6월 2주차 학습 내용 정리

 

 

 

Android

 

1. Activity와 Intent

 - Activity : 안드로이드폰에 나타나는 화면 하나하나를 말하며 여러개의 Activity를 사용하여 화면을 구성할 수 있음

 - 일반적으로 액티비티 하나 당 xml 파일 하나를 만들어 사용

 - Intent : Activity, Service와 같은 안드로이드의 4대 컴포넌트가 서로 데이터를 주고받기 위한 메시지 객체.

   명시적 인텐트와 암시적 인텐트로 구분됨

 - 명시적 인텐트(explicit intent) : 다른 액티비티의 이름을 명확히 지정할 때 사용

 - 암시적 인텐트(implicit intent) : 약속된 액션을 지정하여 안드로이드에서 제공하는 기존 응용 프로그램 실행

 - 양방향 액티비티 : 두개의 액티비티가 서로 데이터를 주고 받음

 - 양방향 액티비티 연습(Main에서 계산할 값을 입력 -> Second에서 값 계산 -> Main에서 결과값 출력)

   * activity_main.xml

<LinearLayout 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=".MainActivity"
    android:orientation="vertical"
    android:padding="20dp">

    <EditText
        android:id="@+id/edit1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
    <EditText
        android:id="@+id/edit2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="20dp"/>
    <RadioGroup
        android:id="@+id/rdGroup"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <RadioButton
            android:id="@+id/rdAdd"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="더하기"
            android:checked="true"/>
        <RadioButton
            android:id="@+id/rdSub"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="빼기"/>
        <RadioButton
            android:id="@+id/rdMul"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="곱하기"/>
        <RadioButton
            android:id="@+id/rdDiv"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="나누기"/>
    </RadioGroup>
    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="계산하기"
        android:layout_marginTop="20dp"/>

</LinearLayout>

   * activity_second.xml

<LinearLayout 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=".SecondActivity"
    android:orientation="vertical"
    android:padding="20dp">

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="돌아가기"/>
</LinearLayout>

   * MainActivity.java

public class MainActivity extends AppCompatActivity {

    EditText edit1, edit2;
    RadioGroup rdGroup;
    Button button;
    final public int ADD = 0;
    final public int SUB = 1;
    final public int MUL = 2;
    final public int DIV = 3;
    int status = ADD;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        edit1 = findViewById(R.id.edit1);
        edit2 = findViewById(R.id.edit2);
        rdGroup = findViewById(R.id.rdGroup);
        button = findViewById(R.id.button);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                float num1 = Float.valueOf(edit1.getText().toString());
                float num2 = Float.valueOf(edit2.getText().toString());
                Intent intent = new Intent(getApplicationContext(), SecondActivity.class);
                intent.putExtra("num1", num1);
                intent.putExtra("num2", num2);
                intent.putExtra("status", status);
                startActivityForResult(intent, 0);
            }
        });

        rdGroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup radioGroup, int i) {
                int id = rdGroup.getCheckedRadioButtonId();
                switch (id) {
                    case R.id.rdAdd:
                        status = ADD;
                        break;
                    case R.id.rdSub:
                        status = SUB;
                        break;
                    case R.id.rdMul:
                        status = MUL;
                        break;
                    case R.id.rdDiv:
                        status = DIV;
                        break;
                }
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent intent) {
        super.onActivityResult(requestCode, resultCode, intent);
        if (resultCode == RESULT_OK) {
            float result = intent.getFloatExtra("result", 0);
            Toast.makeText(this, "결과 : " + result, Toast.LENGTH_LONG).show();
        }
    }
}

   * SecondActivity.java

public class SecondActivity extends AppCompatActivity {

    Button button;
    int status;
    float result, num1, num2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

        button = findViewById(R.id.button);

        Intent intent = getIntent();
        num1 = intent.getFloatExtra("num1", 0);
        num2 = intent.getFloatExtra("num2", 0);
        status = intent.getIntExtra("status", 0);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getApplicationContext(), MainActivity.class);
                switch (status) {
                    case 0 :
                        result = num1 + num2;
                        break;
                    case 1:
                        result = num1 - num2;
                        break;
                    case 2:
                        result = num1 * num2;
                        break;
                    case 3:
                        result = num1 / num2;
                        break;
                }
                intent.putExtra("result", result);
                setResult(RESULT_OK, intent);
                finish();
            }
        });
    }
}

 

 

