我收到此NullPointerException错误，我不知道原因。我对编码很新，所以我不完全理解将它们整理出来的解释。我将尝试在此提供相关信息。
我在this tutorial工作。
以下是Logcat的堆栈跟踪：
11-30 20:28:34.415 1294-1313/system_process I/ActivityManager: Displayed com.brasiltradefx.btfxalerts/.UserProfile: +1s84ms
11-30 20:28:34.433 13772-13802/com.brasiltradefx.btfxalerts E/Surface: getSlotFromBufferLocked: unknown buffer: 0xab7d7980
11-30 20:28:37.164 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 10.648ms
11-30 20:28:37.237 1294-1306/system_process I/ActivityManager: START u0 {cmp=com.brasiltradefx.btfxalerts/.AlertMainActivity} from uid 10059 on display 0
11-30 20:28:37.315 13772-13772/com.brasiltradefx.btfxalerts D/AndroidRuntime: Shutting down VM
11-30 20:28:37.315 13772-13772/com.brasiltradefx.btfxalerts E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.brasiltradefx.btfxalerts, PID: 13772
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.brasiltradefx.btfxalerts/com.brasiltradefx.btfxalerts.AlertMainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'com.android.volley.toolbox.ImageLoader com.brasiltradefx.btfxalerts.app.AppController.getImageLoader()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'com.android.volley.toolbox.ImageLoader com.brasiltradefx.btfxalerts.app.AppController.getImageLoader()' on a null object reference
at com.brasiltradefx.btfxalerts.adapter.FeedListAdapter.<init>(FeedListAdapter.java:32)
at com.brasiltradefx.btfxalerts.AlertMainActivity.onCreate(AlertMainActivity.java:48)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
11-30 20:28:37.317 1294-1441/system_process W/ActivityManager: Force finishing activity com.brasiltradefx.btfxalerts/.AlertMainActivity
11-30 20:28:37.324 1294-1441/system_process W/ActivityManager: Force finishing activity com.brasiltradefx.btfxalerts/.UserProfile
11-30 20:28:37.383 1294-1793/system_process I/OpenGLRenderer: Initialized EGL, version 1.4
11-30 20:28:37.542 1294-1793/system_process W/EGL_emulation: eglSurfaceAttrib not implemented
11-30 20:28:37.542 1294-1793/system_process W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0x9cbb11e0, error=EGL_SUCCESS
11-30 20:28:37.831 1294-1308/system_process W/ActivityManager: Activity pause timeout for ActivityRecord{198e9e9 u0 com.brasiltradefx.btfxalerts/.AlertMainActivity t34 f}
11-30 20:28:47.251 1294-1308/system_process W/ActivityManager: Launch timeout has expired, giving up wake lock!
11-30 20:28:47.330 1294-1308/system_process W/ActivityManager: Activity destroy timeout for ActivityRecord{b9d213b u0 com.brasiltradefx.btfxalerts/.UserProfile t34 f}
11-30 20:28:54.408 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 9.171ms
11-30 20:28:57.300 1294-1308/system_process W/ActivityManager: Activity destroy timeout for ActivityRecord{198e9e9 u0 com.brasiltradefx.btfxalerts/.AlertMainActivity t34 f}
11-30 20:29:19.308 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 8.771ms
11-30 20:29:46.339 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 9.186ms
11-30 20:29:56.702 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 31.840ms
11-30 20:30:19.788 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 8.535ms
11-30 20:30:41.479 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 8.854ms
11-30 20:30:59.203 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 11.610ms
11-30 20:31:06.733 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 19.746ms
11-30 20:31:16.218 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 7.017ms
11-30 20:31:34.588 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 6.590ms
11-30 20:32:10.567 1294-1668/system_process D/ConnectivityService: reportNetworkConnectivity(100, false) by 10007
11-30 20:32:10.568 1294-1874/system_process D/NetworkMonitor/NetworkAgentInfo [MOBILE (UMTS) - 100]: Forcing reevaluation for UID 10007
11-30 20:32:10.627 1294-1874/system_process D/NetworkMonitor/NetworkAgentInfo [MOBILE (UMTS) - 100]: Checking http://connectivitycheck.gstatic.com/generate_204 on epc.tmobile.com, connectivitycheck.gstatic.com=74.125.21.139
11-30 20:32:10.656 1920-17221/com.google.android.gms I/EventLogService: Aggregate from 1448931729741 (log), 1448931729741 (data)
11-30 20:32:10.725 1294-1874/system_process D/NetworkMonitor/NetworkAgentInfo [MOBILE (UMTS) - 100]: isCaptivePortal: ret=204 headers={null=[HTTP/1.1 204 No Content], Content-Length=[0], Date=[Tue, 01 Dec 2015 01:40:19 GMT], Server=[GFE/2.0], X-Android-Received-Millis=[1448933530725], X-Android-Response-Source=[NETWORK 204], X-Android-Selected-Protocol=[http/1.1], X-Android-Sent-Millis=[1448933530679]}
11-30 20:32:10.726 1294-1335/system_process D/ConnectivityService: setProvNotificationVisibleIntent null visible=false networkType=MOBILE extraInfo=null highPriority=false
11-30 20:32:10.727 1294-1335/system_process D/ConnectivityService: NetworkAgentInfo [MOBILE (UMTS) - 100] validation passed
11-30 20:32:10.836 1813-1826/com.google.process.gapps W/art: Suspending all threads took: 13.693ms
11-30 20:32:10.853 1813-1826/com.google.process.gapps I/art: Background sticky concurrent mark sweep GC freed 8892(951KB) AllocSpace objects, 0(0B) LOS objects, 18% free, 5MB/6MB, paused 15.651ms total 33.468ms
11-30 20:32:11.082 1813-17230/com.google.process.gapps I/PhenotypeFlagCommitter: Experiment Configs successfully retrieved for com.google.android.gms.playlog.uploader
11-30 20:32:11.085 1813-17230/com.google.process.gapps I/GoogleURLConnFactory: Using platform SSLCertificateSocketFactory
11-30 20:32:33.446 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 13.292ms
11-30 20:33:17.374 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 11.145ms
11-30 20:33:21.985 13772-13785/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 12.440ms
11-30 20:33:37.367 13772-13772/com.brasiltradefx.btfxalerts I/Process: Sending signal. PID: 13772 SIG: 9
11-30 20:33:37.395 1294-1793/system_process E/Surface: getSlotFromBufferLocked: unknown buffer: 0xa1a9d4c0
11-30 20:33:37.451 1294-1668/system_process D/GraphicsStats: Buffer count: 6
11-30 20:33:37.452 1294-1668/system_process I/WindowState: WIN DEATH: Window{afedcc3 u0 com.brasiltradefx.btfxalerts/com.brasiltradefx.btfxalerts.GoogleInAppBilling}
11-30 20:33:37.496 1294-1686/system_process I/ActivityManager: Process com.brasiltradefx.btfxalerts (pid 13772) has died
11-30 20:33:37.528 18411-18411/? I/art: Not late-enabling -Xcheck:jni (already on)
11-30 20:33:37.528 18411-18411/? I/art: Late-enabling JIT
11-30 20:33:37.535 1294-1686/system_process I/ActivityManager: Start proc 18411:com.brasiltradefx.btfxalerts/u0a59 for activity com.brasiltradefx.btfxalerts/.GoogleInAppBilling
11-30 20:33:37.582 18411-18411/? I/art: JIT created with code_cache_capacity=2MB compile_threshold=1000
11-30 20:33:37.732 18411-18411/? W/System: ClassLoader referenced unknown path: /data/app/com.brasiltradefx.btfxalerts-1/lib/x86
11-30 20:33:38.016 18411-18438/com.brasiltradefx.btfxalerts I/GMPM: App measurement is starting up
11-30 20:33:38.021 18411-18438/com.brasiltradefx.btfxalerts E/GMPM: getGoogleAppId failed with status: 10
11-30 20:33:38.022 18411-18438/com.brasiltradefx.btfxalerts E/GMPM: Uploading is not possible. App measurement disabled
11-30 20:33:38.131 18411-18411/com.brasiltradefx.btfxalerts E/c3+U6b5T6IHUG94DJ22teQVKojk=:: PMSeT4Q8FLTjYUOwNpnShvIlw4E=
11-30 20:33:38.310 18411-18426/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 23.876ms
11-30 20:33:38.453 18411-18426/com.brasiltradefx.btfxalerts I/art: Background sticky concurrent mark sweep GC freed 11632(697KB) AllocSpace objects, 8(160KB) LOS objects, 65% free, 1265KB/3MB, paused 160.467ms total 230.843ms
11-30 20:33:38.485 18411-18422/com.brasiltradefx.btfxalerts W/art: Suspending all threads took: 28.821ms
11-30 20:33:38.694 1294-1313/system_process I/Choreographer: Skipped 65 frames! The application may be doing too much work on its main thread.
