Cách truyền dữ liệu giữa hai Fragment trong Android

Giới thiệu

Fragment không nên giao tiếp trực tiếp với nhau. Cách chuẩn: Fragment → Interface → Activity → Fragment. Activity đóng vai trò trung gian (mediator).

Kiến trúc

FirstFragment --(interface)--> MainActivity --(method)--> SecondFragment

Các bước thực hiện

Bước 1: Giao diện Activity chứa 2 Fragment (res/layout/activity_main.xml)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <fragment
        android:name="com.example.myapplication.FirstFragment"
        android:id="@+id/fragment_first"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />

    <fragment
        android:name="com.example.myapplication.SecondFragment"
        android:id="@+id/fragment_second"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />

</LinearLayout>

Bước 2: Interface truyền dữ liệu (src/OnDataPassListener.java)

package com.example.myapplication;

public interface OnDataPassListener {
    void onDataPass(String data);
}

Bước 3: FirstFragment - Gửi dữ liệu (src/FirstFragment.java)

package com.example.myapplication;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;

public class FirstFragment extends Fragment {

    private OnDataPassListener listener;
    private EditText etInput;
    private Button btnSend;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_first, container, false);
        etInput = view.findViewById(R.id.etInput);
        btnSend = view.findViewById(R.id.btnSend);

        btnSend.setOnClickListener(v -> {
            String data = etInput.getText().toString().trim();
            if (!data.isEmpty() && listener != null) {
                listener.onDataPass(data);
            }
        });
        return view;
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnDataPassListener) {
            listener = (OnDataPassListener) context;
        } else {
            throw new RuntimeException(context.toString() + " must implement OnDataPassListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        listener = null;
    }
}

Bước 4: SecondFragment - Nhận dữ liệu (src/SecondFragment.java)

package com.example.myapplication;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class SecondFragment extends Fragment {

    private TextView tvReceived;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_second, container, false);
        tvReceived = view.findViewById(R.id.tvReceived);
        return view;
    }

    // Gọi từ Activity
    public void updateData(String data) {
        tvReceived.setText("Nhận được: " + data);
    }
}

Bước 5: MainActivity - Trung gian (src/MainActivity.java)

package com.example.myapplication;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;

public class MainActivity extends FragmentActivity implements OnDataPassListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public void onDataPass(String data) {
        // Tìm SecondFragment và truyền dữ liệu
        SecondFragment secondFragment = (SecondFragment) getSupportFragmentManager()
                .findFragmentById(R.id.fragment_second);
        if (secondFragment != null) {
            secondFragment.updateData(data);
        }
    }
}

Bước 6: Layout Fragment First (res/layout/fragment_first.xml)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp"
    android:gravity="center">

    <EditText
        android:id="@+id/etInput"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Nhập dữ liệu..." />

    <Button
        android:id="@+id/btnSend"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="Gửi sang Fragment 2" />

</LinearLayout>

Bước 7: Layout Fragment Second (res/layout/fragment_second.xml)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center">

    <TextView
        android:id="@+id/tvReceived"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Chờ dữ liệu..."
        android:textSize="18sp" />

</LinearLayout>

Chạy ứng dụng

Nhấn Run. Nhập text ở Fragment trên → nhấn "Gửi" → Fragment dưới hiển thị "Nhận được: [text]".

Các cách khác (Hiện đại)

• ViewModel chia sẻ (Shared ViewModel): Cả 2 Fragment dùng ViewModelProviders.of(requireActivity()) để lấy cùng instance ViewModel → quan sát LiveData.
• Fragment Result API (API 1.3.0+): setFragmentResultListener() / setFragmentResult() - không cần Interface/Activity.
• EventBus / RxBus / Flow: Thư viện bên thứ 3.

Ví dụ Shared ViewModel (Khuyên dùng)

public class SharedViewModel extends ViewModel {
    private MutableLiveData<String> data = new MutableLiveData<>();

    public void setData(String value) { data.setValue(value); }
    public LiveData<String> getData() { return data; }
}

// Trong FirstFragment:
SharedViewModel vm = ViewModelProviders.of(requireActivity()).get(SharedViewModel.class);
btnSend.setOnClickListener(v -> vm.setData(etInput.getText().toString()));

// Trong SecondFragment:
SharedViewModel vm = ViewModelProviders.of(requireActivity()).get(SharedViewModel.class);
vm.getData().observe(getViewLifecycleOwner(), s -> tvReceived.setText("Nhận: " + s));