I'm learning Delphi Prism, and i don't find how to write the following code with it :
type
TRapportItem = record
Label : String;
Value : Int16;
AnomalieComment : String;
end;
type
TRapportCategorie = record
Label : String;
CategoriesItems : Array of TRapportItem;
end;
type
TRapportContent = record
Categories : array of TRapportCategorie;
end;
Then, somewhere, i try to put items in the array :
rapport.Categories[i].Label:=l.Item(i).InnerText;
But it doesn't work.. Can someone enlight me?
Thanks!
You didn't specify exactly what "didn't work". You should include the error in questions like this.
Arrays are reference types, and they start out with the value nil. They need to be initialized before elements can be accessed.
You can do this with the new operator:
rapport.Categories = new TRapportCategorie[10]; // 0..9
Arrays are quite a low-level type. Usually it's better to work with List<T> instead.
So you'd declare:
Categories: List<TRapportCategorie>;
But lists also need initializing, using the new operator. Also, modifying the return value of the indexer on a list containing a value type will be modifying a copy, not the original, which leads to the next point.
Records are usually not the best data type for representing data, as they are not reference types; it's very easy to end up modifying a copy of the data, rather than the original data. It's usually best to use classes instead, where you can put all the initialization code (such as allocating the array or list) in the constructor.
Related
can someone tell me what is the difference between coping one transaction(item) to the another like in examples bellow (add_method_port_1 and add_method_port_2):
add_method_port_1 (added_item: item_s) is {
var new_item: new_item_s;
gen new_item keeping {
it.my_trans_s == added_item.as_a(t_trans_s);
};
};
add_method_port_2 (added_item: item_s) is {
var new_item : new_item_s = deep_copy(added_item.as_a(t_trans_s));
};
Where new_item_s looks like:
struct new_item_s like item_s {
%my_trans_s: t_trans_s;
};
Thanks,
Andrija
Actually, the results of the two methods are different even if the assumption mentioned in Rodion's answer does hold.
With the first method, new_item points to the same my_trans_s object as the original added_item, because the constraint it.my_trans_s == added_item.as_a(t_trans_s) means pointer equality.
With the second method, new_item points to a copy of the original my_trans_s, because deep_copy copies everything recursively.
In this specific example, assuming that new_item_s has only one field my_trans_s, there is no difference in outcome.
In practice, the meaning and the goal of "gen keeping" and deep_copy is quite different:
gen keeping, even with '==' constraints, practically assignments, means random-constraint generating an item executing iGen logic engine; if this is a struct then pre_generate and post_generate methods are invoked, and all the fields not mentioned in 'keeping {}' block are also randomly generated according to existing constraints and their type properties. It is usually used to create a new item for which only some properties are known.
deep_copy creates an exact copy (up to some minor nuances) of the given struct, and if it has fields which are also structs - copy of all connected graph topology. There is no random generation, no special methods, no logical engine executed. Usually it used to capture the data at some point for later analysis.
In other words, if the assumption "new_item_s has only one field my_trans_s" is wrong, the result are going to be very much different.
I have solved the issue now, thanks for your help. I shouldn't have tried to save arrays with UITextViews, but I should have saved their text as strings instead. Here was the original question:
I have tried a lot, and googled a lot, but I can't solve this problem on my own. Whenever I try to save an array in userdefaults, it just is not working. I get the following error:
Thread 1: "Attempt to insert non-property list object (\n "<UITextView: 0x14001f800; frame = (0 0; 355 180); text = 'D'; clipsToBounds = YES; gestureRecognizers = <NSArray: 0x600003f01d10>; layer = <CALayer: 0x6000031c83e0>; contentOffset: {0, 0}; contentSize: {355, 30}; adjustedContentInset: {0, 0, 0, 0}>"\n) for key content"
I don't know what a non-property list object is. And I do not know how to solve the problem. Below is the lines of code that do not work.
var contentList: [Any] = []
let cl = defaults.array(forKey: "content")!
if cl.count != 0{
contentList += cl
}
contentList.append(label)
defaults.setValue(contentList, forKey: "content")
If I take out the last line of code by turning it into a comment everything runs just fine. How should I replace that line of code? I essentially want to save an array of UITextViews and make it larger every time I call a fucntion (this code is part of a larger function). The reason why I have created another two lists (cl and contentList) is that it helps me with a problem down the line. What I cannot understand however, is why the last line of code doesn't work. If anyone has any ideas, please help me, it would be much appreciated.
