How to send ArrayList<Object> to other Fragment/Activity without init (start) the next Activity?

Question

I have an ArrayList and I need to send it to another fragment. I tried to use Parcelable, but to send the data I need the "startIntent" method which starts the fragment. I don't want the fragment to be started.

I need send data array list object to another fragment without going to this other fragment. I only need to send the data. The user is free to chose when to change between activities/fragments. And the data sent earlier should already be there.

Example using Parcelable:

Class that must be to sent:

import android.os.Parcel;
import android.os.Parcelable;

public class Doenca implements Parcelable {

    private String nome;
    private String causa;
    private String efeito;
    private String cuidados;
    private String prevencao;
    private String categoria;

    public Doenca(String nome, String causa, String efeito, String cuidados, String prevencao, String categoria) {
        this.nome = nome;
        this.causa = causa;
        this.efeito = efeito;
        this.cuidados = cuidados;
        this.prevencao = prevencao;
        this.categoria = categoria;
    }

    protected Doenca(Parcel in) {
        nome = in.readString();
        causa = in.readString();
        efeito = in.readString();
        cuidados = in.readString();
        prevencao = in.readString();
        categoria = in.readString();
    }

    public static final Creator<Doenca> CREATOR = new Creator<Doenca>() {
        @Override
        public Doenca createFromParcel(Parcel in) {
            return new Doenca(in);
        }

        @Override
        public Doenca[] newArray(int size) {
            return new Doenca[size];
        }
    };

    public String getNome() {
        return nome;
    }

    public void setNome(String nome) {
        this.nome = nome;
    }

    public String getCausa() {
        return causa;
    }

    public void setCausa(String causa) {
        this.causa = causa;
    }

    public String getEfeito() {
        return efeito;
    }

    public void setEfeito(String efeito) {
        this.efeito = efeito;
    }

    public String getCuidados() {
        return cuidados;
    }

    public void setCuidados(String cuidados) {
        this.cuidados = cuidados;
    }

    public String getPrevencao() {
        return prevencao;
    }

    public void setPrevencao(String prevencao) {
        this.prevencao = prevencao;
    }

    public String getCategoria() {
        return categoria;
    }

    public void setCategoria(String categoria) {
        this.categoria = categoria;
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(nome);
        dest.writeString(causa);
        dest.writeString(efeito);
        dest.writeString(cuidados);
        dest.writeString(prevencao);
        dest.writeString(categoria);
    }
}


import android.os.Parcel;
import android.os.Parcelable;

public class Doenca implements Parcelable {

    private String nome;
    private String causa;
    private String efeito;
    private String cuidados;
    private String prevencao;
    private String categoria;

    public Doenca(String nome, String causa, String efeito, String cuidados, String prevencao, String categoria) {
        this.nome = nome;
        this.causa = causa;
        this.efeito = efeito;
        this.cuidados = cuidados;
        this.prevencao = prevencao;
        this.categoria = categoria;
    }

    protected Doenca(Parcel in) {
        nome = in.readString();
        causa = in.readString();
        efeito = in.readString();
        cuidados = in.readString();
        prevencao = in.readString();
        categoria = in.readString();
    }

    public static final Creator<Doenca> CREATOR = new Creator<Doenca>() {
        @Override
        public Doenca createFromParcel(Parcel in) {
            return new Doenca(in);
        }

        @Override
        public Doenca[] newArray(int size) {
            return new Doenca[size];
        }
    };

    public String getNome() {
        return nome;
    }

    public void setNome(String nome) {
        this.nome = nome;
    }

    public String getCausa() {
        return causa;
    }

    public void setCausa(String causa) {
        this.causa = causa;
    }

    public String getEfeito() {
        return efeito;
    }

    public void setEfeito(String efeito) {
        this.efeito = efeito;
    }

    public String getCuidados() {
        return cuidados;
    }

    public void setCuidados(String cuidados) {
        this.cuidados = cuidados;
    }

    public String getPrevencao() {
        return prevencao;
    }

    public void setPrevencao(String prevencao) {
        this.prevencao = prevencao;
    }

    public String getCategoria() {
        return categoria;
    }

    public void setCategoria(String categoria) {
        this.categoria = categoria;
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(nome);
        dest.writeString(causa);
        dest.writeString(efeito);
        dest.writeString(cuidados);
        dest.writeString(prevencao);
        dest.writeString(categoria);
    }
}

Answer 1

Try Using EventBus.

To use EventBus, you need to first add it to in the app module build.gradle file

    implementation 'org.greenrobot:eventbus:3.1.1'

and then sync your project.

An Event Subscriber

A subscriber simply subscribes to an event by registering in the event bus and can also unregister that event. To be a subscriber, you have to do three main things:

1. Register the subscriber in the event bus with register(). This informs the event bus that you want to begin receiving events. In an activity, this is in the onStart() method, while in a fragment put this in the onAttact(Activity activity) method.

   @Override
   public void onStart() {
      super.onStart();
      EventBus.getDefault().register(this);
        }
   

2. Unregister the subscriber, which means tell the event bus to stop sending me events. In an activity, this is in the onStop() method, while in a fragment put this in the onDetach() method.

       @Override
        public void onStop() {
           super.onStop();
          EventBus.getDefault().unregister(this);
            }
   

3. Implement the onEvent() to indicate the type of event you want to receive and action to take when you receive the event. Notice the @Subscribe annotation at the top of this method.

   @Subscribe
   public void onEvent(MessageEvent event) {
   Toast.makeText(this, "Hey, my message" + event.getMessage(), 
      Toast.LENGTH_SHORT).show();.
              }
   

Defining Event Messages

The events in greenrobot EventBus are just objects that you define. You can have different event classes if you want. They do not inherit any base class or interface—they're just POJO (Plain Old Java Objects).

      public class MessageEvent {
        public final List<SomeItem> items;
        public MessageEvent(List<SomeItem> items) {
          this.items= items;
              }
               }

Post Event

EventBus.getDefault().post(new MessageEvent("Hey event subscriber!"));

Answer 2

There are multiple ways with different complexity for the implementation.

1. Use a database to store what you need there
2. Store the data in the host activity containing the tabs. As soon as you switch the fragment, all you need to do is read the data from the place where you have stored it.
3. Use LiveData. LiveData would be my personal preference. There you can easily store any data you need and the second fragment simply observes the livedata and can easily react to changes. So you could even switch in both directions as often as you want to.