Android,NetworkInfo.getTypeName(),NullpointerException

Question

我有一个显示一些List条目的活动.当我点击列表项时,我的应用程序通过NetworkInfo.getTypeName()检查哪些连接类型可用("WIF"或"MOBILE").一旦我调用这个方法,我就会得到一个NullpointerException.为什么？

我在模拟器上对此进行了测试,因为我的手机目前无法使用(它已损坏......).我认为这是问题所在？这是我唯一的解释,如果不是这样,我不知道为什么这将是null.

这是一些代码片段:

public class VideoList extends ListActivity{
 ...
 public void onCreate(Bundle bundle){
  final ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
  ...
  listview.setOnItemClickListener(new OnItemClickListener(){
   public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
    ...
    NetworkInfo ni = cm.getActiveNetworkInfo();
    String connex = ni.getTypeName(); //Nullpointer exception here
    if(connex.equals("WIFI")doSomething();
   }
  });
 }
}

Answer 1

getActiveNetworkInfo()如果没有活动网络,则调用可以返回null,您需要检查该调用.下面是从源代码在这里.

/**
 * Return NetworkInfo for the active (i.e., connected) network interface.
 * It is assumed that at most one network is active at a time. If more
 * than one is active, it is indeterminate which will be returned.
 * @return the info for the active network, or {@code null} if none is active
 */
public NetworkInfo getActiveNetworkInfo() {
    enforceAccessPermission();
    for (NetworkStateTracker t : mNetTrackers) {
        NetworkInfo info = t.getNetworkInfo();
        if (info.isConnected()) {
            return info;
        }
    }
    return null;
}

请特别注意javadoc:"返回活动网络的信息,如果没有活动网络则返回null".