package cc.testnetworkchange;
import android.os.Bundle;
import android.app.Activity;
/**
 * Demo描写叙述:
 * 利用广播监听设备网络连接的变化情况
 * 亦可借此监測到设备是否已经断开网络
 */
public class MainActivity extends Activity {

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

NetWorkChangeBroadcastReceiver例如以下:

package cc.testnetworkchange;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.NetworkInfo.State;

public class NetWorkChangeBroadcastReceiver extends BroadcastReceiver {

	@Override
	public void onReceive(Context context, Intent intent) {
		ConnectivityManager connectivityManager=
		(ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
		if (connectivityManager!=null) {
			NetworkInfo [] networkInfos=connectivityManager.getAllNetworkInfo();
			for (int i = 0; i < networkInfos.length; i++) {
				State state=networkInfos[i].getState();
				if (NetworkInfo.State.CONNECTED==state) {
					System.out.println("------------> Network is ok");
					return;
				}
			}
		}
		
		//没有运行return,则说明当前无网络连接
		System.out.println("------------> Network is validate");
		intent.setClass(context, NetWorkErrorActivity.class);
		intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP|Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(intent);
	}

}

package cc.testnetworkchange;
import android.os.Bundle;
import android.app.Activity;
public class NetWorkErrorActivity extends Activity {

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

<RelativeLayout 
    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" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:text="利用广播监听设备网络连接的变化情况"
     />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="cc.testnetworkchange"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="8" />
    
    
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="cc.testnetworkchange.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
            
        </activity>
        
         <!-- 注冊显示错误的Activity-->
        <activity android:name="cc.testnetworkchange.NetWorkErrorActivity"></activity>
        
        <!-- 注冊广播 -->
        <receiver android:name="cc.testnetworkchange.NetWorkChangeBroadcastReceiver">
            <intent-filter>
                 <action android:name="android.net.conn.CONNECTIVITY_CHANGE" />
             </intent-filter>
        </receiver>
    </application>

</manifest>