Check if NSDictionary is empty

问题

I want to check if an NSDictionary is empty. I am doing it like this.

  mutDictValues = [[[NSUserDefaults standardUserDefaults] objectForKey:@"dicValues"]mutableCopy];
    NSLog(@"dictValues are %@",mutDictValues);
    if(mutDictValues == NULL){
        arrCities = [[NSMutableArray alloc]init];
        NSLog(@"no cities seleceted");
    }else{
          arrCities = [[NSMutableArray alloc]init];
          arrCities = [mutDictValues objectForKey:@"cities"];
          [self placeCities];
    }

But it alwasy crashes on this line arrCities = [mutDictValues objectForKey:@"cities"]; with the following error:

-[__NSCFConstantString objectForKey:]:

Can someone help me with this ?

回答1:

While retrieving the dictionary values from NSUserDefaults that dictionary automatically converted into string that is the reason for getting crashed and for checking dictionary use
[dictionary count];

EDIT:- use dictionaryForKey: method

NSDictionary *dict =[[NSDictionary alloc]initWithObjectsAndKeys:@"hi",@"one",nil];
[[NSUserDefaults standardUserDefaults] setObject:dict forKey:@"dic"];
NSDictionary *dictn = [[NSUserDefaults standardUserDefaults] dictionaryForKey:@"dic"];
NSLog(@"%@",[dictn objectForKey:@"one"]);

回答2:

if ( [mutDictValues count] == 0 ) {
    //code here
}
else {
    //code here
}

After having your dic retrieved this should do

回答3:

try this,

if([myDict count] > 0)
    NSLog(@"Dictionary is not empty");
else
    NSLog(@"Dictionary is empty");

回答4:

Somewhere you treat a nsstring (a concrete subclass) as NSdictionary.

回答5:

I had a bit different issue but it is related so i would like to share it here.

I was fetching the webservices & storing data in NSDictionary & again Fetching objectForKey which was Null. So the solution i found is as under

NSMutableDictionary *result = [NSJSONSerialization JSONObjectWithData:[str dataUsingEncoding:NSUTF8StringEncoding] options:0 error:nil];

    // NSLog(@"%@" , result);

    NSMutableDictionary *sup = [result objectForKey:@"keysupplied"];
    NSNull *n=[NSNull null];
    if ( sup ! = n ){
      //Your code if its not null
    }

The reason behind using NSNull was it was returning (NSNull *) when i debugged the application So i finally figured out this way.

回答6:

As most of the answers have correctly pointed out that you are passing un-recognized selector objectForKey: to a NSString instance instead of NSDictionary, hence observing exception

-[__NSCFConstantString objectForKey:]:

Check NSUserDefaults to see whether cities returns a dictionary or something else. You can do this by two ways

I. NSLog all data in NSUserDefaults

NSLog(@"%@", [[NSUserDefaults standardUserDefaults] dictionaryRepresentation]);

II. Check the plist file which store the NSUserDefaults from the Application folder. Check this answer for more details.

Hope that helps.

回答7:

BOOL containsKeyABC = [myDict: valueForKey:@"ABC"];

int items = dict.count;

if (items > 0) {
     //not empty
}

回答8:

try this code

NSMutableDictionary *dict = ...

BOOL isEmpty = ([dict count] == 0);

来源：https://stackoverflow.com/questions/17745336/check-if-nsdictionary-is-empty

标签

iphone

ios

objective-c

nsmutablearray

nsdictionary