Sometimes, I get sad when I can't use Python. In Python, I handle an array of arguments, unpacking them as such:
name, handle, parent_handle, [left, top, right, bottom], showing, scrollable = data
I must now do the same in Objective-C, with NSArrays. Am I doomed to 11 lines of:
NSString *name = (NSString *)[data objectAtIndex:0];
NSNumber *handle = (NSNumber *)[data objectAtIndex:1];
//....
or is there a better way?
Yes. You are doomed. DOOMED! Mwah ha ha ha ha!
You can omit the casts and use subscripting to make it a little bit shorter though:
NSString *name = data[0];
NSNumber *handle = data[1];
// ...
You can omit the casts because both objectAtIndex: and subscripting return type id, which can be converted to any Objective-C class type without casting.
Related
#import <Foundation/Foundation.h>
int main (int argc, char * argv[])
{
#autoreleasepool {
NSString *str = #"Programming is fun";
NSLog (#"%#", str);
}
return 0;
}
In the line
NSString *str = #"Programming is fun";
the constant string object Programming is fun is assigned to the NSString variable str. Its value is then displayed using NSLog .
The NSLog format characters %# can be used to display not just NSString objects, but other objects as well.
/*****/
The previous paragraph was from a book I read, what is really confusing to me is why is he keep using the words variable and objects interchangeably? are objects and varaibles the same thing? so far this is the only confusing part about obj-c to me.
please explain, thank you
An object is an instance of a class. Something that is allocated in memory.
A variable is a name which you use to access something like an object (NSString for example) or a primitive (int for example).
In your case so your object is an instance of NSString, that contains #"Programming is fun":
NSString *str = #"Programming is fun";
The variable to access that object is str.
I need my user to enter numbers to type his telephone number.The user can only enter 8 numbers(for eg. XXXXXXXX). I need to change the phone number to be in the format XX-XX-XXXX.
This is what I have tried:
[tfDID.text insertString:#"-" atIndex:2];
[tfDID.text insertString:#"-" atIndex:5];
But it is returning me an error saying:
No Visible #interface for 'NSString' declares the selector 'insertString:atIndex:'
Need some guidance on this. Sorry if this is a stupid question.
No Visible #interface for 'NSString' declares the selector 'insertString:atIndex:'
As you are trying to mutate the textbox's value, which returns you NSString.
NSString object can not be mutated, so convert it into a mutable string then manupulate it.
Make your string NSMutableString.
As,
NSMutableString *tfDIDString=[NSMutableString stringWithString:tfDID.text];
[tfDIDString insertString:#"-" atIndex:2];
[tfDIDString insertString:#"-" atIndex:5];
[UITextField text] is NSString, you need to declare local variable of NSMutableString and perform insertString operations on it
Hope it helps you
Implement <UITextFieldDelegate> and then do:
-(void)textFieldDidChange:(UITextField*)textField
{
if( textField.text.length == 2 || textField.text.length == 5 ){
textField.text = [textField.text stringByAppendingString:#"-"];
}
}
Completely agree with the answer suggesting making it a mutable string.
Just to play devils advocate you could do:
NSString *partOne = [NSString stringWithRange:NSMakeRange(0,2)];
NSString *partTwo = [NSString stringWithRange:NSMakeRange(2,2)];
NSString *partThree = [NSString stringWithRange:NSMakeRange(4,4)];
NSString *formattedNumber = [NSString stringWithFormat:#"%#-%#-%#",partOne,partTwo,partThree];
I've written it out longhand but you could compress the string declarations for the parts in to the stringWithFormat call if you don't mind nesting and sacrifcing a bit of readability.
I have an NSString object and want to convert it into a std::string.
How do I do this in Objective-C++?
NSString *foo = #"Foo";
std::string bar = std::string([foo UTF8String]);
Edit: After a few years, let me expand on this answer. As rightfully pointed out, you'll most likely want to use cStringUsingEncoding: with NSASCIIStringEncoding if you are going to end up using std::string. You can use UTF-8 with normal std::strings, but keep in mind that those operate on bytes and not on characters or even graphemes. For a good "getting started", check out this question and its answer.
Also note, if you have a string that can't be represented as ASCII but you still want it in an std::string and you don't want non-ASCII characters in there, you can use dataUsingEncoding:allowLossyConversion: to get an NSData representation of the string with lossy encoded ASCII content, and then throw that at your std::string
As Ynau's suggested in the comment, in a general case it would be better to keep everything on the stack instead of heap (using new creates the string on the heap), hence (assuming UTF8 encoding):
NSString *foo = #"Foo";
std::string bar([foo UTF8String]);
As noted on philjordan.eu it could also be that the NSString is nil. In such a case the cast should be done like this:
// NOTE: if foo is nil this will produce an empty C++ string
// instead of dereferencing the NULL pointer from UTF8String.
