我正在尝试运行此活动以查询数据库以填充表。 我试图按照我在网上找到的一个片段，唯一的问题是，无论如何，我都会收到“connectionandroid.os.NetworkOnMainThreadException”错误。
我试图像许多论坛中所建议的那样使用AsyncTask并在后台进行处理，但仍然没有。 我知道将长查询发送到数据库时会出现错误，但此查询可能需要0.1秒。我在本地拥有数据库，虽然使用公共IP访问它，并且数据库非常小。
这是我的PHP代码：
<?php
$hostname_localhost ="localhost";
$database_localhost ="DB";
$username_localhost ="root";
$password_localhost ="pwd";
mysql_connect($hostname_localhost,$username_localhost,$password_localhost);
mysql_select_db($database_localhost);
$sql=mysql_query("select * from friendlist where Id1 = 1");
while($row=mysql_fetch_assoc($sql))
$output[]=$row;
print(json_encode($output));
mysql_close();
?>
代码有效，好像我转到页面，我看到显示结果（我目前只有3行）。
这是java部分：
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.net.ParseException;
import android.os.Bundle;
import android.util.Log;
import android.widget.Toast;
public class MySQLAndroidActivity extends ListActivity {
JSONArray jArray;
String result = null;
InputStream is = null;
StringBuilder sb=null;
HttpResponse response;
HttpEntity entity;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
//http post
try{
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://X.X.X.X/test.php");
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
response = httpclient.execute(httppost);
entity = response.getEntity();
is = entity.getContent();
}catch(Exception e){
Log.e("log_tag", "Error in http connection"+e.toString());
System.exit(1);
}
//convert response to string
try{
BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
sb = new StringBuilder();
sb.append(reader.readLine() + "\n");
String line="0";
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result=sb.toString();
}catch(Exception e){
Log.e("log_tag", "Error converting result "+e.toString());
}
//parsing data
String idfriend;
String id1;
String id2;
try{
jArray = new JSONArray(result);
JSONObject json_data=null;
for(int i=0;i<jArray.length();i++){
json_data = jArray.getJSONObject(i);
idfriend=json_data.getString("Idfriend");
id1=json_data.getString("Id1");
id2=json_data.getString("Id2");
System.out.println("id1: " + id1);
}
}
catch(JSONException e1){
Toast.makeText(getBaseContext(), "No Id found" ,Toast.LENGTH_LONG).show();
} catch (ParseException e1) {
e1.printStackTrace();
}
}
}
我还尝试使用简单的Activity而不是ListActivity。
我有一个几乎相似的代码，但是那个使用了不同的方法。事实上，它没有得到结果，在php上，它只返回一个字符，无论是否检索到0行或更多行。在这种情况下，我需要更高级别的东西，因为我需要获取某些特定字段的值。
编辑：
根据要求，堆栈跟踪：
Error in http connectionandroid.os.NetworkOnMainThreadException
04-17 06:44:17.921: W/System.err(24207): java.lang.Exception
04-17 06:44:17.921: W/System.err(24207): at com.mysql.android.MySQLAndroidActivity.onCreate(MySQLAndroidActivity.java:56)
04-17 06:44:17.921: W/System.err(24207): at android.app.Activity.performCreate(Activity.java:4465)
04-17 06:44:17.921: W/System.err(24207): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
04-17 06:44:17.921: W/System.err(24207): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
04-17 06:44:17.921: W/System.err(24207): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
04-17 06:44:17.921: W/System.err(24207): at android.app.ActivityThread.access$600(ActivityThread.java:123)
04-17 06:44:17.921: W/System.err(24207): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
04-17 06:44:17.921: W/System.err(24207): at android.os.Handler.dispatchMessage(Handler.java:99)
04-17 06:44:17.921: W/System.err(24207): at android.os.Looper.loop(Looper.java:137)
04-17 06:44:17.931: W/System.err(24207): at android.app.ActivityThread.main(ActivityThread.java:4424)
04-17 06:44:17.931: W/System.err(24207): at java.lang.reflect.Method.invokeNative(Native Method)
04-17 06:44:17.931: W/System.err(24207): at java.lang.reflect.Method.invoke(Method.java:511)
04-17 06:44:17.931: W/System.err(24207): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
04-17 06:44:17.931: W/System.err(24207): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
04-17 06:44:17.931: W/System.err(24207): at dalvik.system.NativeStart.main(Native Method)
EDIT2：
这与我使用AsyncTask的版本非常相似（我正在创建它，没有编译器，所以它可能不完美;但它与我之前做的非常相似）：< / p>
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
new LoadTask().execute();
}
private class LoadTask extends AsyncTask<Void, Integer, Void> {
@Override
protected void onPreExecute() {
}
@Override
protected Void doInBackground(Void... params) {
synchronized (this) {
Looper.prepare();
doStuff() //this method basically contains what it is inside the onCreate.
