动态注册监听网络变化

在MainActivity中动态注册/取消广播

public class MainActivity extends AppCompatActivity {

    /**
     * 意图过滤器，当我们隐式的启动系统组件的时候，就会根据IntentFilter来筛选出合适的进行启动
     */
    private IntentFilter intentFilter;

    private NetworkChangeReceiver networkChangeReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        intentFilter = new IntentFilter();
        // 网络发生变化时会发出值为：android.net.conn.CONNECTIVITY_CHANGE的广播
        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE"); //在监听广播
        networkChangeReceiver = new NetworkChangeReceiver();
        registerReceiver(networkChangeReceiver, intentFilter); //动态注册广播接收器
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(networkChangeReceiver); //取消注册广播接收器
    }

    class NetworkChangeReceiver extends BroadcastReceiver {

        @Override
        public void onReceive(Context context, Intent intent) { //该方法在每次网络发生变化时执行
            Toast.makeText(context, "network changes", Toast.LENGTH_SHORT).show();
        }
    }
}

效果图

提示用户是否能连接Internet

修改MainActivity中的代码

        @Override
        public void onReceive(Context context, Intent intent) { //该方法在每次网络发生变化时执行

            ConnectivityManager connectivityManager =
                    (ConnectivityManager) getSystemService(context.CONNECTIVITY_SERVICE);

            NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
            if (networkInfo != null && networkInfo.isAvailable()) {
                Toast.makeText(context, "network is available", Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(context, "network is unavailable", Toast.LENGTH_SHORT).show();
            }
        }

配置权限

配置<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />声明网络访问权限

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.mybroadcast" >

    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.ListViewApplication" >
        <activity
            android:name=".MainActivity"
            android:exported="true" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

效果图