Use only String as stated in comments :
var contentList: [String] = []
let cl = defaults.array(forKey: "content")!
if cl.count != 0{
contentList += cl
}
If lbText = label.text {
contentList.append(lbText)
defaults.setValue(contentList, forKey: "content")
}
You can only store a very limited list of data types into UserDefaults, commonly referred to as "property list objects" (Since property list (or plist) files will only store the same data types.
To quote the Xcode docs on UserDefaults, in the section titled "Storing Default Objects":
A default object must be a property list—that is, an instance of (or for collections, a combination of instances of) NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary [or Data, String, NSNumber, Date, Array, or Dictionary types in Swift.] If you want to store any other type of object, you should typically archive it to create an instance of Data.
(I added the equivalent Swift types to the above quote in square brackets, since it looks like Apple hasn't updated it for Swift.)
That's worded a little awkwardly. The idea is that you can only store data of the types listed. Because the Array and Dictionary types are "container" types, you can store any combination of arrays and dictionaries that contain combinations of any of the above types. For example, you can store an array that contains a dictionary, 3 dates, 2 floats, a Double, some Data, and 2 arrays, and those dictionaries and arrays can contain other dictionaries and/or arrays.)
It is almost always wrong to archive UIView objects like UITextViews. You should save the text properties of your text views instead.
If you want to manage a vertical stack of UITextView objects, I suggest adding a vertical stack view to your user interface, and then writing code that adds or removes UITextView subviews to your stack view. You should be able to find plenty of examples of adding and removing objects from stack views online. (It's really easy.)
If you want to manage a scrolling list of feeds of arbitrary length, you might want to use a table view or collection view instead. Those require that you set up a data model and implement a "data source". That takes a little practice to get right, but is very powerful.
I'm creating a button that when clicked adds the current date and time to an array but when I try to append to the array it only appends once and not repeating the process
the Entries struct:
struct Enteries {
var dates:[String] = []
}
convert date to String:
func DateConverter(){
format.timeZone = .current
format.dateFormat = "yyyy-MM-dd HH:mm"
dateString = format.string(from: currentDate)
}
The function that appends: also its called later whenever an IBAction is triggered
func AddToDatabase () {
var entery = Enteries()
entery.dates.append(dateString)
print(entery.dates)
}
`
Yikes, there's a lot going on here.
First of all, Swift's convention is to use lowerCamelCase for functions. Only type names should be UpperCamelCase.
Secondly, function names should be verbs or verb phrases, type names should be nouns. If I saw DateConverter in some code, I would expect it to be a type. It's an UpperCamelCase noun, that's how types should be named. But yours is a function (which would be a total surprise to every other Swift developer, because it violates the expectations they've built up from Swift's naming conventions), that function should probably be called parseDate.
Which way does DateConverter convert? From String to Date, Date to String, or both? What's its input? What's it's output? These things should be obvious from a good function name, but are totally unknown here without looking at the implementation.
Critically, the DateConverter function doesn't take input from parameters, and doesn't return a result, instead it takes input from a side effect (accessing the variable currentDate) and returns a result via side effect (writing to an a variable dateString). This is really bad, for several reasons:
It's not reusable. You have no way to use this date parsing code somewhere else without copy/pasting it, which is how code duplication and complexity arise. If you ever decide to change the date format in your app, you won't have a central source-of-truth that you can change, instead you'll have to manually hunt down every copy of this function, and change it, hoping you don't miss any. Not good.
It's not thread safe
It's more complex than a simple function that has type (Date) -> String. It obfuscates what's going on.
It defies peoples' expectations, without justification.
Enteries.dates has a default value of [], which doesn't seem to be a good idea if you're going to be appending to it as soon as you create it. Instead, take the array via an initializer parameter.
Enteries.dates has type [String]. Why?! You already have Date objects, store those!
They're smaller (in memory)
They're presentation-agnostic, meaning you can properly format them for different interfaces and different locales at a later time, as necessary
They support date math. I often see people storing dates as strings, and ask questions like "How do I sort my array of dates?" (which are actually stored as strings), "How do I add 1 day to "2019-12-24", and they start doing funky parsing, splitting, joining, and it's all just an absolute mess
Here's how I would improve this code:
struct Entries {
var entries: [Entry]
}
struct Entry {
let date: Date
}
// Call this from your view layer, only when you're about to present a `Date` to a user.
func parse(date: Date) -> String {
let df = DateFormatter()
df.timeZone = .current
df.dateFormat = "yyyy-MM-dd HH:mm"
return format.string(from: currentDate)
}
var entries = Entries(entries: [])
func addToDatabase(entry: Entry) {
entries.append(entry)
print(enteries.entries)
}
you are creating a new entery object eveytime the function is called. SO its creating a new object everytime. Declare your entery object outside the function.
var entery = Enteries()
func AddToDatabase () {
entery.dates.append(dateString)
print(entery.dates)
}
Is there any way in Matlab R2011b to apply logical-indexing to object-arrays? The objects which fulfill specific condition(s) regarding their properties should be returned. At best the solution is also possible with object-arrays that are a property of another object (aggregation).
