App crashes when trying to run it on my phone at the end of this video

Aha!! We have an answer!

Change:

<Button
  android:id="@+id/ShowFactButton"

to:

<Button
  android:id="@+id/showFactButton"

Lower case S. So, your layout wasn't linking to your code because the names didn't match.

Let me know if that fixes it.

Steve.

Sorry, I didnt see the answer box I just edited my original comment.

This new error continues even without me running the app I dont think I can get the null pointer. As soon as I plugged my phone back in loop continues

As soon as I open android studio those messages start again, it is much more than what I pasted in my original comment. When I hit run the app still crashes immediately

If you have your device connected to the computer, it'll chat constantly in Logcat. They aren't errors, they're just notifications of what is going on.

If the app in crashing, you can filter the Logcat output to just show messages from your app. Give that a go and paste it in here.

Logcat doesn't just show errors, it talks constantly about the state of everything. You need to filter it down to the relevant messages. You can filter by message-type or by source-application.

If your app is crashing, there will be Logcat output to say why. That's what it does.

Steve.

03-22 18:57:53.011 4968-4968/? E/Zygote: v2 03-22 18:57:53.012 4968-4968/? E/Zygote: accessInfo : 0 03-22 18:57:53.312 4968-4968/com.georgesapps.myapplication E/AndroidRuntime: FATAL EXCEPTION: main Process: com.georgesapps.myapplication, PID: 4968 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.georgesapps.myapplication/com.georgesapps.myapplication.FunFactsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2984) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045) at android.app.ActivityThread.-wrap14(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6776) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at com.georgesapps.myapplication.FunFactsActivity.onCreate(FunFactsActivity.java:29) at android.app.Activity.performCreate(Activity.java:6955) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2927) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045)  at android.app.ActivityThread.-wrap14(ActivityThread.java)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:154)  at android.app.ActivityThread.main(ActivityThread.java:6776)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)

I think this is the code around the exception:

 final TextView factTextView = findViewById(R.id.factTextView);

Button showFactButton = findViewById(R.id.showFactButton);

        View.OnClickListener listener = new View.OnClickListener() {

            @Override

            public void onClick(View view) {

                // The button was clicked so update the fact TextView with a new fact

                String newFact = "Ostriches can run faster than horses";

                factTextView.setText(newFact);

            }
        };
        showFactButton.setOnClickListener(listener);

I'm going to make a guess here. You have declared your TextView to be final. That makes it unmodifiable; i.e. a constant. Now, that might be OK, as you have assigned R.id.factTextView into it and that doesn't change. But I might be wrong - maybe you can't call setText() on a constant. I'd delete the final keyword - it isn't there in the video.

Secondly, have you redeclared both your factTextView and your showFactButton? You should have created these variables outside of onCreate; that's where your code is taken from. At the top of the class, you should have:

public class FunFacstActivity extends AppCompatActivity {
  private TextView factTextView;
  private Button showFactButton

The in onCreate you should have:

protected void onCreate(Bundle savedInstanceState){
  // call to super etc

  factTextView = (TextView) findViewById(R.id.factTextView);
  showFactButton = (Button) findViewById(R.id.showFactButton);

  // onClick
}

So, you don't repeat the TextView or Button keyword prefix - if you do, you change the scope of the variable, so maybe post the whole of your activity code so I can see what you have got. Also, note the type cast when returning the view by id - in older Android versions, you need to prefix the assignment with (TextView) and (Button) to make sure the returned view is changed to the correct type. I don't think this persists in newer Android versions, but maybe leave it in here if it isn't throwing errors.

So, best to post all your code in here so we can make sure we've caught everything.

Steve.

Thanks - try changing this:

        TextView factTextView = findViewById(R.id.factTextView);
        Button showFactButton = findViewById(R.id.showFactButton);

to this:

        factTextView = findViewById(R.id.factTextView);
        showFactButton = findViewById(R.id.showFactButton);

You are redeclaring your variables which will cause scope issues which may generate a null pointer if access is attempted outside their existing scope.

Steve.

I removed the Textview and Button prefixes and attempted to run the app and got this error:

Process: com.georgesapps.myapplication, PID: 13756 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.georgesapps.myapplication/com.georgesapps.myapplication.FunFactsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

Oops! I forgot the cast - add the data types to cast the returned views:

        factTextView = (TextView) findViewById(R.id.factTextView);
        showFactButton = (Button) findViewById(R.id.showFactButton);

I'm sorry I can't find where it says the line number where the error occured. I will copy the entire error message.

03-23 10:58:36.883 17260-17260/? E/Zygote: isWhitelistProcess - Process is Whitelisted 03-23 10:58:36.884 17260-17260/? E/libpersona: scanKnoxPersonas 03-23 10:58:36.884 17260-17260/? E/libpersona: Couldn't open the File - /data/system/users/0/personalist.xml - No such file or directory 03-23 10:58:37.266 17260-17260/com.georgesapps.myapplication E/AndroidRuntime: FATAL EXCEPTION: main Process: com.georgesapps.myapplication, PID: 17260 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.georgesapps.myapplication/com.georgesapps.myapplication.FunFactsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2955) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3030) at android.app.ActivityThread.-wrap11(Unknown Source:0) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696) at android.os.Handler.dispatchMessage(Handler.java:105) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6938) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at com.georgesapps.myapplication.FunFactsActivity.onCreate(FunFactsActivity.java:32) at android.app.Activity.performCreate(Activity.java:7174) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1220) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2908) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3030)  at android.app.ActivityThread.-wrap11(Unknown Source:0)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696)  at android.os.Handler.dispatchMessage(Handler.java:105)  at android.os.Looper.loop(Looper.java:164)  at android.app.ActivityThread.main(ActivityThread.java:6938)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)

line 32: showFactButton.setOnClickListener(listener);

when I cast, the "(Button)" has a squiggly line under it saying casting to button is redundant. I'm not sure that the cast is the issue because I have a very recent version of android studio

Yes!! Thank you very much that seems to have done the trick!