I created three string, that bind it data with method argument. However, i face issue that all of three string share same memory, therefore, it show the same text. Here is how i create it:
-(void)buildViewsWIithTitle:(NSString*)eventTitle{
NSString *firstStr = #"";
NSString *secondStr = #"";
NSString *thirdStr = #"";
Next i set label text to all of this three string. I set it value like:
thirdStr = [NSString stringWithFormat:#"%#", eventTitle];
secondStr = [NSString stringWithFormat:#"%#", eventTitle]
firstStr = [NSString stringWithFormat:#"%#", eventTitle];
In console i output its memory just after creation:
NSLog(#"memory %p , %p , %p", firstStr, secondStr, thirdStr);
memory 0x109af82d8 , 0x109af82d8 , 0x109af82d8
Any idea how make memory address different for them?
As you are using NSString for all 3 objects, which can't be mutated, The compiler will check the value of the string, which is the same empty to all strings. The compiler will optimise the memory usage by pointing the same memory.
The iOS compiler optimizes references to string objects that have the same value (i.e., it reuses them rather than allocating identical string objects redundantly), so all three pointers are in fact pointing to same address.
If you used the NSMutableString, still it may point to the same object, but when you try to mutate the string, it will be copied to the new memory(Lazy memory allocation).
if you want the different memory for each string then you can allocate the memory then initialize the string, like
NSMutableString *str1 = [[NSMutableString alloc]initWithString:#""]
NSMutableString *str2 = [[NSMutableString alloc]initWithString:#""]
NSMutableString *str3 = [[NSMutableString alloc]initWithString:#""]
But note that NSMutableString is mutable.
That's because your all string have address of [NSString stringWithFormat:#"%#", eventTitle]; and this is same for all strings.
For example if you will write below code in your viewdidload then you will get different memory address,
NSString *firstStr = #"";
NSString *secondStr = #"";
NSString *thirdStr = #"";
thirdStr = [NSString stringWithFormat:#"%#", #"eventTitle"];
secondStr = [NSString stringWithFormat:#"%#", #"eventTitle"];
firstStr = [NSString stringWithFormat:#"%#", #"eventTitle"];
NSLog(#"memory %p , %p , %p", firstStr, secondStr, thirdStr);
Because everystring has own memory and not pointing to any single string.
Maybe there's some kind of compiler optimisation going on. It determines (correctly) that the strings are the same so it optimises while compiling. As soon as you change your code so the strings will not be the same and recompile then the compiler won't optimise those particular strings.
thirdStr = [NSString stringWithFormat:#"a %#", eventTitle];
secondStr = [NSString stringWithFormat:#"b %#", eventTitle];
firstStr = [NSString stringWithFormat:#"c %#", eventTitle];
Related
I have an NSString that hold data (actually that could be presented an NSArray). and i want to output that on a label.
In NSLog my NSString output is:
(
"cristian_camino",
"daddu_02",
"_ukendt_babe_",
"imurtaza.zoeb"
)
What i want is, to present it like :"cristian_camino","daddu_02","_ukendt_babe_","imurtaza.zoeb"
In a single line.
I could accomplish that turning string to an array and do following: arrayObjectAtIndex.0, arrayObjectAtIndex.1, arrayObjectAtIndex.2, arrayObjectAtIndex.3.
But thats look not good, and that objects may be nil, so i prefer NSString to hold data.
So, how could i write it in a single lane?
UPDATE:
There is the method i want to use to set text for UILabel:
-(void)setLikeLabelText:(UILabel*)label{
//Likes
NSString* likersCount = [self.photosDictionary valueForKeyPath:#"likes.count"];
NSString* likersRecent = [self.photosDictionary valueForKeyPath:#"likes.data.username"];
NSString *textString = [NSString stringWithFormat:#"%# - amount of people like it, recent "likes": %#", likersCount, likersRecent];
label.text = textString;
NSLog(#"text String is %#", textString);
}
valueForKeyPath: returns an NSArray, not an NSString. Whilst you've declared likersCount and likersRecent as instances of NSString, they're actually both arrays of values. You should be able to do something like the following to construct a string:
NSArray* likersRecent = [self.photosDictionary valueForKeyPath:#"likes.data.username"];
NSString *joined = [likersRecent componentsJoinedByString:#"\", \""];
NSString *result = [NSString stringWithFormat:#"\"%#\"", joined];
NSLog(#"Result: %#", result);
componentsJoinedByString: will join the elements of the array with ", ", and then the stringWithFormat call will add a " at the beginning and end.
