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Attempting to call the virtual method 'android.view.Window $ Callback android.view.Window.getCallback ()' to reference a null object

When my SplashActivity opens LoginActivity , my application crashes.

Below is my SplashActivity.java :

 package com.example.android.appName; import android.content.Intent; import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import java.util.Timer; import java.util.TimerTask; public class SplashActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_splash); Timer timer = new Timer(); timer.schedule(new TimerTask() { public void run() { Intent intent = new Intent(SplashActivity.this, LoginActivity.class); startActivity(intent); finish(); } }, 1500); } }

and my LoginActivity.java :

 package com.example.android.appName; import android.content.Intent; import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.view.KeyEvent; import android.view.Menu; import android.view.MenuInflater; import android.view.MenuItem; import android.view.View; import android.widget.EditText; import android.widget.ProgressBar; import android.widget.TextView; public class LoginActivity extends AppCompatActivity { private EditText usernameField = (EditText)findViewById(R.id.username), passwordField = (EditText)findViewById(R.id.password); private TextView error = (TextView)findViewById(R.id.error); private ProgressBar progress = (ProgressBar)findViewById(R.id.progress); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_login); } @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.login_menu, menu); return true; } @Override public boolean onKeyDown(int keyCode, KeyEvent event) { if (android.os.Build.VERSION.SDK_INT > 5 && keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) { onBackPressed(); return true; } return super.onKeyDown(keyCode, event); } public void exit(MenuItem item) { finish(); } public void signIn(View view) { Intent intent = new Intent(this, MainActivity.class); startActivity(intent); finish(); } }

Part of AndroidManifest.xml :

 <activity android:name=".SplashActivity" android:theme="@style/NoActionBar"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name=".LoginActivity" android:label="@string/title_activity_login" />

Logcat error:

 04-16 23:24:16.124 4015-4015/com.example.android.appName E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.android.appName, PID: 4015 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.appName/com.example.android.appName.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2993) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3248) at android.app.ActivityThread.access$1000(ActivityThread.java:197) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1681) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:6872) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:68) at android.support.v7.app.AppCompatDelegateImplV7.<init>(AppCompatDelegateImplV7.java:145) at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:28) at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:42) at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:186) at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:168) at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:508) at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:180) at com.example.android.appName.LoginActivity.<init>(LoginActivity.java:20) at java.lang.reflect.Constructor.newInstance(Native Method) at java.lang.Class.newInstance(Class.java:1690) at android.app.Instrumentation.newActivity(Instrumentation.java:1080) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2983) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3248) at android.app.ActivityThread.access$1000(ActivityThread.java:197) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1681) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:6872) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)
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1 answer

An Activity not fully initialized and is ready to view views until setContentView(...) is called in onCreate() .

Declare fields only as follows:

 private EditText usernameField, passwordField; private TextView error; private ProgressBar progress;

and then assign values ​​to onCreate :

 @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_login); usernameField = (EditText)findViewById(R.id.username); passwordField = (EditText)findViewById(R.id.password); error = (TextView)findViewById(R.id.error); progress = (ProgressBar)findViewById(R.id.progress); }

This may not be part of the problem, but as an additional recommendation, Timer runs TimerTask in the background thread, and this should be avoided in this case. Instead, replace the Timer with a Handler to run it in the user interface thread.

 new Handler().postDelayed(new Runnable() { @Override public void run() { Intent intent = new Intent(SplashActivity.this, LoginActivity.class); startActivity(intent); finish(); } }, 1500);
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