Question

Why is my app crashing?

Following is an app that takes notes from users and shows it's encrypted string. It also decrypt and encrypted strings. It saves the note in a file and also loads it back. Please help me identify what I am doing wrong?

activity_krypto_note.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".KryptoNoteActivity">

    <EditText
        android:id="@+id/key"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:ems="10"
        android:hint="Cryptographic Key"
        android:inputType="number"
        app:layout_constraintEnd_toStartOf="@+id/encrypt"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/encrypt"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:onClick="enryptClicked"
        android:text="ENCRYPT"
        android:textSize="9sp"
        app:layout_constraintEnd_toStartOf="@+id/decrypt"
        app:layout_constraintStart_toEndOf="@+id/key"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/decrypt"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginTop="8dp"
        android:onClick="decryptClicked"
        android:text="DECRYPT"
        android:textSize="9sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/encrypt"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/file"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:ems="10"
        android:hint="File Name"
        android:inputType="textCapWords"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/key" />

    <Button
        android:id="@+id/save"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginLeft="1dp"
        android:layout_marginStart="1dp"
        android:onClick="saveClicked"
        android:text="SAVE"
        android:textSize="11sp"
        app:layout_constraintEnd_toStartOf="@+id/load"
        app:layout_constraintStart_toEndOf="@+id/file"
        app:layout_constraintTop_toBottomOf="@+id/encrypt" />

    <Button
        android:id="@+id/load"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:onClick="loadClicked"
        android:text="LOAD"
        android:textSize="11sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/save"
        app:layout_constraintTop_toBottomOf="@+id/decrypt" />

    <ScrollView
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/file">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

            <EditText
                android:id="@+id/data"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:ems="10"
                android:hint="..."
                android:inputType="textCapWords"
                tools:layout_editor_absoluteX="16dp"
                tools:layout_editor_absoluteY="134dp" />
        </LinearLayout>
    </ScrollView>

</android.support.constraint.ConstraintLayout>

KryptoNoteActivity.java

package com.example.furquanhassan.kryptonote;

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

import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;

public class KryptoNoteActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_krypto_note);
    }
        private String key = ((EditText) findViewById(R.id.key)).getText().toString();
        public static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        public  String makePad(String note)
        {
            StringBuilder pad = new StringBuilder(this.key);
            for (;pad.length()< note.length();)
            {
                pad.append(this.key);
            }
            return pad.toString();
        }

        public String encrypt(String note){
            String pad = makePad(note);
            StringBuilder result = new StringBuilder();
            for (int i = 0; i< note.length();i++)
            {
                String c = note.substring(i,i+1);
                int position = ALPHABET.indexOf(c);
                int shift = Integer.parseInt(pad.substring(i,i+1));
                int newPosition = (position+shift) % ALPHABET.length();
                result.append(ALPHABET.substring(newPosition, newPosition + 1));
            }
            return result.toString();
        }

        public String decrypt(String note)
        {
            String pad = makePad(note);
            StringBuilder result = new StringBuilder();
            for (int i = 0; i< note.length();i++)
            {
                String c = note.substring(i,i+1);
                int position = ALPHABET.indexOf(c);
                int shift = Integer.parseInt(pad.substring(i,i+1));
                int newPosition = (position-shift) % ALPHABET.length();
                result.append(ALPHABET.substring(newPosition, newPosition + 1));
            }
            return result.toString();
        }

    public void encryptClicked(View v){
        try {
            String note = ((EditText) findViewById(R.id.file)).getText().toString();
            String result = this.encrypt(note);
            ((EditText) findViewById(R.id.data)).setText(result);
        } catch (Exception e)
        {
            Toast label = Toast.makeText(this, e.getMessage(),Toast.LENGTH_SHORT);
            label.show();
        }
    }

    public void decryptClicked(View v)
    {
        try
        {
            String note = ((EditText) findViewById(R.id.file)).getText().toString();
            String result = this.decrypt(note);
            ((EditText) findViewById(R.id.data)).setText(result);
        } catch (Exception e)
        {
            Toast label = Toast.makeText(this, e.getMessage(),Toast.LENGTH_SHORT);
            label.show();
        }
    }


    public void saveClicked(View v)
    {
        try
        {
            String name = ((EditText) findViewById(R.id.file)).getText().toString();
            File dir = this.getFilesDir();
            File file = new File(dir,name);
            FileWriter fw = new FileWriter(file);
            fw.write(((EditText) findViewById(R.id.data)).getText().toString());
            fw.close();

        }catch (Exception e)
        {
           Toast label =  Toast.makeText(this,"Note Saved",Toast.LENGTH_LONG);
           label.show();
        }
    }

    public void loadClicked(View v)
    {
        try
        {
            String name = ((EditText) findViewById(R.id.file)).getText().toString();
            File dir = this.getFilesDir();
            File file = new File(dir,name);
            FileReader fr = new FileReader(file);
            StringBuilder show = new StringBuilder();
            for (int c = fr.read(); c!=-1;c=fr.read())
            {
                show.append((char) c);
            }
            fr.close();
            ((EditText) findViewById(R.id.data)).setText(show.toString());
        }catch (Exception e)
        {
            Toast label =  Toast.makeText(this,"File not found",Toast.LENGTH_LONG);
            label.show();
        }
    }
}

Use android studio if possible. Thank you!

