A second screen: Intents

Goal Give the note page its layout, class and manifest line.

• Resources res › values › strings.xml
• Layout res › layout › activity_note.xml · Split
• Java kotlin+java › com.yourname.notes › NoteActivity.java
• Manifest manifests › AndroidManifest.xml

1. Paste The page’s 3 texts, in strings.xml.

   1. In Project, open res › values › strings.xml.
   2. In the panel below, click Copy 3 lines.
   3. Click at the end of line 22, then press Enter.
   4. Press Ctrl+V: lines 23 to 25 appear.

   res › values › strings.xmlAdd the marked lines

   ⋯ lines 1–20<resources>    <string name="app_name">Notes</string>    <string name="logo_description">Notes logo</string>    <string name="count_start">0</string>    <string name="title_hint">Title</string>    <string name="body_hint">Write something…</string>    <string name="error_no_title">Give your note a title first.</string>    <string name="counter_start">0 / 140</string>    <string name="counter">%1$d / 140</string>    <string name="clear">Clear</string>    <string name="add">Add</string>    <string name="your_notes">YOUR NOTES</string>    <string name="list_hint">Tap to open · hold to delete</string>    <string name="empty">No notes yet.\nWrite your first one above.</string>    <string name="note_added">Note added</string>    <string name="note_deleted">Note deleted</string>    <string name="seed_title_1">Saturday</string>    <string name="seed_body_1">Football at 10, then revise ConstraintLayout.</string>    <string name="seed_title_2">Ideas for the app</string>    <string name="seed_body_2">Pastel cards, a Share button, maybe a photo one day. Then save the notes, so that turning the phone loses nothing.</string>    <string name="seed_title_3">Exam: the lifecycle</string>    <string name="seed_body_3">onCreate, onStart, onResume… then onPause, onStop, onDestroy.</string>    <string name="note_kicker">NOTE</string>    <string name="back_to_notes">Back to notes</string>    <string name="share">Share</string></resources>

2. Paste The layout activity_note.xml, a new file (step 2.1 made the first one).

   1. In Project, right-click res › layout.
   2. Choose NewLayout Resource File.
   3. A New Resource File window opens: in File name, type activity_note, then click OK.
   4. It opens in Design: click Code, at the top right of the editor.
   5. Click Copy the file, on the panel below.
   6. Click in the code, press Ctrl+A, then Ctrl+V.

   res › layout › activity_note.xmlReplace the whole file

   ⋯ lines 1–10<?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"    android:fitsSystemWindows="true"    tools:context=".NoteActivity">
       <LinearLayout        android:id="@+id/noteSheet"⋯ lines 12–32        android:layout_width="0dp"        android:layout_height="0dp"        android:layout_margin="16dp"        android:background="@drawable/bg_note_butter"        android:orientation="vertical"        android:padding="24dp"        app:layout_constraintBottom_toTopOf="@id/buttonShare"        app:layout_constraintEnd_toEndOf="parent"        app:layout_constraintStart_toStartOf="parent"        app:layout_constraintTop_toTopOf="parent">
           <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:letterSpacing="0.1"            android:text="@string/note_kicker"            android:textColor="@color/muted"            android:textSize="12sp"            android:textStyle="bold" />
           <TextView            android:id="@+id/textTitle"⋯ lines 34–42            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:layout_marginTop="8dp"            android:fontFamily="sans-serif-black"            android:textColor="@color/ink"            android:textSize="24sp"            tools:text="Ideas for the app" />
           <TextView            android:id="@+id/textBody"⋯ lines 44–53            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:layout_marginTop="12dp"            android:lineSpacingMultiplier="1.25"            android:textColor="@color/ink"            android:textSize="18sp"            tools:text="Pastel cards, a Share button, maybe a photo one day." />    </LinearLayout>
       <Button        android:id="@+id/buttonShare"⋯ lines 55–64        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_marginEnd="16dp"        android:layout_marginBottom="16dp"        android:text="@string/share"        app:cornerRadius="12dp"        app:layout_constraintBottom_toBottomOf="parent"        app:layout_constraintEnd_toEndOf="parent" />
       <Button        android:id="@+id/buttonBack"⋯ lines 66–75        style="@style/Widget.Material3.Button.OutlinedButton"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_marginEnd="8dp"        android:text="@string/back_to_notes"        app:cornerRadius="12dp"        app:layout_constraintBaseline_toBaselineOf="@id/buttonShare"        app:layout_constraintEnd_toStartOf="@id/buttonShare" />
   </androidx.constraintlayout.widget.ConstraintLayout>

   NoteActivity reads 4 of the marked ids now; buttonShare from step 8.5. tools:text fills the preview only.

