str 赋值

private static final Intent intent = null;
ListView listView;
IntentFilter intentFilter;
public String str;
public BroadcastReceiver intentReceiver= new BroadcastReceiver(){
@Override
public void onReceive(Context context, Intent intent) {
//TODO Auto-generated method stub
str = intent.getExtras().getString("sms");
}
};i
为什么 str = intent.getExtras().getString("sms")获取的值（很确定已经获得了相应的值），不能赋值给 public String str;中的str,
求大神指点，谢谢！