android:fragment给activity发送消息

一，代码

activity xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".activity.Message2Activity">

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <TextView
            android:id="@+id/textReceive"
            android:layout_gravity="center"
            android:layout_marginTop="30dp"
            android:text="接收到的消息"
            android:textSize="20sp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <TextView
            android:id="@+id/text"
            android:layout_gravity="center"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="20sp"
            android:text="我是Activity" />

        <FrameLayout
            android:id="@+id/fragment_container"
            android:layout_width="match_parent"
            android:layout_height="500dp"/>
    </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

activity java

package com.example.okdemo1.activity;

import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

import com.example.okdemo1.R;
import com.example.okdemo1.fragment.Msg2Fragment;
import com.example.okdemo1.fragment.MsgFragment;
import com.example.okdemo1.interfaces.FragmentCommunicator;

public class Message2Activity extends AppCompatActivity implements FragmentCommunicator {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EdgeToEdge.enable(this);
        setContentView(R.layout.activity_message2);

        // 步骤1：获取FragmentManager
        // FragmentManager fragmentManager = getFragmentManager();
        FragmentManager fragmentManager = getSupportFragmentManager();
        // 步骤2：获取FragmentTransaction
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

        // 步骤3：创建需要添加的Fragment
        final Msg2Fragment fragment = new Msg2Fragment();

        // 步骤4：动态添加fragment
        // 即将创建的fragment添加到Activity布局文件中定义的占位符中（FrameLayout）
        fragmentTransaction.add(R.id.fragment_container, fragment);
        fragmentTransaction.commitNow();

    }

    @Override
    public void onMessageReceived(String message) {

        TextView text2 = findViewById(R.id.text);
        text2.setText("接收到消息:"+message);
        // 处理消息
        Toast.makeText(this, "接收到消息:"+message, Toast.LENGTH_LONG).show();
    }
}

fragment xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".fragment.Msg2Fragment">

    <!-- TODO: Update blank fragment layout -->
    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#ffff00"
        >

        <TextView
            android:id="@+id/fragment"
            android:text="我是fragment"
            android:layout_gravity="center"
            android:textSize="30dp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            />

        <Button
            android:id="@+id/button"
            android:layout_gravity="center"
            android:layout_marginTop="30dp"
            android:text="点击发送消息"
            android:textSize="20sp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

    </LinearLayout>

</FrameLayout>

fragment java

package com.example.okdemo1.fragment;

import android.content.Context;
import android.os.Bundle;

import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

import com.example.okdemo1.R;
import com.example.okdemo1.interfaces.FragmentCommunicator;

/**
 * A simple {@link Fragment} subclass.
 * Use the {@link Msg2Fragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class Msg2Fragment extends Fragment {

    // TODO: Rename parameter arguments, choose names that match
    // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    // TODO: Rename and change types of parameters
    private String mParam1;
    private String mParam2;

    private FragmentCommunicator mListener;

    public Msg2Fragment() {
        // Required empty public constructor
    }


    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        try {
            mListener = (FragmentCommunicator) context;
        } catch (ClassCastException e) {
            throw new ClassCastException(context.toString() + " must implement FragmentCommunicator");
        }
    }

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

    /**
     * Use this factory method to create a new instance of
     * this fragment using the provided parameters.
     *
     * @param param1 Parameter 1.
     * @param param2 Parameter 2.
     * @return A new instance of fragment Msg2Fragment.
     */
    // TODO: Rename and change types and number of parameters
    public static Msg2Fragment newInstance(String param1, String param2) {
        Msg2Fragment fragment = new Msg2Fragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View contentView = inflater.inflate(R.layout.fragment_msg2, container, false);

        //给按钮增加点击事件
        Button button2 = contentView.findViewById(R.id.button);
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //发送消息
                String message = "夜凉疑有雨，院静似无僧";
                sendMessageToActivity(message);
            }
        });

        return contentView;
    }

    //发送消息
    public void sendMessageToActivity(String message) {
        if (mListener != null) {
            mListener.onMessageReceived(message);
        }
    }
}

interface

package com.example.okdemo1.interfaces;

public interface FragmentCommunicator {
    void onMessageReceived(String message);
}

二，测试效果: