Java Android：调用方法

Question

我正在构建一个列表视图android应用程序。 我想要一个消息被返回时，从列表中点击一个网址，告诉用户该网站是否离线或联机。我通过一个快速的ping来完成这个工作，它返回一个布尔值来说明这一点。我是一个java新手，我知道这是我调用pinUrl（）方法的方式，因为当我从onListItemClick（）移除所述if语句时，该应用程序不会崩溃。

这里是我的参考MainActivity：

package com.seven.webtools; 

import java.io.IOException; 
import java.net.HttpURLConnection; 
import java.net.MalformedURLException; 
import java.net.URL; 

import android.annotation.SuppressLint; 
import android.app.ListActivity; 
import android.content.res.Resources; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.View; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 
import android.widget.Toast; 

@SuppressLint("UseValueOf") 
public class MainActivity extends ListActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    Resources res = getResources(); 
    String[] Sites = res.getStringArray(R.array.Sites); 
    setListAdapter(new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,Sites)); 

} 

@Override 
protected void onListItemClick(ListView l, View v, int position, long id) { 
    // Get the selected url 
    super.onListItemClick(l, v, position, id); 
    Object o = this.getListAdapter().getItem(position); 
    String address = o.toString(); 

    //Ping the address 
    String Status = "offline"; 
    if (MainActivity.pingUrl(address) == true){ 
     Status = "online"; 
    } 

    //Return the result 
    Toast.makeText(this, address + " is " + Status, Toast.LENGTH_LONG).show(); 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.main, menu); 
    return true; 
} 

public static boolean pingUrl(final String address) { 
    try { 
     final URL url = new URL("http://" + address); 
     final HttpURLConnection urlConn = (HttpURLConnection) url.openConnection(); 
     urlConn.setConnectTimeout(1000 * 10); // mTimeout is in seconds 
     final long startTime = System.currentTimeMillis(); 
     urlConn.connect(); 
     final long endTime = System.currentTimeMillis(); 
     if (urlConn.getResponseCode() == HttpURLConnection.HTTP_OK) { 
     System.out.println("Time (ms) : " + (endTime - startTime)); 
     System.out.println("Ping to "+address +" was success"); 
     return true; 
     } 
    } catch (final MalformedURLException e1) { 
     e1.printStackTrace(); 
    } catch (final IOException e) { 
     e.printStackTrace(); 
    } 
    return false; 
    } 

} 

非常感谢你，如果你能帮助我:)

Answer 1

看看你的堆栈跟踪，我想你可能会得到一个NetworkOnMaintThreadException，因为您正在执行Main/UI线程上的HTTP连接。做一个单独的线程，也许通过使用AsyncTask，那么你应该没问题。

Answer 2

您正在使用哪个Android版本？该应用程序可能会因为您正在UI-Main-Thread上进行网络调用而崩溃，这意味着在网络调用期间UI会冻结。在旧版本中，它的工作原理没有发生异常。自从版本2.3.x（纠正我，如果我错了），你会得到android.os.NetworkOnMainThreadException。

以在这个岗位看看更多的信息，如何解决这个问题： - How to fix android.os.NetworkOnMainThreadException?

Answer 3

您应该使用一个AsyncTask或Thread和Handler。

这里的Thread和Handler一个例子：

public class MainActivity extends ListActivity 
{ 
    @Override 
    protected void onCreate(Bundle savedInstanceState) 
    { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     Resources res = getResources(); 
     String[] Sites = res.getStringArray(R.array.Sites); 
     setListAdapter(new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,Sites)); 
    } 

    // Here is where we create our Handler that will receive the Message from the thread. 
    private Handler handler = new Handler() 
    { 
     @Override 
     public void handleMessage(Message msg) 
     { 
      StringBuilder str = new StringBuilder(); 
      str.append((String) msg.obj).append("\r\n"); 
      str.append("response: " + msg.arg1).append("\r\n"); 
      str.append("time: " + msg.arg2).append("\r\n"); 

      System.out.println(str.toString()); 
     } 
    }; 

    @Override 
    protected void onListItemClick(ListView l, View v, int position, long id) 
    { 
     super.onListItemClick(l, v, position, id); 

     final String address = l.getItemAtPosition(position).toString(); 

     // We create a new thread and implements the Runnable interface 
     new Thread(new Runnable() 
     { 
      public void run() 
      { 
       URL url; 
       HttpURLConnection connection = null; 

       try 
       { 
        url = new URL(address); 

        connection = (HttpURLConnection) url.openConnection(); 
        connection.setConnectTimeout(10 * 1000); 
        connection.setReadTimeout(10 * 1000); 

        long start = System.currentTimeMillis(); 

        connection.connect(); 

        int response = connection.getResponseCode(); 

        long end = System.currentTimeMillis(); 

        // Here we create a new Message to send to the Handler object on the Activity 
        // Send the response code, ping time, and the address 
        Message msg = Message.obtain(handler); 
        msg.arg1 = response; 
        msg.arg2 = (int) (end - start); 
        msg.obj = address; 
        msg.sendToTarget(); 
       } 
       catch(MalformedURLException e) 
       { 
        e.printStackTrace(); 
       } 
       catch(IOException e) 
       { 
        e.printStackTrace(); 
       } 
       finally 
       { 
        connection.disconnect(); 
       } 
      } 
     }).start(); 
    } 
}