Android: activity crashes when called.

[Bod MacNeil]

Hello,

I am making a Rock-Paper-Scissors game.  When I call the activity with no code, it calls ok.  But when I add this bit of code, it crashes straight away:

import android.content.Intent;
import android.graphics.Color;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import java.util.Random;

public class Rock_Paper_Scissor extends AppCompatActivity {



    private ImageView rock2 = (ImageView) findViewById(R.id.rock2);
    private ImageView paper2 = (ImageView) findViewById(R.id.paper2);
    private ImageView scissors2 = (ImageView) findViewById(R.id.scissors2);
    private TextView phoneScore = (TextView) findViewById(R.id.phoneScore);
    private TextView yourScore  = (TextView) findViewById(R.id.yourScore);
    private int choice = 0;
    static int userWins = 0;
    static int phoneWins = 0;
    private String sPhoneWins;
    private String sUserWins;
    private Toast toast;
    String sRock = "Phone picked rock";
    String sPaper = " Phone picked paper";
    String sScissors = "Phone picked scissors";
    String sError = "Error, try again";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_rock__paper__scissor);

        ImageButton rockButton = (ImageButton) findViewById(R.id.rock);
        ImageButton paperButton = (ImageButton) findViewById(R.id.paper);
        ImageButton scissorsButton = (ImageButton) findViewById(R.id.scissors);
        rockButton.setOnClickListener(RPSButton);
        paperButton.setOnClickListener(RPSButton);
        scissorsButton.setOnClickListener(RPSButton);


    }



            View.OnClickListener RPSButton = new View.OnClickListener() {
                @Override
                public void onClick(View view) {

                    switch (view.getId()) {
                        case R.id.rock:
                            //rockChoice();
                            phoneScore.setText("1");
                            break;
                        case R.id.paper:
                            //paperChoice();
                            phoneScore.setText("2");
                            break;
                        case R.id.scissors:
                            //scissorsChoice();
                            phoneScore.setText("3");
                            break;
                        default:
                            break;
                    }
                }
            };

Can anyone see any problems, or have any advice on how to sort this.  Thank you

[Bod MacNeil]

I should add that that it not all of the code.  I commented out most of it as a test and it still didn't work.  It complies without any errors also.  

[Dave Tolls]

What error is there in the logs?
There should be a stacktrace and exception.

[Bod MacNeil]

12-14 10:02:54.690 21533-21533/macson.fifteendaysofjava E/AndroidRuntime: FATAL EXCEPTION: main
                                                                         java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{macson.fifteendaysofjava/macson.fifteendaysofjava.Rock_Paper_Scissor}: java.lang.NullPointerException
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1880)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
                                                                             at android.app.ActivityThread.access$600(ActivityThread.java:123)
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:99)
                                                                             at android.os.Looper.loop(Looper.java:137)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:4424)
                                                                             at java.lang.reflect.Method.invokeNative(Native Method)
                                                                             at java.lang.reflect.Method.invoke(Method.java:511)
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
                                                                             at dalvik.system.NativeStart.main(Native Method)
                                                                          Caused by: java.lang.NullPointerException
                                                                             at android.app.Activity.findViewById(Activity.java:1794)
                                                                             at macson.fifteendaysofjava.Rock_Paper_Scissor.<init>(Rock_Paper_Scissor.java:19)
                                                                             at java.lang.Class.newInstanceImpl(Native Method)
                                                                             at java.lang.Class.newInstance(Class.java:1319)
                                                                             at android.app.Instrumentation.newActivity(Instrumentation.java:1023)
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1871)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 
                                                                             at android.app.ActivityThread.access$600(ActivityThread.java:123) 
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 
                                                                             at android.os.Handler.dispatchMessage(Handler.java:99) 
                                                                             at android.os.Looper.loop(Looper.java:137) 
                                                                             at android.app.ActivityThread.main(ActivityThread.java:4424) 
                                                                             at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                             at java.lang.reflect.Method.invoke(Method.java:511) 
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
                                                                             at dalvik.system.NativeStart.main(Native Method) 

[Dave Tolls]

Caused by: java.lang.NullPointerException
at android.app.Activity.findViewById(Activity.java:1794)
at macson.fifteendaysofjava.Rock_Paper_Scissor.<init>(Rock_Paper_Scissor.java:19)

There is an issue with the view you are attempting to get on line 19.
Does it exist on the page associated with this activity?