The statement is incorrect, the internal quote marks (" that you want to display) need to be escaped:
NSString *textString = [NSString stringWithFormat:#"%# - amount of people like it, recent \"likes\": %#", likersCount, likersRecent];
If somebody curious how i fix it, there it is:
for (int i =0; i < [likersRecent count]; i++){
stringOfLikers = [stringOfLikers stringByAppendingString:[NSString stringWithFormat:#" %#", [likersRecent objectAtIndex:i]]];
}
Not using commas or dots though.
I need to concatenate a string and a variable together - I kind of find lots of examples of adding a string prior to a variable but not the other way round - how do I do this?
NSString *theImage = [[self.detailItem valueForKey:#" resimagefiletitle"] description], #"'add on the end";
Something like this:
NSString *theImage = [NSString stringWithFormat:#"%# %#",[self.detailItem valueForKey:#" resimagefiletitle"], #"'add on the end"];
Or:
NSString *theImage = [NSString stringWithFormat:#"%# add on the end",[self.detailItem valueForKey:#" resimagefiletitle"]];
Try this
NSString *theImage = [NSString stringWithFormat:#"%# '>",[[self.detailItem valueForKey:#"resimagefiletitle"] description]];
Here I am considering [[self.detailItem valueForKey:#"resimagefiletitle"] description] gives NSString
We can concat diffrent type of datatypes into string by mention the format for it.
like if your want to concat two or more strings together then you can use the following code:
NSString *NewString = [NSString stringWithFormat:#"%#%#",#"This Is",#"way to concate string"];
and if your want concat integer value then you can mention the data format for it "%i".
eg:
int OutOf = 150;
NSString *NewString = [NSString stringWithFormat:#"%#%i",#"I got 100 out of ",OutOf];
this may help you.
Will this bit of code produce any memory leaks? Is it the correct way to change NSString values?
NSString * enemiesAndElementsTextureFileName = #"bla bla";
enemiesAndElementsTextureFileName = #"bl";
That way of doing it won't cause any memory leaks and it is indeed correct. In this case you wouldn't need an NSMutableString because you aren't altering the string literal itself, you are simply replacing the string value with a new one (replacing #"bla bla" with #"bl").
In this case, however, your string will now be 'bl', so you can delete that first line value and just have NSString * enemiesAndElementsTextureFileName = #"bl";
Yes NSString allocated once. This is one of the way
Yes, use NSMutableString with the following method as your needs:
// Allocate
NSMutableString *str = [[NSMutableString alloc] initWithCapacity:10];
// set string content
[str setString:#"1234"];
// Append
[str appendString:#"567"];
// Concat
[str appendFormat:#"age is %i and height is %.2f", 27, 1.55f];
// Replace
NSRange range = [str rangeOfString:#"height"];//查找字符串height的位置
[str replaceCharactersInRange:range withString:#"no"];
// Insert
[str insertString:#"abc" atIndex:2];
// Delete
range = [str rangeOfString:#"age"];
[str deleteCharactersInRange:range];
NSLog(#"%#", str);
In my app, I have a view where user have to fill a form. But, sometime the app crash here, in this function, that simple cacth the value field and built a url to give
-(NSString*)urlToUpload{
NSString *string1 =[[NSString alloc]init];
string1= [NSString stringWithFormat:#"?nombre="];
NSString *string2 = [string1 stringByAppendingString:nameAdded];
//crash here
NSString *string3 = [string2 stringByAppendingString:#"&horario="];
NSString *string4 = [string3 stringByAppendingString:horarioAdded];
NSString *string5 = [string4 stringByAppendingString:#"&info="];
NSString *string6 = [string5 stringByAppendingString:infoAdded];
NSString *string7 = [string6 stringByAppendingString:#"&offerta="];
NSString *string8 = [string7 stringByAppendingString:offertaAdded];
NSString *lat_string = [[[NSString alloc] initWithFormat:#"%f",locationToUpload2.latitude] autorelease];
NSString *lon_string = [[[NSString alloc] initWithFormat:#"%f",locationToUpload2.longitude] autorelease];
NSString *string9 = [string8 stringByAppendingString:#"&latitude="];
NSString *string10 = [string9 stringByAppendingString:lat_string];
NSString *string11 = [string10 stringByAppendingString:#"&longitude="];
NSString *string12 = [string11 stringByAppendingString:lon_string];
NSString *url1 = [NSString stringWithFormat:#"http://myserverside/mysql_up.php"];
NSString *url = [url1 stringByAppendingString:string12];
return url;
}
EDIT:
It seems problem appers on nameAdded when there is a white space into textField(i.e. MisterB not crash, Mister B yes ).
But I am using:
nameAdded =[[nameField.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
and NSLOg give of nameAdded is Mister%20B.
The crash still appearing...
