Android中检查网络连接状态的变化无网络时跳转到设置界面

<uses-permission android:name="android.permission.access_network_state" />
<intent-filter> 
  <action android:name="android.net.conn.connectivity_change" />
</intent-filter>

@override
protected void oncreate(bundle savedinstancestate) {
  super.oncreate(savedinstancestate);
  setcontentview(r.layout.activity_main);
  checknetwork();
  if (!checknetwork()) {
    toast.maketext(this, "没有网络", toast.length_long).show();
    intent intent = new intent("android.settings.wireless_settings");
    startactivity(intent);
    return;
  }
}
private boolean checknetwork() {
  connectivitymanager conn = (connectivitymanager) getsystemservice(context.connectivity_service);
  networkinfo net = conn.getactivenetworkinfo();
  if (net != null && net.isconnected()) {
    return true;
  }
  return false;
}