11-30 20:33:38.718 1294-1313/system_process W/AppOps: Finishing op nesting under-run: uid 1000 pkg android code 24 time=0 duration=0 nesting=0
FeedListAdapter.java
package com.brasiltradefx.btfxalerts.adapter;
import com.brasiltradefx.btfxalerts.FeedImageView;
import com.brasiltradefx.btfxalerts.R;
import com.brasiltradefx.btfxalerts.app.AppController;
import com.brasiltradefx.btfxalerts.data.FeedItem;
import java.util.List;
import android.app.Activity;
import android.content.Context;
import android.text.Html;
import android.text.TextUtils;
import android.text.format.DateUtils;
import android.text.method.LinkMovementMethod;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.NetworkImageView;
/**
* Created by Deryk on 11/30/2015.
*/
public class FeedListAdapter extends BaseAdapter {
private Activity activity;
private LayoutInflater inflater;
private List<FeedItem> feedItems;
ImageLoader imageLoader = AppController.getInstance().getImageLoader();
public FeedListAdapter(Activity activity, List<FeedItem> feedItems) {
this.activity = activity;
this.feedItems = feedItems;
}
@Override
public int getCount() {
return feedItems.size();
}
@Override
public Object getItem(int location) {
return feedItems.get(location);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (inflater == null)
inflater = (LayoutInflater) activity
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null)
convertView = inflater.inflate(R.layout.feed_item, null);
if (imageLoader == null)
imageLoader = AppController.getInstance().getImageLoader();
TextView name = (TextView) convertView.findViewById(R.id.name);
TextView timestamp = (TextView) convertView
.findViewById(R.id.timestamp);
TextView statusMsg = (TextView) convertView
.findViewById(R.id.txtStatusMsg);
TextView url = (TextView) convertView.findViewById(R.id.txtUrl);
TextView order_type = (TextView) convertView.findViewById(R.id.tvOrder_type);
TextView pair = (TextView) convertView.findViewById(R.id.tvPair);
TextView rate = (TextView) convertView.findViewById(R.id.tvRate);
TextView quick_target = (TextView) convertView.findViewById(R.id.tvQuick_Target);
TextView long_target = (TextView) convertView.findViewById(R.id.tvLong_Target);
TextView stop_loss = (TextView) convertView.findViewById(R.id.tvStop_Loss);
TextView break_even = (TextView) convertView.findViewById(R.id.tvBreak_Even);
FeedImageView feedImageView = (FeedImageView) convertView
.findViewById(R.id.feedImage1);
FeedItem item = feedItems.get(position);
name.setText(item.getName());
// Converting timestamp into x ago format
CharSequence timeAgo = DateUtils.getRelativeTimeSpanString(
Long.parseLong(item.getTimeStamp()),
System.currentTimeMillis(), DateUtils.SECOND_IN_MILLIS);
timestamp.setText(timeAgo);
// Chcek for empty status message
if (!TextUtils.isEmpty(item.getStatus())) {
statusMsg.setText(item.getStatus());
statusMsg.setVisibility(View.VISIBLE);
} else {
// status is empty, remove from view
statusMsg.setVisibility(View.GONE);
}
// Checking for null feed url
if (item.getUrl() != null) {
url.setText(Html.fromHtml("<a href=\"" + item.getUrl() + "\">"
+ item.getUrl() + "</a> "));
// Making url clickable
url.setMovementMethod(LinkMovementMethod.getInstance());
url.setVisibility(View.VISIBLE);
} else {
// url is null, remove from the view
url.setVisibility(View.GONE);
}
// Feed image
if (item.getImge() != null) {
feedImageView.setImageUrl(item.getImge(), imageLoader);
feedImageView.setVisibility(View.VISIBLE);
feedImageView
.setResponseObserver(new FeedImageView.ResponseObserver() {
@Override
public void onError() {
}
@Override
public void onSuccess() {
}
});
} else {
feedImageView.setVisibility(View.GONE);
}
return convertView;
}
}
AlertMainActivity.java
package com.brasiltradefx.btfxalerts;