}
return null;
}
}
}
- 我记得我被迫使用'Looper.prepare（）;'。 所以我在'doStuff（）;'
之前添加了它编辑2：
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.net.ParseException;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Looper;
import android.util.Log;
import android.widget.Toast;
public class MySQLAndroidActivity extends ListActivity {
JSONArray jArray;
String result = null;
InputStream is = null;
StringBuilder sb = null;
HttpResponse response;
HttpEntity entity;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
new LoadTask.execute();
}
private class LoadTask extends AsyncTask < Void, Integer, Void > {@Override
protected void onPreExecute() {
}
@Override
protected Void doInBackground(Void...params) {
Looper.prepare();
doStuff();
return null;
}
}
public void doStuff() {
ArrayList < NameValuePair > nameValuePairs = new ArrayList < NameValuePair > ();
//http post
try {
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://X.X.X.X/test.php");
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
response = httpclient.execute(httppost);
entity = response.getEntity();
is = entity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http connection" + e.toString());
System.exit(1);
}
//convert response to string
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);
sb = new StringBuilder();
sb.append(reader.readLine() + "\n");
String line = "0";
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result = sb.toString();
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
//parsing data
String idfriend;
String id1;
String id2;
try {
jArray = new JSONArray(result);
JSONObject json_data = null;
System.out.println("Length " + jArray.length());
Log.d("DB", "Length " + jArray.length());
for (int i = 0; i < jArray.length(); i++) {
System.out.println("counter " + i);
json_data = jArray.getJSONObject(i);
idfriend = json_data.getString("Idfriend");
id1 = json_data.getString("Id1");
id2 = json_data.getString("Id2");
System.out.println("id1: " + id1);
}
} catch (JSONException e1) {
Log.d("DB", "Error somewhere");
} catch (ParseException e1) {
e1.printStackTrace();
}
}
}
提前致谢，
<磷>氮答案 0 :(得分：3)
我听说从ICS开始，不允许在UI（主）线程上执行网络操作。因此，您必须在单独的线程中执行此操作。因此，要么使用 AsyncTask ，线程或 HandlerThread 使用Looper和Handler 来执行Web操作。如果你在运行froyo或gingerbread的设备上尝试它，那就没关系，但ICS上没有。
关于您尝试通过处理程序或AsyncTask运行它，它取决于您是如何做到的。粘贴该代码，以便我看到问题。
<强>更新
public class MySQLAndroidActivity extends ListActivity {
private static final String url = "http://X.X.X.X/test.php";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity2);
LoadTask t = new LoadTask();
t.execute(null);
}
private static class LoadTask extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
}
@Override
protected Void doInBackground(Void... params) {
doStuff();
return null;
}
}
public static void doStuff() {
JSONArray jArray;
String result = null;
InputStream is = null;
StringBuilder sb = null;
HttpResponse response;
HttpEntity entity;
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
// http post
try {
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(url);
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
response = httpclient.execute(httppost);
entity = response.getEntity();
is = entity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http connection" + e.toString());
System.exit(1);
}
// convert response to string
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);
sb = new StringBuilder();
sb.append(reader.readLine() + "\n");
String line;
while ((line = reader.readLine()) != null) {
sb.append(line);
}
is.close();
result = sb.toString();
Log.i("json string", result);
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
// parsing data
String idfriend;
String id1;
String id2;
try {
jArray = new JSONArray(result);
JSONObject json_data = null;
System.out.println("Length " + jArray.length());
Log.d("DB", "Length " + jArray.length());
for (int i = 0; i < jArray.length(); i++) {
System.out.println("counter " + i);
json_data = jArray.getJSONObject(i);
idfriend = json_data.getString("idfriend");
id1 = json_data.getString("id1");
id2 = json_data.getString("id2");
System.out.println("id1: " + id1);
}
} catch (JSONException e1) {
Log.d("DB", "Error somewhere");
} catch (ParseException e1) {
e1.printStackTrace();
}
}
}
*有一些方法调用问题，最重要的是你从JSONObject中取出键作为 Idfriend，Id1，Id2 ，这是错误的，因为在你的json字符串中键是像 idfriend，id1，id2 。它区分大小写，这就是崩溃的原因。
答案 1 :(得分：0)
你应该阅读abou模型 - 视图 - 控制器模式（在谷歌查找）。这种模式定义了你应该从模型（数据库访问，读取Dao模式）和控制器（运行应用程序的逻辑，例如这些是主类）中单独实现视图（用户界面）。
希望这能帮到你！