我試圖獲得從MySQL服務器發送和接收數據的Android應用程序的基礎知識(我的實現與此學習示例無關)。這裏是到目前爲止的代碼:Android無法正確連接到MySQL數據庫
package com.davekelley.polling;
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.ParseException;
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.ActionBar;
import android.app.Activity;
import android.app.ListActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;
public class Chart extends Activity {
JSONArray jArray;
String result = null;
InputStream is = null;
StringBuilder sb=null;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.chartfragment);
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
//http post
try{
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost("http://www.davidjkelley.net/city.php");
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
}catch(Exception e){
Log.e("log_tag", "Error in http connection "+e.toString());
}
//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());
}
//paring data
int ct_id;
String ct_name;
try{
jArray = new JSONArray(result);
JSONObject json_data=null;
for(int i=0;i<jArray.length();i++){
json_data = jArray.getJSONObject(i);
ct_id=json_data.getInt("CITY_ID");
ct_name=json_data.getString("CITY_NAME");
}
}
catch(JSONException e1){
Toast.makeText(getBaseContext(), "No City Found" ,Toast.LENGTH_LONG).show();
} catch (ParseException e1) {
e1.printStackTrace();
}
}
}
而這裏的XML文件 'chartfragment' 代碼:
<?xml version="1.0" encoding="utf-8"?>
<ListView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/list"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<!-- <LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/chartTitleTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge" android:gravity="center"/>
-->
</ListView>
這裏是logcat的問題我遇到:
03-26 20:34:13.782: E/log_tag(1025): Error in http connection android.os.NetworkOnMainThreadException
03-26 20:34:13.802: E/log_tag(1025): Error converting result java.lang.NullPointerException
03-26 20:34:13.802: D/AndroidRuntime(1025): Shutting down VM
03-26 20:34:13.802: W/dalvikvm(1025): threadid=1: thread exiting with uncaught exception (group=0x409c01f8)
03-26 20:34:13.832: E/AndroidRuntime(1025): FATAL EXCEPTION: main
03-26 20:34:13.832: E/AndroidRuntime(1025): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.davekelley.polling/com.davekelley.polling.Chart}: java.lang.NullPointerException
03-26 20:34:13.832: E/AndroidRuntime(1025): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
03-26 20:34:13.832: E/AndroidRuntime(1025): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
03-26 20:34:13.832: E/AndroidRuntime(1025): at android.app.ActivityThread.access$600(ActivityThread.java:123)
03-26 20:34:13.832: E/AndroidRuntime(1025): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
03-26 20:34:13.832: E/AndroidRuntime(1025): at android.os.Handler.dispatchMessage(Handler.java:99)
03-26 20:34:13.832: E/AndroidRuntime(1025): at android.os.Looper.loop(Looper.java:137)
03-26 20:34:13.832: E/AndroidRuntime(1025): at android.app.ActivityThread.main(ActivityThread.java:4424)
03-26 20:34:13.832: E/AndroidRuntime(1025): at java.lang.reflect.Method.invokeNative(Native Method)
03-26 20:34:13.832: E/AndroidRuntime(1025): at java.lang.reflect.Method.invoke(Method.java:511)
03-26 20:34:13.832: E/AndroidRuntime(1025): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
03-26 20:34:13.832: E/AndroidRuntime(1025): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
03-26 20:34:13.832: E/AndroidRuntime(1025): at dalvik.system.NativeStart.main(Native Method)
03-26 20:34:13.832: E/AndroidRuntime(1025): Caused by: java.lang.NullPointerException
03-26 20:34:13.832: E/AndroidRuntime(1025): at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:116)
03-26 20:34:13.832: E/AndroidRuntime(1025): at org.json.JSONTokener.nextValue(JSONTokener.java:94)
03-26 20:34:13.832: E/AndroidRuntime(1025): at org.json.JSONArray.<init>(JSONArray.java:87)
03-26 20:34:13.832: E/AndroidRuntime(1025): at org.json.JSONArray.<init>(JSONArray.java:103)
03-26 20:34:13.832: E/AndroidRuntime(1025): at com.davekelley.polling.Chart.onCreate(Chart.java:68)
03-26 20:34:13.832: E/AndroidRuntime(1025): at android.app.Activity.performCreate(Activity.java:4465)
03-26 20:34:13.832: E/AndroidRuntime(1025): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
03-26 20:34:13.832: E/AndroidRuntime(1025): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
03-26 20:34:13.832: E/AndroidRuntime(1025): ... 11 more
所以很顯然,主線程問題上的網絡連接意味着我需要將它移入一個Asynctask,對吧?但有了這麼多的錯誤,我不知道我是否錯過了其他的東西,這很明顯?我最終希望能夠將用戶/密碼註冊到數據庫中,然後獲得查詢併發送響應,所以這基本上只是一個熱身。如果轉到http://www.davidjkelley.net/city.php,您可以看到數據庫確實正確響應了我在Android代碼中鏈接的查詢PHP文件,所以這不是問題。
編輯〜我應該注意到我的Activity之前的擴展列表Activity,按照這個教程:http://blog.sptechnolab.com/2011/02/10/android/android-connecting-to-mysql-using-php/這就是爲什麼我的XML現在只是一個ListView,因爲這有助於清除一個錯誤,說我需要一個ListView組件id'list'。
編輯〜我的PHP代碼:
<?php
mysql_connect("127.0.0.1","***","***");
mysql_select_db("***");
$sql=mysql_query("select * from CITY where CITY_NAME like 'A%'");
while($row=mysql_fetch_assoc($sql))
$output[]=$row;
print(json_encode($output));
mysql_close();
?>
很明顯的恆星集合是正確的信息,當你訪問上面貼的鏈接時,SQL讀出正常顯示。
如果你得到的是NetworkOnMainThreadException,它是最基本的。首先解決它。你用MySQL DB打到一個.php頁面的事實在這一點上是一個問題。你甚至可能還沒有發送SYN數據包...... – 2012-03-26 21:03:19
你願意澄清嗎?我問及如何爲此創建一個Asynctask ... – Davek804 2012-03-26 21:04:19
對於異步,這看起來像一個地方開始:http://www.vogella.de/articles/AndroidPerformance/article.html特別是見第5節。 – 2012-03-27 13:40:34