This would lead you to such a conversion:
NSString *foo = #"Foo";
std::string bar = std::string([foo UTF8String], [foo lengthOfBytesUsingEncoding:NSUTF8StringEncoding]);
Trying to implement the following structure from "c" to use NSArray in objective-c:
In standard-c:
struct structDog{
char *name;
int age;
};
struct structLitter{
struct structDog puppy[10];
};
Then I use malloc to allocate space.
But since I am using NSArray.
But in Objective-c I am using NSArray... so ???
NSArray struct structDog *puppy; // <<---this doesn't work
thanks
Assuming that you are trying to do is get your struct into your NSArray you need to use NSValue. For instance you can do something like:
NSArray* myArray = [NSArray arrayWithObjects:[NSValue valueWithPointer: myDog],
[NSValue valueWithPointer: myPuppy],
nil];
structDog* dog = (structDog*)[[myArray objectAtIndex:0] pointerValue];
I thought that I knew how to use fast enumeration, but there is something I don't understand about it. If I create three NSString objects and three NSNumber objects and put them in an NSMutableArray:
NSString *str1 = #"str1";
NSString *str2 = #"str2";
NSString *str3 = #"str3";
NSNumber *nb1 = [NSNumber numberWithInt:1];
NSNumber *nb2 = [NSNumber numberWithInt:2];
NSNumber *nb3 = [NSNumber numberWithInt:3];
NSArray *array = [[NSArray alloc] initWithObjects:str1, str2, str3, nb1, nb2, nb3, nil];
then I make do fast enumeration on all NSString objects, like this:
for (NSString *str in array) {
NSLog(#"str : %#", str);
}
In the console, I get this result :
2011-08-02 13:53:12.873 FastEnumeration[14172:b603] str : str1
2011-08-02 13:53:12.874 FastEnumeration[14172:b603] str : str2
2011-08-02 13:53:12.875 FastEnumeration[14172:b603] str : str3
2011-08-02 13:53:12.875 FastEnumeration[14172:b603] str : 1
2011-08-02 13:53:12.876 FastEnumeration[14172:b603] str : 2
2011-08-02 13:53:12.876 FastEnumeration[14172:b603] str : 3
I logged only the NSStrings, but I get a line for every object in the array, even the NSNumbers and I don't understand why. Does fast enumeration always use every object contained in an array?
When you write a forin loop like that, it casts every object in the array as an NSString, then prints them out as requested.
If you want only the NSStrings, you would need to write something like this:
for (id obj in array) {
if ([obj isKindOfClass:[NSString class]]) {
NSLog(#"str: %#", obj);
}
}
The for all loop doesn't know the difference between NSStrings and Integers -- it will simply go through the entire array, cast each as an NSString, and print them out as you asked.
I'm pretty sure that fast enumeration returns all objects in the array- all that you're doing in for (NSString *str in array) is typecasting str to an NSString. In the body of the loop you need to check the class of the returned object to make sure that it is an NSString.
for(NSString *str in array)
{
if([str isKindOfClass:[NSString class]])
NSLog(#"str : %#", str);
}
Objective-C is dynamically typed, meaning that at runtime (when the loop actually runs), objects are all effectively one type (id) with different classes. The language allows optional compile-time static typing, but all that does is check whether the messages you're sending are valid for the type you've marked. It doesn't actually change the behavior of your program. If you cast an object to be a different type than it actually is, all you're doing is lying to the compiler and defeating its type-checker.
Every object that descends from NSObject implements the method - (NSString)description, %# in Objective-C formate string will take the corresponding argument for the %# and call its description method, Most subclasses of NSObject will implement there own version of - (NSString)description. The same thing happens when you type
> po anObject
in the debugger.
for (NSString *str in array) {
is a way to enumerate through all the elements in array.
You expectative that by specifying NSString you get only the objects of that type is not correct. Rather, all the objects pointers are cast to that type (NSString*).
Have a look at Fast Enumeration in The Objective-C Programming Language guide.
I don't understand where is the unexpected behavior, using the enhanced for loop in an NSMutableArray will just iterate thru every single object in the array which in your case is 6, the result is correct and expected.
The numbers will just get casted to Strings.
in fast enumeration no typecasting,just assigning the pointer into new object