Question

在我的doInBackground方法中，我试图创建一个HTTPGet并创建一个JSONResponseHandler，而不是将它们都传递给mClient.execute（）。该应用程序在doInBackgroundMethod中崩溃。任何帮助都会很棒。我对Android很新，可能会解释我的一些编码实践。这是我的代码：

public class Downloader extends AsyncTask <String, Void, List<Bitmap>>{

private static final String URL = "http://......";

private MainActivity mParentActivity;
private Context mApplicationContext;

AndroidHttpClient mClient = AndroidHttpClient.newInstance("");

// Constructor
    public Downloader(MainActivity parentActivity) {
        super();

        mParentActivity = parentActivity;
        mApplicationContext = parentActivity.getApplicationContext();

    }


@Override
protected List<Bitmap> doInBackground(String... params) {

    log("Entered doInBackground()");
    HttpGet request = new HttpGet(URL);
    JSONResponseHandler responseHandler = new JSONResponseHandler();

    try {
        return mClient.execute(request, responseHandler);
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;


}

@Override
protected void onPostExecute(List<Bitmap> result)
{
    mParentActivity.setImages(result);

}

private void log(String msg)
{
    Log.i(TAG, msg);
}

private class JSONResponseHandler implements ResponseHandler<List<Bitmap>> {

    private static final String IMAGE = "cover";
    private static final String LIST = "data";

    @Override
    public List<Bitmap> handleResponse(HttpResponse response)
            throws ClientProtocolException, IOException {
        List<Bitmap> result = new ArrayList<Bitmap>();
        String JSONResponse = new BasicResponseHandler()
                .handleResponse(response);
        try {

            // Get top-level JSON Object - a Map
            JSONObject responseObject = (JSONObject) new JSONTokener(
                    JSONResponse).nextValue();

            // Extract value of "Data" key -- a List
            JSONArray images = responseObject
                    .getJSONArray(LIST);

            InputStream is = null;

            // Iterate over data list
            for (int idx = 0; idx < images.length(); idx++) {

                // Get single piece of data - a Map
                JSONObject image = (JSONObject) images.get(idx);

                // open the url
                URL coverURL = (java.net.URL) image.get(IMAGE);
                HttpURLConnection conn = (HttpURLConnection) coverURL.openConnection();
                conn.setReadTimeout(10000 /* milliseconds */);
                conn.setConnectTimeout(15000 /* milliseconds */);
                conn.setRequestMethod("GET");
                conn.setDoInput(true);
                // Starts the query
                conn.connect();
                int r = conn.getResponseCode();
                Log.d(TAG, "The response is: " + r);
                is = conn.getInputStream();

                // creates an image from the inputStream
                Bitmap imageMap = BitmapFactory.decodeStream(is);


            result.add(imageMap);

            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return result;
    }
}
}

我的LogCat如下：

02-27 21:37:32.540: E/AndroidRuntime(1536): FATAL EXCEPTION: AsyncTask #1
02-27 21:37:32.540: E/AndroidRuntime(1536): Process: com.example.test, PID: 1536
02-27 21:37:32.540: E/AndroidRuntime(1536): java.lang.RuntimeException: An error occured   while executing doInBackground()
02-27 21:37:32.540: E/AndroidRuntime(1536):     at android.os.AsyncTask$3.done(AsyncTask.java:300)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at java.util.concurrent.FutureTask.run(FutureTask.java:242)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at java.lang.Thread.run(Thread.java:841)
02-27 21:37:32.540: E/AndroidRuntime(1536): Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to java.net.URL
02-27 21:37:32.540: E/AndroidRuntime(1536):     at com.example.test.DownloadStories$JSONResponseHandler.handleResponse(DownloadStories.java:109)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at com.example.test.DownloadStories$JSONResponseHandler.handleResponse(DownloadStories.java:1)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:657)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:627)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:616)
02-27 21:37:32.540: E/AndroidRuntime(1536):     at android.net.http.AndroidHttpClient.execute(AndroidHttpClient.java:273)

Answer 1

将以下行添加到您的下载程序构造函数中，

mClient = AndroidHttpClient.newInstance("", mApplicationContext);

我认为您必须传递上下文才能获得实例。

Answer 2

我相信你的代码崩溃了，因为在这行

期间内存不足

 Bitmap imageMap = BitmapFactory.decodeStream(is);


        result.add(imageMap);

但是我无法理解的是你为什么不在该步骤中将图片保存到特定位置并释放内存

      void downloadFile(String fileUrl, String fileName) {
    URL myFileUrl = null;
    try {
        myFileUrl = new URL(fileUrl);
        HttpURLConnection conn = (HttpURLConnection) myFileUrl.openConnection();
        conn.setDoInput(true);
        conn.connect();
        InputStream is = conn.getInputStream();

        if (bmImg != null) {
            bmImg.recycle();
        }

        bmImg = BitmapFactory.decodeStream(is);
        FileOutputStream out = new FileOutputStream(path + "/" + fileName + ".jpg");
        bmImg.compress(Bitmap.CompressFormat.JPEG, 50, out);

    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
        // Toast.makeText(this, e.getMessage(), Toast.LENGTH_LONG).show();
    }
}

因此，通过此步骤，您无需创建List<Bitmap>，我假设应用程序崩溃的原因

Answer 3

在日志中：

权限被拒绝（缺少INTERNET权限？

在INTERNET中添加AndroidManifest权限：

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

Android：尝试使用AsyncTask和JSON下载图像时崩溃

3 个答案: