java - 通过创建不同的对象来使用相同的 AsyncTask

Question

我正在制作一个小图像，下载 Android 应用程序作为一个项目。它获取两个图像的 URL，下载它们并将它们显示在 ImageView 中。目前，我正在使用两个单独的 ImageDownloader，即 ImageDownloader1 和 ImageDownloader2，它们都扩展 AsyncTask 并实例化它们的对象，然后下载图像。这两个类都在不同的 ImageView 上执行相同的工作。我希望通过只创建一个像 ImageDownloader 这样的类，然后创建两个实例来为每个 ImageView 下载图像来完成此操作？有什么办法可以做到这一点，请建议我吗？

Java 代码:

public class MainActivity extends AppCompatActivity {

    Button image1Button,image2Button,resetButton;

    ImageView upperImageIV,lowerImageIV;

    ProgressBar upperImagePB,lowerImagePB;

    ImageDownloader1 image1;
    ImageDownloader2 image2;

    TextView textView1,textView2;

    boolean status1,status2;


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

        image1Button = (Button) findViewById(R.id.button1);
        image2Button = (Button) findViewById(R.id.button2);
        resetButton = (Button) findViewById(R.id.button3);

        upperImageIV = (ImageView) findViewById(R.id.imageView1);
        lowerImageIV = (ImageView) findViewById(R.id.imageView2);

        upperImagePB = (ProgressBar) findViewById(R.id.pbarUpperIMG);
        lowerImagePB = (ProgressBar) findViewById(R.id.pbarLLowerIMG);

        status1 = false;
        status2 = false;

        textView1 = (TextView) findViewById(R.id.editText1);
        textView2 = (TextView) findViewById(R.id.editText2);
    }

    public void downloadImage1(View view){
        upperImageIV.setVisibility(View.GONE);
        String url;
        url = textView1.getText().toString();
        if(!url.isEmpty()) {
            status1 = true;
            image1 = new ImageDownloader1();
            upperImagePB.setVisibility(View.VISIBLE);
            image1.execute(url);
        }
        else if(url.isEmpty()){
            upperImageIV.setVisibility(View.GONE);
        }
    }


    public class ImageDownloader1 extends AsyncTask<String,Void,Bitmap>{


        @Override
        protected Bitmap doInBackground(String... params) {
            try {
                URL url = new URL(params[0]);
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.connect();
                System.out.println("Content Type = "+connection.getContentType());
                if(connection.getContentType().contains("image")){
                    InputStream inputStream = connection.getInputStream();
                    return BitmapFactory.decodeStream(inputStream);
                }
            }
            catch (Exception e) {
                e.printStackTrace();
            }
            while(image1.cancel(true) == false ){
                if (isCancelled())
                    break;
            }
            return null;
        }

        @Override
        protected void onPostExecute(Bitmap bitmap){
            super.onPostExecute(bitmap);
            try {
                upperImageIV.setImageBitmap(image1.get());
                upperImagePB.setVisibility(View.GONE);
                upperImageIV.setVisibility(View.VISIBLE);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }




    public void downloadImage2(View view){
        lowerImageIV.setVisibility(View.GONE);
        String url;
        url = textView2.getText().toString();
        if(!url.isEmpty()) {
            status2 = true;
            image2 = new ImageDownloader2();
            lowerImagePB.setVisibility(View.VISIBLE);
            image2.execute(url);
        }
        else if(url.isEmpty()){
            lowerImageIV.setVisibility(View.GONE);
        }
    }


    public class ImageDownloader2 extends AsyncTask<String,Void,Bitmap>{

        @Override
        protected Bitmap doInBackground(String... params) {
            try {
                URL url = new URL(params[0]);
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.connect();
                if(connection.getContentType().contains("image")){
                    InputStream inputStream = connection.getInputStream();
                    return BitmapFactory.decodeStream(inputStream);
                }
            }
            catch (Exception e) {
                e.printStackTrace();
            }
            while(image2.cancel(true) == false ){
                if (isCancelled())
                    break;
            }
            return null;
        }

        @Override
        protected void onPostExecute(Bitmap bitmap){
            super.onPostExecute(bitmap);
            try {
                lowerImageIV.setImageBitmap(image2.get());
                lowerImagePB.setVisibility(View.GONE);
                lowerImageIV.setVisibility(View.VISIBLE);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }




    public void reset(View view){
        System.out.println("Reset Button pressed");
        upperImageIV.setVisibility(View.GONE);
        upperImagePB.setVisibility(View.GONE);

        lowerImageIV.setVisibility(View.GONE);
        lowerImagePB.setVisibility(View.GONE);

        if(status1 == true && status2 == false){
            image1.cancel(true);
        }
        else if(status1 == false && status2 == true){
            image2.cancel(true);
        }
        else if(status1 == true && status2 == true){
            image1.cancel(true);
            image2.cancel(true);
        }
        else {
        }
    }
}

XML 代码:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="match_parent"
    tools:context="com.example.syeddanish.downloadingimages.MainActivity">

    <EditText
        android:id="@+id/editText1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="URL here"
        android:textSize="24sp"/>

    <EditText
        android:id="@+id/editText2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="URL here"
        android:textSize="24sp"
        android:layout_below="@id/editText1"/>

    <LinearLayout
        android:id="@+id/buttonsLinearLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:layout_below="@+id/editText2">

        <Button
            android:id="@+id/button1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="downloadImage1"
            android:text="Image 1" />

        <Button
            android:id="@+id/button2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="downloadImage2"
            android:text="Image 2" />

        <Button
            android:id="@+id/button3"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:onClick="reset"
            android:text="Reset" />
    </LinearLayout>


    <LinearLayout
        android:id="@+id/imagesLinearLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/buttonsLinearLayout"
        android:orientation="vertical"
        android:weightSum="1">

        <RelativeLayout
            android:id="@+id/upperIMGRL"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical"
            android:layout_weight="0.5">

            <ProgressBar
                android:id="@+id/pbarUpperIMG"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:indeterminate="true"
                android:layout_centerInParent="true"
                android:visibility="gone" />

            <ImageView
                android:id="@+id/imageView1"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:visibility="gone"/>

        </RelativeLayout>

        <RelativeLayout
            android:id="@+id/lowerIMGRL"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical"
            android:layout_weight="0.5">

            <ProgressBar
                android:id="@+id/pbarLLowerIMG"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:indeterminate="true"
                android:layout_centerInParent="true"
                android:visibility="gone" />


            <ImageView
                android:id="@+id/imageView2"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:visibility="gone"/>


        </RelativeLayout>
    </LinearLayout>

</RelativeLayout>

Answer 1

使用 Picasso 库，您可以执行以下操作

Picasso.with(context).load(url).centerCrop().into(imageView)