Any one please help me to understand the String comparison technique in Objective-C
NSString *strNew1 = #"AA";
NSString *strNew2 = #"AA";
So to compare both the strings we could use,
Method 1. if (strNew1 == strNew2) {
NSLog(#"Equal");
}
or
Method 2: if ([strNew1 isEqualToString:strNew2]) {
NSLog(#"Equal");
}
In this condition both of them are success. But am aware that method 1 will get failed at certain other condition. And also I have tried the below conditions(All are success).
NSString *strNew = #"AA";
NSString *strNew1 = #"AA";
NSString *strNew11 = [[NSString alloc] initWithString:strNew1];
NSString *strNew3 = strNew;
NSArray *arr = #[#"AA"];
NSString *strNew4 = [arr objectAtIndex:0];
NSString *strNew5 = [arr objectAtIndex:0];
_test = strNew5;
_test1 = #"AA";
if ([strNew isEqualToString:strNew1]) {
NSLog(#"Equal");
}
if (strNew == strNew3) {
NSLog(#"Equal1");
}
if (strNew == [arr objectAtIndex:0]){
NSLog(#"Equal2");
}
if (strNew == strNew4){
NSLog(#"Equal3");
}
if (strNew5 == strNew4){
NSLog(#"Equal4");
}
if (strNew4 == [arr objectAtIndex:0]){
NSLog(#"Equal5");
}
if (strNew11 == [arr objectAtIndex:0]){
NSLog(#"Equal11");
}
if (self.test == strNew4){
NSLog(#"Equal3");
}
if (self.test == self.test1){
NSLog(#"Equal3");
}
TEST *test = [TEST new]; // Tried with a class with NSString property with value "AA" . (test.strTest value is #"AA")
if (strNew == test.strTest) {
NSLog(#"Equal"); //success
}
I knew most of them are redundant. Am not able to understand the basics behind this. Please anyone give clear explanation on the concept behind this. Thanks.
In the cases you defined the strings created are internally treated as string literals. The runtime will not allocate different memory space to such strings.
Essentially all the strings that contain the same string literal ("AA" in your case) will point to the same memory location. This is done as a part of memory optimization by Apple.
When you change the value of any string (say to "AB") a new address will be allocated to that NSString object and then == will fail.
You need to use below instance method of NSString class.
- (BOOL)isEqualToString:(NSString *)aString;
So, In your case simply follow below:
if ([strNew isEqualToString strNew4]){
NSLog(#"Equal3");
}
By doing (strNew == strNew4),
You are only comparing the addresses of the objects.
The first way compares pointers, while the second way compares objects.
That is, the first way compares if the pointers have the same value. In this case it is likely that they don't, in the second case the objects will be compared. Since they are initialized the same way they could be equal. (Note, it appears that with the UIButton's implementation of isEqual: the result is always false.)
In most cases using == is not what you want. However, what is appropriate depends on your objective.
if (strNew1 == strNew2) //This compared your pointers
{
}
and
if ([strNew1 isEqualToString:strNew2]) //Compares NSString object
{
}
Remember that isEqualToString: comes with a WARNING
[string1 isEqualToString: string2]
will effectively return false is both strings are nil.
Related
I'm trying to change name(UILabel).text to nameString(NSString) but it does not present it on the screen (it does change - is it the value when I debug and it the correct value).
Code:
NSString *namesString = [self.names objectAtIndex:i];
infoWindow.storeAddressLabel.text = namesString;
Note: if I type:
infoWindow.storeAddressLabel.text=#"someText";
It works
Does anybody know why is it? Thanks!
You're referencing two different variables. On the 1st line you define nameString, and then on the next line you set using namesString with an extra s
If infoWindow.storeAddressLabel.text=#"someText"; works, then storeAddressLabel object isn't nil. The only possibility can be that the string being returned from the code NSString *namesString=[self.names objectAtIndex:i]; is being returned nil. Please check and verify.
Thanks.
