应用程序从 web 服务加载图像。应用程序在 android 中等待很多

Question

我正在开发一个 Android 应用程序，它使用在 .ashx 请求处理程序中开发的 Web 服务。

• 应用程序在第一次启动 aap 时等待很多并显示黑屏。
• 有时它会给出内存超出 VM 预算的错误。

这是一些代码。

 public class Home extends Activity implements AdapterView.OnItemClickListener {
        /** Called when the activity is first created. */

        Context context = Home.this;
        HashMap<String, String> map = new HashMap<String, String>();
        ArrayList<String> BookTitle = new ArrayList<String>();
        ArrayList<String> BookCoverPhotos = new ArrayList<String>();

        URL bookImageURL = null;
        Bitmap bitMapImage = null;

        View homeTabLayout;
        View reviewLayout;
        ArrayList<String> ImageUrl = new ArrayList<String>();
        ImageButton btnBack;


        // XML Parsing
        ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();

        // All static variables
        static final String URL = "http://www.my_url_goes_here.com/rxxxxxxxandler.ashx";
        // XML node keys
        static final String KEY_ITEM = "Book"; // parent node
        static final String KEY_ID = "BookID";
        static final String KEY_BOOKTITLE = "BookTitle";
        static final String KEY_BOOKCODE = "BookCode";
        static final String KEY_BOOKIMAGE = "BookImage";

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.home_activity);
            // Get XML Data in a Array List

            XMLParser parser = new XMLParser();
            String xml = parser.getXmlFromUrl(URL, "Imam Ali"); // getting XML
            Document doc = parser.getDomElement(xml); // getting DOM element

            NodeList nl = doc.getElementsByTagName(KEY_ITEM);

            // looping through all item nodes <item>
            for (int i = 0; i < nl.getLength(); i++) {
                // creating new HashMap
                Node node = nl.item(i);
                Element e = (Element) nl.item(i);
                // adding each child node to HashMap key => value
                map.put(KEY_ID, parser.getValue(e, KEY_ID));
                BookTitle.add(parser.getValue(e, KEY_BOOKTITLE));
                BookCoverPhotos.add("http://shiaislamicbooks.com/books_Snaps/"+parser.getValue(e, KEY_BOOKCODE)+"/1.jpg");
                Log.i("URLs", BookCoverPhotos.toString());
                // String
                // imgUrl="http://shiaislamicbooks.com/books_Snaps/"+parser.getValue(e,
                // KEY_BOOKCODE);
                map.put(KEY_BOOKTITLE, parser.getValue(e, KEY_BOOKTITLE));
                map.put(KEY_BOOKCODE, parser.getValue(e, KEY_BOOKCODE));
                map.put(KEY_BOOKIMAGE, parser.getValue(e, KEY_BOOKIMAGE));

                // adding HashList to ArrayList
                menuItems.add(map);

                Log.i("Array List", menuItems.toString());
            }

            homeTabLayout = findViewById(R.id.rel_HomeLayout);
            reviewLayout = findViewById(R.id.scroll_ReviewLayout);
            reviewLayout.setVisibility(View.GONE);

            btnBack = (ImageButton) findViewById(R.id.btnBack);
            btnBack.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    reviewLayout.setVisibility(View.GONE);
                    homeTabLayout.setVisibility(View.VISIBLE);

                }
            });

            final GridView gridView = (GridView) findViewById(R.id.gridview);
            gridView.setAdapter(new ImageAdapter(this));
            gridView.setOnItemClickListener(new OnItemClickListener() {

                @Override
                public void onItemClick(AdapterView<?> arg0, View arg1, int pos,
                        long arg3) {


                }
            });

       }
        public class ImageAdapter extends BaseAdapter {
            private Context context;
            public ImageAdapter(Context c) {
                context = c;
            }

            // ---returns the number of images---
            public int getCount() {

                return BookCoverPhotos.size();
            }

            // ---returns the ID of an item---
            public Object getItem(int position) {
                return position;
            }

            public long getItemId(int position) {
                return position;
            }
            // ---returns an ImageView view---
            public View getView(int position, View convertView, ViewGroup parent) {
                // ImageView bmImage;
                ImageView img_BookCoverPhoto;
                img_BookCoverPhoto = new ImageView(context);
                LayoutInflater inflater = (LayoutInflater) context
                        .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                View row = inflater.inflate(R.layout.grid_style, parent, false);
                TextView txt_BooksTitle = (TextView) row
                        .findViewById(R.id.txt_BookTitle);
                txt_BooksTitle.setText(BookTitle.get(position) + "");
                img_BookCoverPhoto = (ImageView) row
                        .findViewById(R.id.imgBookCover);
                try {
                    bookImageURL = new URL(
                            BookCoverPhotos.get(position));
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                    Toast.makeText(context, "Network Error", Toast.LENGTH_LONG).show();
                    Log.i("URL", "ERROR");
                }

                try {
                    bitMapImage = BitmapFactory.decodeStream(bookImageURL
                            .openConnection().getInputStream());
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    Toast.makeText(context, "Bitmap Error", Toast.LENGTH_LONG).show();
                    Log.i("BITMAP", "ERROR");
                }

                img_BookCoverPhoto.setImageBitmap(bitMapImage);

                return row;
            }
        }

    }

还有一件事要告诉大家，我正在使用 this 教程使用 XML 解析。

• 我的应用中是否有多余的不需要的代码。
• 有什么方法可以加载第一个基本 UI，然后应用程序应该开始从 Web 服务器下载数据（即位图中的图像和文本数据）。
• 建议我应该使用 AsyncTask，请提供一些有关 AsyncTask 基本教程的链接。

请提供带有一些描述的代码。

Answer 1

使用Asynctask 执行网络操作，例如从服务器获取数据。所有的网络握手都可以在 AsyncTask 类的doInBackground() 中完成。 UI更新可以在onPostExecute()进行

Example

Study