异步任务不能执行两次

Question

我正在开发一个需要将文件上传到服务器的应用程序。但是要上传文件，必须先登录（已实现），然后获取URL（已实现），然后进行上传（强制关闭）。

日志记录：

10-13 14:10:27.494: E/AndroidRuntime(26578): FATAL EXCEPTION: main
10-13 14:10:27.494: E/AndroidRuntime(26578): java.lang.IllegalStateException: Cannot execute task: the task has already been executed (a task can be executed only once)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:578)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at android.os.AsyncTask.execute(AsyncTask.java:534)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.spxc.bayfiles.FilesActivity.onOptionsItemSelected(FilesActivity.java:294)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.actionbarsherlock.app.SherlockActivity.onMenuItemSelected(SherlockActivity.java:208)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.actionbarsherlock.ActionBarSherlock.callbackOptionsItemSelected(ActionBarSherlock.java:603)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.actionbarsherlock.internal.ActionBarSherlockNative.dispatchOptionsItemSelected(ActionBarSherlockNative.java:93)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.actionbarsherlock.app.SherlockActivity.onOptionsItemSelected(SherlockActivity.java:159)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at android.app.Activity.onMenuItemSelected(Activity.java:2566)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.android.internal.policy.impl.PhoneWindow.onMenuItemSelected(PhoneWindow.java:986)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.android.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:735)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:874)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.android.internal.view.menu.ActionMenuView.invokeItem(ActionMenuView.java:547)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.android.internal.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:115)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at android.view.View.performClick(View.java:4240)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at android.view.View$PerformClick.run(View.java:17721)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at android.os.Handler.handleCallback(Handler.java:730)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at android.os.Handler.dispatchMessage(Handler.java:92)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at android.os.Looper.loop(Looper.java:137)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at android.app.ActivityThread.main(ActivityThread.java:5103)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at java.lang.reflect.Method.invokeNative(Native Method)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at java.lang.reflect.Method.invoke(Method.java:525)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:112)
10-13 14:10:27.494: E/AndroidRuntime(26578):    at dalvik.system.NativeStart.main(Native Method)

我的代码：（handleJsonObject）：

private void handleJsonObject(JSONObject object) {

        try {
            sUpload = object.getString("uploadUrl");            
            HttpClient httpclient = new DefaultHttpClient();

            //post request to send the video 

            File sdCardRoot = Environment.getExternalStorageDirectory();
            File myDir = new File(sdCardRoot, "Download");

            HttpPost httppost = new HttpPost(sUpload);
            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
            StrictMode.setThreadPolicy( policy);
            FileBody video_file1 = new FileBody(new File(myDir + "/test.txt"));
            MultipartEntity reqEntity = new MultipartEntity();
            reqEntity.addPart("file=", video_file1);                    
            httppost.setEntity(reqEntity);

            // DEBUG
            System.out.println( "executing request " + httppost.getRequestLine( ) );
            HttpResponse response = null;
            try {
                response = httpclient.execute( httppost );
            } catch (ClientProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            HttpEntity resEntity = response.getEntity( );

            // DEBUG
            System.out.println( response.getStatusLine( ) );
            if (resEntity != null) {
              try {
                System.out.println( EntityUtils.toString( resEntity ) );
            } catch (org.apache.http.ParseException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            } // end if
            if (resEntity != null) {
              try {
                resEntity.consumeContent( );
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            } // end if

            httpclient.getConnectionManager( ).shutdown( );


        } catch (JSONException e) {
            Log.e("log_tag", "Error parsing data: " + e.toString());
            Crouton.makeText(this, "Something went wrong!", Style.ALERT).show();
        }
    }

调用 post 代码（handleJsonObject）的异步代码（aSync）：

asyncTask.setJsonListener(new JsonListener() {
                public void onObjectReturn(JSONObject object) {
                    handleJsonObject(object);
                }
            });
            asyncTask.execute("http://api.bayfiles.net/v1/file/uploadUrl?session=" + sessionId);

我不明白为什么代码无法运行？ 非常感谢您的帮助！

- Stian Instebo

---

错误源于您的活动。您需要发布该代码。 - SBerg413

Answer 1

正如异常本身所解释的那样，您不能执行一个AsyncTask多次，除非您创建一个new实例并调用.execute。

例如：

async = new AsyncTask();
async.execute();

为了执行多次，您需要重新创建该实例（使用 new）要执行的次数。

- waqaslam

---

我只需要调用它一次，是吗？ - Stian Instebo

Answer 2

我使用这段代码，对我来说是有效的：

    if ((eliminar_op_async != null) && eliminar_op_async.getStatus() == AsyncTask.Status.RUNNING) {
        if (eliminar_op_async.isCancelled()) {
            eliminar_op_async = new EliminarOperacion();

            eliminar_op_async.execute(id_operacion,posicion_operacion);
        }
        else {
            // Nada
        }
    }

    if ((eliminar_op_async != null) && eliminar_op_async.getStatus() == AsyncTask.Status.PENDING) {
        eliminar_op_async.execute(id_operacion,posicion_operacion);
    }

    if ((eliminar_op_async != null) && eliminar_op_async.getStatus() == AsyncTask.Status.FINISHED) {
        eliminar_op_async = new EliminarOperacion();

        eliminar_op_async.execute(id_operacion,posicion_operacion);
    }

    if (eliminar_op_async == null) {
        eliminar_op_async = new EliminarOperacion();

        eliminar_op_async.execute(id_operacion,posicion_operacion);
    }

- yader_centeno

Answer 3

您可以通过调用async实例的async.cancel(true)来取消操作，以确保只有一个async实例在运行。

- He Termis

Answer 4

你不能执行超过一次的AsyncTask，因此要解决这个错误，只需像这样将其包装在条件语句中： async = new AsyncTask();

                 if (async==null){

                   async.execute();

                    }

这个错误通常发生在你试图在ViewPager中运行Asynctask时。当你在一个Fragment中运行Asynctask并滑动到下一个Fragment，返回到前一个Fragment会触发该Fragment中的Asynctask重新执行，导致应用程序崩溃。因此，你必须通过将其包装在条件语句中来检查Asynctask是否已经被执行。

- boakye_wozniac