Android,NetworkInfo.getTypeName(),NullpointerException

我有一个活动显示一些列表条目.当我点击列表项目时,我的应用程序通过NetworkInfo.getTypeName()检查可用的连接类型(“WIF”或“MOBILE”).一旦我调用这个方法,我得到一个NullpointerException.为什么？

我在模拟器上测试了这个,因为我的手机目前不可用(坏了…).我假设这是问题？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.

以下是一些代码段：

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();
   }
  });
 }
}

解决方法

如果没有活动网络,则调用getActiveNetworkInfo()可以返回null,并且需要检查.这是 here的源代码.

/**
 * 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;
}

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