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Closed 10 years ago.
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String comparison in Objective-C
I realize that the question is not very specific. I am working on a simple trivia game to test a couple of things, right now it has 5 arrays, one for the questions, one for the first answer option, one for the second answer option, one for the third, and one that says which one is correct.
I have an if statement in that checks wether the button pressed matches the correct answer.
Answer2 is connected to the button that would select option b in my trivia app, strCorrect is the string array that holds the single character that says which option out of the three is right, intCurrentQuestion is just an integer I use to reference the index of the arrays.
-(IBAction)Answer2{
if ([strCorrect objectAtIndex:intCurrentQuestion] == [NSString stringWithFormat:#"B"]){
//do these things blah blah
}
}
The problem is that there are no errors when it is compiled but it doesn't work either. How do I go about making this work?
For testing purpose I am cheating and passing the strCorrect to a hidden label in the nib and then comparing the label text to #"B" and it works but its...well its just awful.
What you're doing in your code above is comparing the memory address of two strings, not their value. Do compare two NSStrings you have to do this:
[[strCorrect objectAtIndex:intCurrentQuestion] isEqualToString:#"B"];
[[strCorrect objectAtIndex:intCurrentQuestion] isEqualToString:#"B"]
Related
My tableViewController with a list of items of various types will provide a button to show a modal dialog box. This dialog box (similar to alert view) will provide the user with an exclusive choice from a list of 6 options.
Based on what the user chooses and confirms, the list in the main tableview controller screen will be filtered down to only show items that match the selected type.
At the moment, I have those six types listed in a typedefed enum. So far so good.
However I also need to be able to populate my custom dialog box with six nsstrings whose names will match the types used in the enumeration.
How to reconciliate this enum with my requirement for a source of those strings, but in such a way that I would ensure some level of consistency between the two? I do not want to hardcode anything.
You need a helper method that returns a string for each enum value. This should be written to deal with possible localization. All of your data and event handling should be based on the enum value. The string should be used for display.
The helper method should take an enum value and use a switch statement to return the proper string.
I can think of a few:
Change the enum to a bunch of strings. This makes things a bit tedious if they need to be integers too (-[NSArray indexOfObject:]).
Make a C array of strings. This lets you use C99's handy syntax:
NSString * const names[] = {
[Foo] = #"Foo",
[Bar] = #"Bar",
};
Autogenerated code to do the above.
Caveats:
Both of these will make i18n rather painful. This might not be relevant if it's contract work that will only need to be in one language, but it's Bad Practice.
Using button indexes as keys works until you decide you need to remove buttons in the middle. String keys work much better in the general case (I wrote a UIAlertView/UIActionSheet wrapper that accept (key,title) pairs and returned the key instead of the button index).
I take your remark that you "do not want to hardcode anything" to mean that you don't want any string constants in your code. So:
You could simply assign the strings to your sheet's UI elements (perhaps check boxes, for example) and give those UI elements tag values that match your enumeration (something you could query as your sheet closes). This has the additional benefit that you can easily localize the sheet.
Or:
If you want to keep the strings separate from your sheet, you could create a .strings file (perhaps you could call it Enumeration.strings or some such) formatted something like this:
"001" = "string one";
"002" = "string two";
.
.
"010" = "string ten";
and you could then retrieve the strings using your enumeration values like this:
NSString *myString = NSLocalizedStringFromTable([NSString stringWithFormat:#"%03d", myEnumerationValue], #"Enumeration", #"");
but then you'd have to have a way of plugging the strings into your UI, keeping track of UI elements through IBOutlets. Note that I used three decimal places here; perhaps you could get by with two, or even one. Finally, you get the ability to localize as in the first suggestion.
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How to dynamically add JSF components
(3 answers)
Closed 6 years ago.
I couldn't find a solution for this in other posts, so here is my problem.
(In advance, I use JSF 2 with Mojarra implementation and Primefaces 3.2 on a JBoss 7.1 AS)
I am building a search-mask that should be generated dynamically during runtime. I know from another post that I should use a dataTable for that. That is what I will do.
But the search-mask consists of 3 parts, the search-criterion (e.g. name, birthday,...), the operator (is, is not, larger than, in range,...) and the operand (what the user will give as search-input).
My goal is to get the search-mask get generated dynamically, BUT the type of input field is dependent on what criterion+operator has been choosen by the user.
So if the user chose criterion: "name" and operator: "is not" from the dropdown boxes, then the input field for the operand should be just a simple p:inputText.
But if the user chose criterion "birthday" and operator: "before", then the input field should be a datepicker like p:calendar.
My idea was to use a p:dataTable for a List of "SearchRow" objects where every object has an array of criteria and operands to use them in a h:selectOneMenu.
Then I add a valueChangeListener to the selectMenues and in there I calculate and create the right type of UIComponent I need as inputfield.
But I have no idea how to add that UICOmponent as the 3rd column inside the dataTable.
So is my idea any good and is there a way at all to solve my problem?
Thanks in advance!
Same solution as to the Problem described here. The article from #BalusC explains very nicely how to add components from the bean.
