I have an array filled with instances of a custom class which contains two String properties, firstname and lastname. Both have a getter method which is equal to the name of the property itself. There is also a method for retrieving the Full name of a person called "getFullName". Consider the example below.
CustomClass *person = [[CustomClass alloc] ...];
person.firstname // Returns "Thomas"
person.lastname // Returns "Meier"
[person getFullName] // Returns "Thomas Meier"
Now I would like to sort this Array by Fullname in a descending Order. I have been looking at some array sorting methods but was not quite able to figure out how to go about this. I guess that I have to create some kind of comparison function which compares two elements, yet how do I tell the SDK which values to pass to this method and where should I place it (in the custom class or in the class where the sorting happens?). Maybe there is another/better way of going about this? Admittedly I have close to none experience with sorting arrays.
Thanks a lot for your help!
Ps. The code should run on iOS 3.2
There are a couple ways to do this. One is to put a comparison method on the custom class. Call it -compare: or something like that. That method should take another object of the same custom type as its input. It should return NSOrderedAscending, NSOrderedDescending, or NSOrderedSame, depending on the result of the comparison. (Inside this compare function is where you look at your own fullName versus the passed-in object's fullName.)
Then you can use NSMutableArray's -sortUsingSelector: method, like this:
[myArray sortUsingSelector:#selector(compare:)];
This works on all versions of iOS. There are block comparison methods available in 4.0+.
Related
I'm developing an iPad App and need some help.
Through a button within my App I want to create one object at a time.
So every time the button is touched one object should be created.
The problem I have is: I want to assign each object a dynamic name to identify this object.
This would be something like: form0, form1, form2, ..., formN.
This Name corresponds to an instance variable within every object.
So the form1 instance has a number attribute which is 1.
But how do I assign this form1, form2, etc. to a new instance?
I tried to initialize a new instance with the return of a method which creates the formX-String:
-(NSString*)giveMeName{
NSString* simpleName = #"form";
NSString* newName = [simpleName stringByAppendingString:[NSString stringWithFormat:#"%d", questionCounter]];
return newName;
}
where questionCounter is a variable which holds the int identifier for both formX and the instance number attribute.
But when I want to initialize a new instance with this function as name it's not working:
TSForm* [self giveMeName] = [[TSForm alloc] initWithInt:questionCounter headline:headlineText intro:introText];
Obviously I got something wrong with the inner working of Objective-C.
Please help me out.
what you're trying to do isn't really possible. One way that you could achieve the affect you're looking for is using an NSDictionary. For every TSForm object you create, you add that object to the dictionary with the key of the giveMeName return value.
So you start by creating your dictionary:
NSMutableDictionary *formDict = [[NSMutableDictionary alloc] init];
Then, every time you create an object, add it to the dictionary:
id *newTSForm = [[TSForm alloc] init]; // Or however you create a TSForm
[formDict setObject:newTSForm forKey:[newTSForm giveMeName]];
Then when you want to pull out the form you're looking for, you just ask the dictionary based on the name you provided:
[formDict valueForKey:nameOfForm]; // nameOfForm is the name provided by giveMeName
Hope this helps!
use NSMutableArray and keep adding your items there.
Even if what you are trying to do is technically possible, that's using tricsk in low-level objective-C runtime and KVC stuff and so on for nothing.
Using a simple NSMutableArray to keep track of all you instances (and using the index in the array to know which form you are dealing with) is the way to go.
I don't think you really need your unique identifier stuff for that (if so, you are probably thinking about your project the wrong way), as long as you have a way in your code to differentiate each form and manipulate them (the first form created will then be at index 0, the second at index 1… of your NSMutableDictionary)
If you really need this special unique identifier anyway for some strange reason, you can still use an NSMutableDictionary and use the unique identifier as your key of your dict and the form as the associated value. But you should probably think twice about your architecture ad the real need for this before, as it seems quite strange app architecture/design to do so based on your description of your needs in your question.
What you are looking for is some kind of variable variable, which don't really exist in objective-C.
This question (Objective C Equivalent of PHP's “Variable Variables”) has some different suggestions for getting similar results.
I want to add items to mutable array from a dictionary. Problem is I want to check existing array items before adding new item. If same item is already there in the array, I want to replace it. else add the new item.
How could I do it?
You could perhaps use an NSMutableSet rather than an NSMutableArray. The addObject method on NSMutableSet will only "add a given object to the set, if it is not already a member."
If you'd like to check membership before adding to the set anyway, you can check the result of:
[mySet containsObject:myObjectFromDictionary]
...which returns a simple BOOL value indicating whether the set already contains an object whose isEqual method returns true when your object is passed to it.
(For a little extra functionality, NSCountedSet will keep track of the number of objects added to the "set" for which isEqual: returns true)
You could compare the result of : [yourArray indexOfObject:yourObject]; against NSNotFound to know if the object is in the array.
It will give you the index of the object to replace, or if it is equal to NSNotFound, you will add it.
Objects equality is tested with isEqual: method.
NSArray class reference.
On the face of it, both Vincent's and Rich's answers are correct.
However, there is a conceptual issue in the original question that hasn't been addressed.
Namely, that "membership in an array" via indexOfObject: (or containsObject: in a set) is ultimately done by comparing the two objects using isEqual:.
If isEqual: returns YES, then the two objects better had damned well be functionally identical in your code or else you have other, significantly more serious, problems in your design and implementation.
Thus, the real question should be "How do I detect if an object is already in an array and not add it?" and Rich's and Vincent's answer are both still correct.
I.e. you should only need to check for presence and, if present, take no action.
(Note that there are esoteric situations where replacement is actually warranted, but they are both truly esoteric and not generally used within the context of a mutable collection)
I recently encountered some problems while trying to sort a set of objects.
The objects I'd like to sort are subclasses of NSManagedObject.
I want to sort the objects by a 'global_index', which is, however, not a property in my model. It's just a getter -(NSInteger)globalIndex {...} each of the objects implements. Inside this method, I do some complex calculation which cannot be done with a simple sort descriptor.
Now, my question: Is there a way to make an NSSortDescriptor sort the objects by the return value of a method?
I really want to use a sort descriptor because it's (IMO) the only way to make use of NSFetchedResultsController's cool features. Or is there a way to tell the controller how to sort the fetched objects? Like...
- (NSArray *)sortObjects:(NSSet *)objects {...}
Thanks in advance!
According to the Core Data Programming Guide,
The SQL store, on the other hand, compiles the predicate and sort descriptors to SQL and evaluates the result in the database itself. This is done primarily for performance, but it means that evaluation happens in a non-Cocoa environment, and so sort descriptors (or predicates) that rely on Cocoa cannot work. The supported sort selectors are compare: and caseInsensitiveCompare:, localizedCompare:, localizedCaseInsensitiveCompare:, and localizedStandardCompare: (the latter is Finder-like sorting, and what most people should use most of the time). In addition you cannot sort on transient properties using the SQLite store.
The easy workaround is to save the order with each object (which is a pain when you need to insert an object between two others, but that's a problem with trying to implement an efficient ordered collection in a database).
Have you tried simply passing #"globalIndex" as the sort descriptor's key? That should work fine since there's an accessor for that key.
You should be able to 'trick' NSSortDescriptor into using your global index method like it would any regular accessor method (the accessor should conform to the expectations of Key-Value Programming). In other words, treat globalIndex as a property of your NSManagedObject subclasses and have the following methods in each one of them.
-(NSInteger) globalIndex {
...
}
-(void) setGlobalIndex: (NSInteger) idx {
...
}
To make things even easier, you can define a subclass of NSManagedObject with your extra methods and extend your subclasses from that (or create a Category, either way). Should work just fine.
I want to populate [MyClass class] from a JSON string.
I use json-framework to get the NSDictionary, and it's dead easy to instantiate and setValue: forKey:... on my data object.
But for more complex data objects with classes as members of MyClass,
ie:
MyOtherClass *classNoTwo
I tried with
Class test = object_getClass(myClass.classNoTwo);
id foo = [[test alloc] init];
But foo is nil/null. The only way I found to get around it is to in my init method of MyClass is to alloc memory for it, and later replace it.
I would also like to know how to get rid of the myClass.classNoTo reference, as I am not supposed to know all the properties in my general parser.
Please don't just tell me to read the documentation, because I've done that, and I can't figure it out.
Thanks in advance
Try calling class_getProperty() to access a property of a particular name and then property_getAttributes() on the property returned by the first function. This will return a string that encodes the property's attributes, including the type. The format of the string is explained in Property Type Strings in the documentation.
Finally, when you have derived the type of the property, use NSClassFromString() to instantiate an object.
Also see the docs for the two functions mentioned for more details.
I have written a very simple dependency injection container called Factory. I do not get your question entirely, but the problems we solve look similar. Take a look at my sources, they are very simple and should get you started. You might be interested especially in the ClassAnalyzer class. It’s just a hack, but you should be able to get what you want from there.
I started to develop my singleton class but I have a problem.
What I want to do is have a search objects containing the values of the search form that I could use in several views.
I want to have the ability to get the singleton in any view in order to perform the search or build the search form.
So I have a set of values with a boolean for each to know if the variable has been initialized by the user or not, cause not all the search fields needs to be filled in.
For example :
NSString name= Bob;
BOOL nameFilled =True;
NSString adress= nil;
BOOL adressFilled=false;
NSNumber numberOfChilds = 0;
BOOL numberOfChildsFilled = false;
So my problem is that I can't retain the boolean in my header file because it's not a class.
How can I do, is there a better solution than what I presented above?
Hope I have been clear
You dont need to have this BOOLean value to see if it is filled, why not just use the object itself to see if it has been initialized so something like
if(name==nil)
//this means i t hasnt been initialized
else
//this means it has
Instead of using int, use NSNumber. Then, for objects that haven't been specified, use 'nil', which is distinct from an NSNumber with 0 as a value.
You don't need to #retain BOOL or other primitive types in Objective-C - you only need use that for object types.
Seriously, don't implement a singleton. It isn't necessary for this application. You should have a model class to handle this.
Try using dependancy injection and/or plist files to save the information. You'll have a much better time debugging and extending functionality.