运行结果

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文件结构

主要代码

MainActivity

package cn.edu.sicnu.threadfiledownload;

import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    EditText editText_url;
    ListView listView;  //heap堆，可以被整个对象所有方法访问
    TextView textView;
    ProgressBar progressBar;

    ArrayList<String> arrayList = new ArrayList<>();
    ArrayList<String> localImages = new ArrayList<>();
    ArrayAdapter<String> arrayAdapter;


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

        arrayList.add("http://img2.imgtn.bdimg.com/it/u=500808421,1575925585&fm=200&gp=0.jpg");
        arrayList.add("http://img1.imgtn.bdimg.com/it/u=2883138594,3332343437&fm=27&gp=0.jpg");
        arrayList.add("http://img0.imgtn.bdimg.com/it/u=2779717376,1807907918&fm=200&gp=0.jpg");
        arrayList.add("http://img0.imgtn.bdimg.com/it/u=416447706,3692155938&fm=27&gp=0.jpg");
        arrayList.add("http://img3.imgtn.bdimg.com/it/u=2058241956,1502683125&fm=27&gp=0.jpg");
        arrayList.add("http://img0.imgtn.bdimg.com/it/u=2779717376,1807907918&fm=200&gp=0.jpg");
        arrayList.add("http://img0.imgtn.bdimg.com/it/u=2779717376,1807907918&fm=200&gp=0.jpg");


        editText_url = findViewById(R.id.editText_url);
        listView = findViewById(R.id.listView);
        arrayAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,arrayList);
        listView.setAdapter(arrayAdapter);

        textView = findViewById(R.id.textView);
        progressBar = findViewById(R.id.progressBar);

        asyncTask = new MyAsyncTask();
    }

    public void add(View view){
        arrayList.add(editText_url.getText().toString());
        arrayAdapter.notifyDataSetChanged();
    }

    public void download(View view){

        switch (asyncTask.getStatus()){
            case PENDING:
                asyncTask.execute(0);
                break;
            case RUNNING:
                break;
            case FINISHED:
                asyncTask = new MyAsyncTask();
                asyncTask.execute(0);
                break;
        }

    }

    class MyAsyncTask extends AsyncTask<Integer,Integer,Integer>{

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            localImages.clear();
        }


        @Override
        protected Integer doInBackground(Integer... integers) {
            //在另外一个线程里面！！！
            for(int i=0;i<arrayList.size();i++){
                String s = arrayList.get(i);
                try {
                    URL url = new URL(s);
                    URLConnection connection = url.openConnection();
                    int size = connection.getContentLength();  //图片大小

                    publishProgress(0,i+1,size);



                    InputStream inputStream = connection.getInputStream();  //流
                    byte[] bytes = new byte[100];
                    int len = -1;

                    //准备好外部存储文件
                    File file = getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS);
                    String filename = file.getAbsolutePath()+"/"+i+".jpg";
                    FileOutputStream fileOutputStream = new FileOutputStream(filename);

                    while ((len=inputStream.read(bytes))!=-1){
                        fileOutputStream.write(bytes,0,len);
//                        Thread.sleep(1);
                        publishProgress(1,len);
                    }

                    fileOutputStream.close();
                    inputStream.close();

                    localImages.add(filename);

                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            return null;
        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);

            switch (values[0]){
                case 0:
                    textView.setText("正在下载第"+values[1]+"个文件！！！");
                    progressBar.setMax(values[2]);
                    progressBar.setProgress(0);
                    break;
                case 1:
                    progressBar.incrementProgressBy(values[1]);
                    break;
            }



        }

        @Override
        protected void onPostExecute(Integer integer) {
            super.onPostExecute(integer);
            textView.setText("下载完成！！！");
            progressBar.setProgress(0);
        }
    }

    public void showImages(View view){
        Intent intent = new Intent(this,Main2Activity.class);
        intent.putExtra("images",localImages);
        startActivity(intent);
    }



}

Main2Activity

package cn.edu.sicnu.threadfiledownload;

import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ImageView;
import android.widget.LinearLayout;

import java.util.ArrayList;

public class Main2Activity extends AppCompatActivity {


    LinearLayout layout;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        layout = findViewById(R.id.layout);

        Intent intent = getIntent();
        ArrayList<String> images = (ArrayList<String>) intent.getSerializableExtra("images");
        for(int i=0;i<images.size();i++){
            String imagePath = images.get(i);
            Bitmap bitmap = BitmapFactory.decodeFile(imagePath);
            ImageView imageView = new ImageView(this);
            imageView.setImageBitmap(bitmap);
            imageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
            imageView.setAdjustViewBounds(true);

            layout.addView(imageView);
        }
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="cn.edu.sicnu.threadfiledownload.MainActivity"
    tools:layout_editor_absoluteY="81dp">

    <EditText
        android:id="@+id/editText_url"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginStart="16dp"
        android:ems="10"
        android:hint="Input image url"
        android:inputType="textPersonName"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/progressBar" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:layout_marginEnd="4dp"
        android:layout_marginStart="16dp"
        android:onClick="add"
        android:text="add"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/button2"
        app:layout_constraintHorizontal_chainStyle="spread_inside"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText_url" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="download"
        android:text="download"
        app:layout_constraintBottom_toBottomOf="@+id/button"
        app:layout_constraintEnd_toStartOf="@+id/button3"
        app:layout_constraintStart_toEndOf="@+id/button" />

    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="17dp"
        android:onClick="showImages"
        android:text="images"
        app:layout_constraintBottom_toBottomOf="@+id/button2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/button2" />

    <ListView
        android:id="@+id/listView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginBottom="13dp"
        android:layout_marginEnd="9dp"
        android:layout_marginStart="9dp"
        android:layout_marginTop="16dp"
        app:layout_constraintBottom_toTopOf="@+id/progressBar"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ProgressBar
        android:id="@+id/progressBar"
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginBottom="110dp"
        android:layout_marginEnd="15dp"
        android:layout_marginStart="15dp"
        android:max="100"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginEnd="13dp"
        android:layout_marginStart="13dp"
        android:layout_marginTop="362dp"
        app:layout_constraintBottom_toTopOf="@+id/progressBar"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

activity_main2.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="cn.edu.sicnu.threadfiledownload.Main2Activity">

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

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            android:id="@+id/layout"/>
    </ScrollView>
</android.support.constraint.ConstraintLayout>

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