android logcat中的运行时异常

Question

我想从服务器（WAMP）数据库中检索数据，并且我想在单个列表视图中显示。我花了很长时间来了解这个最终我实现了，但logcat显示了几个android运行时错误。我修复了一些错误，并发布了一些我无法修复的错误。 我的java文件：

package com.example.least; 

import java.util.ArrayList; 
import java.util.HashMap; 

import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 

import android.app.ListActivity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.AdapterView.OnItemClickListener; 
import android.widget.ListAdapter; 
import android.widget.ListView; 
import android.widget.SimpleAdapter; 
import android.widget.TextView; 

public class MainActivity extends ListActivity { 

    // url to make request 
    private static String url = "http://localhost/android_connect/final.php"; 

    // JSON Node names 
    private static final String TAG_CONTACTS = "opass"; 
    private static final String TAG_ID = "User_ID"; 

    // contacts JSONArray 
    JSONArray contacts = null; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     // Hashmap for ListView 
     ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>(); 

     // Creating JSON Parser instance 
     JSONParser jParser = new JSONParser(); 

     // getting JSON string from URL 
     JSONObject json = jParser.getJSONFromUrl(url); 

     try { 
      // Getting Array of Contacts 
      contacts = json.getJSONArray(TAG_CONTACTS); 

      // looping through All Contacts 
      for(int i = 0; i < contacts.length(); i++){ 
       JSONObject c = contacts.getJSONObject(i); 

       // Storing each json item in variable 
       String id = c.getString(TAG_ID); 

       // Phone number is agin JSON Object 

       // creating new HashMap 
       HashMap<String, String> map = new HashMap<String, String>(); 

       // adding each child node to HashMap key => value 
       map.put(TAG_ID, id); 

       // adding HashList to ArrayList 
       contactList.add(map); 
      } 
     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 


     /** 
     * Updating parsed JSON data into ListView 
     * */ 
     ListAdapter adapter = new SimpleAdapter(this, contactList, 
       R.layout.list_item, 
       new String[] { TAG_ID }, new int[] { 
         R.id.textView1}); 

     setListAdapter(adapter); 

     // selecting single ListView item 
     ListView lv = getListView(); 

     // Launching new screen on Selecting Single ListItem 
     lv.setOnItemClickListener(new OnItemClickListener() { 

      @Override 
      public void onItemClick(AdapterView<?> parent, View view, 
        int position, long id) { 
       // getting values from selected ListItem 
       String name = ((TextView) view.findViewById(R.id.textView1)).getText().toString(); 


       // Starting new intent 
       Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class); 
       in.putExtra(TAG_ID, name); 

       startActivity(in); 
      } 
     }); 
    } 

} 

logcat的例外：

04-25 19:35:02.353: D/AndroidRuntime(5650): Shutting down VM 
04-25 19:35:02.353: W/dalvikvm(5650): threadid=1: thread exiting with uncaught exception (group=0x40a71930) 
04-25 19:35:02.393: E/AndroidRuntime(5650): FATAL EXCEPTION: main 
04-25 19:35:02.393: E/AndroidRuntime(5650): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.least/com.example.least.MainActivity}: android.os.NetworkOnMainThreadException 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.app.ActivityThread.access$600(ActivityThread.java:141) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.os.Handler.dispatchMessage(Handler.java:99) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.os.Looper.loop(Looper.java:137) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.app.ActivityThread.main(ActivityThread.java:5041) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at java.lang.reflect.Method.invokeNative(Native Method) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at java.lang.reflect.Method.invoke(Method.java:511) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at dalvik.system.NativeStart.main(Native Method) 
04-25 19:35:02.393: E/AndroidRuntime(5650): Caused by: android.os.NetworkOnMainThreadException 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1117) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at java.net.InetAddress.lookupHostByName(InetAddress.java:385) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at java.net.InetAddress.getAllByName(InetAddress.java:214) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:137) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at com.example.least.JSONParser.getJSONFromUrl(JSONParser.java:39) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at com.example.least.MainActivity.onCreate(MainActivity.java:45) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.app.Activity.performCreate(Activity.java:5104) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 
04-25 19:35:02.393: E/AndroidRuntime(5650):  ... 11 more 
04-25 19:35:02.603: D/dalvikvm(5650): GC_CONCURRENT freed 211K, 13% free 2588K/2944K, paused 24ms+30ms, total 226ms 

主要Activity.xml文件：

<ListView 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@android:id/list"> 
</ListView> 

所以我是新到Android我与这些类型的错误挣扎请帮我修复

Answer 1

问题是Caused by: java.lang.RuntimeException: Binary XML file line #1: You must supply a layout_width attribute.和它在线at com.example.least.MainActivity.onCreate(MainActivity.java:36)

因此检查您的布局文件R.layout.activity_main哪里缺少layout_width属性。

顺便说一句，尽管你是Android的新手，但你至少应该先阅读logcat，然后再发布到网络上，因为在很多情况下（这是其中之一），logcat告诉你错误在哪里以及它是由什么引起的通过。

Answer 2

问题是，您正在尝试在创建时进行网络相关操作。 Android只允许网络相关的操作，例如从webservice内部线程或AsyncTask获取值。所以尝试添加Asynctask或线程