import com.brasiltradefx.btfxalerts.adapter.FeedListAdapter;
import com.brasiltradefx.btfxalerts.app.AppController;
import com.brasiltradefx.btfxalerts.data.FeedItem;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.List;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.view.Menu;
import android.widget.ListView;
import com.android.volley.Cache;
import com.android.volley.Cache.Entry;
import com.android.volley.Request.Method;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.VolleyLog;
import com.android.volley.toolbox.JsonObjectRequest;
public class AlertMainActivity extends Activity {
private static final String TAG = AlertMainActivity.class.getSimpleName();
private ListView listView;
private FeedListAdapter listAdapter;
private List<FeedItem> feedItems;
private String URL_FEED = "http://www.contrariantradefx.info/android/btfxalerts/fetchalertdata.json"; //todo change URL here -done!
@SuppressLint("NewApi")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_alert_main);
listView = (ListView) findViewById(R.id.list);
feedItems = new ArrayList<FeedItem>();
listAdapter = new FeedListAdapter(this, feedItems);
listView.setAdapter(listAdapter);
// We first check for cached request
Cache cache = AppController.getInstance().getRequestQueue().getCache();
Entry entry = cache.get(URL_FEED);
if (entry != null) {
// fetch the data from cache
try {
String data = new String(entry.data, "UTF-8");
try {
parseJsonFeed(new JSONObject(data));
} catch (JSONException e) {
e.printStackTrace();
}
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
} else {
// making fresh volley request and getting json
JsonObjectRequest jsonReq = new JsonObjectRequest(Method.GET,
URL_FEED, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
VolleyLog.d(TAG, "Response: " + response.toString());
if (response != null) {
parseJsonFeed(response);
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
VolleyLog.d(TAG, "Error: " + error.getMessage());
}
});
// Adding request to volley request queue
AppController.getInstance().addToRequestQueue(jsonReq);
}
}
/**
* Parsing json reponse and passing the data to feed view list adapter
* */
private void parseJsonFeed(JSONObject response) {
try {
JSONArray feedArray = response.getJSONArray("feed");
for (int i = 0; i < feedArray.length(); i++) {
JSONObject feedObj = (JSONObject) feedArray.get(i);
FeedItem item = new FeedItem();
item.setId(feedObj.getInt("id"));
item.setName(feedObj.getString("name"));
// Image might be null sometimes
String image = feedObj.isNull("image") ? null : feedObj
.getString("image");
item.setImge(image);
item.setStatus(feedObj.getString("status"));
item.setProfilePic(feedObj.getString("profilePic"));
item.setTimeStamp(feedObj.getString("timeStamp"));
// url might be null sometimes
String feedUrl = feedObj.isNull("url") ? null : feedObj
.getString("url");
item.setUrl(feedUrl);
item.setOrder_type(feedObj.getString("order_type"));
item.setPair(feedObj.getString("pair"));
item.setRate(feedObj.getString("rate"));
item.setQuick_target(feedObj.getString("quick_target"));
item.setLong_target(feedObj.getString("long_target"));
item.setStop_loss(feedObj.getString("stop_loss"));
item.setBreak_Even(feedObj.getString("break_even"));
feedItems.add(item);
}
// notify data changes to list adapter
listAdapter.notifyDataSetChanged();
} catch (JSONException e) {
e.printStackTrace();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
我认为它也与AppController有关，所以我已将其包括在内。
package com.brasiltradefx.btfxalerts.app;
import com.brasiltradefx.btfxalerts.volley.LruBitmapCache;
import android.app.Application;
import android.text.TextUtils;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.Volley;
/**
* Created by Deryk on 11/30/2015.
