0
我的申請似乎遇到競爭條件,我不確定原因。它只發生在我第一次打開應用程序時。根據錯誤,MainActivity中的靜態變量實例爲空,但在啓動服務之前設置了變量。看起來服務在onCreate在活動內完成之前開始運行,但我不相信這是可能的。任何想法發生了什麼?背景服務競賽條件
錯誤消息
E/AndroidRuntime: FATAL EXCEPTION: Timer-
java.lang.NullPointerException
at NetworkCalls.getRequestQueue(NetworkCalls.java:42)
at NetworkCalls.addToRequestQueue(NetworkCalls.java:48)
at NetworkCalls.createLocationPost(NetworkCalls.java:72)
at StaticMethods.handleWarnings(StaticMethods.java:84)
at LocationService.checkInPost(LocationService.java:73)
at LocationService$1.run(LocationService.java:66)
at java.util.Timer$TimerImpl.run(Timer.java:284)
網絡類
public class NetworkCalls {
private static NetworkCalls singleton;
private RequestQueue mRequestQueue;
private static Context warningCtx = WarningActivity.instance;
private static Context mCtx = MainActivity.instance;
private NetworkCalls() {
}
public static synchronized NetworkCalls getInstance() {
if (singleton == null) {
singleton = new NetworkCalls();
}
return singleton;
}
private RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
//Problem here is that mCtx is null
if(mCtx == null){
Log.e("Error", "It's FUBAR");
}else {
Log.e("Error", "It's Okay");
}
mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
}
return mRequestQueue;
}
private <T> void addToRequestQueue(Request<T> req) {
getRequestQueue().add(req);
}
public void createLocationPost(LocationData locationData) {
String url = "http://httpbin.org/post";
HashMap<String, String> params = new HashMap<>();
params.put("Token", "key");
JsonObjectRequest jsObj = new JsonObjectRequest(url, new JSONObject(params), new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
try {
Log.i("NetworkCalls Successful", response.getJSONObject("json").toString());
} catch (JSONException ex) {
Log.i("Parsing response", "Unable to get json string");
}
// On Response recieved
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.i("NetworkCalls Error", error.toString());
}
});
addToRequestQueue(jsObj);
}
主要acivity
public class MainActivity extends AppCompatActivity {
public static MainActivity instance = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ColorDrawable colorDrawable = new ColorDrawable(Color.parseColor("#000000"));
getSupportActionBar().setBackgroundDrawable(colorDrawable);
this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LOCKED);
instance = MainActivity.this;
startService(new Intent(getBaseContext(), QueuePostService.class));
}
}
}
這很好,謝謝。我不會想到類加載器是如何工作的,而且幾乎不可能跟蹤這個問題。節省了我幾個小時的頭痛! – Ubarjohade
不要考慮類加載器是如何加載的:請記住,Java變量是值而不是引用,因此對「引用」變量的後續更改不會反映在「引用」變量中。 –