我正在為 Android App Login 編寫代碼。應用程序將使用 volley 庫從網站 api 發出請求。一切似乎都很好，但是當我在登錄框中輸入電子郵件和密碼并單擊登錄按鈕時，應用程序崩潰了。Logcat 顯示嘗試調用虛擬方法。我試圖弄清楚一整天，但沒有任何解決方案這就是 Logcat 顯示的內容java.lang.NullPointerException: Attempt to invoke virtual method 'void my.afamily.rrmn.app.AppController.addToRequestQueue(com.android.volley.Request, java.lang.String)' on a null object referenceat my.afamily.rrmn.LoginActivity.checkLogin(LoginActivity.java:174)    at my.afamily.rrmn.LoginActivity.access$200(LoginActivity.java:30)    at my.afamily.rrmn.LoginActivity$1.onClick(LoginActivity.java:75)    at android.view.View.performClick(View.java:6325)    at android.view.View$PerformClick.run(View.java:25098)    at android.os.Handler.handleCallback(Handler.java:790)    at android.os.Handler.dispatchMessage(Handler.java:99)    at android.os.Looper.loop(Looper.java:192)    at android.app.ActivityThread.main(ActivityThread.java:6717)    at java.lang.reflect.Method.invoke(Native Method)    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:445)    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:875)這是 AppController 類的代碼import android.app.Application;import android.text.TextUtils;import com.android.volley.Request;import com.android.volley.RequestQueue;import com.android.volley.toolbox.Volley;public class AppController extends Application {public static final String TAG = AppController.class.getSimpleName();private RequestQueue mRequestQueue;private static AppController mInstance;@Overridepublic 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;}