Just use a single stringWithFormat::
- (NSString *)urlToUpload {
NSString *url = [NSString stringWithFormat:#"http://myserverside/mysql_up.php?nombre=%#&horario=%#&info=%#&offerta=%#&latitude=%f&longitude=%f",
[nameAdded stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding],
[horarioAdded stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding],
[infoAdded stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding],
[offertaAdded stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding],
locationToUpload2.latitude, locationToUpload2.longitude];
return url;
}
Make sure the referenced variables are valid.
In your original code there is no need to alloc/init an NSString then assign another string to the same variable. That's a memory leak (string1).
If you really want to structure your code the way you have it, at least use an NSMutableString and append to that one mutable string. Creating over a dozen NSString variables is the wrong way to do it.
Updated: Ensure each of the strings added to the URL are properly escaped.
It looks like nameAdded may be the cause of your problems. Is it nil at that point?
Also
You are allocating a string, setting it to string1 and then immediately setting string1 to the class function stringWithFormat which allocates another string. Also you are using stringWithFormat but you aren't using any format so you could simply use NSString *string1 = #"?nombre=";
Rather than declaring all of those variables you should just use NSMutableString and build it all in one variabl
I've got a string that shows the stock amount using "-" as separators.
It's built up like this: localStock-wareHouseStock-supplierStock
Now I want to update the supplierStock at the end of the string, but as you can see in the code below it goes wrong when the original string returns more than a single-space value (such as 20).
Is there a way to remove all characters until the last "-" (or remove characters after the second "-")?
NSMutableString *string1 = [NSMutableString stringWithString: p1.colorStock];
NSLog(#"string1: %#",string1);
NSString *newString = [string1 substringToIndex:[string1 length]-2];
NSLog(#"newString: %#",newString);
NSString *colorStock = [NSString stringWithFormat:#"%#-%#",newString,p2.supplierStock];
NSLog(#"colorstock: %#",colorStock);
p1.colorStock = colorStock;
NSLog1
string1: 0-0-0
newString: 0-0
colorstock: 0-0-20
NSLog2
string1: 0-0-20
newString: 0-0-
colorstock: 0-0--20
EDIT: Got it working thanks to Srikar!
NSString *string1 = [NSString stringWithString: p1.colorStock];
NSLog(#"string1: %#",string1);
NSString *finalString = [string1 stringByReplacingOccurrencesOfString:[[string1 componentsSeparatedByString:#"-"] lastObject] withString:p2.supplierStock.stringValue];
NSLog(#"finalString: %#",finalString);
p1.colorStock = finalString;
Why not use componentsSeparatedByString followed by lastObject ?
NSString *supplierStock = [[string1 componentsSeparatedByString:#"-"] lastObject];
The above works if the "stock amount" is always in sets of 3's separated by a "-". Also since you always want supplierStock, lastObject is perfect for your needs.
Of course after splitting string1 with - you get a NSArray instance and you can access the individual components using objectAtIndex:index. So if you want localStock you can get by
NSString *localStock = [[string1 componentsSeparatedByString:#"-"] objectAtIndex:0];
I would suggest splitting the string into the 3 parts using [NSString componentsSeparatedByString:#"-"] and then building it back up again:
NSArray *components = [p1.colorStock componentsSeparatedByString:#"-"];
p1.colorStock = [NSString stringWithFormat:#"%#-%#-%#",
[components objectAtIndex:0],
[components objectAtIndex:1],
p2.supplierStock];
With a string that looks like
NSString *myString = #"Hello-World";
you can separate it with the componentsSeparatedByString: method of the NSString object as
NSArray *myWords = [myString componentsSeparatedByString:#"-"];
The myWords - array will then contain the two NSString objects Hello and World.
To access the strings:
NSString *theHelloString = [myWords objectAtIndex:0];
NSString *theWorldString = [myWords objectAtIndex:1];
Hope it helps!
None of these examples show how to do this if you are unaware of how many of these separator occurrences you're going to have in the original string.
Here's what I believe the correct the correct code should be for dismantling the original string and rebuilding it until you reach the final separator, regardless of how many separators it contains.
NSString *seperator = #" ";
NSString *everythingBeforeLastSeperator;
NSArray *stringComponents = [originalString componentsSeparatedByString:seperator];
if (stringComponents.count!=0) {
everythingBeforeLastSeperator = [stringComponents objectAtIndex:0];
for (int a = 1 ; a < (stringComponents.count - 1) ; a++) {
everythingBeforeLastSeperator = [NSString stringWithFormat:#"%#%#%#", everythingBeforeLastSeperator, seperator, [stringComponents objectAtIndex:a]];
}
}
return everythingBeforeLastSeperator;