Question

我在从服务器下载图像并使用Android中的AsyncTask在ListView中显示时遇到了一些问题。

它向我显示下载图像在主（UI）线程中的错误但是我正在使用AsyncTask来实现此目的。

这是我的MainActivity.java代码。

public class MainActivity extends AppCompatActivity {

    private String[] imageURLArray = new String[]{
            "http://farm8.staticflickr.com/7315/9046944633_881f24c4fa_s.jpg",
            "http://farm4.staticflickr.com/3777/9049174610_bf51be8a07_s.jpg",
            "http://farm8.staticflickr.com/7324/9046946887_d96a28376c_s.jpg",
            "http://farm3.staticflickr.com/2828/9046946983_923887b17d_s.jpg",
            "http://farm4.staticflickr.com/3810/9046947167_3a51fffa0b_s.jpg",
            "http://farm4.staticflickr.com/3773/9049175264_b0ea30fa75_s.jpg",
            "http://farm4.staticflickr.com/3781/9046945893_f27db35c7e_s.jpg",
            "http://farm6.staticflickr.com/5344/9049177018_4621cb63db_s.jpg",
            "http://farm8.staticflickr.com/7307/9046947621_67e0394f7b_s.jpg",
            "http://farm6.staticflickr.com/5457/9046948185_3be564ac10_s.jpg",
            "http://farm4.staticflickr.com/3752/9046946459_a41fbfe614_s.jpg",
            "http://farm8.staticflickr.com/7403/9046946715_85f13b91e5_s.jpg",
            "http://farm8.staticflickr.com/7315/9046944633_881f24c4fa_s.jpg",
            "http://farm4.staticflickr.com/3777/9049174610_bf51be8a07_s.jpg",
            "http://farm8.staticflickr.com/7324/9046946887_d96a28376c_s.jpg",
            "http://farm3.staticflickr.com/2828/9046946983_923887b17d_s.jpg",
            "http://farm4.staticflickr.com/3810/9046947167_3a51fffa0b_s.jpg",
            "http://farm4.staticflickr.com/3773/9049175264_b0ea30fa75_s.jpg",
            "http://farm4.staticflickr.com/3781/9046945893_f27db35c7e_s.jpg",
            "http://farm6.staticflickr.com/5344/9049177018_4621cb63db_s.jpg",
            "http://farm8.staticflickr.com/7307/9046947621_67e0394f7b_s.jpg",
            "http://farm6.staticflickr.com/5457/9046948185_3be564ac10_s.jpg",
            "http://farm4.staticflickr.com/3752/9046946459_a41fbfe614_s.jpg",
            "http://farm8.staticflickr.com/7403/9046946715_85f13b91e5_s.jpg"};
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ListView listView = (ListView)this.findViewById(R.id.listView);
        ImageAdapter imageAdapter = new ImageAdapter(this, R.layout.imageitem, imageURLArray);
        listView.setAdapter(imageAdapter);
    }
}

这是我的ImageAdapter.java代码。

public class ImageAdapter extends ArrayAdapter<String> {
    private String[] imageURLArray;
    private LayoutInflater inflater;

    public ImageAdapter(Context context, int textViewResourceId,
                        String[] imageArray) {
        super(context, textViewResourceId, imageArray);
        // TODO Auto-generated constructor stub

        inflater = ((Activity) context).getLayoutInflater();
        imageURLArray = imageArray;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        ViewHolder viewHolder = null;
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.imageitem, null);
            viewHolder = new ViewHolder();
            viewHolder.imageView = (ImageView) convertView.findViewById(R.id.testImage);
            convertView.setTag(viewHolder);
        }

        viewHolder = (ViewHolder) convertView.getTag();
        Bitmap imageBitmap = null;
        try {
            URL imageURL = new URL(imageURLArray[position]);
            imageBitmap = BitmapFactory.decodeStream(imageURL.openStream());
            viewHolder.imageView.setImageBitmap(imageBitmap);
        } catch (IOException e) {
            // TODO: handle exception
            Log.e("error", "Downloading Image Failed");
            viewHolder.imageView.setImageResource(R.mipmap.ic_launcher);
        }

        return convertView;
    }

    private static class ViewHolder {
        Bitmap bitmap;
        String imageURL;
        ImageView imageView;
    }

    private class DownloadAsyncTask extends AsyncTask<ViewHolder, Void, ViewHolder> {
        @Override
        protected ViewHolder doInBackground(ViewHolder... params) {
            // TODO Auto-generated method stub
            //load image directly
            ViewHolder viewHolder = params[0];
            try {
                URL imageURL = new URL(viewHolder.imageURL);
                viewHolder.bitmap = BitmapFactory.decodeStream(imageURL.openStream());
            } catch (IOException e) {
                // TODO: handle exception
                Log.e("error", "Downloading Image Failed");
                viewHolder.bitmap = null;
            }

            return viewHolder;
        }

        @Override
        protected void onPostExecute(ViewHolder result) {
            if (result.bitmap == null) {
                result.imageView.setImageResource(R.mipmap.ic_launcher);
            } else {
                result.imageView.setImageBitmap(result.bitmap);
            }
        }
    }
}

