如何使用 URL 为 ImageView 设置 setImageBitmap

Question

in manifest：

<uses-permission android:name="android.permission.INTERNET">

在 onCreate 方法中：

    webImage = (ImageView) findViewById(R.id.webimage); 
   String urlImage = "https://thetab.com/blogs.dir/91/files/2017/01/maxresdefault-1.jpg";
// Set setImageBitmap to Bitmap created by getURLBitmap method
webImage.setImageBitmap(getURLBitmap(urlImage));

在 getURLBitmap 方法中：

         if(!urlString.isEmpty() || urlString != null) {
    InputStream inputStream = null;
    // pass the string into a URL object
    try {
        URL urlForImage = new URL(urlString);
        // cast url openConnection into HttpURLConnection
        HttpURLConnection connection = (HttpURLConnection) urlForImage.openConnection();
        // Set HttpURLConnection setDoInput to true
        connection.setDoInput(true);
        // Start HttpURLConnection connection
        connection.connect();
        if(connection.getResponseCode() == 200) {
            // Start reading Http inputStream (getInputStream) and use it to initialize a InputStream object
            inputStream = connection.getInputStream();
            // pass InputStream object into a BitmapFactory's decodeStream (is a static method)
            Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
            // set Bitmap object to decodedStream
            return bitmap;
        }
        // return Bitmap
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
    return null;

我不断收到此错误：

D/网络安全配置：未指定网络安全配置，使用平台默认值

E/Android运行时：致命异常：主进程：com.example.EX.perfectmoment，PID：26747java.lang.RuntimeException： 无法启动活动 ComponentInfo{com.example.EX.perfectmoment/com.example.EX.perfectmoment.MemeMainActivity}： android.os.NetworkOnMainThreadException

Answer 1

您收到此错误是因为您在 UI 线程上运行网络操作，这在 Android Dev 中非常被看不起，因为它通常会导致 UI 无响应，从而导致糟糕的用户体验。我建议创建自己的ASyncTask，它将在另一个线程中执行网络操作并将其反馈到UI线程，或者使用Android上许多流行的图像库之一，例如Picasso或Glide。

Answer 2

如上面的评论中所述，不再支持在 android 中的 UI 线程上运行网络任务，因此您必须使用 AsyncTask 或其他可用的线程机制在单独的线程上执行 UI 阻止任务。

因此，通过使用AsynTask，您可以像下面的代码片段一样进行操作。

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.ImageView;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class MainActivity extends AppCompatActivity{
    ImageView webImage;
    private static final String TAG = MainActivity.class.getSimpleName();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        webImage = (ImageView) findViewById(R.id.imageView1);
        new SetImage().execute();
    }
    private class SetImage extends AsyncTask<Void, Void, Bitmap>{
        final String urlImage = "https://thetab.com/blogs.dir/91/files/2017/01/maxresdefault-1.jpg";
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }
        @Override
        protected Bitmap doInBackground(Void... params) {
            Bitmap image = getURLBitmap(urlImage);
            return image;
        }
        @Override
        protected void onPostExecute(Bitmap bitmap) {
            super.onPostExecute(bitmap);
            webImage.setImageBitmap(bitmap);
        }
    }
    private Bitmap getURLBitmap(String urlString){
        if(!urlString.isEmpty() || urlString != null) {
            InputStream inputStream = null;
            // pass the string into a URL object
            try {
                URL urlForImage = new URL(urlString);
                // cast url openConnection into HttpURLConnection
                HttpURLConnection connection = (HttpURLConnection) urlForImage.openConnection();
                // Set HttpURLConnection setDoInput to true
                connection.setDoInput(true);
                // Start HttpURLConnection connection
                connection.connect();
                if(connection.getResponseCode() == 200) {
                    // Start reading Http inputStream (getInputStream) and use it to initialize a InputStream object
                    inputStream = connection.getInputStream();
                    // pass InputStream object into a BitmapFactory's decodeStream (is a static method)
                    Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
                    // set Bitmap object to decodedStream
                    return bitmap;
                }
                // return Bitmap
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }
}