循环中的NSRangeException

Question

I'm still learning by doing, so please, if this sounds like a noob question, that's probably what it is.

I'm trying to iterate through a NSDictionary (messeges) and grab the value on a certain key.

When I run this code I get the following error" * Terminating app due to uncaught exception 'NSRangeException', reason: '* -[__NSArrayI objectAtIndex:]: index 4 beyond bounds [0 .. 3]'"

NSArray* keys = [messages allKeys];

int count = [keys count] ;
for (int i=0; i < count; i++) {
  for(NSString* key in keys) {
    if ([key isEqualToString:@"messagesinconversation"]) {
        NSArray* arr = [messages objectForKey:key];
        NSString *sentby = [[arr valueForKey:@"sentby"] objectAtIndex:i];

        NSLog (@"%@", sentby);

    }
}
}

Could somebody point me in the right direction?

Answer 1

I think the problem occured in

NSString *sentby = [[arr valueForKey:@"sentby"] objectAtIndex:i];

May be the arr array count is lessthan keys array count. But you are running the for loop based on the keys count. Replace

 NSString *sentby = [[arr valueForKey:@"sentby"] objectAtIndex:i];  
 NSLog (@"%@", sentby);  

code with below code

 for(NSDictionary *dictionary in arr){  
 NSString *sentby=[dictionary objectForKey:@"sentby"];  
 NSLog(@"sentby is %@",sentby);  
 }  

Answer 2

I guess problem is your running two loops

Check this,

NSArray* keys = [messages allKeys];

int count = [keys count] ;
for (int i=0; i < count; i++) {
    NSString *key=[keys objectAtIndex:i];
        if ([key isEqualToString:@"messagesinconversation"])
        {
            NSArray* arr = [messages objectForKey:key];
            NSString *sentby = [[arr valueForKey:@"sentby"] objectAtIndex:i];

            NSLog (@"%@", sentby);

        }

}

Answer 3

Don't need to get value on objectAtIndex in this array.So please see my edited code

NSArray* keys = [messages allKeys];
  for(NSString* key in keys)
  {
    if ([key isEqualToString:@"messagesinconversation"])
    {
        NSArray* arr = [messages objectForKey:key];
        NSString *sentby = [arr valueForKey:@"sentby"]; // here's your problem. 

        NSLog (@"%@", sentby);

    }
 }

Answer 4

It's unclear exactly what you want to do, but the root cause is the fact that i is the current index into the keys array, not the arr array.

Perhaps you want:

NSArray *inconversation = [messages objectForKey:@"messagesinconversation"];
if (inconversation) {
    NSArray *sentBy = [inconversation valueForKey:@"sentby"];
    for (NSString *sender in sentBy) {
        NSLog (@"%@", sender);
    }
}

(why bother iterating through the dictionary keys when you want one specific element anyway?)

Answer 5

The Problem is NSString *sentby = [[arr valueForKey:@"sentby"] objectAtIndex:i];

i is greater than array count, check the i value and array count .

better make a if condition when retrieving the value

if (i <= [array count]) like this