Hint:

Your Activity object is destroyed and then recreated on a rotation. This 
means that all your *new* Activity's fields have been set to 0/false/null 
again.
Read the documentation about the `onSaveInstanceState(...)` method and how 
this stores data in the `savedInstanceState` parameter of the onCreate(...).

On Tuesday, April 12, 2016 at 2:15:46 AM UTC-4, Jesse Clark wrote:
>
> I am new to Android development.  I am experimenting with making a simple 
> app that displays a number that increases by one when the Up button is 
> pressed and decreases by one when the Down button is pressed.  It works 
> correctly, except when I rotate the device from landscape to portrait or 
> vice versa, the number is reset to 0.  Here is the code:
>
> package com.example.jz.counter;
>
> import android.app.Activity;
> import android.content.Intent;
> import android.os.Bundle;
> import android.view.View;
> import android.widget.Button;
> import android.widget.TextView;
>
> public class MainActivity extends Activity implements View.OnClickListener
> {
>     private int counter = 0;
>     private TextView OutputViewObject;
>
>     @Override
>     protected void onCreate(Bundle savedInstanceState)
>     {
>         super.onCreate(savedInstanceState);
>         setContentView(R.layout.activity_main);
>         OutputViewObject = (TextView)findViewById(R.id.outputView);
>         OutputViewObject.setText("" + counter);
>         final Button buttonUp = (Button)findViewById(R.id.up_button);
>         final Button buttonDown = (Button)findViewById(R.id.down_button);
>         buttonUp.setOnClickListener(this);
>         buttonDown.setOnClickListener(this);
>     }
>
>     @Override
>     public void onClick(View view)
>     {
>         switch (view.getId())
>         {
>             case R.id.up_button:
>                 counter++;
>                 OutputViewObject.setText("" + counter);
>                 break;
>             case R.id.down_button:
>                 counter--;
>                 OutputViewObject.setText("" + counter);
>                 break;
>         }
>     }
> }
>
>

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