Answer 1

You have error in your project  because of spelling mistake of function name in file

 KryptoNoteActivity.java

 encryptClicked(View v)

does not match with spelling in xml file

 activity_krypto_note.xml

 android:onClick="enryptClicked" 

You need to keep function/method name same as defined in xml file

Error fixed code

activity_krypto_note.xml

<?xml version="1.0" encoding="utf-8"?> <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".KryptoNoteActivity"> <EditText android:id="@+id/key" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginStart="8dp" android:layout_marginLeft="8dp" android:layout_marginTop="8dp" android:ems="10" android:hint="Cryptographic Key" android:inputType="number" app:layout_constraintEnd_toStartOf="@+id/encrypt" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" /> <Button android:id="@+id/encrypt" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_marginTop="8dp" android:onClick="enryptClicked" android:text="ENCRYPT" android:textSize="9sp" app:layout_constraintEnd_toStartOf="@+id/decrypt" app:layout_constraintStart_toEndOf="@+id/key" app:layout_constraintTop_toTopOf="parent" /> <Button android:id="@+id/decrypt" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_marginTop="8dp" android:layout_marginEnd="16dp" android:layout_marginRight="16dp" android:onClick="decryptClicked" android:text="DECRYPT" android:textSize="9sp" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toEndOf="@+id/encrypt" app:layout_constraintTop_toTopOf="parent" /> <EditText android:id="@+id/file" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginStart="8dp" android:layout_marginLeft="8dp" android:layout_marginTop="8dp" android:ems="10" android:hint="File Name" android:inputType="textCapWords" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toBottomOf="@+id/key" /> <Button android:id="@+id/save" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_marginStart="1dp" android:layout_marginLeft="1dp" android:onClick="saveClicked" android:text="SAVE" android:textSize="11sp" app:layout_constraintEnd_toStartOf="@+id/load" app:layout_constraintStart_toEndOf="@+id/file" app:layout_constraintTop_toBottomOf="@+id/encrypt" /> <Button android:id="@+id/load" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_marginEnd="16dp" android:layout_marginRight="16dp" android:onClick="loadClicked" android:text="LOAD" android:textSize="11sp" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toEndOf="@+id/save" app:layout_constraintTop_toBottomOf="@+id/decrypt" /> <ScrollView android:layout_width="0dp" android:layout_height="0dp" android:layout_marginStart="8dp" android:layout_marginLeft="8dp" android:layout_marginTop="8dp" android:layout_marginEnd="8dp" android:layout_marginRight="8dp" android:layout_marginBottom="8dp" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toBottomOf="@+id/file"> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical"> <EditText android:id="@+id/data" android:layout_width="match_parent" android:layout_height="wrap_content" android:ems="10" android:hint="..." android:inputType="textCapWords" tools:layout_editor_absoluteX="16dp" tools:layout_editor_absoluteY="134dp" /> </LinearLayout> </ScrollView> </androidx.constraintlayout.widget.ConstraintLayout>

KryptoNoteActivity.java

package com.example.furquanhassan.kryptonote; import android.os.Bundle; import android.view.View; import android.widget.EditText; import android.widget.Toast; import androidx.appcompat.app.AppCompatActivity; import java.io.File; import java.io.FileReader; import java.io.FileWriter; public class KryptoNoteActivity extends AppCompatActivity { private String key; public static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_krypto_note); //key should be taken after view is loaded key= ((EditText) findViewById(R.id.key)).getText().toString(); } public String makePad(String note) { StringBuilder pad = new StringBuilder(this.key); for (; pad.length() < note.length(); ) { pad.append(this.key); } return pad.toString(); } public String encrypt(String note) { String pad = makePad(note); StringBuilder result = new StringBuilder(); for (int i = 0; i < note.length(); i++) { String c = note.substring(i, i + 1); int position = ALPHABET.indexOf(c); int shift = Integer.parseInt(pad.substring(i, i + 1)); int newPosition = (position + shift) % ALPHABET.length(); result.append(ALPHABET.substring(newPosition, newPosition + 1)); } return result.toString(); } public String decrypt(String note) { String pad = makePad(note); StringBuilder result = new StringBuilder(); for (int i = 0; i < note.length(); i++) { String c = note.substring(i, i + 1); int position = ALPHABET.indexOf(c); int shift = Integer.parseInt(pad.substring(i, i + 1)); int newPosition = (position - shift) % ALPHABET.length(); result.append(ALPHABET.substring(newPosition, newPosition + 1)); } return result.toString(); } public void enryptClicked(View v) { try { String note = ((EditText) findViewById(R.id.file)).getText().toString(); String result = this.encrypt(note); ((EditText) findViewById(R.id.data)).setText(result); } catch (Exception e) { Toast label = Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT); label.show(); } } public void decryptClicked(View v) { try { String note = ((EditText) findViewById(R.id.file)).getText().toString(); String result = this.decrypt(note); ((EditText) findViewById(R.id.data)).setText(result); } catch (Exception e) { Toast label = Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT); label.show(); } } public void saveClicked(View v) { try { String name = ((EditText) findViewById(R.id.file)).getText().toString(); File dir = this.getFilesDir(); File file = new File(dir, name); FileWriter fw = new FileWriter(file); fw.write(((EditText) findViewById(R.id.data)).getText().toString()); fw.close(); } catch (Exception e) { Toast label = Toast.makeText(this, "Note Saved", Toast.LENGTH_LONG); label.show(); } } public void loadClicked(View v) { try { String name = ((EditText) findViewById(R.id.file)).getText().toString(); File dir = this.getFilesDir(); File file = new File(dir, name); FileReader fr = new FileReader(file); StringBuilder show = new StringBuilder(); for (int c = fr.read(); c != -1; c = fr.read()) { show.append((char) c); } fr.close(); ((EditText) findViewById(R.id.data)).setText(show.toString()); } catch (Exception e) { Toast label = Toast.makeText(this, "File not found", Toast.LENGTH_LONG); label.show(); } } }

Output