3. Paste The class NoteActivity, which receives the note.

   1. In Project, right-click the plain kotlin+java › com.yourname.notes, without (test) or (androidTest).
   2. Choose NewJava Class.
   3. A New Java Class popup opens: type NoteActivity, then press Enter.
   4. The class opens: click Copy the file, on the panel below.
   5. Click in the class, press Ctrl+A, then Ctrl+V.

   kotlin+java › com.yourname.notes › NoteActivity.javaReplace the whole file

   ⋯ lines 1–9package com.yourname.notes;
   import android.os.Bundle;import android.util.Log;import android.widget.TextView;
   import androidx.appcompat.app.AppCompatActivity;
   public class NoteActivity extends AppCompatActivity {
       public static final String EXTRA_TITLE = "com.yourname.notes.EXTRA_TITLE";    public static final String EXTRA_BODY = "com.yourname.notes.EXTRA_BODY";    public static final String EXTRA_BACKGROUND = "com.yourname.notes.EXTRA_BACKGROUND";    private static final String TAG = "Lifecycle";⋯ lines 15–20
       @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_note);        Log.d(TAG, "Note onCreate");
           String title = getIntent().getStringExtra(EXTRA_TITLE);        String body = getIntent().getStringExtra(EXTRA_BODY);        int background = getIntent().getIntExtra(EXTRA_BACKGROUND, R.drawable.bg_note_butter);
   ⋯ lines 26–30        TextView textTitle = findViewById(R.id.textTitle);        TextView textBody = findViewById(R.id.textBody);        textTitle.setText(title);        textBody.setText(body);        findViewById(R.id.noteSheet).setBackgroundResource(background);
           findViewById(R.id.buttonBack).setOnClickListener(v -> finish());    }⋯ lines 34–40
       @Override    protected void onDestroy() {        super.onDestroy();        Log.d(TAG, "Note onDestroy");    }}

   An Intent, the message that opens a screen, carries values under keys: its extras. This class reads 3, which step 8.2 sends. Back to notes calls finish(): the page closes.

4. Paste The manifest line that declares the page.

   1. In Project, open manifests › AndroidManifest.xml.
   2. In the panel below, click Copy 3 lines.
   3. Click at the end of line 21, </activity>, then press Enter.
   4. Press Ctrl+V: lines 22 to 24 appear.

   manifests › AndroidManifest.xmlAdd the marked lines

   ⋯ lines 1–19<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools">
       <application        android:allowBackup="true"        android:dataExtractionRules="@xml/data_extraction_rules"        android:fullBackupContent="@xml/backup_rules"        android:icon="@mipmap/ic_launcher"        android:label="@string/app_name"        android:roundIcon="@mipmap/ic_launcher_round"        android:supportsRtl="true"        android:theme="@style/Theme.Notes">        <activity            android:name=".MainActivity"            android:exported="true">            <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>        <activity            android:name=".NoteActivity"            android:exported="false" />    </application>
   </manifest>

   exported="false": only your own app may open this screen.

5. The note page’s preview.

   1. Click the activity_note.xml tab.
   2. Click Split, at the top right: the preview shows.

   activity_note.xml · preview Layout editor · centreFull size

   

Goal Make a tap on a card open its note page.

• Java kotlin+java › com.yourname.notes › MainActivity.java
• Emulator

1. Type A tap on a card calls openNote().

   1. Open kotlin+java › com.yourname.notes › MainActivity.java.
   2. In addNote(), click in the empty line above card.setOnLongClickListener, then press Enter.
   3. Completion lists open as you type: keep typing.
   4. Type the marked line. openNote stays red until action b writes it.