以下是包含完整项目的链接。

http://www.mediafire.com/download/70pxv6ib584x9j7/DownloadImagesInListView.rar

这是显示的错误堆栈。

09-29 18:33:37.859    5550-5550/com.example.android.downloadimagesinlistview E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.android.downloadimagesinlistview, PID: 5550
    android.os.NetworkOnMainThreadException
            at 

    android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1161)
                at java.net.InetAddress.lookupHostByName(InetAddress.java:418)
                at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252)
                at java.net.InetAddress.getAllByName(InetAddress.java:215)
                at com.android.okhttp.HostResolver$1.getAllByName(HostResolver.java:29)
                at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:232)
                at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:124)
                at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:272)
                at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:211)
                at com.android.okhttp.internal.http.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:382)
                at com.android.okhttp.internal.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:332)
                at com.android.okhttp.internal.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:199)
                at java.net.URL.openStream(URL.java:470)
                at com.example.android.downloadimagesinlistview.ImageAdapter.getView(ImageAdapter.java:48)
                at android.widget.AbsListView.obtainView(AbsListView.java:2347)
                at android.widget.ListView.makeAndAddView(ListView.java:1864)
                at android.widget.ListView.fillDown(ListView.java:698)
                at android.widget.ListView.fillFromTop(ListView.java:759)
                at android.widget.ListView.layoutChildren(ListView.java:1673)
                at android.widget.AbsListView.onLayout(AbsListView.java:2151)
                at android.view.View.layout(View.java:15689)
                at android.view.ViewGroup.layout(ViewGroup.java:5040)
                at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
                at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
                at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
                at android.view.View.layout(View.java:15689)
                at android.view.ViewGroup.layout(ViewGroup.java:5040)
                at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
                at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
                at android.view.View.layout(View.java:15689)
                at android.view.ViewGroup.layout(ViewGroup.java:5040)
                at android.support.v7.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:437)
                at android.view.View.layout(View.java:15689)
                at android.view.ViewGroup.layout(ViewGroup.java:5040)
                at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
                at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
                at android.view.View.layout(View.java:15689)
                at android.view.ViewGroup.layout(ViewGroup.java:5040)
                at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703)
                at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557)
                at android.widget.LinearLayout.onLayout(LinearLayout.java:1466)
                at android.view.View.layout(View.java:15689)
                at android.view.ViewGroup.layout(ViewGroup.java:5040)
                at android.widget.FrameLayout.layoutChildren(FrameLayout.java:579)
                at android.widget.FrameLayout.onLayout(FrameLayout.java:514)
                at android.view.View.layout(View.java:15689)
                at android.view.ViewGroup.layout(ViewGroup.java:5040)
                at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2116)
                at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1873)
                at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1084)
                at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5990)
                at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
                at android.view.Choreographer.doCallbacks(Choreographer.java:580)
                at android.view.Choreographer.doFrame(Choreographer.java:550)
                at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
                at android.os.Handler.handleCallback(Handler.java:739)
                at android.os.Handler.dispatchMessage(Handler.java:95)
                at android.os.Looper.loop(Looper.java:135)
                at android.app.ActivityThread.main(ActivityThread.java:5343)
                at java.lang.reflect.Method.invoke(

Answer 1

在主线程上执行网络相关操作时会发生此异常。要下载图像，您必须在AsyncTask中执行操作或使用picasso库。

使用Picasso使用此

Picasso.with(MainActivity.this).load(imageURLArray[position]).error(R.mipmap.ic_launcher).into(viewHolder.imageView);

在

的地方

Bitmap imageBitmap = null;
try {
  URL imageURL = new URL(imageURLArray[position]);
  imageBitmap = BitmapFactory.decodeStream(imageURL.openStream());
  viewHolder.imageView.setImageBitmap(imageBitmap);
} catch (IOException e) {
  // TODO: handle exception
  Log.e("error", "Downloading Image Failed");
  viewHolder.imageView.setImageResource(R.mipmap.ic_launcher);
}

使用AsyncTask

1 个答案: