AsyncTask 未在 oncreate 中执行

Question

我正在做一个项目，我想从一个文件夹中下载图片，我有这个代码：

private class DownloadTask extends AsyncTask<ArrayList<URL>, Integer, List<Bitmap>> {
    // Before the tasks execution
    protected void onPreExecute() {
        // Display the progress dialog on async task start
        mProgressDialog.show();
        mProgressDialog.setProgress(0);
    }

    // Do the task in background/non UI thread
    protected List<Bitmap> doInBackground(ArrayList<URL>... urls) {
        int count = urls[0].size();
        HttpURLConnection connection = null;
        List<Bitmap> bitmaps = new ArrayList<>();

        // Loop through the urls
        for (int i = 0; i < count; i++) {
            URL currentURL = urls[0].get(i);
            // So download the image from this url
            try {
                // Initialize a new http url connection
                connection = (HttpURLConnection) currentURL.openConnection();

                // Connect the http url connection
                connection.connect();

                // Get the input stream from http url connection
                InputStream inputStream = connection.getInputStream();

                // Initialize a new BufferedInputStream from InputStream
                BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);

                // Convert BufferedInputStream to Bitmap object
                Bitmap bmp = BitmapFactory.decodeStream(bufferedInputStream);

                // Add the bitmap to list
                bitmaps.add(bmp);

                // Publish the async task progress
                // Added 1, because index start from 0
                publishProgress((int) (((i + 1) / (float) count) * 100));
                if (isCancelled()) {
                    break;
                }

            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                // Disconnect the http url connection
                connection.disconnect();
            }
        }
        // Return bitmap list
        return bitmaps;
    }

    // On progress update
    protected void onProgressUpdate(Integer... progress) {
        // Update the progress bar
        mProgressDialog.setProgress(progress[0]);
    }

    // On AsyncTask cancelled
    protected void onCancelled() {
        //Snackbar.make(mCLayout,"Task Cancelled.",Snackbar.LENGTH_LONG).show();
    }

    // When all async task done
    protected void onPostExecute(List<Bitmap> result) {
        // Hide the progress dialog
        mProgressDialog.dismiss();


        // Loop through the bitmap list
        for (int i = 0; i < result.size(); i++) {

            Bitmap bitmap = result.get(i);
            saveToSdCard(bitmap,arrayID.get(i).toString());
        }
    }
}

// Custom method to convert string to url
protected URL stringToURL(String urlString) {
    try {
        URL url = new URL(urlString);
        return url;
    } catch (MalformedURLException e) {
        e.printStackTrace();
    }
    return null;
}


public static String saveToSdCard(Bitmap bitmap, String filename) {
    String stored = null;
    File sdcard = Environment.getExternalStorageDirectory();
    File folder = new File(sdcard.getAbsoluteFile(), "/imagens");
    folder.mkdir();
    File file = new File(folder.getAbsoluteFile(), filename);

    try {
        FileOutputStream out = new FileOutputStream(file);
        bitmap.compress(Bitmap.CompressFormat.JPEG, 90, out);
        out.flush();
        out.close();
        stored = "success";
    } catch (Exception e) {
        e.printStackTrace();
    }
    return stored;
}

然后我使用如下按钮单击开始此过程：

mButtonDo.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            // Execute the async task

            ArrayList<URL>arrayURL=new ArrayList<URL>();

            for (Integer i:arrayID)
            {
                URL url = stringToURL(getString(R.string.link)+i.toString()+".jpg");
                arrayURL.add(url);
            }

            mMyTask = new DownloadTask().execute(arrayURL);
        }
    });

它也能如我所愿。但现在的问题是，我希望这个过程是自动的，并在 Activity 启动时执行，所以我将这段代码放在 OnCreate 方法中：

ArrayList<URL>arrayURL=new ArrayList<URL>();

            for (Integer i:arrayID)
            {
                URL url = stringToURL(getString(R.string.link)+i.toString()+".jpg");
                arrayURL.add(url);
            }

            mMyTask = new DownloadTask().execute(arrayURL);

但它不会做任何事情，点击按钮它开始正常，但在 OnCreate 方法中它不会做任何事情，有人知道如何解决这个问题吗？感谢您的帮助和时间。

已编辑 并使用此代码填充我的 arrayID:

 public void BuscarIdProduto_Imagens()
{
    new Thread(new Runnable() {
        public void run() {

            String SOAP_ACTION = "http://p4.com/BuscarIdProdutos";
            String METHOD_NAME = "BuscarIdProdutos";


            //Criar um Pedido SOAP
            SoapObject request = new SoapObject(NAMESPACE, METHOD_NAME);

            //Parametrização do SOAP
            SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11);


            //O envelope SOAP que se associa ao pedido
            envelope.setOutputSoapObject(request);

            //Classe: Indicar como o Servidor de WS pode ser alcançado
            HttpTransportSE androidHttpTransport = new HttpTransportSE(URL);

            try{
                //SOAP Request(Pedido)
                androidHttpTransport.call(SOAP_ACTION, envelope);


                //IR buscar a Resposta que me foi enviado pelo Servidor de WS
                SoapObject response = (SoapObject) envelope.bodyIn;

                if (response.getPropertyCount() > 0) {

                    for (int i = 0; i < response.getPropertyCount(); i++) {

                        SoapPrimitive soapObject = ((SoapPrimitive) response.getProperty(i));
                        //instanciar    o   canal   de  output

                        arrayID.add(Integer.valueOf(soapObject.toString()));
                    }
                }

                System.out.println();
            } catch (Exception ex) {
                System.out.println("------------------------------>" + ex.toString());
            }

        }
    }).start();
}

我调试了程序，我认为 KSOAP 在 AsyncTask 启动后完成了他的线程，这不可能是可能的，因为我需要填充数组，有没有什么方法可以在 ksoap 线程完成后启动异步任务？

Answer 1

因此，根据您的代码片段，我认为问题是在 onCreate 中调用了两种方法，但两种方法都进行了网络调用。所以基本上当你调用这部分代码时：

ArrayList<URL>arrayURL=new ArrayList<URL>();

for (Integer i:arrayID) {
     URL url = stringToURL(getString(R.string.link)+i.toString()+".jpg");
     arrayURL.add(url);
   }

mMyTask = new DownloadTask().execute(arrayURL);

在这种情况下 arrayID 还没有得到值，可能 for 循环被跳过，一个空的 list 或 arrayURL 被传递给 AsyncTask.这也将回答为什么代码在 onClick 上工作，因为同时 arrayID 填充了来自网络的数据。

所以你想要的是在你调用我上面粘贴的部分代码之前确保 arrayID 填充了数据。因此，在 Activity 中创建一个 interface 例如：

 public interface OnDataFetched {
   void fetchSuccess(ArrayList<URL> arrayID);
 }

现在转到您的 Activity 和 implement 这个 interface 和 override 方法 fetchSuccess:

public class YourAcitivity extends AppCompatActivity implements OnDataFetched
...

@Override
public void fetchSuccess(ArrayList<URL> arrayID) {

}

之后在同一个 Activity 创建一个字段：

private OnDataFetched onDataFetched;

里面 onCreate:

onDataFetched = this;

然后在 for 循环之后进入你的 BuscarIdProduto_Imagens 方法：

if (response.getPropertyCount() > 0) {

                for (int i = 0; i < response.getPropertyCount(); i++) {

                    SoapPrimitive soapObject = ((SoapPrimitive) response.getProperty(i));
                    //instanciar    o   canal   de  output

                    arrayID.add(Integer.valueOf(soapObject.toString()));
                }
             if(onDataFetched != null)
                onDataFetched.fetchSuccess(arrayID);
     }

最后一件事移动 AsyncTask ovirrieded 中的代码 fetchSuccess:

@Override
public void fetchSuccess(ArrayList<URL> arrayID) {
for (Integer i:arrayID) {
     URL url = stringToURL(getString(R.string.link)+i.toString()+".jpg");
     arrayURL.add(url);
    }
    mMyTask = new DownloadTask().execute(arrayURL);
   }

AsyncTask 未在 oncreate 中执行

AsyncTask not executiong in oncreate

android

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android-asynctask