Android_Java(32) - ImageDownload

1. Async 클래스 사용
        - AsynTask 클래스
            - 작업 스레드와 관련된 복잡한 부분을 쉽게 처리해주는 클래스 
            - onPreExecute() : UI 스레드에서 실행되며, 작업을 설정하는데 사용됨 
            - doInBackground() : 작업 스레드에서 수행할 작업을 기술하는 곳임 
            - onProgressUpdate() : UI 스레드에서 호출되고, 작업 진행률 업데이트에 사용됨 
            - onPostExecute() : 작업 완료되면 UI에 결과를 업데이트하는데 사용됨 

            - AsyncTask<Params, Progress, Result>
                - Params : 실행 시에 작업에 전달되는 값의 타입임
                - Progress : 작업 진행 정도를 나타내는 값의 타입 
                - Result : 작업 결과 값을 나타내는 값의 타입 

---

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="kr.co.imagedownload">
    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.ImageDownload">
        <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>

---

<?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">

    <EditText
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:id="@+id/editText"
        android:inputType="textUri"
        android:text="https://www.apple.com/v/imac/n/images/overview/imac27__evbw33241ouq_small_2x.jpg"/>
    <Button
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Download"
        android:id="@+id/button"/>
    <ImageView
        android:layout_width="fill_parent"
        android:layout_height="223dp"
        android:id="@+id/imageview"/>

</LinearLayout>

---

package kr.co.imagedownload;

import androidx.appcompat.app.AppCompatActivity;

import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.BitmapDrawable;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

public class MainActivity extends AppCompatActivity {
    public String URL = "";
    EditText editText;
    ImageView imageView;
    Button button;
    ProgressDialog mProgressDialog;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getSupportActionBar().setDisplayShowHomeEnabled(true);
        getSupportActionBar().setIcon(R.drawable.ic_launcher);

        editText = findViewById(R.id.editText);
        button = findViewById(R.id.button);
        imageView = findViewById(R.id.imageview);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                URL = editText.getText().toString();
                new DownloadImage().execute(URL);
            }
        });
    }

    //AsyncTask 클래스 이용하여 스레드를 간접적으로 사용함
    private class DownloadImage extends AsyncTask<String, Void, Bitmap>{

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

            mProgressDialog = new ProgressDialog(MainActivity.this);
            mProgressDialog.setTitle("이미지 다운로드 - 네트워크");
            mProgressDialog.setMessage("이미지 다운로드 중입니다.");
            mProgressDialog.setIndeterminate(false);
            mProgressDialog.show();
        }

        @Override
        protected Bitmap doInBackground(String... url) {
            String imageURL = url[0];
            Bitmap bitmap = null;

            try {
                //네트워크 이미지
                InputStream input = new URL(imageURL).openStream();
                bitmap = BitmapFactory.decodeStream(input);
            } catch (IOException e) {
                e.printStackTrace();
            }
            return bitmap;
        }

        //다운로드된 이미지를 화면에 표시
        @Override
        protected void onPostExecute(Bitmap bitmap) {
            super.onPostExecute(bitmap);

            imageView.setImageBitmap(bitmap);
            mProgressDialog.dismiss();

        }
    }

}

---

[결과 출력]

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