用于检查在线连接的动态BroadcastReceiver

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.widget.Toast;

public class NetworkChangeReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetwork = connectivityManager.getActiveNetworkInfo();
        boolean isConnected = activeNetwork != null && activeNetwork.isConnectedOrConnecting();

        if (isConnected) {
            Toast.makeText(context, "网络已连接", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(context, "网络未连接", Toast.LENGTH_SHORT).show();
        }
    }
}

import android.content.IntentFilter;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    private NetworkChangeReceiver networkChangeReceiver;

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

        networkChangeReceiver = new NetworkChangeReceiver();
    }

    @Override
    protected void onResume() {
        super.onResume();
        IntentFilter filter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
        registerReceiver(networkChangeReceiver, filter);
    }

    @Override
    protected void onPause() {
        super.onPause();
        unregisterReceiver(networkChangeReceiver);
    }
}