelegate ((AppDelegate *)[[UIApplication sharedApplication] delegate])
// ^----------------------parenthesis--------------------------^
As this question and its answers demonstrate, leaning on the preprocessor is usually a bad idea.
It's easy to get things wrong. We all develop good instincts for operator precedence, but the preprocessor has no clue. To defend against unexpected context problems, you often need to wrap everything in extra parens and braces.
It's easy to convince yourself that you're doing one thing when the code is doing another. When things break, neither the compiler's error messages nor the debugger are likely to help much.
Most important, the preprocessor can let you take a bad idea and spread it pervasively through the program. The bad idea here is using the App Delegate globally.
Global variables are a code smell. Efforts to make global variables even more global by stuffing them into precompiled headers are a code smell. If the framework thought you should have access to the AppDelegate from everywhere, you wouldn't need to jump through these (modest) hoops!
So, when tempted to do something like this, it's nice to know the preprocessor is there and the pch headers are there, but keep in mind that you're fighting the framework and almost certainly making a design error. That might be OK in your context, but it's something to know.
You need to import AppDelegate file where you are declare delegate macro:
#import "AppDelegate.h"
And then define
#define Appdelegate (((AppDelegate *)[[UIApplication sharedApplication] delegate]))
Related
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.
The first approach that comes to my mind is to put the singleton object in the appDelegate object as property. In this way you can access it from anywhere using
#import "myAppDelegate.h"
// ...
[[(myAppDelegate *)[UIApplication sharedApplication] delegate] SingletonObj]
The downside is you have to explicitly cast and import the header of your delegate to tell the class you're working with that SingletonObj is actually a property of the delegate. And I think this makes the code smell a little.
The second approach is to create a legit singleton class. This, however, require more work. And I personally think that one Singleton class, is more than enough.
I'm not a programmer so I would greatly appreciate corrections on my reasoning, and opinions on the subject.
Singletons are most often handled in a class via a method like +sharedInstance.
Here is a good write-up.
I found a xcode template for easy singleton generation on the net.
Best practice is to only ever put UIApplicationDelegate-related things in your AppDelegate class. Evarr.
Decide if you really need a singleton. If you do, just make a legit singleton class. It will be easier in the long run; did you notice how long it took to type that monster of a line, where you tried to get the singleton object out of the AppDelegate? Agh.
(Also, just a little bit of idiom: classes start with a capital letter, and methods start with a lowercase letter; hence, you problem meant [[(MyAppDelegate *)[UIApplication sharedApplication] delegate] singletonObj].)
(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.
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.