   kotlin+java › com.yourname.notes › MainActivity.javaAdd the marked lines

   ⋯ lines 1–94package com.yourname.notes;
   import android.content.Intent;import android.os.Bundle;import android.text.Editable;import android.text.TextWatcher;import android.util.Log;import android.view.LayoutInflater;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.LinearLayout;import android.widget.TextView;import android.widget.Toast;
   import androidx.appcompat.app.AppCompatActivity;
   public class MainActivity extends AppCompatActivity {
       private static final String TAG = "Lifecycle";    private static final int[] NOTE_BACKGROUNDS = {            R.drawable.bg_note_butter,            R.drawable.bg_note_mint,            R.drawable.bg_note_lavender,            R.drawable.bg_note_peach    };
       private TextView textCount;    private TextView textEmpty;    private LinearLayout notesContainer;    private int notesAdded = 0;
       private EditText editTitle;    private EditText editBody;    private TextView textError;    private TextView textCounter;
       private final TextWatcher formWatcher = new TextWatcher() {        @Override        public void beforeTextChanged(CharSequence s, int start, int count, int after) {        }
           @Override        public void onTextChanged(CharSequence s, int start, int before, int count) {        }
           @Override        public void afterTextChanged(Editable s) {            updateForm();        }    };
       @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Log.d(TAG, "Main onCreate");
           textCount = findViewById(R.id.textCount);        textEmpty = findViewById(R.id.textEmpty);        notesContainer = findViewById(R.id.notesContainer);
           addNote(getString(R.string.seed_title_1), getString(R.string.seed_body_1));        addNote(getString(R.string.seed_title_2), getString(R.string.seed_body_2));        addNote(getString(R.string.seed_title_3), getString(R.string.seed_body_3));        updateCount();
           editTitle = findViewById(R.id.editTitle);        editBody = findViewById(R.id.editBody);        textError = findViewById(R.id.textError);        textCounter = findViewById(R.id.textCounter);
           Button buttonAdd = findViewById(R.id.buttonAdd);        buttonAdd.setOnClickListener(v -> addNoteFromComposer());
           editTitle.addTextChangedListener(formWatcher);        editBody.addTextChangedListener(formWatcher);    }
       private void updateCount() {        int count = notesContainer.getChildCount();        textCount.setText(String.valueOf(count));        textEmpty.setVisibility(count == 0 ? View.VISIBLE : View.GONE);    }
       private void addNote(String title, String body) {        View card = LayoutInflater.from(this).inflate(R.layout.item_note, notesContainer, false);        TextView cardTitle = card.findViewById(R.id.textNoteTitle);        TextView cardBody = card.findViewById(R.id.textNoteBody);        cardTitle.setText(title);        cardBody.setText(body);        cardBody.setVisibility(body.isEmpty() ? View.GONE : View.VISIBLE);        int background = NOTE_BACKGROUNDS[notesAdded % NOTE_BACKGROUNDS.length];        card.setBackgroundResource(background);        notesAdded++;
           card.setOnClickListener(v -> openNote(title, body, background));        card.setOnLongClickListener(v -> {            notesContainer.removeView(card);⋯ lines 100–181            updateCount();            Toast.makeText(this, R.string.note_deleted, Toast.LENGTH_SHORT).show();            return true;        });
           notesContainer.addView(card, 0);    }
       private void addNoteFromComposer() {        String title = editTitle.getText().toString().trim();        String body = editBody.getText().toString().trim();        if (title.isEmpty()) {            textError.setVisibility(View.VISIBLE);            return;        }        textError.setVisibility(View.GONE);        addNote(title, body);        updateCount();        editTitle.setText("");        editBody.setText("");        Toast.makeText(this, R.string.note_added, Toast.LENGTH_SHORT).show();    }
       private void updateForm() {        int length = editBody.length();        textCounter.setText(getString(R.string.counter, length));        int colour = length >= 120 ? R.color.error : R.color.muted;        textCounter.setTextColor(getColor(colour));        if (editTitle.length() > 0) {            textError.setVisibility(View.GONE);        }    }
       public void onClearClicked(View view) {        editTitle.setText("");        editBody.setText("");    }
       private void openNote(String title, String body, int background) {        Intent intent = new Intent(this, NoteActivity.class);        intent.putExtra(NoteActivity.EXTRA_TITLE, title);        intent.putExtra(NoteActivity.EXTRA_BODY, body);        intent.putExtra(NoteActivity.EXTRA_BACKGROUND, background);        startActivity(intent);    }
       @Override    protected void onStart() {        super.onStart();        Log.d(TAG, "Main onStart");    }
       @Override    protected void onResume() {        super.onResume();        Log.d(TAG, "Main onResume");    }
       @Override    protected void onPause() {        super.onPause();        Log.d(TAG, "Main onPause");    }
       @Override    protected void onStop() {        super.onStop();        Log.d(TAG, "Main onStop");    }
       @Override    protected void onRestart() {        super.onRestart();        Log.d(TAG, "Main onRestart");    }
       @Override    protected void onDestroy() {        super.onDestroy();        Log.d(TAG, "Main onDestroy");    }}

   Each card’s lambda keeps that card’s own title, body and background.

2. Type The method openNote(), which sends the note in an Intent.

   1. Click right after the } that ends onClearClicked(), at the end of its line.
   2. Press Enter twice: the caret is now where private void openNote(… begins.
   3. Completion lists open as you type: keep typing.
   4. Type from private void openNote(… down to startActivity(intent);. The method’s closing } arrives by itself: do not type it.
   5. If Intent is red, click it, then press Alt+Enter.
   6. If a list opens, choose Import class: the import arrives on line 3.

   kotlin+java › com.yourname.notes › MainActivity.javaAdd the marked lines

   ⋯ lines 1–134package com.yourname.notes;
   import android.content.Intent;import android.os.Bundle;import android.text.Editable;import android.text.TextWatcher;import android.util.Log;import android.view.LayoutInflater;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.LinearLayout;import android.widget.TextView;import android.widget.Toast;
   import androidx.appcompat.app.AppCompatActivity;
   public class MainActivity extends AppCompatActivity {
       private static final String TAG = "Lifecycle";    private static final int[] NOTE_BACKGROUNDS = {            R.drawable.bg_note_butter,            R.drawable.bg_note_mint,            R.drawable.bg_note_lavender,            R.drawable.bg_note_peach    };
       private TextView textCount;    private TextView textEmpty;    private LinearLayout notesContainer;    private int notesAdded = 0;
       private EditText editTitle;    private EditText editBody;    private TextView textError;    private TextView textCounter;
       private final TextWatcher formWatcher = new TextWatcher() {        @Override        public void beforeTextChanged(CharSequence s, int start, int count, int after) {        }
           @Override        public void onTextChanged(CharSequence s, int start, int before, int count) {        }
           @Override        public void afterTextChanged(Editable s) {            updateForm();        }    };
       @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Log.d(TAG, "Main onCreate");
           textCount = findViewById(R.id.textCount);        textEmpty = findViewById(R.id.textEmpty);        notesContainer = findViewById(R.id.notesContainer);
           addNote(getString(R.string.seed_title_1), getString(R.string.seed_body_1));        addNote(getString(R.string.seed_title_2), getString(R.string.seed_body_2));        addNote(getString(R.string.seed_title_3), getString(R.string.seed_body_3));        updateCount();
           editTitle = findViewById(R.id.editTitle);        editBody = findViewById(R.id.editBody);        textError = findViewById(R.id.textError);        textCounter = findViewById(R.id.textCounter);
           Button buttonAdd = findViewById(R.id.buttonAdd);        buttonAdd.setOnClickListener(v -> addNoteFromComposer());
           editTitle.addTextChangedListener(formWatcher);        editBody.addTextChangedListener(formWatcher);    }
       private void updateCount() {        int count = notesContainer.getChildCount();        textCount.setText(String.valueOf(count));        textEmpty.setVisibility(count == 0 ? View.VISIBLE : View.GONE);    }
       private void addNote(String title, String body) {        View card = LayoutInflater.from(this).inflate(R.layout.item_note, notesContainer, false);        TextView cardTitle = card.findViewById(R.id.textNoteTitle);        TextView cardBody = card.findViewById(R.id.textNoteBody);        cardTitle.setText(title);        cardBody.setText(body);        cardBody.setVisibility(body.isEmpty() ? View.GONE : View.VISIBLE);        int background = NOTE_BACKGROUNDS[notesAdded % NOTE_BACKGROUNDS.length];        card.setBackgroundResource(background);        notesAdded++;
           card.setOnClickListener(v -> openNote(title, body, background));        card.setOnLongClickListener(v -> {            notesContainer.removeView(card);            updateCount();            Toast.makeText(this, R.string.note_deleted, Toast.LENGTH_SHORT).show();            return true;        });
           notesContainer.addView(card, 0);    }
       private void addNoteFromComposer() {        String title = editTitle.getText().toString().trim();        String body = editBody.getText().toString().trim();        if (title.isEmpty()) {            textError.setVisibility(View.VISIBLE);            return;        }        textError.setVisibility(View.GONE);        addNote(title, body);        updateCount();        editTitle.setText("");        editBody.setText("");        Toast.makeText(this, R.string.note_added, Toast.LENGTH_SHORT).show();    }
       private void updateForm() {        int length = editBody.length();        textCounter.setText(getString(R.string.counter, length));        int colour = length >= 120 ? R.color.error : R.color.muted;        textCounter.setTextColor(getColor(colour));        if (editTitle.length() > 0) {            textError.setVisibility(View.GONE);        }    }
       public void onClearClicked(View view) {        editTitle.setText("");        editBody.setText("");    }
       private void openNote(String title, String body, int background) {        Intent intent = new Intent(this, NoteActivity.class);        intent.putExtra(NoteActivity.EXTRA_TITLE, title);        intent.putExtra(NoteActivity.EXTRA_BODY, body);        intent.putExtra(NoteActivity.EXTRA_BACKGROUND, background);        startActivity(intent);    }
   ⋯ lines 146–181    @Override    protected void onStart() {        super.onStart();        Log.d(TAG, "Main onStart");    }
       @Override    protected void onResume() {        super.onResume();        Log.d(TAG, "Main onResume");    }
       @Override    protected void onPause() {        super.onPause();        Log.d(TAG, "Main onPause");    }
       @Override    protected void onStop() {        super.onStop();        Log.d(TAG, "Main onStop");    }
       @Override    protected void onRestart() {        super.onRestart();        Log.d(TAG, "Main onRestart");    }
       @Override    protected void onDestroy() {        super.onDestroy();        Log.d(TAG, "Main onDestroy");    }}

