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Attempt to de-reference a null object: list initialization

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3

I initialize the list at the beginning of the code. In one of the methods, I add values ​​to it. In another method, the list is already empty. But I need these values ​​in the second method. How to save them to get after?

public static List<String> listsIds = new List<String>();

@AuraEnabled
public static List<Object> getLists()
//If I initialize the list here, nothing will change: "listsIds" will be null

 Http http = new Http();
 HttpRequest request = new HttpRequest();
 request.setEndpoint('myEndpointIsHere');
 request.setMethod('GET'); 
 HttpResponse response = http.send(request);

 Map<String, Object> results = (Map<String, Object>) JSON.deserializeUntyped(response.getBody());
 List<Object> lists = (List<Object>) results.get('lists');
 List<String> listsNames = new List<String>();

 for(Object oneList : lists)
 String listInText = String.valueOf(oneList);
 String listName = listInText.substringBetween('name=', '');
 String listId = listInText.substringBetween('id=', ',');
 listsNames.add(listName);
 //Here I added the values:
 listsIds.add(listId);
 
 return listsNames;
}

@AuraEnabled
public static void testIt()
 //Empty List:
 System.debug(listsIds);

apex error list null

share|improve this question

edited 8 hours ago

MichaelLev19

asked 8 hours ago

MichaelLev19MichaelLev19

13088 bronze badges

add a comment | 

3

I initialize the list at the beginning of the code. In one of the methods, I add values ​​to it. In another method, the list is already empty. But I need these values ​​in the second method. How to save them to get after?

public static List<String> listsIds = new List<String>();

@AuraEnabled
public static List<Object> getLists()
//If I initialize the list here, nothing will change: "listsIds" will be null

 Http http = new Http();
 HttpRequest request = new HttpRequest();
 request.setEndpoint('myEndpointIsHere');
 request.setMethod('GET'); 
 HttpResponse response = http.send(request);

 Map<String, Object> results = (Map<String, Object>) JSON.deserializeUntyped(response.getBody());
 List<Object> lists = (List<Object>) results.get('lists');
 List<String> listsNames = new List<String>();

 for(Object oneList : lists)
 String listInText = String.valueOf(oneList);
 String listName = listInText.substringBetween('name=', '');
 String listId = listInText.substringBetween('id=', ',');
 listsNames.add(listName);
 //Here I added the values:
 listsIds.add(listId);
 
 return listsNames;
}

@AuraEnabled
public static void testIt()
 //Empty List:
 System.debug(listsIds);

apex error list null

share|improve this question

edited 8 hours ago

MichaelLev19

asked 8 hours ago

MichaelLev19MichaelLev19

13088 bronze badges

add a comment | 

I initialize the list at the beginning of the code. In one of the methods, I add values ​​to it. In another method, the list is already empty. But I need these values ​​in the second method. How to save them to get after?

public static List<String> listsIds = new List<String>();

@AuraEnabled
public static List<Object> getLists()
//If I initialize the list here, nothing will change: "listsIds" will be null

 Http http = new Http();
 HttpRequest request = new HttpRequest();
 request.setEndpoint('myEndpointIsHere');
 request.setMethod('GET'); 
 HttpResponse response = http.send(request);

 Map<String, Object> results = (Map<String, Object>) JSON.deserializeUntyped(response.getBody());
 List<Object> lists = (List<Object>) results.get('lists');
 List<String> listsNames = new List<String>();

 for(Object oneList : lists)
 String listInText = String.valueOf(oneList);
 String listName = listInText.substringBetween('name=', '');
 String listId = listInText.substringBetween('id=', ',');
 listsNames.add(listName);
 //Here I added the values:
 listsIds.add(listId);
 
 return listsNames;
}

@AuraEnabled
public static void testIt()
 //Empty List:
 System.debug(listsIds);

apex error list null

share|improve this question

edited 8 hours ago

MichaelLev19

asked 8 hours ago

MichaelLev19MichaelLev19

13088 bronze badges

public static List<String> listsIds = new List<String>();

@AuraEnabled
public static List<Object> getLists()
//If I initialize the list here, nothing will change: "listsIds" will be null

 Http http = new Http();
 HttpRequest request = new HttpRequest();
 request.setEndpoint('myEndpointIsHere');
 request.setMethod('GET'); 
 HttpResponse response = http.send(request);