2. AdapterView - ListView / GridView

 - 어댑터뷰 : 그리드뷰, 리스트뷰, 스피너 등을 묶어서 어댑터뷰라고 함

 - 어댑터뷰를 사용할 때는 어댑터뷰의 모양을 설정하고 데이터를 채워주는 ArrayAdapter<T> 클래스,

    또는 사용자가 정의한 Adapter 클래스를 사용함

 - ListView : 데이터를 리스트 모양으로 보여주고 그 중 하나를 선택하는 용도로 사용

    ex) 폰 설정창

 - GridView : 사진이나 그림을 격자 모양으로 배치

 - Adapter 클래스를 정의하여 ListView 설정하기 연습(나라별 국기, 이름, 수도가 있는 리스트뷰)

   * activity_main.xml

<LinearLayout 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=".MainActivity"
    android:orientation="vertical">

    <ListView
        android:id="@+id/listView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
        
</LinearLayout>

   * view_cell.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:padding="20dp"
    android:id="@+id/viewLayout">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/flag1"
        android:layout_marginRight="30dp"/>
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:layout_gravity="center_vertical">
        <TextView
            android:id="@+id/textNation"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="대한민국"
            android:textSize="25sp"
            android:layout_marginBottom="5dp"/>
        <TextView
            android:id="@+id/textCapital"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="서울"
            android:textSize="15sp"
            android:layout_marginLeft="1dp"/>
    </LinearLayout>

</LinearLayout>

   * MainActivity.java

public class MainActivity extends AppCompatActivity {

    ListView listView;
    List<NationDto> list = new ArrayList<>();
    String[] nations = {"대한민국", "몰디브", "싱가포르", "태국",
                        "가나", "이집트", "그리스", "네덜란드",
                        "모나코", "스위스", "미국", "캐나다", "호주"};
    String[] capitals = {"서울", "말레", "싱가포르", "방콕",
                        "아크라", "카이로", "아테네", "암스테르담",
                        "모나코", "베른", "워싱턴", "오타와", "캔버라"};
    MyAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        listView = findViewById(R.id.listView);

        for (int i = 0; i < nations.length; i++) {
            int drawable = getResources().getIdentifier("flag" + (i+1),
                                                "drawable", getPackageName());
            String nation = nations[i];
            String capital = capitals[i];
            NationDto dto = new NationDto(drawable, nation, capital);
            list.add(dto);
        }
        adapter = new MyAdapter(getApplicationContext(), R.layout.view_cell, list);
        listView.setAdapter(adapter);
    }
}

   * MyAdapter.java

public class MyAdapter extends BaseAdapter {

    Context context;
    int resource;
    List<NationDto> list;

    public MyAdapter(Context context, int resource, List<NationDto> list) {
        this.context = context;
        this.resource = resource;
        this.list = list;
    }

    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int i) {
        return list.get(i);
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {
        if (view == null) {
            view = View.inflate(context, resource, null);
        }
        ImageView imageView = view.findViewById(R.id.imageView);
        TextView textNation = view.findViewById(R.id.textNation);
        TextView textCapital = view.findViewById(R.id.textCapital);
        LinearLayout viewLayout = view.findViewById(R.id.viewLayout);

        NationDto dto = list.get(i);
        int drawable = dto.getDrawable();
        String nation = dto.getNation();
        String capital = dto.getCapital();

        imageView.setImageResource(drawable);
        textNation.setText(nation);
        textCapital.setText(capital);

        if ((i%2) == 0) viewLayout.setBackgroundColor(Color.rgb(234, 250, 241));
        else viewLayout.setBackgroundColor(Color.rgb(235, 245, 251 ));
        // 인덱스에 따른 레이아웃 컬러 설정은 Main이 아니라 여기서 설정해야 함

        return view;
    }
}

   * NationDto.java

public class NationDto {
    int drawable;
    String nation, capital;

    public NationDto(int drawable, String nation, String capital) {
        this.drawable = drawable;
        this.nation = nation;
        this.capital = capital;
    }

    public int getDrawable() {
        return drawable;
    }

    public void setDrawable(int drawable) {
        this.drawable = drawable;
    }

    public String getNation() {
        return nation;
    }

    public void setNation(String nation) {
        this.nation = nation;
    }

    public String getCapital() {
        return capital;
    }

    public void setCapital(String capital) {
        this.capital = capital;
    }

    @Override
    public String toString() {
        return "NationDto{" + "drawable=" + drawable + ", nation='" + nation + '\'' +
               				 ", capital='" + capital + '\'' + '}';
    }
}

 

 

