딩코딩 : Computer Science 블로그

버튼을 눌렀을 때 새로운 Activity를 호출하는 예시이다.

package com.example.harudemo.fragments

import android.content.Context
import android.content.Intent
import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import androidx.fragment.app.Fragment
import com.example.harudemo.R
import com.example.harudemo.sns.SnsTestActivity

class SnsFragment: Fragment() {
    companion object{
        const val TAG : String = "로그"

        fun newInstance() : SnsFragment {
            return SnsFragment()
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        Log.d(TAG, "HomeFragment - on Create() called" )
    }


    override fun onAttach(context: Context) {
        super.onAttach(context)
        Log.d(TAG, "HomeFragment - onAttach() called")
    }

    //뷰가 생성되었을 때
    //프래그먼트와 레이아웃을 연결시켜주는 부분이다.
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        Log.d(TAG, "HomeFragment - onCreateView() called")

        val view = inflater.inflate(R.layout.fragment_sns, container, false)

        return view
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        //버튼이 클릭되면 액비티비 호출
        val btnActivity: Button = view.findViewById(R.id.btn_newActivity)
        btnActivity.setOnClickListener{
            activity?.let{
                val intent = Intent(it, SnsTestActivity::class.java)
                it.startActivity(intent)
            }
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<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"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/tvInput"
        android:layout_width="match_parent"
        android:layout_height="250dp"
        android:background="@color/light_gray"
        android:padding="10dp"
        android:textSize="40dp"
        android:text=""
        android:gravity="right|bottom"
        />
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:layout_margin="0dp">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:orientation="horizontal">

            <Button
                android:id="@+id/btnOne"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_margin="2dp"
                android:layout_weight="1"
                android:onClick="onDigit"
                android:text="@string/_1" />

            <Button
                android:id="@+id/btnTwo"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_margin="2dp"
                android:layout_weight="1"
                android:onClick="onDigit"
                android:text="@string/_2" />

            <Button
                android:id="@+id/btnThree"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_margin="2dp"
                android:layout_weight="1"
                android:onClick="onDigit"
                android:text="@string/_3" />

            <Button
                android:id="@+id/btnSubtract"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_margin="2dp"
                android:layout_weight="1"
                android:onClick="onOperator"
                android:text="@string/minus" />
        </LinearLayout>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:layout_weight="1"
            >
            <Button
                android:id="@+id/btnFour"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_4"/>
            <Button
                android:id="@+id/btnFive"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_5"/>
            <Button
                android:id="@+id/btnSix"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_6"/>
            <Button
                android:id="@+id/btnMultiply"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onOperator"
                android:text="@string/multiply"/>
        </LinearLayout>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:layout_weight="1"
            >
            <Button
                android:id="@+id/btnSeven"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_7"/>
            <Button
                android:id="@+id/btnEight"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_8"/>
            <Button
                android:id="@+id/btnNine"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="@string/_9"/>
            <Button
                android:id="@+id/btnDivide"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onOperator"
                android:text="@string/div"/>
        </LinearLayout>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:layout_weight="1"
            >
            <Button
                android:id="@+id/btnDot"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDecimalPoint"
                android:text="."/>
            <Button
                android:id="@+id/btnZero"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onDigit"
                android:text="0"/>
            <Button
                android:id="@+id/btnClr"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onClear"
                android:text="CLR"/>
            <Button
                android:id="@+id/btnAdd"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:layout_margin="2dp"
                android:onClick="onOperator"
                android:text="+"/>
        </LinearLayout>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:layout_weight="1"
            >
            <Button
                android:id="@+id/btnEqaul"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="2"
                android:layout_margin="2dp"
                android:onClick="onEqaul"
                android:text="="/>
        </LinearLayout>

    </LinearLayout>


</LinearLayout>

MainActivity.kt

package com.example.mycalculator

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.TextView
import android.widget.Toast
import java.lang.ArithmeticException

class MainActivity : AppCompatActivity() {

    private var tvInput: TextView? = null
    var lastNumeric : Boolean = false
    var lastDot : Boolean = false

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        tvInput = findViewById(R.id.tvInput)
    }

    fun onDigit(view:View){
        tvInput?.append((view as Button).text)
        lastNumeric = true
        Toast.makeText(this, "Button clicked", Toast.LENGTH_LONG).show()
    }

    fun onDecimalPoint(view:View){
        if(lastNumeric && !lastDot){
            tvInput?.append(".")
            lastNumeric = false
            lastDot = true
        }
    }

    fun onClear(view: View){
        tvInput?.text = ""
    }

    fun onOperator(view: View){
        tvInput?.text?.let {
            if (lastNumeric && !isOperatorAdded(it.toString())){
                tvInput?.append((view as Button).text)
                lastNumeric = false
                lastDot = false
            }
        }
    }

    fun onEqaul(view : View){
        if(lastNumeric){
            var tvValue = tvInput?.text.toString()
            var prefix = ""
            try{
                if(tvValue.startsWith("-")){
                    prefix = "-"
                    tvValue = tvValue.substring(1)
                }
                if(tvValue.contains("-")){
                    val splitValue = tvValue.split("-")
                    var one = splitValue[0]
                    var two = splitValue[1]

                    if(prefix.isNotEmpty()){
                        one = prefix + one
                    }

                    tvInput?.text = removeZeroAfterDot((one.toDouble() - two.toDouble()).toString())
                } else if(tvValue.contains("+")){
                    val splitValue = tvValue.split("+")
                    var one = splitValue[0]
                    var two = splitValue[1]

                    if(prefix.isNotEmpty()){
                        one = prefix + one
                    }

                    tvInput?.text = removeZeroAfterDot((one.toDouble() + two.toDouble()).toString())
                }else if(tvValue.contains("*")){
                    val splitValue = tvValue.split("*")
                    var one = splitValue[0]
                    var two = splitValue[1]

                    if(prefix.isNotEmpty()){
                        one = prefix + one
                    }

                    tvInput?.text = removeZeroAfterDot((one.toDouble() * two.toDouble()).toString())
                }else if(tvValue.contains("/")){
                    val splitValue = tvValue.split("/")
                    var one = splitValue[0]
                    var two = splitValue[1]

                    if(prefix.isNotEmpty()){
                        one = prefix + one
                    }

                    tvInput?.text = removeZeroAfterDot((one.toDouble() / two.toDouble()).toString())
                }
            }catch(e: ArithmeticException){
                e.printStackTrace()
            }
        }
    }

    private fun removeZeroAfterDot(result: String) : String{
        var value = result
        if(result.contains(".0"))
            value = result.substring(0, result.length-2)

        return value
    }


    private fun isOperatorAdded(value : String) : Boolean{
        return if(value.startsWith("-")){
            false
        }else{
            value.contains("/") || value.contains("*") || value.contains("+") || value.contains("-")
        }
    }

}

package com.example.customnavexample;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.drawerlayout.widget.DrawerLayout;

import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private DrawerLayout drawerLayout;
    private View drawerView;

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

        drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawerView = (View) findViewById(R.id.drawer);

        Button btn_open = (Button)findViewById(R.id.btn_open);
        btn_open.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                drawerLayout.openDrawer(drawerView);
            }
        });

        Button btn_close = (Button)findViewById(R.id.btn_close);
        btn_close.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                drawerLayout.closeDrawers();
            }
        });


        drawerLayout.setDrawerListener(listener);
        drawerView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View view, MotionEvent motionEvent) {
                return true;
            }
        });

    }
    DrawerLayout.DrawerListener listener = new DrawerLayout.DrawerListener() {
        @Override
        public void onDrawerSlide(@NonNull View drawerView, float slideOffset) {

        }

        @Override
        public void onDrawerOpened(@NonNull View drawerView) {

        }

        @Override
        public void onDrawerClosed(@NonNull View drawerView) {

        }

        @Override
        public void onDrawerStateChanged(int newState) {

        }
    };


}

<?xml version="1.0" encoding="utf-8"?>

<androidx.drawerlayout.widget.DrawerLayout 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:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <Button
            android:id="@+id/btn_open"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="열려라 참깨"/>
    </LinearLayout>

    <!-- drawer.xml 연결-->
    <include layout="@layout/activity_drawer"/>

</androidx.drawerlayout.widget.DrawerLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="240dp"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    android:background="#632196F3"
    android:id="@+id/drawer"
    android:orientation="vertical">

    <Button
        android:id="@+id/btn_close"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="메뉴닫기"/>
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="LMJ Menu"/>


    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="5dp"
        android:background="#2196F3"
        android:orientation="vertical"
        >

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:text="Test Menu"
            />

    </LinearLayout>
</LinearLayout>

   <WebView
        android:id="@+id/webView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        ></WebView>

activity xml에 WebView 컴포넌트를 추가해준다.

