Question

I am making an app where when we click on add button it adds 1 to the number and when we click subtract it subtracts the number.

I am doing everything right but dont know why its giving error while processing in Emulator.

Below is my source code :

XML Code

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/total"
    android:id="@+id/tvDisplay"
    android:textSize="20dp"
    android:layout_gravity="center"
    android:layout_marginTop="30dp"
    android:layout_marginBottom="30dp"
    />
    <Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/add"
    android:layout_gravity="center"
    android:textSize="20dp"
    android:id="@+id/bAdd"
    android:layout_marginTop="25dp"
    android:layout_marginBottom="2dp"
    />
    <Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/sub"
    android:layout_gravity="center"
    android:textSize="20dp"
    android:id="@+id/bSub"
    android:layout_marginTop="25dp"
    android:layout_marginBottom="25dp"
    />

    </LinearLayout>

Java Code

  package com.example.plus.minus;

  import android.os.Bundle;
  import android.app.Activity;
  import android.view.View;
  import android.widget.Button;
  import android.widget.TextView;

  public class PlusMinus extends Activity {

int counter;
Button add , sub;
TextView display; 

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    counter = 0;
    add = (Button) findViewById(R.id.bAdd);
    sub = (Button) findViewById(R.id.bSub);
    display = (Button) findViewById(R.id.tvDisplay);

    add.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // Adds 1 to the counter
            counter = counter + 1;
            display.setText(" Your total is :" + counter);
        }
    });

    sub.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // Subtract 1 from counter
            counter = counter - 1;
            display.setText(" Your total is :" + counter);
        }
    });
}
}

Also please let me know how can I find runtime errors myself.
And also how to debug errors myself.
Thanks In Advance

Answer 1

It should be TextView instead of Button