Question

i displayed a expression on the screen “2+3=?” and what i want to do is when i press 5 the question mark gets replaced by 5 and when i press # displays “correct” in green

package org.example.question;

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

public class QuestionActivity extends Activity implements View.OnClickListener {
    /** Called when the activity is first created. */

    //variable for different questions

    //variable and type declaration for buttons and text

TextView display;
TextView displayGuess;
TextView displayQuestion;
TextView Correct;
TextView guess;
TextView question;


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

        //display text on screen
        displayGuess = (TextView) findViewById(R.id.Guess);
        displayQuestion = (TextView) findViewById(R.id.Question);


        //Creating and setting onClickerLIstener on each button
        Button one = (Button) findViewById(R.id.keypad_1);
        one.setOnClickListener(this);

        Button two = (Button) findViewById(R.id.keypad_2);
        two.setOnClickListener(this);

        Button three = (Button) findViewById(R.id.keypad_3);
        three.setOnClickListener(this);

        Button four = (Button) findViewById(R.id.keypad_4);
        four.setOnClickListener(this);

        Button five = (Button) findViewById(R.id.keypad_5);
        five.setOnClickListener(this);

        Button six = (Button) findViewById(R.id.keypad_6);
        six.setOnClickListener(this);

        Button seven = (Button) findViewById(R.id.keypad_7);
        seven.setOnClickListener(this);

        Button eight = (Button) findViewById(R.id.keypad_8);
        eight.setOnClickListener(this);

        Button nine = (Button) findViewById(R.id.keypad_9);
        nine.setOnClickListener(this);

        Button del = (Button) findViewById(R.id.keypad_delete);
        del.setOnClickListener(this);

        Button zero = (Button) findViewById(R.id.keypad_0);
        zero.setOnClickListener(this);

        Button hash = (Button) findViewById(R.id.keypad_hash);
        hash.setOnClickListener(this);

        Button minus = (Button) findViewById(R.id.keypad_minus);
        minus.setOnClickListener(this);

    }

        //method to tell what each button does
        public void onClick(View argh0) {



            switch(argh0.getId()) {

            case R.id.keypad_hash:

                if("2+3=5".equals(display.getText().toString()))
                {
                    display.setText("CORRECT".setColor."#00ff00");

                }
                break;

            case R.id.keypad_5:
                String str5 = display.getText().toString();
                display.setText(str5.replace("?","5"));
                break;






            case R.id.keypad_1:

                display.setText("1");
            break;
            }
        }
}

<?xml version="1.0" encoding="utf-8"?>   
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >   
   <TextView
        android:id="@+id/Guess"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="15dp"
        android:text="Guess: "
        android:textSize="25dp" />
   <TextView
        android:id="@+id/Question"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="15dp"
        android:text="2+3=?"
        android:textSize="25dp" />
   <TextView
        android:id="@+id/CORRECT"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="15dp"
        android:text=""
        android:textSize="25dp" />
   <TextView
        android:id="@+id/INCORRECT"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="15dp"
        android:text=""
        android:textSize="25dp" />









<TableLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/keypad"
android:orientation="vertical"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:stretchColumns="*" >




<TableRow>
<Button android:id="@+id/keypad_1"
android:text="1" >
</Button>
<Button android:id="@+id/keypad_2"
android:text="2" >
</Button>
<Button android:id="@+id/keypad_3"
android:text="3" >
</Button>
</TableRow>
<TableRow>
<Button android:id="@+id/keypad_4"
android:text="4" >
</Button>
<Button android:id="@+id/keypad_5"
android:text="5" >
</Button>

so far i can display the question but when i press “5” the application crashes

really will appreciate the help

Answer 1

I don’t know whether you posted the whole code or not, but from what I see you never initialize the variable “display” (TextView display;). Then when you use it you will get a NullPointerException.

I think you missed a line like display = (TextView) findViewById(R.id.display..);