build java method to change two textViews

Question

I have two buttons and two textViews , when i click "add2_A" ,then "score1" is updated and increment by 2 .

the same is "add2_B" will increment "score2"

i want to use only one method for both of them ..the problem is that the app crash !

this is my java code :

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class app2 extends AppCompatActivity implements View.OnClickListener 
{
public int number =0;
public int id;
TextView txt1= (TextView) findViewById(R.id.score1);
TextView txt2 = (TextView) findViewById(R.id.score2);
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_app2);

}
@Override
public void onClick(View v){
   id=v.getId();
}

public void increment2(){
    number =number +2;
    if(id ==R.id.add2_A)
        txt1.setText(number);
    if(id== R.id.add2_B)
        txt2.setText(String.valueOf(number));
}}

edit : this is XML code for calling "increment2" method :

<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/points2"
android:layout_margin="8dp"
android:id="@+id/add2_A"
android:onClick="increment2"/>

edit : i solved it and it works now ..this is the code after editing :

public class app2 extends AppCompatActivity  {
public int number =0;
public int id;
public TextView txt1;
public TextView txt2;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_app2);
    txt1= (TextView) findViewById(R.id.score1);
    txt2 = (TextView) findViewById(R.id.score2);
}

public void increment2(View v) {
    number = number + 2;
    id = v.getId();
    if (id == R.id.add2_A) {
        txt1 = (TextView) findViewById(R.id.score1);
        txt1.setText(String.valueOf(number));
    }
    if (id == R.id.add2_B) {
        txt2 = (TextView) findViewById(R.id.score2);
        txt2.setText(String.valueOf(number));
    }
}

edit : this is what appears in the logcat and there's no other messages in the message bar :

  Process: com.example.mayouza.myapplication2, PID: 2553
                                                                              java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.mayouza.myapplication2/com.example.mayouza.myapplication2.app2}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
                                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2567)
                                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                                                  at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                  at android.os.Looper.loop(Looper.java:154)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                                               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
                                                                                  at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:120)
                                                                                  at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:151)
                                                                                  at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:31)
                                                                                  at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:55)
                                                                                  at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:33)
                                                                                  at android.support.v7.app.AppCompatDelegateImplN.<init>(AppCompatDelegateImplN.java:33)
                                                                                  at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:201)
                                                                                  at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:185)
                                                                                  at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
                                                                                  at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
                                                                                  at com.example.mayouza.myapplication2.app2.<init>(app2.java:11)
                                                                                  at java.lang.Class.newInstance(Native Method)
                                                                                  at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
                                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2557)
                                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
                                                                                  at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                  at android.os.Looper.loop(Looper.java:154) 
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:6119) 
                                                                                  at java.lang.reflect.Method.invoke(Native Method) 
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

The error doesn't come from this activity, but probably missing ComponentInfo. — Vega, Aug 22 '17 at 23:48
`increment2` is never called in your code... Put all that code into onClick. Don't store `id` as a field — OneCricketeer, Aug 23 '17 at 00:15
Whenever you use `android:onClick` that method must be 1) public 2) void 3) accept a View parameter. Otherwise, your code crashes — OneCricketeer, Aug 23 '17 at 00:28
@cricket_007 thanks i could solve it using this answer i was missing the view parameter ..i need to note that the duplicated question you mentioned in the link didn't solve the problem that's why i asked again. — mai amer, Aug 23 '17 at 12:30
It actually does solve the stacktrace you've posted and the code in the question. The onClick problem is a different error completely, and also tells you that the method needs a View parameter if you read it — OneCricketeer, Aug 23 '17 at 12:33
Note: your views aren't changing after onCreate, so you should only use findViewById once for each view, not everytime a click happens — OneCricketeer, Aug 23 '17 at 12:35
i'm not good at reading stacktrace yet ,,and thanks for the note you're right — mai amer, Aug 23 '17 at 14:06

Zamrony P. Juhara · Answer 1 · 2017-08-23T00:10:57.197

0

You will not be able to successfully call findViewById() before you call setContentView() because view hiearchy has not built yet.

You need to move call to findViewById() after call to setContentView().

setContentView(R.layout.activity_app2);
txt1= (TextView) findViewById(R.id.score1);
txt2 = (TextView) findViewById(R.id.score2);

edited Aug 23 '17 at 00:10

answered Aug 22 '17 at 23:39

Zamrony P. Juhara

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i did ,, the app opened but when i click the button it crashes again – mai amer Aug 22 '17 at 23:56
1

post your code where you call increment2(). – Zamrony P. Juhara Aug 23 '17 at 00:13

build java method to change two textViews

1 Answers1