3. SQLite

 - 컴퓨터에서 구동되는 데이터베이스와 동일한 역할을 하며 모바일 환경에 최적화한 데이터베이스

 - 사용자가 선택한 날짜에 작성한 텍스트를 데이터베이스에 저장, 수정, 삭제, 조회 기능 구현

   * activity_main.xml

<LinearLayout 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=".MainActivity"
    android:orientation="vertical"
    android:padding="20dp">

    <DatePicker
        android:id="@+id/datePicker"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:datePickerMode="spinner"
        android:calendarViewShown="false"
        android:layout_gravity="center"/>

    <EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="#FBEBFD"
        android:layout_marginBottom="10dp"
        android:gravity="top"
        android:padding="20dp"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/btnInsert"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:text="입력하기"
            android:backgroundTint="#BD54CF"
            android:layout_weight="1"
            android:layout_marginRight="5dp"/>
        <Button
            android:id="@+id/btnDelete"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:text="삭제하기"
            android:backgroundTint="#BD54CF"
            android:layout_weight="1"
            android:layout_marginLeft="5dp"/>
    </LinearLayout>

</LinearLayout>

   * MyDiaryVo.java

public class MyDiaryVo {
    String text, date;

    public MyDiaryVo(String date, String text) {
        this.text = text;
        this.date = date;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }

    @Override
    public String toString() {
        return "MyDiaryDto{" + "text='" + text + '\'' + ", date='" + date + '\'' + '}';
    }
}

   * MyDiaryDao.java

public class MyDiaryDao {
    MyHelper helper;

    public MyDiaryDao(MyHelper helper) {
        this.helper = helper;
    }

    private void closeAll(SQLiteStatement statement, SQLiteDatabase sqLiteDatabase, Cursor cursor) {
        if (statement != null) statement.close();
        if (sqLiteDatabase != null) sqLiteDatabase.close();
        if (cursor != null) cursor.close();
    }

    // 입력
    public boolean insert(MyDiaryVo vo) {
        SQLiteDatabase sqLiteDatabase = helper.getWritableDatabase();
        String sql = "insert into tbl_diary" +
                "       values(?, ?)";
        SQLiteStatement statement = sqLiteDatabase.compileStatement(sql);
        statement.bindString(1, vo.getDate());
        statement.bindString(2, vo.getText());
        statement.executeInsert();
        closeAll(statement, sqLiteDatabase, null);

        return true;
    }

    // 수정
    public boolean update(MyDiaryVo vo) {
        SQLiteDatabase sqLiteDatabase = helper.getWritableDatabase();
        String sql = "update tbl_diary set text = ? where date = ?";
        SQLiteStatement statement = sqLiteDatabase.compileStatement(sql);
        statement.bindString(1, vo.getText());
        statement.bindString(2, vo.getDate());
        statement.executeUpdateDelete();
        closeAll(statement, sqLiteDatabase, null);
        return true;
    }

    // 삭제
    public boolean delete(String date) {
        SQLiteDatabase sqLiteDatabase = helper.getWritableDatabase();
        String sql = "delete from tbl_diary where date = ?";
        SQLiteStatement statement = sqLiteDatabase.compileStatement(sql);
        statement.bindString(1, date);
        statement.executeUpdateDelete();
        closeAll(statement, sqLiteDatabase, null);
        return true;
    }

    // 조회
    public String select(String date) {
        SQLiteDatabase sqLiteDatabase = helper.getReadableDatabase();
        String sql = "select * from tbl_diary where date = '" + date +"'";
        Cursor cursor = sqLiteDatabase.rawQuery(sql, null);
        String text = "";
        while (cursor.moveToNext()) { // while문이 없으면 오류가 발생하는데 가져올 값이 한개여도 꼭 써야하는지?
            text = cursor.getString(1);
        }
        closeAll(null, sqLiteDatabase, cursor);
        return text;
    }

}

   * MyHelper.java

public class MyHelper extends SQLiteOpenHelper {

    public MyHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        String sql = "create table tbl_diary(" +
                "       date char(10) primary key," +
                "       text varchar(300))";
        sqLiteDatabase.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {}
}

