I am new in the forum and perhaps I asking a silly question, but I would like to know if I am running into a dead end.
I would like to change the name of a mutable array by a string which has been generated programmatically. Is this possible?
I have tried to get empty mutable arrays from an array in case the user needs some, but I think it is not very good solution.
I have not found any reference making some comments on it like .name, .label.text or similar which might help me.
The code is very simple
rowNumber is a string which is generated programmatically
zeroRow is a mutable array which transfers its values to new mutable array.
NSString *newMutableArrayName = [#"row" stringByAppendingString:rowNumber];
NSMutableArray *newMutableArray = zeroRow;
At this point I would like to change the name of the mutable array to the given by newMutableArrayName.
Am I asking for an unpossible thing?
Thanks in advance for your help.
if you want change name mean you can change all object into another NSMutableArray array
just like
NSmutableArray *array = [[NSMutableArray alloc]initWithArray:#"arrayName"];
Related
I'm trying to use some of the new diffing classes built into iOS 13 along with Core Data. The problem I am running into is that controllerdidChangeContentWith doesn't work as expected. It passes me a snapshot reference, which is a reference to a
NSDiffableDataSourceSnapshot<Section, NSManagedObjectID>
meaning I get a list of sections/Object ID's that have changed.
This part works wonderfully. But the problem comes when you get to the diffing in the collection view. In the WWDC video they happily call
dataSource.apply(snapshot, animatingDifferences: true)
and everything works magically, but that is not the case in the actual API.
In my initial attempt, I tried this:
resolvedSnapshot.appendItems(snapshot.itemIdentifiersInSection(withIdentifier: section).map {
controller.managedObjectContext.object(with: $0 as! NSManagedObjectID) as! Activity
}, toSection: .all)
And this works for populating the cells, but if data is changed on a cell (IE. the cell title) the specific cell is never reloaded. I took a look at the snapshot and it appears the issue is simply that I have references to these activity objects, so they are both getting updated simultaneously (Meaning the activity in the old snapshot is equivalent to the one in the new snapshot, so the hashes are equal.)
My current solution is using a struct that contains all my Activity class variables, but that disconnects it from CoreData. So my data source became:
var dataSource: UICollectionViewDiffableDataSource<Section, ActivityStruct>
That way the snapshot actually gets two different values, because it has two different objects to compare. This works, but it seems far from elegant, is this how we were meant to use this? Or is it just in a broken state right now? The WWDC video seems to imply it shouldn't require all this extra boilerplate.
I ran into the same issue and I think I figured out what works:
There are two classes: UICollectionViewDiffableDataSource and UICollectionViewDiffableDataSourceReference
From what I can tell, when you use the first, you're taking ownership as the "Source of Truth" so you create an object that acts as the data source. When you use the second (the data source reference), you defer the "Source of Truth" to another data source (in this case, CoreData).
You would instantiate a ...DataSourceReference essentially the same way as a ...DataSource:
dataSourceReference = UICollectionViewDiffableDataSourceReference(collectionView: collectionView, cellProvider: { (collectionView, indexPath, object) -> UICollectionViewCell? in
let identifier = <#cell identifier#>
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: identifier, for: indexPath)
<#cell configuration#>
return cell
})
And then later when you implement the NSFetchedResultsControllerDelegate, you can use the following method:
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith snapshot: NSDiffableDataSourceSnapshotReference)
{
dataSourceReference.applySnapshot(snapshot, animatingDifferences: true)
}
I watched the WWDC video as well and didn't see this referenced. Had to make a few mistakes to get here. I hope it works for you!
In this post there is the description of "subclass" usage in VBA. I'm looking for the next step of it: when I have first subitem added I want to use it and don't know how.
When I write baseItem(1).itemName it doesn't work.
I assume it's just because that baseItem is not a collection or an array, but I don't know any other way.
Welcome to SO!
In vba like many other languages it is a Property. You call them directly and not numerically, but you need to write GET/LET methods unless the class is public (that is not really encapsulation to simply access directly).
baseItem.itemName would be your call.
But ... As I said before, better that you write accessor(s) to your class as methods.
Here is a guy that sets the tone for OOP in VBA (for me):
https://stackoverflow.com/a/45570268/8716187
He is a driver of the Rubberduck project.
I would ask you to ask yourself if you really need a class, I will often use 4-10 dictionaries of keys holding arrays. I could wrap them in a class but why bother? What I need is a searchable and editable ("array"-the dictionary of arrays).
I have very few class modules written, it seems that one can operate without it many times.
-WWC
I assume it's just because that baseItem is not a collection or an
array...
The baseItem itself is not a collection nor an array. It is just an object of type BaseClass. But this object baseItem wrapps a collection so we maybe could say it is almost a collection.