   Whole file shows line 3 in grey: Android Studio writes it.

3. The note page, on the phone.

   1. Click ▶ Run 'app' (↻ Rerun if the app is running).
   2. On the phone, tap Ideas for the app.

You should see The note page, mint like its card, its text whole.

Done I see the note page in its card’s colour.

YesNo

Why new Intent(this, NoteActivity.class) names the screen to open: an explicit Intent. Its keys are NoteActivity’s constants, whose values start with your package: Android’s rule for your own extras.

package com.yourname.notes;
import android.content.Intent;import android.os.Bundle;import android.text.Editable;import android.text.TextWatcher;import android.util.Log;import android.view.LayoutInflater;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.LinearLayout;import android.widget.TextView;import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
public class MainActivity extends AppCompatActivity {
    private static final String TAG = "Lifecycle";    private static final int[] NOTE_BACKGROUNDS = {            R.drawable.bg_note_butter,            R.drawable.bg_note_mint,            R.drawable.bg_note_lavender,            R.drawable.bg_note_peach    };
    private TextView textCount;    private TextView textEmpty;    private LinearLayout notesContainer;    private int notesAdded = 0;
    private EditText editTitle;    private EditText editBody;    private TextView textError;    private TextView textCounter;
    private final TextWatcher formWatcher = new TextWatcher() {        @Override        public void beforeTextChanged(CharSequence s, int start, int count, int after) {        }
        @Override        public void onTextChanged(CharSequence s, int start, int before, int count) {        }
        @Override        public void afterTextChanged(Editable s) {            updateForm();        }    };
    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Log.d(TAG, "Main onCreate");
        textCount = findViewById(R.id.textCount);        textEmpty = findViewById(R.id.textEmpty);        notesContainer = findViewById(R.id.notesContainer);
        addNote(getString(R.string.seed_title_1), getString(R.string.seed_body_1));        addNote(getString(R.string.seed_title_2), getString(R.string.seed_body_2));        addNote(getString(R.string.seed_title_3), getString(R.string.seed_body_3));        updateCount();
        editTitle = findViewById(R.id.editTitle);        editBody = findViewById(R.id.editBody);        textError = findViewById(R.id.textError);        textCounter = findViewById(R.id.textCounter);
        Button buttonAdd = findViewById(R.id.buttonAdd);        buttonAdd.setOnClickListener(v -> addNoteFromComposer());
        editTitle.addTextChangedListener(formWatcher);        editBody.addTextChangedListener(formWatcher);    }
    private void updateCount() {        int count = notesContainer.getChildCount();        textCount.setText(String.valueOf(count));        textEmpty.setVisibility(count == 0 ? View.VISIBLE : View.GONE);    }
    private void addNote(String title, String body) {        View card = LayoutInflater.from(this).inflate(R.layout.item_note, notesContainer, false);        TextView cardTitle = card.findViewById(R.id.textNoteTitle);        TextView cardBody = card.findViewById(R.id.textNoteBody);        cardTitle.setText(title);        cardBody.setText(body);        cardBody.setVisibility(body.isEmpty() ? View.GONE : View.VISIBLE);        int background = NOTE_BACKGROUNDS[notesAdded % NOTE_BACKGROUNDS.length];        card.setBackgroundResource(background);        notesAdded++;