   * MainActivity.java

public class MainActivity extends AppCompatActivity {

    DatePicker datepicker;
    EditText editText;
    Button btnInsert, btnDelete;
    int year, month, day;
    MyDiaryDao dao;
    MyHelper helper;
    String prevText;
    boolean isThere;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        datepicker = findViewById(R.id.datePicker);
        editText = findViewById(R.id.editText);
        btnInsert = findViewById(R.id.btnInsert);
        btnDelete = findViewById(R.id.btnDelete);

        helper = new MyHelper(this, "diary.db", null, 1);
        dao = new MyDiaryDao(helper);

        initCalandar();

        btnInsert.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String date = year + "_" + month + "_" + day;
                String text = editText.getText().toString();
                String str = "";
                boolean result = false;
                if (!isThere) {
                    result = dao.insert(new MyDiaryVo(date, text));
                    str = "입력";
                } else {
                    Log.d("mytag", "edit");
                    result = dao.update(new MyDiaryVo(date, text));
                    str = "수정";
                }
                if (result)
                    Toast.makeText(MainActivity.this,
                            str + " 완료", Toast.LENGTH_SHORT).show();
            }
        });

        btnDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String date = year + "_" + month + "_" + day;
                boolean result = dao.delete(date);
                if (result) Toast.makeText(MainActivity.this,
                            "삭제 완료", Toast.LENGTH_SHORT).show();
                editText.setText("");
                btnInsert.setText("입력하기");
            }
        });

        datepicker.setOnDateChangedListener(new DatePicker.OnDateChangedListener() {
            @Override
            public void onDateChanged(DatePicker datePicker, int year, int month, int day) {
                MainActivity.this.year = year;
                MainActivity.this.month = month + 1;
                MainActivity.this.day = day;
                String date = year + "_" + (month+1) + "_" + day;
                setPrevText(date);
            }
        });
    }

    private void initCalandar() {
        Calendar cal = Calendar.getInstance();
        int year = cal.get(Calendar.YEAR);
        int month = cal.get(Calendar.MONTH) + 1;
        int day = cal.get(Calendar.DAY_OF_MONTH);
        String date = year + "_" + month + "_" + day;
        setPrevText(date);
    }

    private void setPrevText(String date) {
        prevText = dao.select(date);
        editText.setText(prevText);
        if (prevText == null || prevText.equals("")) {
            btnInsert.setText("입력하기");
            isThere = false;
        } else {
            btnInsert.setText("수정하기");
            isThere = true;
        }
    }
}

 

4. MediaPlayer

 - 멀티미디어를 동작시키기 위해 제공되는 클래스로 음악, 동영상을 재생하게 해줌

 - mp3 플레이어 앱 만들기 연습

   * activity_main.xml

<LinearLayout 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=".MainActivity"
    android:orientation="vertical"
    android:padding="20dp">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="6">
        <ListView
            android:id="@+id/listView"
            android:layout_width="match_parent"
            android:layout_height="match_parent">
        </ListView>
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:gravity="center_vertical">
        <Button
            android:id="@+id/btnPlay"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="듣기"
            android:layout_marginRight="5dp"
            android:backgroundTint="@color/purple_200"/>
        <Button
            android:id="@+id/btnPause"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="일시정지"
            android:layout_marginRight="5dp"
            android:backgroundTint="@color/purple_200"/>
        <Button
            android:id="@+id/btnStop"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="중지"
            android:layout_marginLeft="5dp"
            android:backgroundTint="@color/purple_200"/>
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:orientation="horizontal"
        android:gravity="center_vertical">
        <TextView
            android:id="@+id/textView"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"/>
        <ProgressBar
            android:id="@+id/progressBar"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:visibility="invisible"/>
    </LinearLayout>

</LinearLayout>

   * AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.READ_MEDIA_AUDIO"/>

    <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.Project13_1"
        tools:targetApi="31">
        <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>

            <meta-data
                android:name="android.app.lib_name"
                android:value="" />
        </activity>
    </application>

</manifest>

   * MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    ListView listView;
    Button btnPlay, btnStop, btnPause;
    TextView textView;
    ProgressBar progressBar;
    List<String> list = new ArrayList<>();
    String selectedFile = list.get(0);
    MediaPlayer player = new MediaPlayer();
    boolean isPause;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // external storage 읽기를 위한 코드
        ActivityCompat.requestPermissions(this,
                new String[] {Manifest.permission.READ_EXTERNAL_STORAGE,
                                Manifest.permission.READ_MEDIA_AUDIO}, MODE_PRIVATE);

        setUI();
        setListener();
        setList();