I reread the explanation a couple of times, but I still don't understand what these are. Can someone explain to me what an argument and a format string are?
I'll answer before this question gets closed or downvoted too severely for not being specific or having much detail:
Format strings are used for passing 1-or-more arguments to compose a NSString object.
Check out this useful Apple documentation on String format specifiers.
Arguments are the parameters passed into a method or function.
And if you are talking about some compiler errors, such as the "format not a string literal and no format arguments" error you might see when trying to log stuff via NSLog, check out the answers to this very related question.
An argument is a variable value that you pass to something else, generally a method. In plain English, if you were to say "go run around the block 30 times", 30 would be the argument. Depending on your method, maybe "block" and "run" would be arguments as well, where you could also say "go walk around the house 10 times".
A format string is a string that describes how to format a series of arguments. These generally take the form of a string that has certain placeholders in it where the arguments will be shown in the result.
My assignment in Visual Basic 2010 is to build a order form that has two text boxes, one for the name and the other for the address.
And we're suppose to use the IndexOf method on the address.
I understand that IndexOf returns the position of a character and the number of characters.
What would be the purpose of using the IndexOf method on the address in this instance?
I don't understand what I would be searching for when the user types in it's address that's going to be numbers and string characters.
I think I understand what the IndexOf method does, somewhat, but why and what would I use it to achieve?
You'd typically use IndexOf to -
See if a string contained something
If someString.IndexOf("Avenue") > - 1 Then
'do something
End If
Get the start position of a value in a string , this could then be used to extract part of the string. e.g. someString.Substring(someString.IndexOf("#"),10) would get then next ten characters starting from where the "#" character was found in your string.
Bear in mind you'll always need to handle scenarios where IndexOf will return -1 if it does not find the string your searching for, so your code will have to handle that eventuality.
Since this is a homework question, I will answer with a question or several:
How would you normally enter a full address into a text box?
How would each part of the address be distinguishable from another?
Once you figure out how this can be done, think about IndexOf again.
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Closed 10 years ago.
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String vs StringBuilder
I just revisited some of the books that I used to pick up VB.NET. I am not sure I've got this in my head, understand how/what StringBuilder is.
What is the guidance for using? Is it best to use it if you are are concatenating 2 strings or 50?
Or when the the total string length is greater than 128 characters?
Or will you see a performance benefit whenever you use it to add strings together?
In which case is it better to use a StringBuilder instance to build a SQL statement than string.format("Select * from x where y = {0}",1)?
It's always struck me that declaring another variable and including a name space is not beneficial for small string concatenations, but I am not sure now.
Sorry, lot of documentation tells you what to use, just not what's best.
I've got an article on this very topic. In summary (copied from the bottom of the page):
Definitely use StringBuilder when you're concatenating in a non-trivial loop - especially if you don't know for sure (at compile time) how many iterations you'll make through the loop. For example, reading a file a character at a time, building up a string as you go using the += operator is potentially performance suicide.
Definitely use the concatenation operator when you can (readably) specify everything which needs to be concatenated in one statement. (If you have an array of things to concatenate, consider calling String.Concat explicitly - or String.Join if you need a delimiter.)
Don't be afraid to break literals up into several concatenated bits - the result will be the same. You can aid readability by breaking a long literal into several lines, for instance, with no harm to performance.
If you need the intermediate results of the concatenation for something other than feeding the next iteration of concatenation, StringBuilder isn't going to help you. For instance, if you build up a full name from a first name and a last name, and then add a third piece of information (the nickname, maybe) to the end, you'll only benefit from using StringBuilder if you don't need the (first name + last name) string for other purpose (as we do in the example which creates a Person object).
If you just have a few concatenations to do, and you really want to do them in separate statements, it doesn't really matter which way you go. Which way is more efficient will depend on the number of concatenations the sizes of string involved, and what order they're concatenated in. If you really believe that piece of code to be a performance bottleneck, profile or benchmark it both ways.
Here is my rule of thumb:
StringBuilder is best used when the exact number of concatenations is unknown at compile time.
Coding Horror has a good article concerning this question, The Sad Tragedy of Micro-Optimization Theater.
Personally I use StringBuilder when I have more than just one or two strings to concatenate. I'm not sure if there's a real performance hit to be gained, but I've always read and been told that doing a regular concatenation with multiple strings creates an extra copy of the string each time you do it, while using StringBuilder keeps one copy until you call the final ToString() method on it.
Someone's figured out experimentally that the critical number is 6. More than 6 concatenations in a row and you should use a StringBuilder. Can't remember where I found this.
However, note that if you just write this in a line:
"qwert" + "yuiop" + "asdf" + "gh" + "jkl;" + "zxcv" + "bnm" + ",."
That gets converted into one function call (I don't know how to write it in VB.net)
String.Concat("qwert", "yuiop", "asdf", "gh", "jkl;", "zxcv", "bnm", ",.");
So if you're doing all concatenations on one line, then don't bother with StringBuilder because String.Concat effectively will do all the concatenations in one go. It's only if you're doing them in a loop or successively concatenating.
My rule - when you're adding to a string in a For or Foreach loop, use the StringBuilder.