java - 如何在Android中使用doInBackground AsyncTask？

Question

我已经在 Android 中实现了 ppt 文件转换，并且正在使用 REST 等 Web 服务。但我的代码在主线程上运行，因此我必须对 AsynchTask 使用 do-In-Background() 。

当我运行应用程序时，我收到如下错误/警告:

View Root CalledFromWrongThreadException only the original thread that created a view hierarchy

没有 do-In-Background() 可以正常运行，但在运行状态下按后退按钮时应用程序崩溃。这是我的代码。

      btnSubmit.setOnClickListener(new View.OnClickListener()
                {

                    @Override
                    public void onClick(View arg0) 
                    {

                       convertToImage();

                    }

                });

         protected void onActivityResult
                (int requestCode, int resultCode, Intent data)


                      {     
                      // TODO Auto-generated method stub 

                        if (requestCode == PATH)    

                         {      
                            if (resultCode == RESULT_OK)

                               {            
                                            if (data != null)

                                {
                                path = data.getStringExtra("path");
                                 System.out.println("Path  : " + path );

                              String strfpath = path ;

                                          String fileName2
                                          =strfpath.substring(strfpath.lastIndexOf("/")+1);

                              System.out.println("fileName2 :" + fileName2 );

                                   function_arg1.setText(fileName2);
                    }       

                  }     

             }

    }

这是我的 doInBackground() 方法

private void convertToImage() 
    {
        httpGetAsynchTask httpGetAsyncTask = new httpGetAsynchTask();
        httpGetAsyncTask.execute();
    }


    class httpGetAsynchTask extends AsyncTask<String , Integer , String>
    {
        protected void onPreExecute() {
               try{
                   dialog.setMessage("Please Wait");
                   dialog.show();
               }
               catch(Exception e)
               {

               }
            }




        @Override
        protected String doInBackground(String... arg0) 
        {
            // TODO Auto-generated method stub

            if (function_arg1.getText().length() == 0)
            {
                AlertDialog.Builder dialog = new AlertDialog.Builder(StorageFolderUploadFile.this);
                dialog.setTitle("Error");
                dialog.setMessage("Please Enter Require Fields");
                dialog.setNeutralButton("Ok", null);
                dialog.show();
            } 


            else 

            {
                fileName = function_arg1.getText().toString();
                System.out.println("File Name :-  " + fileName);

                folderName="tazeen";

                Folder obj = new Folder();

                try 
                {
                    response = obj.uploadFile(path/*, folderName*/);
                    Log.e("",""+response);
                    if (response) 

                    {
                        result.append("File Uploaded Successfully \n");

                        Document docObj=new Document( fileName /*folderName*/);
                        count = docObj.getSlideCount();


                        if (count > 0) 
                        {
                            result.append(" \n Numbers Of Slides = " + count);
                            System.out.println("Number Of Slides " + count );



                            for(int i=1; i <= count ; i++)
                            {                          

                               System.out.println("________________________________________");

                                System.out.println("i  :-> " + i );

                                String outputPath = fileName + "_Tazeen" + i + ".jpg" ;
                                System.out.println("outputPath :-> " + outputPath);

                                slideNumber = i;
                                System.out.println("slideNumber :-> " + slideNumber);

                                Document docObj2=new Document(fileName);
                                System.out.println("docObj2 :-> " + docObj2);

                                docObj2.saveSlideAs(outputPath.toString().trim(), slideNumber, imageFormat);
                                System.out.println("docObj2 :-> " + docObj2);

                                result.append("slide is converted and save to your sdcard \n");

                                String imagePath = path + "/" + outputPath ;
                                System.out.println("imagePath : " + imagePath );


                            }

                        }

                    }

                    else 

                    {
                        result.append("Oops..Something went wrong");
                        }
                } 


                           catch (Exception e)
                           {
                            // TODO Auto-generated catch block
                               e.printStackTrace();


                           }



            }


            return fileName;
        }




        @Override
        public void onPostExecute(String values)
        {

            convertToImage(); 

            try
            {
                if(dialog.isShowing())
                {
                    dialog.dismiss();
                }
            }
            catch(Exception e)
            {}
        }

    }

Answer 1

您无法从后台线程访问与用户界面有关的任何内容。因此，所有 AlertDialog.Builder 对话框 都是不允许的，如果 function_arg1 是 View 那么也应该避免这种情况。

注意:我担心 System.out 是否被允许，但根据评论应该没问题。

如果有帮助的话，当我使用AsyncTask时，我通常创建一个类来保存所有可能的结果，包括错误消息和抛出的任何异常。然后，该对象可以按照 onPostExecute 中的要求反射(reflect)到用户界面。