Android：方法的异步线程

Question

我意识到，为了让我的应用程序的一部分工作，我可能需要在单独的线程上运行它。在此之后，我的选择似乎是异步和线程，我认为异步似乎是更好的选择，因为我在使用线程方面几乎没有经验。我正在尝试在单独的线程上运行 PetroPriceString，但我没有这样做的知识。对此的任何帮助将不胜感激

编辑：我整个班级的补充

package org.me.myandroidstuff;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;

//import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class PetrolPriceActivity extends Menu 
{
    private TextView response;
    private TextView errorText;
    private String result;
    private String petrolPriceURL;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) 
    {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.list);

        Bundle extras = getIntent().getExtras();
        if(extras!=null){
        petrolPriceURL =extras.getString("URLString");
        }
        // Get the TextView object on which to display the results
        response = (TextView)findViewById(R.id.error);
        response = (TextView)findViewById(R.id.title);
        try
        {
            // Get the data from the RSS stream as a string
            result =  petrolPriceString(petrolPriceURL);

            // Do some processing of the data to get the individual parts of the RSS stream
            // At some point put this processing into a separate thread of execution
            // Display the string in the TextView object just to demonstrate this capability
            // This will need to be removed at some point
            response.setText(result);
        }
        catch(IOException ae)
        {
            // Handle error
            response.setText("Error");
            // Add error info to log for diagnostics
            errorText.setText(ae.toString());
        } 

    }

    // End of onCreate

    // Method to handle the reading of the data from the RSS stream
    private static String petrolPriceString(String urlString)throws IOException
    {
        String result = "";
        InputStream anInStream = null;
        int response = -1;
        URL url = new URL(urlString);
        URLConnection conn = url.openConnection();

        // Check that the connection can be opened
        if (!(conn instanceof HttpURLConnection))
                throw new IOException("Not an HTTP connection");
        try
        {
            // Open connection
            HttpURLConnection httpConn = (HttpURLConnection) conn;
            httpConn.setAllowUserInteraction(false);
            httpConn.setInstanceFollowRedirects(true);
            httpConn.setRequestMethod("GET");
            httpConn.connect();
            response = httpConn.getResponseCode();
            // Check that connection is Ok
            if (response == HttpURLConnection.HTTP_OK)
            {
                // Connection is OK so open a reader 
                anInStream = httpConn.getInputStream();
                InputStreamReader in= new InputStreamReader(anInStream);
                BufferedReader bin= new BufferedReader(in);

                // Read in the data from the RSS stream
                String line = new String();
                while (( (line = bin.readLine())) != null)
                {
                    result = result + "\n" + line;
                }
            }
        }
        catch (Exception ex)
        {
                throw new IOException("Error connecting");
        }

        // Return result as a string for further processing
        return result;
    }
    // End of petrolPriceString
 // End of Activity class
}

我的应用程序目前没有错误，但是我得到的输出不是我想要的，所以我相信一个单独的线程就是答案

Answer 1

AsyncTask 可用于在后台进行缓慢的工作（如网络交互）并在主/UI 线程上进行最后一点处理/交互。如果我正确理解了您的要求，您可以尝试以下操作：

new AsyncTask<String, Void, String>() {
    @Override protected String doInBackground(String... params) {
        // we do this part in the background on another thread
        return petrolPriceString(params[0]);
    }
    @Override protected void onPostExecute(String result) {
        // result is the value returned from our call to petrolPriceString
        // anything we put in here is done on the main/UI thread
    }
}.execute(urlString);

如果您想捕获由 PetroPriceString 引发的异常，并相应地执行一些逻辑，一种可能的解决方案是将其保存为 AsyncTask 中的本地成员。类似于以下内容...

new AsyncTask<String, Void, String>() {
    IOException exception = null;
    @Override protected String doInBackground(String... params) {
        try {
            return petrolPriceString(params[0]);
        } catch (IOException e) {
            exception = e;
            return null;
        }
    }
    @Override protected void onPostExecute(String result) {
        if (exception != null) {
            // handle our exception
        } else {
            // handle our result
        }
    }
}.execute(urlString);