 Map<String, Object> results = (Map<String, Object>) JSON.deserializeUntyped(response.getBody());
 List<Object> lists = (List<Object>) results.get('lists');
 List<String> listsNames = new List<String>();

 for(Object oneList : lists)
 String listInText = String.valueOf(oneList);
 String listName = listInText.substringBetween('name=', '');
 String listId = listInText.substringBetween('id=', ',');
 listsNames.add(listName);
 //Here I added the values:
 listsIds.add(listId);
 
 return listsNames;
}

@AuraEnabled
public static void testIt()
 //Empty List:
 System.debug(listsIds);

share|improve this question

edited 8 hours ago

MichaelLev19

asked 8 hours ago

MichaelLev19MichaelLev19

13088 bronze badges

share|improve this question

edited 8 hours ago

MichaelLev19

asked 8 hours ago

MichaelLev19MichaelLev19

13088 bronze badges

asked 8 hours ago

MichaelLev19MichaelLev19

13088 bronze badges

asked 8 hours ago

MichaelLev19MichaelLev19

13088 bronze badges

1 Answer
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6

static methods share state (in the form of static variables) only in the context of a single transaction. Each Lightning server call to an @AuraEnabled method takes place in a separate transaction; no state is stored on the server across such invocations. Each such method will start with the same value for listIds, which is an empty list - your initializer will be run anew on each invocation.

Your state needs to be stored on the client, in attributes of your Lightning component. Your client-side controller can then pass needed state to your Apex methods as a parameter. You will not be able to store it on the server in this way unless you choose to persist it as an object, which will add a lot of complexity and is likely something you'd want to do only if the data is large, long-lived, and expensive to compute.

share|improve this answer

edited 8 hours ago

answered 8 hours ago

David Reed♦David Reed

45.6k88 gold badges2626 silver badges6565 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Beat me to it :)
  
  – gNerb
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you :))))
  
  – MichaelLev19
  8 hours ago
  

  
  
  
  

add a comment | 

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6

static methods share state (in the form of static variables) only in the context of a single transaction. Each Lightning server call to an @AuraEnabled method takes place in a separate transaction; no state is stored on the server across such invocations. Each such method will start with the same value for listIds, which is an empty list - your initializer will be run anew on each invocation.

Your state needs to be stored on the client, in attributes of your Lightning component. Your client-side controller can then pass needed state to your Apex methods as a parameter. You will not be able to store it on the server in this way unless you choose to persist it as an object, which will add a lot of complexity and is likely something you'd want to do only if the data is large, long-lived, and expensive to compute.

share|improve this answer

edited 8 hours ago

answered 8 hours ago

David Reed♦David Reed

45.6k88 gold badges2626 silver badges6565 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Beat me to it :)
  
  – gNerb
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you :))))
  
  – MichaelLev19
  8 hours ago
  

  
  
  
  

add a comment | 

6

static methods share state (in the form of static variables) only in the context of a single transaction. Each Lightning server call to an @AuraEnabled method takes place in a separate transaction; no state is stored on the server across such invocations. Each such method will start with the same value for listIds, which is an empty list - your initializer will be run anew on each invocation.

Your state needs to be stored on the client, in attributes of your Lightning component. Your client-side controller can then pass needed state to your Apex methods as a parameter. You will not be able to store it on the server in this way unless you choose to persist it as an object, which will add a lot of complexity and is likely something you'd want to do only if the data is large, long-lived, and expensive to compute.

share|improve this answer

edited 8 hours ago

answered 8 hours ago

David Reed♦David Reed

45.6k88 gold badges2626 silver badges6565 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Beat me to it :)
  
  – gNerb
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thank you :))))
  
  – MichaelLev19
  8 hours ago
  

  
  
  
  

add a comment | 

static methods share state (in the form of static variables) only in the context of a single transaction. Each Lightning server call to an @AuraEnabled method takes place in a separate transaction; no state is stored on the server across such invocations. Each such method will start with the same value for listIds, which is an empty list - your initializer will be run anew on each invocation.

Your state needs to be stored on the client, in attributes of your Lightning component. Your client-side controller can then pass needed state to your Apex methods as a parameter. You will not be able to store it on the server in this way unless you choose to persist it as an object, which will add a lot of complexity and is likely something you'd want to do only if the data is large, long-lived, and expensive to compute.

share|improve this answer

edited 8 hours ago

answered 8 hours ago

David Reed♦David Reed

45.6k88 gold badges2626 silver badges6565 bronze badges

share|improve this answer

edited 8 hours ago

answered 8 hours ago

David Reed♦David Reed

45.6k88 gold badges2626 silver badges6565 bronze badges

answered 8 hours ago

David Reed♦David Reed

45.6k88 gold badges2626 silver badges6565 bronze badges

answered 8 hours ago

David Reed♦David Reed

45.6k88 gold badges2626 silver badges6565 bronze badges