Try this see what happens,
NSString *nameString=[sef.names objectAtIndex:i];
if( nameString!=nil && nameString.length >0){
NSLog(#"nameString %#",nameString);
infoWindow.storeAddressLabel.text=namesString;
}
else{
infoWindow.storeAddressLabel.text=#"nameString variable was nil so I am being set as label text";
}
In correction to above code which contains many bugs, i have written following answer:
NSString *nameString = [sef.names objectAtIndex:i];
if(nameString)
{
infoWindow.storeAddressLabel.text = nameString;
}
else
{
infoWindow.storeAddressLabel.text = #"nameString variable was nil so I am being set as label text";
}
Try using a class method to assign the text property - (check for nil first of course as stringWithString: must be passed a non-nil NSString)
infoWindow.storeAddressLabel.text = [NSString stringWithString:(NSString*)[self.names objectAtIndex:i]];
If your namesString is not nil then it should be displayed..
try like this,
NSString *namesString = [self.names objectAtIndex:i];
infoWindow.storeAddressLabel.text = [NSString stringWithFormat:#"%#",namesString];
I am using iTunes Search APIs to return the number of users that have reviewed my current app version. Since I haven't released the app yet, I have to handle the case where the iT search API returns nothing.
Here's the pertinent code:
NSDictionary *iTunesDict = [NSJSONSerialization
JSONObjectWithData:iTunesData options:0 error:&error];
NSArray *resultCount = #[[iTunesDict valueForKey:#"resultCount"]];
NSLog(#"%#", [resultCount objectAtIndex:0]);
if ([resultCount objectAtIndex:0] == 0) {
self.numberOfReviewers = #"0";
} else {
NSArray *reviewers = #[[[iTunesDict valueForKey:#"results"] valueForKey:#"userRatingCountForCurrentVersion"]];
if ([reviewers objectAtIndex:0] == nil) {
self.numberOfReviewers = #"0";
} else {
NSString *howManyReviewed = [[[reviewers objectAtIndex:0] objectAtIndex:0] stringValue];
self.numberOfReviewers = howManyReviewed;
}
My problem centers around the first if statement. Upon inspection, the value of...
[resultCount objectAtIndex:0] is: (__NSCFNumber *)(long)0
does not satisfy the condition in my first if.
What do I need to make a **(__NSCFNumber *)(long)0 **== 0??
It's returning the data as an NSNumber object. Use the compare: comparison function:
if ([resultCount[0] compare:#0] == NSOrderedSame) {
...
}
else {
...
}
What this is doing is comparing the resultCount object to an NSNumber with the value of 0 (you can use the literal #0 to short-hand an NSNumber as I've done above). compare: returns one of three values:
NSOrderedDescending
NSOrderedSame
NSOrderedAscending
This reads from left to right. So if I was to use NSOrderedDescending, this would read logically "is 0 smaller than resultCount" (in descending order from left to right).
For further reading, check out the comparing NSNumber objects documentation.
Alternatively, because you know it's a long, you can use the longValue method on NSNumber:
if ([resultCount longValue] == 0) {
....
}
I am using Mantle to parse some JSON data from Yelp.
For each business returned I get an NSArray of categories. This would be an example:
yelpCategories = (
(
"Wine Bars",
"wine_bars"
),
(
"Ice Cream & Frozen Yogurt",
icecream
)
);
yelpCategories is the name of the array that I save. Later on I am trying to parse the array into a string:
NSMutableString *yelpCats = [[NSMutableString alloc] init];
for (NSObject * obj in business.yelpCategories)
{
[yelpCats appendString:[NSString stringWithFormat:#"%#,",[obj description]]];
}
The issue is with the above. I am being returned a string just as "(" so I must be accessing the array incorrectly. How can I correctly access each object, ideally I would be looking for the end string o be #"Wine Bars, Ice Cream & Frozen Yogurt".
EDIT
The categories array: (
(
Pubs,
pubs
)
)
FINAL EDIT - Proposed Solution
for (NSArray *cats in business.yelpCategories)
{
NSString *category = [cats objectAtIndex:0];
if ([category length] > 0) {
category = [category substringToIndex:[category length] - 1];
}
if (cats == business.yelpCategories.lastObject) {
[yelpCats appendString:[NSString stringWithFormat:#"%#",category]];
} else {
[yelpCats appendString:[NSString stringWithFormat:#"%#, ",category]];
}
}
cell.yelpCategories.text = yelpCats;
Using the description of the object gives you what you see in the debugger, which includes extra carriage returns.