In my project there are a lot of entities which have to be identified by their manifold features. Matlab objects with their properties provide a clear data foundation for this purpose. The alternative of using structs (or cells) and arrays of indices seems to be too confusing. Unfortunately the access to the properties of objects is a little bit complicated.
For Example, all Objects in myArray with Element.val==3 should be returned:
elementsValIsThree = myElements(Element.val==3);
Best solution so far:
find([myElements.val]==3);
But this doesn't return the objects and not the absolute index if a subset of myElements is input.
Another attempt returns only the first Element and needs constant properties:
myElements(Element.val==3);
A minimal example with class definition etc. for clarification:
% element.m
classdef Element
properties
val
end
methods
function obj = Element(value)
if nargin > 0 % to allow empty construction
obj.val = value;
end
end
end
end
Create array of Element-Objects:
myElements(4) = Element(3)
Now myElements(4) has val=3.
I'm not sure I understood the question, but the logical index can be generated as
arrayfun(#(e) isequal(e.val,3), myElements);
So, to pick the elements of myElements whose val field equals 3:
elementsValIsThree = myElements(arrayfun(#(e) isequal(e.val,3), myElements));
I need to create a class containing an array of record objects but trying to use SetLength raise an Access Violation errror.
Consider the following example of a tree object with fruits.
type
TFruit = record
color: string;
weight: double;
end;
type
TObjectTree = class
Public
Fruits: array of TFruit;
constructor Create;
procedure AddFruit;
end;
In the implementation, when trying to resize the array of Fruit objects or initializing to nil generates problems.
constructor TObjectTree.Create;
begin
inherited Create;
Fruits:=nil; //Raises an error
end;
procedure TObjectTree.AddFruit(FruitColor: string; FruitWeight: integer);
begin
SetLength(Fruits, Length(Fruits)+1); //Raises an error (when I comment Fruits:=nil; in the constructor)
Fruits[Length(Fruits)].color:=FruitColor;
Fruits[Length(Fruits)].weight:=FruitWeight;
end;
How can I use dynamic arrays in a class?
Replace
Fruits[Length(Fruits)].color:=FruitColor;
Fruits[Length(Fruits)].weight:=FruitWeight;
with
Fruits[High(Fruits)].color:=FruitColor;
Fruits[High(Fruits)].weight:=FruitWeight;
then it works.
Something tells me you've neglected to create an instance of TObjectTree. You've declared a TObjectTree variable, but you've either not called TObjectTree.Create, or you've called it directly on the variable you declared instead of assigning a new value to that variable:
var
Tree: TObjectTree;
begin
// This is wrong.
Tree.Create;
// This is right.
Tree := TObjectTree.Create;
Without properly instantiating TObjectTree, there is no valid memory to back the Fruits field you attempt to use, so assigning a value to it gives an error.
As an addition to the answers of iamjoosy and Rob Kennedy, I would code this like so:
procedure TObjectTree.AddFruit(FruitColor: string; FruitWeight: integer);
var
NewCount: Integer;
begin
NewCount := Length(Fruits)+1;
SetLength(Fruits, NewCount);
Fruits[NewCount-1].color := FruitColor;
Fruits[NewCount-1].weight := FruitWeight;
end;
It is clearer, in my view, to call Length() just once.
You do not need to assign Fruits := nil in the constructor since that happens automatically. All fields are zero-initialised when an object is instantiated. That said, Fruits := nil should not raise an error. If it does it is probably a result of a memory corruption due to the out-of-bounds array accessing.
A further point to make is that enabling range checking would have resulted in an informative error that would have explained the problem. This is much more helpful than relying on access violations. I can't recommend range checking highly enough.
Finally, the SetLength(..., Length(...)+1) pattern typically leads to very inefficient memory usage and can lead to performance problems for large lists. If you have Delphi 2009+, I would recommend using TList<TFruit> instead.