MainActivity.java

package com.example.webview;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.KeyEvent;
import android.webkit.WebChromeClient;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class MainActivity extends AppCompatActivity {

    private WebView webView;
    private String url = "https://google.com";

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

        webView = (WebView) findViewById(R.id.webView);
        webView.getSettings().setJavaScriptEnabled(true);
        webView.loadUrl(url);
        webView.setWebChromeClient(new WebChromeClient());
        webView.setWebViewClient(new WebViewClientClass());

    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()){
            webView.goBack();
            return true;
        }

        return super.onKeyDown(keyCode, event);
    }

    private class WebViewClientClass extends WebViewClient {
        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            view.loadUrl(url);
            return true;
        }
    }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.example.webview">

    <!--  인터넷 권한 설정  -->
    <uses-permission android:name="android.permission.INTERNET"/>
    
    <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.WebView"
        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>
        </activity>
    </application>

</manifest>

package com.example.sharedpreferences;

import androidx.appcompat.app.AppCompatActivity;

import android.content.SharedPreferences;
import android.os.Bundle;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {
    EditText et_save;
    String shared = "file";

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

        et_save = (EditText) findViewById(R.id.et_save);

        //앱이 꺼질 때 저장된 정보를 불러오는 코드
        SharedPreferences sharedPreferences = getSharedPreferences(shared, 0);
        String value = sharedPreferences.getString("key", "");
        et_save.setText(value);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();

        //앱이 꺼졋을 때 정보를 저장하는 코드
        SharedPreferences sharedPreferences = getSharedPreferences(shared, 0);
        SharedPreferences.Editor editor = sharedPreferences.edit();
        String value = et_save.getText().toString();
        editor.putString("key", value);
        editor.commit();

    }
}

SharedPreferences 를 이용하면 앱에서 뒤로가기를 눌러도

데이터를 임시 저장할 수 있다

단 앱을 삭제하거나 완전히 종료할 때는 정보를 저장하는 것이 불가능하다.

이때는 데이터베이스를 추가적으로 이용해야한다.

package com.example.listexample01;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    private ListView list;

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

        list = (ListView) findViewById(R.id.list);
        List<String> data = new ArrayList<>();

        ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, data);
        list.setAdapter(adapter);

        data.add("LMJ");
        data.add("Fighting!");
        data.add("Fighting!");
        adapter.notifyDataSetChanged();

    }
}

<?xml version="1.0" encoding="utf-8"?>
<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"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ListView
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
    </ListView>

</LinearLayout>

ArrayList 와 실제 레이아웃의 ListView를 연결해주기 위해서는

다음과 같이 adapter를 이용하여 둘을 연결해주어야 한다.

        list = (ListView) findViewById(R.id.list);
        List<String> data = new ArrayList<>();

        ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, data);
        list.setAdapter(adapter);

        data.add("LMJ");
        data.add("Fighting!");
        data.add("Fighting!");
        adapter.notifyDataSetChanged();

XML에서 gravity를 이용해 요소를 가운데 배치하기

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center">
        <ImageView
            android:id="@+id/test"
            android:layout_width="100dp"
            android:layout_height="100dp"
            android:src="@mipmap/ic_launcher" />
    </LinearLayout>

LinearLayout 안에 요소를 넣고

LinearLayout의 gravity property를 center로 주면

요소를 가운데로 배치할 수 있다

Intent를 이용하여 다른 컴포넌트로 이동할 수 있고,

putExtra와 getExtra에 키값을 주어 데이터를 전달 할 수 있다.

MainActivity

package com.example.firstapp;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {
    EditText et_id;
    Button btn_test;

    private EditText et_test;
    private Button btn_move;
    private String str;

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

        btn_move = findViewById(R.id.btn_move);
        btn_move.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this, SubActivity.class);
                str = et_test.getText().toString();
                intent.putExtra("str", str);
                startActivity(intent);
            }
        });

        et_id = findViewById(R.id.et_id);
        btn_test = findViewById(R.id.btn_test);

        btn_test.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                et_id.setText("LMJ");
            }
        });
    }
}

SubActivity

package com.example.firstapp;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;

public class SubActivity extends AppCompatActivity {

    private TextView tv_sub;

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

        tv_sub = findViewById(R.id.tv_sub);

        Intent intent = getIntent();
        String str = intent.getStringExtra("str");

        tv_sub.setText(str);
    }
}