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Asked: 2026-06-03T16:47:37+00:00

I am trying to get a random string from an array when I press

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I am trying to get a random string from an array when I press a button.

So far it works with getting a random string when the application starts up, but I cannot get it to work on press of a button after startup.

EDIT:
It now crashes on start up??

My new code: 

private String[] myString;
private static final Random rgenerator = new Random();


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);



    TextView tv = (TextView) findViewById(R.id.joke);
  Resources res = getResources();

    myString = res.getStringArray(R.array.Jokes); 

    String q = myString[rgenerator.nextInt(myString.length)];    
    tv.setText(q);
    Button btn = (Button)findViewById(R.id.button);


 btn.setOnClickListener(new OnClickListener() { 
public void onClick(View v) {

    myString = res.getStringArray(R.array.Jokes); 

    String q = myString[rgenerator.nextInt(myString.length)];    
    tv.setText(q);
  }
});

}
}

Logcat says:

03-31 22:47:35.777: W/dalvikvm(1152): threadid=3: thread exiting with uncaught exception (group=0x4001b188)
03-31 22:47:35.777: E/AndroidRuntime(1152): Uncaught handler: thread main exiting due to uncaught exception
03-31 22:47:35.903: E/AndroidRuntime(1152): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.jc.dkjokes/com.jc.dkjokes.DanskeJokesMain}: java.lang.NullPointerException
03-31 22:47:35.903: E/AndroidRuntime(1152):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2417)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at android.app.ActivityThread.access$2200(ActivityThread.java:119)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at android.os.Looper.loop(Looper.java:123)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at android.app.ActivityThread.main(ActivityThread.java:4363)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at java.lang.reflect.Method.invokeNative(Native Method)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at java.lang.reflect.Method.invoke(Method.java:521)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at dalvik.system.NativeStart.main(Native Method)
03-31 22:47:35.903: E/AndroidRuntime(1152): Caused by: java.lang.NullPointerException
03-31 22:47:35.903: E/AndroidRuntime(1152):     at android.app.Activity.findViewById(Activity.java:1612)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at com.jc.dkjokes.DanskeJokesMain.<init>(DanskeJokesMain.java:17)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at java.lang.Class.newInstanceImpl(Native Method)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at java.lang.Class.newInstance(Class.java:1479)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
03-31 22:47:35.903: E/AndroidRuntime(1152):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2409)
03-31 22:47:35.903: E/AndroidRuntime(1152):     ... 11 more
03-31 22:47:35.963: I/dalvikvm(1152): threadid=7: reacting to signal 3
03-31 22:47:36.148: I/dalvikvm(1152): Wrote stack trace to '/data/anr/traces.txt'
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1 Answer

  1. Editorial Team

    To achieve that you need to declare one button in your main.xml file then you have to initialize that in your activity. Then after you have to set on click event listener on that button. 

    <Button
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
    android:id="@+id/buttonClick"
    />

    Code

    TextView tv = (TextView) findViewById(R.id.joke);
Button btn = (Button)findViewbyId(R.id.buttonClick);
    btn.setonclickListener(new onClickListner(){
          public void onclick()
          {
               myString =  getResources().getStringArray(R.array.Jokes); 
               String q = myString[rgenerator.nextInt(myString.length)];
               tv.setText(q);
          }
    });
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