[Bod MacNeil]

hmmm that means this line is causing the problem:

private ImageView rock2 = (ImageView) findViewById(R.id.rock2);

I've just looked and there is a rock2 ImageView in my XML:

<ImageView  
        android:id="@+id/rock2"
        android:layout_width="120dp"
        android:layout_height="120dp"
        android:src="@drawable/rock"
        android:background="#006195"
        android:cropToPadding="true"
        android:layout_above="@+id/paper2"
        android:layout_alignLeft="@+id/scissors2"
        android:layout_alignStart="@+id/scissors2"
        android:layout_gravity="center_vertical" />

above is code from the activity_rock__paper__scissor.xml which has been added to my activity

setContentView(R.layout.activity_rock__paper__scissor);

[Tim Moores]

Line 19 seems to be about scissors2, not rock2.

[Bod MacNeil]

I missed out the package name when I posted the code here so its a little off.  line 19 is for rock2 on my Android Studio.  I was thinking maybe there is a problem which is triggering this which I haven't spotted yet?

[Bod MacNeil]

I've tried commenting out line 19 but when I re-run the program the error moved to line 20 and so on.  Its just going thought my instant variables.  Has it anything to do with where I'm putting them?

[Bod MacNeil]

The code works ok when I comment out these :

ImageView rock2 = (ImageView) findViewById(R.id.rock2);
    ImageView paper2 = (ImageView) findViewById(R.id.paper2);
    ImageView scissors2 = (ImageView) findViewById(R.id.scissors2);
    TextView phoneScore = (TextView) findViewById(R.id.phoneScore);
    TextView yourScore  = (TextView) findViewById(R.id.yourScore);

Its weird that it only happens at run time.  Any ideas?

[Bod MacNeil]

Sorry for the constant posts.  But I fixed the problem by putting them in onCreate().  If anyone could explain why this works that would be good

ImageView rock2;
    ImageView paper2; 
    ImageView scissors2;
    TextView phoneScore;
    TextView yourScore;
    private int choice = 0;
    static int userWins = 0;
    static int phoneWins = 0;
    private String sPhoneWins;
    private String sUserWins;
    private Toast toast;
    String sRock = "Phone picked rock";
    String sPaper = " Phone picked paper";
    String sScissors = "Phone picked scissors";
    String sError = "Error, try again";
    //AlertDialog.Builder builder = new AlertDialog.Builder(this);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_rock__paper__scissor);

        rock2 = (ImageView) findViewById(R.id.rock2);
        paper2 = (ImageView) findViewById(R.id.paper2);
        scissors2 = (ImageView) findViewById(R.id.scissors2);
        phoneScore = (TextView) findViewById(R.id.phoneScore);
        yourScore  = (TextView) findViewById(R.id.yourScore);

        ImageButton rockButton = (ImageButton) findViewById(R.id.rock);
        ImageButton paperButton = (ImageButton) findViewById(R.id.paper);
        ImageButton scissorsButton = (ImageButton) findViewById(R.id.scissors);
        rockButton.setOnClickListener(RPSButton);
        paperButton.setOnClickListener(RPSButton);
        scissorsButton.setOnClickListener(RPSButton);


    }

[Campbell Ritchie]

Don't know, unless onCreate is some sort of analogue of a constructor. Initialising all fields in the constructor is one way to avoid nulls, so maybe the same happens in onCreate. Otherwise, don't know.
No doubt somebody else will know.

[Tim Moores]

Oh, I completely missed that.

You had two variables for each GUI element. The ones defined at class level (rock2 etc.) get instantiated when the object is constructed - when there is no layout, and hence they are null.

The objects instantiated in onCreate (rockButton etc) are accessible only in that method, and hence of little use.

The latest code version is doing it correctly.

[Dave Tolls]

Ha!
Of course.
That's what happens when you don't do this stuff for a while...you miss the forest for the trees...