        card.setOnClickListener(v -> openNote(title, body, background));        card.setOnLongClickListener(v -> {            notesContainer.removeView(card);            updateCount();            Toast.makeText(this, R.string.note_deleted, Toast.LENGTH_SHORT).show();            return true;        });
        notesContainer.addView(card, 0);    }
    private void addNoteFromComposer() {        String title = editTitle.getText().toString().trim();        String body = editBody.getText().toString().trim();        if (title.isEmpty()) {            textError.setVisibility(View.VISIBLE);            return;        }        textError.setVisibility(View.GONE);        addNote(title, body);        updateCount();        editTitle.setText("");        editBody.setText("");        Toast.makeText(this, R.string.note_added, Toast.LENGTH_SHORT).show();    }
    private void updateForm() {        int length = editBody.length();        textCounter.setText(getString(R.string.counter, length));        int colour = length >= 120 ? R.color.error : R.color.muted;        textCounter.setTextColor(getColor(colour));        if (editTitle.length() > 0) {            textError.setVisibility(View.GONE);        }    }
    public void onClearClicked(View view) {        editTitle.setText("");        editBody.setText("");    }
    private void openNote(String title, String body, int background) {        Intent intent = new Intent(this, NoteActivity.class);        intent.putExtra(NoteActivity.EXTRA_TITLE, title);        intent.putExtra(NoteActivity.EXTRA_BODY, body);        intent.putExtra(NoteActivity.EXTRA_BACKGROUND, background);        startActivity(intent);    }
    @Override    protected void onStart() {        super.onStart();        Log.d(TAG, "Main onStart");    }
    @Override    protected void onResume() {        super.onResume();        Log.d(TAG, "Main onResume");    }
    @Override    protected void onPause() {        super.onPause();        Log.d(TAG, "Main onPause");    }
    @Override    protected void onStop() {        super.onStop();        Log.d(TAG, "Main onStop");    }
    @Override    protected void onRestart() {        super.onRestart();        Log.d(TAG, "Main onRestart");    }
    @Override    protected void onDestroy() {        super.onDestroy();        Log.d(TAG, "Main onDestroy");    }}

Goal Come back; read the round trip in Logcat.

• Emulator
• Logcat package:mine tag:Lifecycle

1. The list as you leave it: one more note, one title typed but not added.

   1. On the phone, tap Back to notes: the list of notes comes back.
   2. Type Groceries in Title, then tap Add.
   3. Type Call Yasmine in Title, without tapping Add.
   4. Close the keyboard with its down arrow, at the bottom left of the phone.

2. One clean round trip, in Logcat.

   1. In Logcat, at the bottom of the window, the query must read package:mine tag:Lifecycle: type it if not.
   2. Click the trash icon, Clear Logcat, at the top of Logcat’s left column.
   3. On the phone, tap the Groceries card: its note page opens.
   4. Tap Back to notes.

You should see10-31 19:00:23.570  7176  7176 D Lifecycle: Main onPause
10-31 19:00:23.595  7176  7176 D Lifecycle: Note onCreate
10-31 19:00:24.338  7176  7176 D Lifecycle: Main onStop
10-31 19:00:30.111  7176  7176 D Lifecycle: Main onRestart
10-31 19:00:30.112  7176  7176 D Lifecycle: Main onStart
10-31 19:00:30.112  7176  7176 D Lifecycle: Main onResume
10-31 19:00:30.698  7176  7176 D Lifecycle: Note onDestroy

Your times and process numbers will differ.

You should see The list as you left it.

Done I see Note onDestroy in Logcat.

YesNo

Goal See Android refuse an undeclared activity.

