如何创建异步任务来构建 RSSReader

Question

在投票之前。是的，我在问这个问题之前阅读了论坛。 RSSReader Async Task

阅读上面的那个，但我仍然不明白。

问题：

我用 Java 编写了 een RSSReader。这在控制台打印我想要的东西等非常有效。但在 Android 中它不起作用，因为它没有使用 een 异步任务。现在我从谷歌文档中了解到，有三种类型可以输入 AsyncTask 之类的东西。我不知道如何在我的代码中实现这一点。我是否需要使用 AsyncTask 创建一个单独的类来扩展它，并创建我的 Reader 的实例，并在它的 doInBackground 方法中调用我的 reader，或者我需要如何执行此操作。

这是我的 RSSReader 的代码：

public class RSSReader {
    //Lists to store headlines, descriptions & images
    String url = "http://www.nu.nl/rss/Algemeen";
    List<String> titleList;
    List<String> descriptionList;
    List<String> imageList;
    public RSSReader(){

        try {
            titleList = readRSS(url, "<title>", "</title>");
            descriptionList = listFilter(readRSS(url, "<description>", "</description>"), "&amp;nbsp;", "");
            imageList = readRSS(url, "<enclosure url \"", "\" length=\"0\" type=\"image/jpeg\"</enclosure>");

        }
        catch (IOException e){

        }
        }
    public List<String> readRSS(String feedUrl, String openTag, String closeTag) throws IOException, MalformedURLException {

        URL url = new URL(feedUrl);
        BufferedReader reader= new BufferedReader(new InputStreamReader(url.openStream()));

        String currentLine;
        List<String> tempList = new ArrayList<String>();
        while((currentLine = reader.readLine()) != null){
            Integer tagEndIndex = 0;
            Integer tagStartIndex = 0;
            while (tagStartIndex >= 0){
                tagStartIndex = currentLine.indexOf(openTag, tagEndIndex);
                if(tagStartIndex >= 0){
                    tagEndIndex = currentLine.indexOf(closeTag, tagStartIndex);
                    tempList.add(currentLine.substring(tagStartIndex + openTag.length(), tagEndIndex) + "\n");
                }
            }
        }
        tempList.remove(0);
        return tempList;
    }

    public List<String> getDesciptionList(){
        return descriptionList;
    }

    public List<String> getTitleList(){
        return titleList;
    }
    public List<String> getImageList(){
        return imageList;
    }

    public List<String> listFilter(List<String> tempList, String require, String 
    replace){
        //Creates new List
        List<String> newList = new ArrayList<>();
        //Loops through old list and checks for the 'require' variable
        for(int i = 0; i < tempList.size(); i++){
            if(tempList.get(i).contains(require)){
                newList.add(tempList.get(i).replace(require, replace));
            }
            else{
                newList.add(tempList.get(i));
            }
        }
        return newList;
    }


}  

Answer 1

在RSSReader#readRSS，你不检查tempList.size()

别忘了加

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

致您的AndroidManifest.xml

例如

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        new RssReaderAsyncTask(new RSSCallBack() {

            @Override
            public void success(RSSReader rssReader) {
                // TODO That Should run on UI Thread if you update UI
                // for example
                final RSSReader reader = rssReader;
                // you can use runOnUiThread or Handler update UI
                runOnUiThread(new Runnable() {

                    @Override
                    public void run() {
                        // TODO Toast 
                        Toast.makeText(MainActivity.this, reader.getTitleList().toString(), Toast.LENGTH_SHORT).show();
                    }
                });
            }

            @Override
            public void failed() {
                // TODO That Should run on UI Thread if you update UI
                Log.e("RSS", "failed");
            }
        }).execute("");

    }

    private class RssReaderAsyncTask extends AsyncTask<String, Integer, Integer> {
        private RSSCallBack rssCallBack;

        public RssReaderAsyncTask(RSSCallBack rssCallBack) {
            this.rssCallBack = rssCallBack;
        }

        @Override
        protected Integer doInBackground(String... params) {
            // TODO
            try {
                RSSReader reader = new RSSReader();
                rssCallBack.success(reader);
            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                rssCallBack.failed();
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                rssCallBack.failed();
                e.printStackTrace();
            }
            return null;
        }

    }

    private interface RSSCallBack {
        void success(RSSReader rssReader);

        void failed();
    }

    public class RSSReader {
        // Lists to store headlines, descriptions & images
        String url = "http://www.nu.nl/rss/Algemeen";
        List<String> titleList;
        List<String> descriptionList;
        List<String> imageList;

        public RSSReader() throws MalformedURLException, IOException {

            titleList = readRSS(url, "<title>", "</title>");
            descriptionList = listFilter(readRSS(url, "<description>", "</description>"), "&amp;nbsp;", "");
            imageList = readRSS(url, "<enclosure url \"", "\" length=\"0\" type=\"image/jpeg\"</enclosure>");

        }

        public List<String> readRSS(String feedUrl, String openTag, String closeTag)
                throws IOException, MalformedURLException {

            URL url = new URL(feedUrl);
            BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));

            String currentLine;
            List<String> tempList = new ArrayList<String>();
            while ((currentLine = reader.readLine()) != null) {
                Integer tagEndIndex = 0;
                Integer tagStartIndex = 0;
                while (tagStartIndex >= 0) {
                    tagStartIndex = currentLine.indexOf(openTag, tagEndIndex);
                    if (tagStartIndex >= 0) {
                        tagEndIndex = currentLine.indexOf(closeTag, tagStartIndex);
                        tempList.add(currentLine.substring(tagStartIndex + openTag.length(), tagEndIndex) + "\n");
                    }
                }
            }
            if (tempList.size() > 0) {
                //TODO you do not check it
                tempList.remove(0);
            }
            return tempList;
        }

        public List<String> getDesciptionList() {
            return descriptionList;
        }

        public List<String> getTitleList() {
            return titleList;
        }

        public List<String> getImageList() {
            return imageList;
        }

        public List<String> listFilter(List<String> tempList, String require, String replace) {
            // Creates new List
            List<String> newList = new ArrayList<String>();
            // Loops through old list and checks for the 'require' variable
            for (int i = 0; i < tempList.size(); i++) {
                if (tempList.get(i).contains(require)) {
                    newList.add(tempList.get(i).replace(require, replace));
                } else {
                    newList.add(tempList.get(i));
                }
            }
            return newList;
        }

    }
}

Answer 2

你是对的，你需要 Asynctask。不过这里解释的太多了，这里已经解释的很透彻了，大家不妨看看：

https://stackoverflow.com/a/9671602/3673616

您需要确保在doInBackground 中运行您的网络调用，您可以在onPreExcute 中操作UI，完成后在onpostExecute 中操作。更多详情请访问链接。

Answer 3

好吧，我假设您已经知道代码，因此 doInBackground 方法中的代码应该是长时间运行的代码，例如从互联网/服务器等获取信息。然后您可以返回一个成功或错误的字符串这将从 onPostExecute 方法中捕获，您可以对结果做任何您喜欢的事情。

所以我想说不需要新类，只需在其中扩展异步任务，实现我提到的 2 个方法，并在方法中调用您已经拥有的正确函数，只需稍作更改即可返回结果。