*/
public class AppController extends Application {
public static final String TAG = AppController.class.getSimpleName();
private RequestQueue mRequestQueue;
private ImageLoader mImageLoader;
LruBitmapCache mLruBitmapCache;
private static AppController mInstance;
@Override
public void onCreate() {
super.onCreate();
mInstance = this;
}
public static synchronized AppController getInstance() {
return mInstance;
}
public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
mRequestQueue = Volley.newRequestQueue(getApplicationContext());
}
return mRequestQueue;
}
public ImageLoader getImageLoader() {
getRequestQueue();
if (mImageLoader == null) {
getLruBitmapCache();
mImageLoader = new ImageLoader(this.mRequestQueue, mLruBitmapCache);
}
return this.mImageLoader;
}
public LruBitmapCache getLruBitmapCache() {
if (mLruBitmapCache == null)
mLruBitmapCache = new LruBitmapCache();
return this.mLruBitmapCache;
}
public <T> void addToRequestQueue(Request<T> req, String tag) {
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
getRequestQueue().add(req);
}
public <T> void addToRequestQueue(Request<T> req) {
req.setTag(TAG);
getRequestQueue().add(req);
}
public void cancelPendingRequests(Object tag) {
if (mRequestQueue != null) {
mRequestQueue.cancelAll(tag);
}
}
}
这是清单。
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.brasiltradefx.btfxalerts">
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="com.android.vending.BILLING" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<application
android:name=".MyApplication"
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme">
<meta-data
android:name="com.facebook.sdk.ApplicationId"
android:value="@string/facebook_app_id" />
<activity
android:name="com.facebook.FacebookActivity"
android:configChanges="keyboard|keyboardHidden|screenLayout|screenSize|orientation"
android:label="BTFX Alerts"
android:theme="@android:style/Theme.Translucent.NoTitleBar" />
<activity android:name=".LoginActivity">
android:label="BTFX Alerts" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".LogoutActivity"
android:label="@string/title_activity_logout" />
<activity android:name=".AlertsPage" />
<activity android:name=".GoogleInAppBilling" />
<activity android:name=".Blog" />
<activity android:name=".ForexNews" />
<activity android:name=".BTFXForum" />
<activity android:name=".ForexShow" />
<activity android:name=".ChartAnalysis" />
<activity android:name=".UserProfile" />
<activity android:name="com.facebook.LoginActivity" />
<activity android:name="com.brasiltradefx.btfxalerts.app.AppController" />
<!--
ATTENTION: This was auto-generated to add Google Play services to your project for
App Indexing. See https://g.co/AppIndexing/AndroidStudio for more information.
-->
<meta-data
android:name="com.google.android.gms.version"
android:value="@integer/google_play_services_version" />
<activity android:name=".AlertPage" />
<activity android:name=".FeedViewImage" />
<activity android:name=".AlertMainActivity" />
<activity android:name=".FeedImageView"></activity>
</application>
</manifest>
给予任何帮助！
答案 0 :(得分：1)
在null类的getInstance()方法中返回一个AppController - 对象，然后尝试在该对象上调用方法。
要修复，请更换
public static synchronized AppController getInstance() {
return mInstance;
}
与
public static synchronized AppController getInstance() {
if(mInstance == null){
mInstance = new AppController();
}
return mInstance;
}
您确定要一个扩展Application的课程吗？
答案 1 :(得分：1)
你在Manifest中指定了MyApplication，它应该是AppController以匹配你的Application子类。
如果查看您正在使用的教程，您会看到他们在AndroidManifest.xml中引用了应用程序类名称：
<application
android:name="info.androidhive.listviewfeed.app.AppController"
在您的情况下，您可以使用带有android:name="com.brasiltradefx.btfxalerts.app.AppController"的AppController类修改AndroidManifest，以使用正确的Application子类：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.brasiltradefx.btfxalerts">
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="com.android.vending.BILLING" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<application
android:name="com.brasiltradefx.btfxalerts.app.AppController"
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme">
<meta-data
android:name="com.facebook.sdk.ApplicationId"
android:value="@string/facebook_app_id" />
//......................