• Manifest manifests › AndroidManifest.xml
• Emulator
• Logcat package:mine

1. The page’s 3 lines in the manifest, made a comment.

   1. Open manifests › AndroidManifest.xml.
   2. Click anywhere in line 22, <activity.
   3. Press Ctrl+/ three times, once a line: lines 22 to 24 become comments, <!-- … -->.

   manifests › AndroidManifest.xmlRead only

   ⋯ lines 1–19<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools">
       <application        android:allowBackup="true"        android:dataExtractionRules="@xml/data_extraction_rules"        android:fullBackupContent="@xml/backup_rules"        android:icon="@mipmap/ic_launcher"        android:label="@string/app_name"        android:roundIcon="@mipmap/ic_launcher_round"        android:supportsRtl="true"        android:theme="@style/Theme.Notes">        <activity            android:name=".MainActivity"            android:exported="true">            <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>        <activity            android:name=".NoteActivity"            android:exported="false" />    </application>
   </manifest>

2. The app asks for the forgotten page.

   1. In Logcat’s query field, delete tag:Lifecycle: keep only package:mine.
   2. Click ▶ Run 'app' (↻ Rerun if the app is running).
   3. On the phone, tap a card.

3. Put them back.

   1. In the manifest, click in line 22 again.
   2. Press Ctrl+/ three times: the comments go.
   3. Click ▶ Run 'app' (↻ Rerun if the app is running).
   4. On the phone, tap a card: its page opens again.

You should see10-31 18:59:41.415  6726  6726 E AndroidRuntime: FATAL EXCEPTION: main
10-31 18:59:41.415  6726  6726 E AndroidRuntime: Process: com.yourname.notes, PID: 6726
10-31 18:59:41.415  6726  6726 E AndroidRuntime: android.content.ActivityNotFoundException: Unable to find explicit activity class {com.yourname.notes/com.yourname.notes.NoteActivity}; have you declared this activity in your AndroidManifest.xml, or does your intent not match its declared <intent-filter>?

Goal Make Share hand the note to an app Android finds.

• Java kotlin+java › com.yourname.notes › NoteActivity.java
• Emulator

1. Type The Share button calls share().

   1. Open kotlin+java › com.yourname.notes › NoteActivity.java.
   2. In onCreate(), click at the end of the buttonBack line, then press Enter.
   3. Completion lists open as you type: keep typing.
   4. Type the marked line. share stays red until action b writes it.

   kotlin+java › com.yourname.notes › NoteActivity.javaAdd the marked lines

   ⋯ lines 1–32package com.yourname.notes;
   import android.content.Intent;import android.os.Bundle;import android.util.Log;import android.widget.TextView;
   import androidx.appcompat.app.AppCompatActivity;
   public class NoteActivity extends AppCompatActivity {
       public static final String EXTRA_TITLE = "com.yourname.notes.EXTRA_TITLE";    public static final String EXTRA_BODY = "com.yourname.notes.EXTRA_BODY";    public static final String EXTRA_BACKGROUND = "com.yourname.notes.EXTRA_BACKGROUND";    private static final String TAG = "Lifecycle";
       @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_note);        Log.d(TAG, "Note onCreate");
           String title = getIntent().getStringExtra(EXTRA_TITLE);        String body = getIntent().getStringExtra(EXTRA_BODY);        int background = getIntent().getIntExtra(EXTRA_BACKGROUND, R.drawable.bg_note_butter);
           TextView textTitle = findViewById(R.id.textTitle);        TextView textBody = findViewById(R.id.textBody);        textTitle.setText(title);        textBody.setText(body);        findViewById(R.id.noteSheet).setBackgroundResource(background);
           findViewById(R.id.buttonBack).setOnClickListener(v -> finish());        findViewById(R.id.buttonShare).setOnClickListener(v -> share(title, body));    }⋯ lines 36–49
       private void share(String title, String body) {        Intent send = new Intent(Intent.ACTION_SEND);        send.setType("text/plain");        send.putExtra(Intent.EXTRA_TEXT, title + "\n" + body);        startActivity(Intent.createChooser(send, null));    }
       @Override    protected void onDestroy() {        super.onDestroy();        Log.d(TAG, "Note onDestroy");    }}

2. Type The method share(), which hands the note to Android.

   1. Click right after the } that ends onCreate(), at the end of its line.
   2. Press Enter twice: the caret is now where private void share(… begins.
   3. Completion lists open as you type: keep typing.
   4. Type from private void share(… down to startActivity(Intent.createChooser(send, null));. The method’s closing } arrives by itself: do not type it.
   5. If Intent is red, click it, then press Alt+Enter.
   6. If a list opens, choose Import class: the import arrives on line 3.