        ArrayAdapter<String> adapter = new ArrayAdapter<>(this,
                            android.R.layout.simple_list_item_single_choice, list);
        listView.setChoiceMode(AbsListView.CHOICE_MODE_SINGLE);
        listView.setAdapter(adapter);
        listView.setItemChecked(0, true);
    }

    private void setList() { // sd카드에 있는 mp3 파일명을 list에 담기
//        String mp3Path = Environment.getExternalStorageDirectory().getPath() + "/Music";
        String mp3Path = "/sdcard/Music";
        File file = new File(mp3Path);
        File[] files = file.listFiles(); // 해당 경로에 있는 파일 전체 가져오기
        for (File aFile : files) {
            String filename = aFile.getName();
            if (checkExt(filename)) list.add(filename);
        }
        Collections.sort(list);
//        Log.d("mytag", list.toString());
    }

    private boolean checkExt(String filename) {
        int extIndex = filename.lastIndexOf(".");
        String ext = filename.substring(extIndex + 1);
        if (ext.equals("mp3")) return true;
        return false;
    }

    private void setListener() {
        btnPlay.setOnClickListener(this);
        btnStop.setOnClickListener(this);
        btnPause.setOnClickListener(this);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
//                Log.d("mytag", "i:" + i + ", l: " + l);
                selectedFile = list.get(i);
            }
        });
    }

    private void setUI() {
        listView = findViewById(R.id.listView);
        btnPlay = findViewById(R.id.btnPlay);
        btnStop = findViewById(R.id.btnStop);
        btnPause = findViewById(R.id.btnPause);
        textView = findViewById(R.id.textView);
        progressBar = findViewById(R.id.progressBar);
    }

    @Override
    public void onClick(View view) {
        if (view == btnPlay) {
            try {
                player.setDataSource("/sdcard/Music/" + selectedFile);
                player.prepare(); // 파일을 읽을 준비(메모리에 올림)
                player.start();
                progressBar.setVisibility(View.VISIBLE);
            } catch (Exception e) {
                e.printStackTrace();
            }
            textView.setText("실행중인 음악 : " + selectedFile);
        } else if (view == btnStop) {
            player.stop();
            player.reset(); // 파일을 메모리에서 제거
            progressBar.setVisibility(View.INVISIBLE);
            textView.setText("현재 재생중이 아님");
        } else if (view == btnPause) {
            if (isPause) {
                player.start();
                btnPause.setText("일시정지");
                isPause = false;
                progressBar.setVisibility(View.VISIBLE);
            }
            else {
                player.pause();
                btnPause.setText("다시 재생");
                isPause = true;
                progressBar.setVisibility(View.INVISIBLE);
            }
        }
    }
}

 

 

5. Thread

 - 여러 작업을 동시에 수행하도록 함(하나의 작업이 끝나기 전에 다른 작업을 동시에 진행시킬 수 있음)

 - Thread 연습

   * activity_main.xml

<LinearLayout 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=".MainActivity"
    android:orientation="vertical"
    android:padding="20dp">

    <TextView
        android:id="@+id/textView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="1번 진행률 : 10%"
        android:layout_marginLeft="135dp"/>
    <SeekBar
        android:id="@+id/seekBar1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:max="100"
        android:progress="10"
        android:layout_marginBottom="20dp"/>
    <TextView
        android:id="@+id/textView2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="2번 진행률 : 30%"
        android:layout_marginLeft="135dp"/>
    <SeekBar
        android:id="@+id/seekBar2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:max="100"
        android:progress="30"
        android:layout_marginBottom="30dp"/>
    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="스레드 시작"
        android:backgroundTint="#A1A0A0"/>

</LinearLayout>

   * MainActivity.java

public class MainActivity extends AppCompatActivity {

    SeekBar seekBar1, seekBar2;
    Button button;
    Thread thread;
    TextView textView1, textView2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        seekBar1 = findViewById(R.id.seekBar1);
        seekBar2 = findViewById(R.id.seekBar2);
        button = findViewById(R.id.button);
        textView1 = findViewById(R.id.textView1);
        textView2 = findViewById(R.id.textView2);

        thread = new Thread(new Runnable() {
            @Override
            public void run() {
                // 0.1초 간격으로 값을 각각 2, 1씩 증가
                for (int i = 0; i < 100; i++) {
                    int progress1 = seekBar1.getProgress() + 2;
                    if (progress1 > seekBar1.getMax()) progress1 = seekBar1.getMax();
                    int progress2 = seekBar2.getProgress() + 1;
                    if (progress2 > seekBar2.getMax()) progress2 = seekBar2.getMax();

                    seekBar1.setProgress(progress1);
                    seekBar2.setProgress(progress2);
                    SystemClock.sleep(100);

                    textView1.setText("1번 진행률 : " + progress1 + "%");
                    textView2.setText("2번 진행률 : " + progress2 + "%");
                }
            }
        });

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                thread.start();
            }
        });
    }
}