How to Put a List in Intent

How to put a List in intent

You have to instantiate the List to a concrete type first. List itself is an interface.

If you implement the Parcelable interface in your object then you can use the putParcelableArrayListExtra() method to add it to the Intent.

put list of objects in `Intent`

It is not recommended to pass a list of objects between your activities. As @IlyaMaier said, a more robust way is to initialize your ViewModel with your application context and then reuse the same LiveData in your MainActivity.

if you want to continue the same way, there are two reasons why your MainActivity is not being called.

1. The observer is not being able to receive new data in your ViewModel Class.
2. The data class should extend Pacelable & also add annotation @Parcelize.

Like this:

@Parcelize
data class Channels (
var Id: Int?,
var Title: String?,
var CallLetter: String?,
var ChannelPosition: Int? 
) : Parcelable

Intent.putExtra List

Assuming that your List is a list of strings make data an ArrayList<String> and use intent.putStringArrayListExtra("data", data)

Here is a skeleton of the code you need:

1. Declare List

    private List<String> test;
   

2. Init List at appropriate place

    test = new ArrayList<String>();
   

   and add data as appropriate to test.

3. Pass to intent as follows:

    Intent intent = getIntent();  
    intent.putStringArrayListExtra("test", (ArrayList<String>) test);
   

4. Retrieve data as follows:

    ArrayList<String> test = getIntent().getStringArrayListExtra("test");
   

How can I pass ListString as an Intent extra?

This is used to send using intent from one activity.

            Intent intent = getIntent();
            intent.putStringArrayListExtra("votedBy",new ArrayList<>(votedBy));

To receive this can be used;

ArrayList<String> votedByList= getIntent().getStringArrayListExtra("votedBy");

intent.putExtra a list of Parcelable objects and enums

You don't need to make List parcelable. To put it, just use existing method.

final Intent i = new Intent(this,SecondActivity.class);
final ArrayList<Product> list = new ArrayList< Product >();
i.putParcelableArrayListExtra(PRODUCT_KEY, list);
startActivity(i);

To retrieve almost in the same way.

final ArrayList<Product> list = this.getIntent()
            .getParcelableArrayListExtra(PRODUCT_KEY);

UPDATE

To answer you newer question. You cannot pass generic List inside. Because by List you could have different collection. To know system, which type to use you need to have explicit type.

// This will work. 
final ArrayList<Department> departments = getSpecificDepartments();
intent.putParcelableArrayListExtra(DEPARTMENTS_KEY, departments);

How to pass ArrayList of Objects from one to another activity using Intent in android?

It works well,

public class Question implements Serializable {
    private int[] operands;
    private int[] choices;
    private int userAnswerIndex;

   public Question(int[] operands, int[] choices) {
       this.operands = operands;
       this.choices = choices;
       this.userAnswerIndex = -1;
   }

   public int[] getChoices() {
       return choices;
   }

   public void setChoices(int[] choices) {
       this.choices = choices;
   }

   public int[] getOperands() {
       return operands;
   }

   public void setOperands(int[] operands) {
       this.operands = operands;
   }

   public int getUserAnswerIndex() {
       return userAnswerIndex;
   }

   public void setUserAnswerIndex(int userAnswerIndex) {
       this.userAnswerIndex = userAnswerIndex;
   }

   public int getAnswer() {
       int answer = 0;
       for (int operand : operands) {
           answer += operand;
       }
       return answer;
   }

   public boolean isCorrect() {
       return getAnswer() == choices[this.userAnswerIndex];
   }

   public boolean hasAnswered() {
       return userAnswerIndex != -1;
   }

   @Override
   public String toString() {
       StringBuilder builder = new StringBuilder();

       // Question
       builder.append("Question: ");
       for(int operand : operands) {
           builder.append(String.format("%d ", operand));
       }
       builder.append(System.getProperty("line.separator"));

       // Choices
       int answer = getAnswer();
       for (int choice : choices) {
           if (choice == answer) {
               builder.append(String.format("%d (A) ", choice));
           } else {
               builder.append(String.format("%d ", choice));
           }
       }
       return builder.toString();
     }
  }

In your Source Activity, use this :

  List<Question> mQuestionList = new ArrayList<Question>;
  mQuestionsList = QuestionBank.getQuestions();
  mQuestionList.add(new Question(ops1, choices1));

  Intent intent = new Intent(SourceActivity.this, TargetActivity.class);
  intent.putExtra("QuestionListExtra", ArrayList<Question>mQuestionList);

In your Target Activity, use this :

  List<Question> questions = new ArrayList<Question>();
  questions = (ArrayList<Question>)getIntent().getSerializableExtra("QuestionListExtra");

Passing a List from one Activity to another

You can pass an ArrayList<E> the same way, if the E type is Serializable.

You would call the putExtra (String name, Serializable value) of Intent to store, and getSerializableExtra (String name) for retrieval.

Example:

ArrayList<String> myList = new ArrayList<String>();
intent.putExtra("mylist", myList);

In the other Activity:

ArrayList<String> myList = (ArrayList<String>) getIntent().getSerializableExtra("mylist");

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Please note that serialization can cause performance issues: it takes time, and a lot of objects will be allocated (and thus, have to be garbage collected).

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