   kotlin+java › com.yourname.notes › NoteActivity.javaAdd the marked lines

   ⋯ lines 1–33package com.yourname.notes;
   import android.content.Intent;import android.os.Bundle;import android.util.Log;import android.widget.TextView;
   import androidx.appcompat.app.AppCompatActivity;
   public class NoteActivity extends AppCompatActivity {
       public static final String EXTRA_TITLE = "com.yourname.notes.EXTRA_TITLE";    public static final String EXTRA_BODY = "com.yourname.notes.EXTRA_BODY";    public static final String EXTRA_BACKGROUND = "com.yourname.notes.EXTRA_BACKGROUND";    private static final String TAG = "Lifecycle";
       @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_note);        Log.d(TAG, "Note onCreate");
           String title = getIntent().getStringExtra(EXTRA_TITLE);        String body = getIntent().getStringExtra(EXTRA_BODY);        int background = getIntent().getIntExtra(EXTRA_BACKGROUND, R.drawable.bg_note_butter);
           TextView textTitle = findViewById(R.id.textTitle);        TextView textBody = findViewById(R.id.textBody);        textTitle.setText(title);        textBody.setText(body);        findViewById(R.id.noteSheet).setBackgroundResource(background);
           findViewById(R.id.buttonBack).setOnClickListener(v -> finish());        findViewById(R.id.buttonShare).setOnClickListener(v -> share(title, body));    }
       private void share(String title, String body) {        Intent send = new Intent(Intent.ACTION_SEND);        send.setType("text/plain");        send.putExtra(Intent.EXTRA_TEXT, title + "\n" + body);        startActivity(Intent.createChooser(send, null));    }
   ⋯ lines 44–49    @Override    protected void onDestroy() {        super.onDestroy();        Log.d(TAG, "Note onDestroy");    }}

   Whole file shows line 3 in grey: Android Studio writes it. createChooser() asks Android for the share sheet.

3. The share sheet, on the phone.

   1. Click ▶ Run 'app' (↻ Rerun if the app is running).
   2. On the phone, tap a card: its note page opens.
   3. Tap Share.

You should see A sheet, “Sharing text”, showing your note.

Done I see my note’s text in the sheet.

YesNo

package com.yourname.notes;
import android.content.Intent;import android.os.Bundle;import android.util.Log;import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
public class NoteActivity extends AppCompatActivity {
    public static final String EXTRA_TITLE = "com.yourname.notes.EXTRA_TITLE";    public static final String EXTRA_BODY = "com.yourname.notes.EXTRA_BODY";    public static final String EXTRA_BACKGROUND = "com.yourname.notes.EXTRA_BACKGROUND";    private static final String TAG = "Lifecycle";
    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_note);        Log.d(TAG, "Note onCreate");
        String title = getIntent().getStringExtra(EXTRA_TITLE);        String body = getIntent().getStringExtra(EXTRA_BODY);        int background = getIntent().getIntExtra(EXTRA_BACKGROUND, R.drawable.bg_note_butter);
        TextView textTitle = findViewById(R.id.textTitle);        TextView textBody = findViewById(R.id.textBody);        textTitle.setText(title);        textBody.setText(body);        findViewById(R.id.noteSheet).setBackgroundResource(background);
        findViewById(R.id.buttonBack).setOnClickListener(v -> finish());        findViewById(R.id.buttonShare).setOnClickListener(v -> share(title, body));    }
    private void share(String title, String body) {        Intent send = new Intent(Intent.ACTION_SEND);        send.setType("text/plain");        send.putExtra(Intent.EXTRA_TEXT, title + "\n" + body);        startActivity(Intent.createChooser(send, null));    }
    @Override    protected void onDestroy() {        super.onDestroy();        Log.d(TAG, "Note onDestroy");    }}

Goal Turn the phone, and see what survives.

• Emulator Running Devices

1. The list with five notes.

   1. In Running Devices, click Back until the list of notes shows.
   2. On the phone, type Groceries in Title, then tap Add.
   3. Type Call Yasmine in Title.
   4. Type About the project, before Friday. in Write something…, then tap Add.

2. A title half typed.

   1. Type Half in Title, without tapping Add.
   2. Close the keyboard with its down arrow, at the bottom left of the phone.

3. The phone turned, then upright again.

   1. In Running Devices, click Rotate Left: the phone turns on its side.
   2. Click Rotate Right: the phone stands upright again.

Rotate

You should see After: the 3 seeds, pill 3, Half still in Title.

Why Turning recreated the screen: onCreate() added the seeds again. A text field with an id keeps its text (chapter 03).