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Hi Leslie,
I prefer the first. The second creates its own SomeClass instance, without any parameters or specialization. So creating two AnotherClass() instances would cause exactly the same things to happen twice. The first snippet makes much more sense to me.
From your snippet it isn't really clear why you need two classes in the first place. I also expect real names for the classes would make things more obvious.
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Luc Pattyn wrote: From your snippet it isn't really clear why you need two classes in the first place. I also expect real names for the classes would make things more obvious.
It was a quick and dirty example. I'll try to do better.
I've been doing iPhone programming, and using the Model/View/Controller pattern (or at least one variation of it) is encouraged by the architecture. Say we have a model.
class Model
{
public:
};
The controller uses the model, but should it also be responsible for creating it? Assume for the sake of argument that an instance of the model isn't used any where else besides the controller class. I guess it then becomes academic, but I seem to remember reading some where that objects shouldn't use the objects they create. I can't remember why or where I read that.
I was wondering if this:
class Controller
{
public:
Controller(Model *model)
{
this->model = model
}
};
Is better than this:
class Controller
{
public:
Controller()
{
this->model = new Model();
}
};
Maybe the reasoning as to why the first approach is better is that if we use polymorphism, we can switch out which model is used by the Controller; we can't do that in the second example without changing the Controller class.
Also, maybe as a general rule factory code should be seperate from the rest of the code?
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I have no authority on the MVP/MVC subject nor on iPhone, however here are some thoughts:
1.
Leslie Sanford wrote: objects shouldn't use the objects they create
does not make much sense to me. When I create objects I want to use them, or pass them on for others to use them.
2.
Leslie Sanford wrote: factory code should be seperate from the rest of the code
I second that. The purpose is you can (and often have to) change the factory, however you don't want to touch the code in the object's users.
3.
You need some overall code anyhow (say the static Main method in a C# app); so it can create Model, View, and Controller; in the right order; and pass the required ones as parameters to the other constructors. Maybe you even want interfaces, rather than actual classes passed in.
So definitely your #1 approach for me.
Suggestion: have a look at some other iPhone apps, there's bound to be some here in CP articles.
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The decision you have to make is all about dependency. The first alternative implements a loose dependency between the controller and model. In the second alternative, the dependency is hard coded into the controller. Therefore I definitely vote for the first one.
However, I am surprised that you are given this choices at all. Without knowing much about IPhone UI programming, all the other UI frameworks I know have some kind of preferred architecture model. While you can program "around it", by doing so you exclude yourself from using certain techniques or tools which could make your application unusable by third parties or make things like customization, styling, themeing etc... exteremly difficult. For example, Microsoft's presentation frameworks like WPF or Silverlight do not enforce a specific model but if you choose not to follow the guidance, you exclude yourself from things like easy data binding, dynamic UI composition, easy cooperation with designer tools and much more...
So follow Luc's advice and have a look at some exemplary IPhone applications or even better on Apple's guidelines about the architecture model for UI.
Cheers,
Paul
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I'm looking for ideas/guidance on how to design serverside functionality for interacting with a database. My situation is pretty typical. I have PHP "scripts" that receive request variables. Based on the parameters passed to it, the script queries a database, formats the returned data in some way, and returns it, usually in JSON format.
I've tried taking various approaches to managing the code for this. For example, I've written sets of functions for querying the databse, e.g. getCustomerByName, getProductsByPrice, etc., with each of these functions containing the necessary SQL code. The problem is that you can have an explosion of these types of functions. And sometimes the queries can get quite nuanced so that you wind up with long named functions like getCustomerByNameAndCountry. This approach doesn't seem to scale well, and has made me a little disillusioned with encapsulating SQL queries in functions.
I was thinking about making functions that are more generalized. Something like getCustomer($columns, $where, $orderBy). In other words, parts of the SQL query would be defined outside of the function and passed in. As long as everything is escaped properly, this should be safe. This approach would mean put the responsibility of parsing the request parameters, determining exactly what is being asked for, and then transforming the request parameters into partial SQL statements that would be passed to general functions for performing the actual query.
But then maybe the functions aren't needed at all?
Anyway, I'm relatively new to DB/severside programming; I've been doing it for less than a year, and I'm still struggling with how to structure a system. Any thoughts are welcome.