The problem with this object though is, that as it is defined now in the answer you mentioned, it provides no way how the clients can get to this collection. The class BaseClass needs to be modified so it provides access to this inner collection for the client of this class. With access e.g. some public function is meant which will return something from this collection.
Add something like this to the BaseClass:
Public Function getSubItem(index As Variant) As SubClass
Set getSubItem = subClassCollection.Item(index)
End Function
Now objects which will be at runtime created based on this class definition will provide access to the inner collection via this function getSubItem. The code which will use this function will look like this. So it is now almost that what you are trying to achieve.
Dim name As String
name = baseItem.getSubItem(1).itemName
Debug.Print name ' Prints "Something" in output window
But it could be made even exactly to what you are trying to achieve. When exporting the file of BaseClass.cls and adding Attribute Value.VB_UserMemId = 0 to the very beginning of function getSubItem and importing it again to project.
Public Function getSubItem(index As Variant) As SubClass
Attribute Value.VB_UserMemId = 0
Set getSubItem = subClassCollection.Item(index)
End Function
Now you can really write your code exactly that way you wanted. HTH
Dim name As String
name = baseItem(1).itemName
Debug.Print name ' Prints "Something" in output window
For more information about Creating A Default Member In VBA have a look e.g. here.
I'm working on a C++ Metro style app and have to pass a string by reference (somehow). At first, I passed the String^ which doesn't work because strings are immutable how I have found out.
What would be a proper way to pass a string by reference?
Edit: OK, it seems that it's not that easy since the answers and comments suggest to use return values. But as far as I think this is not applicable in my situation: In this Metro app I have two pages and a string should be "shared" across those two pages.
So in the main page I do this in a click event:
this->Frame->Navigate(newPage, this->TestString);
In the OnNavigatedTo event of the second page I convert the second parameter to a String^ and change it. Then I use this->Frame->GoBack() to navigate back to the first page. There I'd like to have access to the changed string. Unfortunately, GoBack() doesn't allow to pass any parameters as far as I know.
You can use a tracking reference:
void ModifyTheParameter(String^% value) {
value = gcnew String("Blah");
}
That would modify the original variable you passed in as parameter (see MSDN for more info and examples). It would then be used just as any other method taking a String^ parameter.
But if possible, avoid using tracking references as parameters. I'd recommend just returning a String^ and assigning that to the original variable.
Yet another possibility: You could just create some kind of View-agnostic DataModel that contains your String (and possibly other data that you work with). You could then pass that DataModel to your method. Since the DataModel variable isn't changed (just a property of it), you wouldn't need to pass a reference to it.
See below an example of a function f which takes as a parameter a reference to a std::string.
std::string someString;
void f(std::string& s);
f(someString);
I recently got started on Core Data, thanks to this tutorial :
http://www.techotopia.com/index.php/An_iPhone_OS_Core_Data_Tutorial
My question is about handling types other than String.
For example let us say I want to add to the existing fields (name,address and phone : which are all String(s) in the example presented), the weight which I want to be a float in my entity.
How would I change the code to handle a float instead of a String ?
I already tried to change one of the fields to float in my entity. First letting the code as it is, and the program crashed. Then I tried to adjust the code in some ways but it did not work. I have the feeling it must be simple, but I can't get it right.
Thanks for any tip.
you should use NSNumber for float (and access it with [myNumber floatValue]).
You can't use primitive values in CoreData entities - only objects. ( NSString, NSDate, NSNumber, NSData ... )
Hope this helps.
Having a problem with objects, not needed any more but still having references.
Result: size of allocated memory is constantly growing due to not collected objects.
How to solve this sort of problem?
Is there any way to find objects with only one reference, or objects with lifetime more than some value? Or any another solution?
Using Lua 5.1 and C++ with luabind.
Thanks.
As someone is mentioning here, you can try using weak tables.
If you have some code like this:
myListOfObjects = {}
...
table.insert(myListOfObject, anObject)
Then once anObject stops being used, it will never be deallocated since myListOfObjects still references it.
You could try removing the reference in myListOfObjects (setting the reference to nil) but a simpler solution is declaring myListOfObjects as a weak table:
myListOfObjects = {}
setmetatable(myListOfObjects, { __mode = 'v' }) --myListOfObjects is now weak
Given that setmetatable returns a reference to the table it modifies, you can use this shorter idiom, which does the same as previous two lines:
myListOfObjects = setmetatable({}, {__mode = 'v' }) --creation of a weak table
I'm not certain about integrating it with C++ but it sounds like the garbage collector isn't being given an opportunity to run.
In your lua you could try explicitly invoking it and see if that helps. There is a function in the core apis collectgarbage(opt [, arg]).