What you want to do is something like:
yelpCats = [yelpCategories componentsJoinedByString:#", "];
#jeffamaphone 's answer is the correct and best way of doing things however what your doing will almost work, I think your just confused on the contents of the array.
The yelpCategories array is an array of strings so you don't need to call stringWithFormat or call the description method. In fact [obj description] will return a string so you didn't even need stringWithFormat in your example and you would have gotten the same output. To make your original method work change to:
NSMutableString *yelpCats = [[NSMutableString alloc] init];
for (id obj in business.yelpCategories)
{
//obj is a string so we can just append it.
[yelpCats appendString:obj]];
}
Also noticed I changed NSObject *obj to just id obj, this is the idiomatic way and shorthand way of declaring NSObjects in objective-c. In this example however I would actually use (NSString *category in business.yelpCategories) instead for better readability. In this case you are declaring to everyone that you expect each object in the array to be a string and then if you wanted to use NSString methods on it inside the loop then you don't have to cast it.
for (NSArray *cats in business.yelpCategories)
{
NSString *category = [cats objectAtIndex:0];
if ([category length] > 0) {
category = [category substringToIndex:[category length] - 1];
}
if (cats == business.yelpCategories.lastObject) {
[yelpCats appendString:[NSString stringWithFormat:#"%#",category]];
} else {
[yelpCats appendString:[NSString stringWithFormat:#"%#, ",category]];
}
}
cell.yelpCategories.text = yelpCats;
I am loading data from a server but I have an issue that the value that I am returning is zero(0) while I can't go inside if. Please where would be the problem?
-(void)method1
{
NSNumber *value = [data objectForKey:#"samount"];
NSLog(#"number is -%#-", value); //number is -0-
if (value == 0)
{
NSLog(#" OK :) ");
}
else
{
NSLog(#" Bad :( ");
}
}
Use isEqual:
if ([value isEqual:#(0)])
That will also evaluate correctly in case value is nil (where == comparison with floatValue or similar methods would fail)
value is an object, and more precisely a NSString object (as per your comments in Alladinian's answer), but you are checking its address. You can convert your string to NSNumber with NSNumberFormatter and then check its value or rely on NSString's built-in methods: integerValue, floatValue, etc.
Assuming value is a NSNumber/NSString:
if ([value integerValue] == 0)
See Getting Numeric Values in NSString documentation and Accessing Numeric Values in the NSNumber documentation and pick the method that best suits your data type.
My if statement won't work. active returns 1 but will not work in the IF statement
JSONDecoder *jsonKitDecoder = [JSONDecoder decoder];
NSDictionary *dict = [jsonKitDecoder objectWithData:jsonData];
NSString *userid = [dict valueForKeyPath:#"users.user_id"];
NSString *active = [dict valueForKeyPath:#"users.active"];
NSLog(#"%#",userid); // 2013-06-20 03:03:21.864 test[81783:c07] (74)
NSLog(#"%#",active); // 2013-06-20 03:03:21.864 test[81783:c07] (1)
if ([active isEqualToString:#"1"]){
// Do something
}
I can't seem to get this IF to work. Do I need to change the NSString to a int?
For starters, use a modern style for retrieving values from dictionaries, rather than valueForKeyPath:.
NSDictionary* users = dict[#"users"];
id active = users[#"active"];
Once you're using a modern style, my guess is that the active value is actually an NSNumber representing a boolean value. So your if block would read:
if([active isKindOfClass:NSNumber] && [active boolValue]) {
//active is an NSNumber, and the user is active
}
The syntax of your if statement is just fine. I would try the alternate method for retrieving values from a dictionary as mentioned above.
NSString *active = #"1";
if ([active isEqualToString:#"1"])
{
// Do something
NSLog(#"It works!");
}
More than likely the "users.active" object being returned from that NSDictionary-ized JSON stream is a "BOOL" or a "NSInteger" as the payload of a NSNumber object and it's not a NSString object.
Try using:
NSNumber * activeNumber = [dict valueForKeyPath: #"users.active"];
and see if "if ([activeNumber boolValue] == YES)" works better for you.