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In my experience, when it comes to "combinatorial explosions", your projections (i.e. $columns) and ordering (i.e. $orderBy) are not as much a problem as the query conditions themselves: you will need to hard-code nearly as many values passed for the $where as the number of 'get<...>by<...>' functions you previously needed to code.
The solution I've been using is generating my 'where' clauses dynamically. This way, instead of pre-made 'where' clauses you'd build collections of uniform items from which your SQL can be generated. For example, a list of name-value pairs could be used to generate a conjunction like name1=value1 AND name2=value2 AND ... nameN=valueN. More advanced solutions include use of expression libraries, such as LINQ's Expression in .NET, to formulate composite queries of arbitrary complexity (with 'OR's, 'AND's, 'NOT's, and function calls).
P.S. Any time you generate SQL dynamically you should be very careful to avoid the SQL Injection Trap; other than that, you should be OK.
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I writing some application that find ( according to some question ) information about some person ( lets say that the information are weight, hight and age of the person ).
In the other hand i have product list ( can be very big one ) and according to the product information i need to find the best matching between the person information and the product ( the product information that i have are water part, nitrogen part and ext. )
I can't use flow chart algorithm or Breadth-first search because the number of the product is dynamically ( read the product list from DB ... )
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Since much detail has been left out (which is expected, given that it's an architecture forum) I'd make an assumption that finding the "best matching" can be expressed mathematically as finding an extremum of a function of some sort, and that the product list is stored in a SQL database.
Suppose that the quality of the match can be evaluated as a function MatchQuality. When you get parameters of a person for whom you're finding a matching product, you can build a SQL query that corresponds to your MatchQuality function and the parameters of the given person. Consider this silly example: suppose your MatchQuality(age, weight, water, nitro) = age^2/nitro + water/weight, and the match is best when MatchQuality is highest. A query for the best product comes in: weight=170lb, age=65yr. The query below returns the best match:
select top 1
from Products
order by (65*65)/nitro + water/170 desc
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Hello friends,
Recently, I have cleared MCTS(70-502)-WPF certification, and have already cleared the MCTS(70-536) which credits to a MCTS certification to me now.
Now, I have been looking forward to MCPD. As there are no training kits/books available for MCPD, as is present for MCTS.
Need some guidance in preparing for the MCPD exam. I do not have much experience in designing the applications and wanted to learn the same.
Please guide me on how to develop an appetite for designing the application without losing focus and which are the best books/tutorials to refer for designing a GUI windows based applications. Also, how to prepare for MCPD.
Apologies if I have posted this question in the wrong forum.
Thanks in advance,
Praveen Raghuvanshi
Software Developer
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Rags1512 wrote: As there are no training kits/books available for MCPD
This list[^] would seem to contradict that assertion.
Just say 'NO' to evaluated arguments for diadic functions! Ash
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Thanks Rich for the information.
However if you visit this page http://www.microsoft.com/learning/en/us/exam.aspx?ID=70-518&locale=en-us#tab3[^] , and move to the Preparation Materials tab, you can see that there are no Microsoft book available. I am basically targeting MCPD 70-518.
I would you appreciate if you can guide me in terms of MCPD 70-518.
Also, If someone can guide on how to learn and adapt designing of application.
Thanks,
Praveen Raghuvanshi
Software Developer
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Sorry, but I don't work for Microsoft. The link I gave you was the result of a Google search which offers various web sites with information that may help.
Just say 'NO' to evaluated arguments for diadic functions! Ash
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I was reading a coding style document put out by a certain company, when I came across an odd claim in their justification for their FOR loop style. I was wondering if someone could shed some light on this for me:
The document states that a pre-increment operator is preferable to a post-increment operator because post-increment introduces potential inefficiencies when iterating over an object. The example they give is C++ code:
std::vector v;
for (std::vector::const_iterator i = v.begin(); i != v.end(); ++i)
{
}
...and an identical sample that uses "i++" instead of "++i" for the increment operation.
I see no difference in the efficiency. Whether using ++i or i++, "i" is going to contain its new value before the termination condition is evaluated. The loop will be iterated an identical number of times.
I was wondering if someone could shed some light on what it is that I'm missing here, or if perhaps the assertion that pre-increment is more efficient. Is there some other language or platform that treats identical FOR loop sytax in a wildly different manner?
