我的问题是,在我的MainActivity的onCreate()方法中,我创建了一个新的Thread对象,我想将该对象传递给this
活动,并且在该线程中使用它来调用getSystemService ()。但最终,当我启动应用程序时,它崩溃,我得到NullPointerException。调用getSystemService()时得到NullPointerException异常
我已经发现问题可能是我传递引用的活动befor super.onCreate(),但在我的代码super.onCreate()是在传递引用之前执行的。
这是我的MainActivity的onCreate()方法
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Instance which contains thread for obtaining wifi info
final WifiInfoThread wifi_info = new WifiInfoThread(this);
....
}
这是我想获得参考系统服务
public class WifiInfoThread extends Thread {
// Constructor for passing context to this class to be able to access xml resources
Activity activity;
WifiInfoThread(Activity current) {
activity = current;
}
// Flag for stopping thread
boolean flag = false;
// Obtain service and WifiManager object
WifiManager current_wifi = (WifiManager) activity.getSystemService(Context.WIFI_SERVICE);
// Runnable object passed to UIThread
Runnable uirunnable = new Runnable() {
@Override
public void run() {
// Get current wifi status
WifiInfo wifi_info = current_wifi.getConnectionInfo();
// Things with showing it on screen
TextView tv_output = (TextView) activity.findViewById(R.id.tv_output);
String info = "SSID: " + wifi_info.getSSID();
info += "\nSpeed: " + wifi_info.getLinkSpeed() + " Mbps";
tv_output.setText(info);
}
};
public void run() {
flag = true;
for(; flag;) {
activity.runOnUiThread(uirunnable);
try {
this.sleep(500);
}
catch(InterruptedException e) {}
}
}
}
亲爱的downvoter,用户刚刚创建了一个帐户,并提出了一个问题,不要急于下调。也许编辑或评论会受到欢迎。 – iceman