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i++;
++i;
In reality most modern compilers will optimise the code so it is of little consequence to the majority of programmers. It only becomes an issue if your program needs to run at sub-atomic speeds.
Just say 'NO' to evaluated arguments for diadic functions! Ash
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Their statement is utter non-sense, as Richard already explained.
And furthermore they should concentrate on the termination test of the for loop; v.end() is getting evaluated over and over, not necessarily what is required (depends on how "alive" v is).
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Yeah, I HATE seeing that in loops. Coders think its efficient because they have less code without thinking that a function call in the conditional part of the loop gets called every itteration.
"It is a remarkable fact that despite the worldwide expenditure of perhaps US$50 billion since 1990, and the efforts of tens of thousands of scientists worldwide, no human climate signal has yet been detected that is distinct from natural variation."
Bob Carter, Research Professor of Geology, James Cook University, Townsville
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I was going to say you should take a look at this code disassembled to see if there is any inefficiency, but Richard has answered that already.
"It is a remarkable fact that despite the worldwide expenditure of perhaps US$50 billion since 1990, and the efforts of tens of thousands of scientists worldwide, no human climate signal has yet been detected that is distinct from natural variation."
Bob Carter, Research Professor of Geology, James Cook University, Townsville
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As Richard and Luc have explained, there is no difference in this case. What they MAY have been referring to is this:
a[i++] = x;
b[++j] = z;
In a primitive CPU, the code might compile to something like this (much liberties taken in pseudo assembler code!)
load r1,i
add r1,=a
load r2,x
store r2,(r1)
load r1,i
inc r1
store r1,i
load r1,j
inc r1
store r1,j
add r1,=b
load r2,z
store r2,(r1)
In the early days of C, there were machines that stupid, but by the time C++ came along, the "issue" was long gone. Essentially, it's about using ++i in an expression compared to using i++. If the value of the side effect isn't used, there's no real difference.
Cheers,
Peter
Software rusts. Simon Stephenson, ca 1994.
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Pre-increment's return value is the iterator itself, while post-increment must return a copy of the iterator before it has been incremented. Since the for loop discards the return value, using the pre-increment version of the ++ operator saves some CPU cycles by not making a copy that will be discarded anyway. A longer explanation is here.[^]
Edit: Oops, I did not see that there were so many replies already. Only the OP was visible at the bottom of the forums window.
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Where's best to start for doing diagrams?
I want to teach myself to plan RIGHT for developing a decent sized project. Is UML still the appropriate standard? What processes should I follow?
I was taught to use Conceptual Schema and Nassi Schneiderman diagrams at school, so I'm looking for something a little more modern. :P
Thanks!
Don't forget to rate my post if it helped! 
"He has no enemies, but is intensely disliked by his friends."
"His mother should have thrown him away, and kept the stork."
"There's nothing wrong with you that reincarnation won't cure."
"He loves nature, in spite of what it did to him."
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dawmail333 wrote: Where's best to start for doing diagrams?
Depends on the job being done, but generally state transition diagrams and event trace diagrams are pretty usefull. (and often the only diagrams done)
"It is a remarkable fact that despite the worldwide expenditure of perhaps US$50 billion since 1990, and the efforts of tens of thousands of scientists worldwide, no human climate signal has yet been detected that is distinct from natural variation."
Bob Carter, Research Professor of Geology, James Cook University, Townsville
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Being a father of children with special needs, I am always asking
myself , with what I know how can I make a difference in my kids
life and others.
What I am looking for here is focus. What platform? What languages
should I learn? So that I can design software that helps individual
that have extra challenges in their life.
We need something cheap, a lot of families that have people with
special needs in them, most extra money goes to medical care, and
other various expenses other have no idea of.
We need something portable and has touch screen. The mouse
and keyboard while a great invention, acts as a barrier sometimes
to people that have disabilities especially mental. Touch is easy.
What platform would met those needs, while having a low cost?
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You can get cheap tablets these days running Android. Here in the UK, Binatone have cheap Android Homesurf tablets on sale for £130. You'd obviously need to develop for Android here, but the good news is that it's free to develop for.
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So that would be using Java and eclipse as my development environment?
Android doesnt have any visual studio tools do they? I have the express
version at home, and use a professional version at work.
I could tackle learning java for that..
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